,illustration3 ,,the ,,great ,,scarlet ,,solar ,,prominences1 ,,which ,,are ,,such ,a ,,notable ,,feature ,,of ,,the ,,solar ,,phenomena1 ,,are ,,immense ,,outbursts ,,of ,,flaming ,,hydrogen ,,rising ,,sometimes ,,to ,a ,,height ,,of #ejj1jjj ,,miles ,,the ,,outline ,,of ,,science ,a ,,plain ,,story ,,simply ,,told ,,edited ,,by ,j4 ,,arthur ,,thomson ,,regius ,,professor ,,of ,,natural ,,history ,,in ,,the ,,university ,,of ,,aberdeen ,,with ,,over #hjj ,,illustrations ,,of ,,which ,,about #dj ,,are ,,in ,,colour ,,in ,,four ,,volumes ,g4 ,p4 ,,putnam',s ,,sons ,,new ,,york ,,and ,,london ,the ,knickerbocker press ,copyright1 #aibb by ,g4 ,p4 ,putnam's ,sons ,first ,printing ,april1 #aibb ,second ,printing ,april1 #aibb ,third ,printing ,april1 #aibb ,fourth ,printing ,april1 #aibb ,fifth ,printing ,june1 #aibb ,sixth ,printing ,june1 #aibb ,seventh ,printing ,june1 #aibb ,eighth ,printing ,june1 #aibb ,ninth ,printing ,august1 #aibb ,tenth ,printing ,september1 #aibb ,eleventh ,printing ,sept41 #aibb ,twelfth ,printing1 ,may1 #aibd ,made in the ,united ,states of ,america ,,introductory ,,note ,by ,professor ,j4 ,arthur ,thomson ,was it not the great philosopher and mathematician ,leibnitz who said that the more knowledge advances the more it becomes possible to condense it into little books8 ,now this ,outline of ,science is certainly not a little book1 and yet it illustrates part of the meaning of ,leibnitz's wise saying4 ,for here within reasonable compass there is a library of little books--an outline of many sciences4 ,it will be profitable to the student in proportion to the discrimination with which it is used4 ,for it is not in the least meant to be of the nature of an ,encyclopdia1 giving condensed and comprehensive articles with a big full stop at the end of each4 ,nor is it a collection of primers1 beginning at the very beginning of each subject and working methodically onwards4 ,that is not the idea4 ,what then is the aim of this book8 ,it is to give the intelligent student-citizen1 otherwise called the man in the street1 a bunch of intellectual keys by which to open doors which have been hitherto shut to him1 partly because he got no glimpse of the treasures behind the doors1 and partly because the portals were made forbidding by an unnecessary display of technicalities4 ,laying aside conventional modes of treatment and seeking rather to open up the subject as one might on a walk with a friend1 the work offers the student what might be called informal introductions to the various departments of knowledge4 ,to put it in another way1 the articles are meant to be clues which the reader may follow till he has left his starting point very far behind4 ,perhaps when he has gone far on his own he will not be ungrateful to the simple book of instructions to travellers which this ,outline of ,science is intended to be4 ,the simple bibliographies appended to the various articles will be enough to indicate first books4 ,each article is meant to be an invitation to an intellectual adventure1 and the short lists of books are merely finger-posts for the beginning of the journey4 ,we confess to being greatly encouraged by the reception that has been given to the ,english serial issue of ,the ,outline of ,science4 ,it has been very hearty--we might almost say enthusiastic4 ,for we agree with ,professor ,john ,dewey1 that the future of our civilisation depends upon the widening spread and deepening hold of the scientific habit of mind4 ,and we hope that this is what ,the ,outline of ,science makes for4 ,information is all to the good2 interesting information is better still2 but best of all is the education of the scientific habit of mind4 ,another modern philosopher1 ,professor ,l4 ,t4 ,hobhouse1 has declared that the evolutionist's mundane goal is the mastery by the human mind of the conditions1 internal as well as external1 of its life and growth4 ,under the influence of this conviction ,the ,outline of ,science has been written4 ,for life is not for science1 but science for life4 ,and even more than science1 to our way of thinking1 is the individual development of the scientific way of looking at things4 ,science is our legacy2 we must use it if it is to be our very own4 ,,contents ,,introduction #c ,i4 ,,the ,,romance ,,of ,,the ,,heavens #g ,the scale of the universe--,the solar system--,regions of the sun--,the surface of the sun--,measuring the speed of light--,is the sun dying8--,the planets--,venus--,is there life on ,mars8--,jupiter and ,saturn--,the moon--,the mountains of the moon--,meteors and comets--,millions of meteorites--,a great comet--,the stellar universe--,the evolution of stars--,the age of stars--,the nebular theory--,spiral nebul--,the birth and death of stars--,the shape of our universe--,astronomical instruments4 ,,ii4 ,,the ,,story ,,of ,,evolution #ec ,the beginning of the earth--,making a home for life--,the first living creatures--,the first plants--,the first animals--,beginnings of bodies--,evolution of sex--,beginning of natural death--,procession of life through the ages--,evolution of land animals--,the flying dragons--,the first known bird--,evidences of evolution--,factors in evolution4 ,,iii4 ,,adaptations ,,to ,,environment #aac ,the shore of the sea--,the open sea--,the deep sea--,the fresh waters--,the dry land--,the air4 ,,iv4 ,,the ,,struggle ,,for ,,existence #ace ,animal and bird mimicry and disguise--,other kinds of elusiveness4 ,v4 ,,the ,,ascent ,,of ,,man #aec ,anatomical proof of man's relationship with a ,simian stock--,physiological proof--,embryological proof--,man's pedigree--,man's arboreal apprenticeship--,tentative men--,primitive men--,races of mankind--,steps in human evolution--,factors in human progress4 ,,vi4 ,,evolution ,,going ,,on #ahc ,evolutionary prospect for man--,the fountain of change2 variability--,evolution of plants--,romance of wheat--,changes in animal life--,story of the salmon--,forming new habits--,experiments in locomotion2 new devices4 ,,vii4 ,,the ,,dawn ,,of ,,mind #bje ,a caution in regard to instinct--,a useful law--,senses of fishes--,the mind of a minnow--,the mind and senses of amphibians--,the reptilian mind--,mind in birds--,intelligence co-operating with instinct--,the mind of the mammal--,instinctive aptitudes--,power of association--,why is there not more intelligence8--,the mind of monkeys--,activity for activity's sake--,imitation--,the mind of man--,body and mind4 ,,viii4 ,,foundations ,,of ,,the ,,universe #bdc ,the world of atoms--,the energy of atoms--,the discovery of ,x-rays--,the discovery of radium--,the discovery of the electron--,the electron theory--,the structure of the atom--,the new view of matter--,other new views--,the nature of electricity--,electric current--,the dynamo--,magnetism--,ether and waves--,light--,what the blue sky means--,light without heat--,forms of energy--,what heat is--,substitutes for coal--,dissipation of energy--,what a uniform temperature would mean--,matter1 ether1 and ,einstein--,the tides--,origin of the moon--,the earth slowing down--,the day becoming longer4 ,,illustrations ,,facing ,,page ,,the ,,great ,,scarlet ,,solar ,,prominences1 ,,which ,,are ,,such ,a ,,notable ,,feature ,,of ,,the ,,solar ,,phenomena1 ,,are ,,immense ,,outbursts ,,of ,,flaming ,,hydrogen ,,rising ,,sometimes ,,to ,a ,,height ,,of #ejj1jjj ,,miles ,coloured ,frontispiece ,,laplace #aj ,,professor ,j4 ,c4 ,,adams #aj ,photo3 ,royal ,astronomical ,society4 ,,professor ,,eddington ,,of ,,cambridge ,,university #aj ,photo3 ,elliot ,fry1 ,ltd4 ,,the ,,planets1 ,,showing ,,their ,,relative ,,distances ,,and ,,dimensions #aa ,,the ,,milky ,,way #ad ,photo3 ,harvard ,college ,observatory4 ,,the ,,moon ,,entering ,,the ,,shadow ,,cast ,,by ,,the ,,earth #ad ,,the ,,great ,,nebula ,,in ,,andromeda1 ,,messier #ca #ae ,from a photograph taken at the ,yerkes ,observatory4 ,,diagram ,,showing ,,the ,,main ,,layers ,,of ,,the ,,sun #ah ,,solar ,,prominences ,,seen ,,at ,,total ,,solar ,,eclipse1 ,,may #bi1 #aiai4 ,,taken ,,at ,,sobral1 ,,brazil #ah ,photo3 ,royal ,observatory1 ,greenwich4 ,,the ,,visible ,,surface ,,of ,,the ,,sun #ai ,photo3 ,mount ,wilson ,observatory4 ,,the ,,sun ,,photographed ,,in ,,the ,,light ,,of ,,glowing ,,hydrogen #ai ,photo3 ,mount ,wilson ,observatory4 ,,the ,,aurora ,,borealis 7,coloured ,illustration7 #bj ,reproduced from ,the ,forces of ,nature 7,messrs4 ,macmillan7 ,,the ,,great ,,sun-,,spot ,,of ,,july #ag1 #aije #bb ,yerkes ,observatory4 ,,solar ,,prominences #bb ,from photographs taken at the ,yerkes ,observatory4 ,,mars1 ,,october #e1 #aiji #bc ,photo3 ,mount ,wilson ,observatory4 ,,jupiter #bc ,,saturn1 ,,november #ai1 #aiaa #bc ,photo3 ,professor ,e4 ,e4 ,barnard1 ,yerkes ,observatory4 ,,the ,,spectroscope1 ,,an ,,instrument ,,for ,,analysing ,,light2 ,,it ,,provides ,,means ,,for ,,identifying ,,substances 7,coloured ,illustration7 #bd ,,the ,,moon #bh ,,mars #bi ,drawings by ,professor ,percival ,lowell4 ,,the ,,moon1 ,,at ,,nine ,,and ,,three ,,quarter ,,days #bi ,a ,,map ,,of ,,the ,,chief ,,plains ,,and ,,craters ,,of ,,the ,,moon #cb ,a ,,diagram ,,of ,a ,,stream ,,of ,,meteors ,,showing ,,the ,,earth ,,passing ,,through ,,them #cb ,,comet1 ,,september #bi1 #aijh #cc ,photo3 ,royal ,observatory1 ,greenwich4 ,,comet1 ,,october #c1 #aijh #cc ,photo3 ,royal ,observatory1 ,greenwich4 ,,typical ,,spectra #cf ,photo3 ,harvard ,college ,observatory4 ,a ,,nebular ,,region ,,south ,,of ,,zeta ,,orionis #cg ,photo3 ,mount ,wilson ,observatory4 ,,star ,,cluster ,,in ,,hercules #cg ,photo3 ,astrophysical ,observatory1 ,victoria1 ,british ,columbia4 ,,the ,,great ,,nebula ,,in ,,orion #dj ,photo3 ,yerkes ,observatory4 ,,giant ,,spiral ,,nebula1 ,,march #bc1 #aiad #da ,photo3 ,lick ,observatory4 ,a ,,spiral ,,nebula ,,seen ,,edge-,,on #dd ,photo3 ,mount ,wilson ,observatory4 #ajj-;,,inch ,,telescope1 ,,mount ,,wilson #de ,photo3 ,h4 ,j4 ,shepstone4 ,,the ,,yerkes #dj-;,,inch ,,refractor #dh ,,the ,,double-,,slide ,,plate-,,holder ,,on ,,yerkes #dj-;,,inch ,,refracting ,,telescope #di ,photo3 ,h4 ,j4 ,shepstone4 ,,modern ,,direct-,,reading ,,spectroscope #di ,by ,a4 ,hilger1 ,ltd4 ,,charles ,,darwin #ef ,photo3 ,rischgitz ,collection4 ,,lord ,,kelvin #ef ,photo3 ,rischgitz ,collection4 ,a ,,giant ,,spiral ,,nebula #eg ,photo3 ,lick ,observatory4 ,,meteorite ,,which ,,fell ,,near ,,scarborough ,,and ,,is ,,now ,,to ,,be ,,seen ,,in ,,the ,,natural ,,history ,,museum #eg ,photo3 ,natural ,history ,museum4 ,a ,,limestone ,,canyon #fj ,reproduced from the ,smithsonian ,report1 #aiae4 ,,geological ,,tree ,,of ,,animals #fa ,,diagram ,,of ,,amoeba #fa ,a ,,piece ,,of ,a ,,reef-,,building ,,coral1 ,,built ,,up ,,by ,a ,,large ,,colony ,,of ,,small ,,sea-,,anemone-,,like ,,polyps1 ,,each ,,of ,,which ,,forms ,,from ,,the ,,salts ,,of ,,the ,,sea ,a ,,skeleton ,,or ,,shell ,,of ,,lime #fd ,from the ,smithsonian ,report1 #aiag4 ,a ,,group ,,of ,,chalk-,,forming ,,animals1 ,,or ,,foraminifera1 ,,each ,,about ,,the ,,size ,,of ,a ,,very ,,small ,,pin',s ,,head #fe ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,a ,,common ,,foraminifer 7,,polystomella7 ,,showing ,,the ,,shell ,,in ,,the ,,centre ,,and ,,the ,,outflowing ,,network ,,of ,,living ,,matter1 ,,along ,,which ,,granules ,,are ,,continually ,,travelling1 ,,and ,,by ,,which ,,food ,,particles ,,are ,,entangled ,,and ,,drawn ,,in #fe ,reproduced by permission of the ,natural ,history ,museum 7after ,max ,schultze74 ,a ,,plant-,,like ,,animal1 ,,or ,,zoophyte1 ,,called ,,obelia #fh ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,trypanosoma ,,gambiense #fi ,reproduced by permission of ,the ,quart4 ,journ4 ,mic4 ,sci4 ,,volvox #fi ,,proterospongia #fi ,,green ,,hydra #gb ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,diagram ,,illustrating ,,the ,,beginning ,,of ,,individual ,,life #gb ,,earthworm #gb ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,glass ,,model ,,of ,a ,,sea-,,anemone #gb ,reproduced from the ,smithsonian ,report1 #aiag4 ,,this ,,drawing ,,shows ,,the ,,evolution ,,of ,,the ,,brain ,,from ,,fish ,,to ,,man #gc ,,okapi ,,and ,,giraffe 7,coloured ,illustration7 #gd ,,diagram ,,of ,a ,,simple ,,reflex ,,arc ,,in ,a ,,backboneless ,,animal ,,like ,,an ,,earthworm #gf ,,the ,,yucca ,,moth #gf ,photo3 ,british ,museum 7,natural ,history74 ,,inclined ,,plane ,,of ,,animal ,,behaviour #gf ,,venus' ,,fly-,,trap #gg ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,a ,,spider ,,sunning ,,her ,,eggs #gg ,reproduced by permission from ,the ,wonders of ,instinct by ,j4 ,h4 ,fabre4 ,,the ,,hoatzin ,,inhabits ,,british ,,guiana #hb ,,peripatus #hc ,photograph1 from the ,british ,museum 7,natural ,history71 of a drawing by ,mr4 ,e4 ,wilson4 ,,rock ,,kangaroo ,,carrying ,,its ,,young ,,in ,a ,,pouch #hc ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,professor ,,thomas ,,henry ,,huxley 7#ahbe-ie7 #hf ,photo3 ,rischgitz4 ,,baron ,,cuvier1 #agfi-ahcb #hf ,,an ,,illustration ,,showing ,,various ,,methods ,,of ,,flying ,,and ,,swooping #hg ,,animals ,,of ,,the ,,cambrian ,,period #ij ,from ,knipe's ,nebula to ,man4 ,a ,,trilobite #ij ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,the ,,gambian ,,mud-,,fish1 ,,protopterus #ia ,photo3 ,british ,museum 7,natural ,history74 ,,the ,,arch,,opteryx #ia ,after ,william ,leche of ,stockholm4 ,,wing ,,of ,a ,,bird1 ,,showing ,,the ,,arrangement ,,of ,,the ,,feathers #ia ,,pictorial ,,representation ,,of ,,strata ,,of ,,the ,,earth',s ,,crust1 ,,with ,,suggestions ,,of ,,characteristic ,,fossils 7,coloured ,illustration7 #ib ,,fossil ,,of ,a ,,pterodactyl ,,or ,,extinct ,,flying ,,dragon #id ,photo3 ,british ,museum 7,natural ,history74 ,,pariasaurus3 ,,an ,,extinct ,,vegetarian ,,triassic ,,reptile #id ,from ,knipe's ,nebula to ,man4 ,,triceratops3 ,a ,,huge ,,extinct ,,reptile #ie ,from ,knipe's ,nebula to ,man4 ,,the ,,duckmole ,,or ,,duck-,,billed ,,platypus ,,of ,,australia #ie ,photo3 ,daily ,mail4 ,,skeleton ,,of ,,an ,,extinct ,,flightless ,,toothed ,,bird1 ,,hesperornis #ajj ,after ,marsh4 ,,six ,,stages ,,in ,,the ,,evolution ,,of ,,the ,,horse1 ,,showing ,,gradual ,,increase ,,in ,,size #aja ,after ,lull and ,matthew4 ,,diagram ,,showing ,,seven ,,stages ,,in ,,the ,,evolution ,,of ,,the ,,fore-,,limbs ,,and ,,hind-,,limbs ,,of ,,the ,,ancestors ,,of ,,the ,,modern ,,horse1 ,,beginning ,,with ,,the ,,earliest ,,known ,,predecessors ,,of ,,the ,,horse ,,and ,,culminating ,,with ,,the ,,horse ,,of ,,to-,,day #ajd ,after ,marsh and ,lull4 ,,what ,,is ,,meant ,,by ,,homology8 ,,essential ,,similarity ,,of ,,architecture1 ,,though ,,the ,,appearances ,,may ,,be ,,very ,,different #aje ,,an ,,eight-,,armed ,,cuttlefish ,,or ,,octopus ,,attacking ,a ,,small ,,crab #aaf ,a ,,common ,,starfish1 ,,which ,,has ,,lost ,,three ,,arms ,,and ,,is ,,regrowing ,,them #aaf ,after ,professor ,w4 ,c4 ,mc,intosh4 ,,the ,,paper ,,nautilus 7,,argonauta71 ,,an ,,animal ,,of ,,the ,,open ,,sea #aag ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,a ,,photograph ,,showing ,a ,,starfish 7,asterias ,forreri7 ,,which ,,has ,,captured ,a ,,large ,,fish #aag ,,ten-,,armed ,,cuttlefish ,,or ,,squid ,,in ,,the ,,act ,,of ,,capturing ,a ,,fish #aah ,,greenland ,,whale #aah ,,minute ,,transparent ,,early ,,stage ,,of ,a ,,sea-,,cucumber #aai ,,an ,,intricate ,,colony ,,of ,,open-,,sea ,,animals 7,physophora ,hydrostatica7 ,,related ,,to ,,the ,,portuguese ,,man-,,of-,,war #aai ,photo3 ,british ,museum 7,natural ,history74 ,a ,,scene ,,in ,,the ,,great ,,depths #aai ,,sea-,,horse ,,in ,,sargasso ,,weed #abj ,,large ,,marine ,,lampreys 7,petromyzon ,marinus7 #abj ,,the ,,deep-,,sea ,,fish ,chiasmodon ,niger #abj ,,deep-,,sea ,,fishes #abj ,,flinty ,,skeleton ,,of ,,venus' ,,flower ,,basket 7,euplectella71 ,a ,,japanese ,,deep-,,sea ,,sponge #aba ,,egg ,,depository ,,of ,semotilus ,atromaculatus #aba ,,the ,,bitterling 7,rhodeus ,amarus7 #abd ,,woolly ,,opossum ,,carrying ,,her ,,family #abd ,photo3 ,w4 ,s4 ,berridge4 ,,surinam ,,toad 7,pipa ,americana7 ,,with ,,young ,,ones ,,hatching ,,out ,,of ,,little ,,pockets ,,on ,,her ,,back #abe ,,storm ,,petrel ,,or ,,mother ,,carey',s ,,chicken 7,procellaria ,pelagica7 #abe ,,albatross3 ,a ,,characteristic ,,pelagic ,,bird ,,of ,,the ,,southern ,,sea #abh ,,the ,,praying ,,mantis 7,mantis ,religiosa7 #ach ,,protective ,,coloration3 ,a ,,winter ,,scene ,,in ,,north ,,scandinavia #ach ,,the ,,variable ,,monitor 7,varanus7 #aci ,photo3 ,a4 ,a4 ,white4 ,,banded ,,krait3 ,a ,,very ,,poisonous ,,snake ,,with ,,alternating ,,yellow ,,and ,,dark ,,bands #adj ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,the ,,warty ,,chameleon #adj ,photos3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,seasonal ,,colour-,,change3 ,,summer ,,scene ,,in ,,north ,,scandinavia #ada ,,protective ,,resemblance #adb ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,when ,,only ,a ,,few ,,days ,,old1 ,,young ,,bittern ,,begin ,,to ,,strike ,,the ,,same ,,attitude ,,as ,,their ,,parents1 ,,thrusting ,,their ,,bills ,,upwards ,,and ,,drawing ,,their ,,bodies ,,up ,,so ,,that ,,they ,,resemble ,a ,,bunch ,,of ,,reeds #adc ,,protective ,,coloration ,,or ,,camouflaging1 ,,giving ,,animals ,a ,,garment ,,of ,,invisibility 7,coloured ,illustration7 #add ,,another ,,example ,,of ,,protective ,,coloration 7,coloured ,illustration7 #add ,,dead-,,leaf ,,butterfly 7,kallima ,inachis7 ,,from ,,india #adf ,,protective ,,resemblance ,,between ,a ,,small ,,spider 7to the left7 ,,and ,,an ,,ant 7to the right7 #adf ,,the ,,wasp ,,beetle1 ,,which1 ,,when ,,moving ,,amongst ,,the ,,branches1 ,,gives ,a ,,wasp-,,like ,,impression #adg ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,hermit-,,crab ,,with ,,partner ,,sea-,,anemones #adg ,,cuckoo-,,spit #adg ,photo3 ,g4 ,p4 ,duffus4 ,,chimpanzee1 ,,sitting #aef ,photo3 ,new ,york ,zoological ,park4 ,,chimpanzee1 ,,illustrating ,,walking ,,powers #aef ,photo3 ,new ,york ,zoological ,park4 ,,surface ,,view ,,of ,,the ,,brains ,,of ,,man ,,and ,,chimpanzee #aeg ,,side-,,view ,,of ,,chimpanzee',s ,,head #aeg ,photo3 ,new ,york ,zoological ,park4 ,,profile ,,view ,,of ,,head ,,of ,,pithecanthropus1 ,,the ,,java ,,ape-,,man1 ,,reconstructed ,,from ,,the ,,skull-,,cap #aeg ,after a model by ,j4 ,h4 ,mc,gregor4 ,,the ,,flipper ,,of ,a ,,whale ,,and ,,the ,,hand ,,of ,a ,,man #aeg ,,the ,,gorilla1 ,,inhabiting ,,the ,,forest ,,tract ,,of ,,the ,,gaboon ,,in ,,africa 7,coloured ,illustration7 #aeh ,,darwin',s ,,point ,,on ,,human ,,ear #afj ,,professor ,,sir ,,arthur ,,keith1 ,m4,d41 ,,ll4,d41 ,f4,r4,s4 #afa ,photo3 ,j4 ,russell ,sons4 ,,skeletons ,,of ,,the ,,gibbon1 ,,orang1 ,,chimpanzee1 ,,gorilla1 ,,man #afa ,after ,t4 ,h4 ,huxley 7by permission of ,messrs4 ,macmillan74 ,,side-,,view ,,of ,,skull ,,of ,,man ,,and ,,gorilla #afd ,,the ,,skull ,,and ,,brain-,,case ,,of ,,pithecanthropus1 ,,the ,,java ,,ape-,,man1 ,,as ,,restored ,,by ,j4 ,h4 ,,mcgregor ,,from ,,the ,,scanty ,,remains #afd ,,suggested ,,genealogical ,,tree ,,of ,,man ,,and ,,anthropoid ,,apes #afe ,,the ,,gibbon ,,is ,,lower ,,than ,,the ,,other ,,apes ,,as ,,regards ,,its ,,skull ,,and ,,dentition1 ,,but ,,it ,,is ,,highly ,,specialized ,,in ,,the ,,adaptation ,,of ,,its ,,limbs ,,to ,,arboreal ,,life #aff ,photo3 ,new ,york ,zoological ,park4 ,,the ,,orang ,,has ,a ,,high ,,rounded ,,skull ,,and ,a ,,long ,,face #aff ,photo3 ,new ,york ,zoological ,park4 ,,comparisons ,,of ,,the ,,skeletons ,,of ,,horse ,,and ,,man #afg ,photo3 ,british ,museum 7,natural ,history74 ,a ,,reconstruction ,,of ,,the ,,java ,,man 7,coloured ,illustration7 #afh ,,profile ,,view ,,of ,,the ,,head ,,of ,,pithecanthropus1 ,,the ,,java ,,ape-,,man--,,an ,,early ,,offshoot ,,from ,,the ,,main ,,line ,,of ,,man',s ,,ascent #agj ,after a model by ,j4 ,h4 ,mc,gregor4 ,,piltdown ,,skull #agj ,from the reconstruction by ,j4 ,h4 ,mc,gregor4 ,,sand-,,pit ,,at ,,mauer1 ,,near ,,heidelberg3 ,,discovery ,,site ,,of ,,the ,,jaw ,,of ,,heidelberg ,,man #aga ,reproduced by permission from ,osborn's ,men of the ,old ,stone ,age4 ,,paintings ,,on ,,the ,,roof ,,of ,,the ,,altamira ,,cave ,,in ,,northern ,,spain1 ,,showing ,a ,,bison ,,and ,a ,,galloping ,,boar 7,coloured ,illustration7 #agb ,,piltdown ,,man1 ,,preceding ,,neanderthal ,,man1 ,,perhaps #ajj1jjj ,,to #aej1jjj ,,years ,,ago #agd ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,,the ,,neanderthal ,,man ,,of ,,la ,,chapelle-,,aux-,,saints #age ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,,restoration ,,by ,a4 ,,forestier ,,of ,,the ,,rhodesian ,,man ,,whose ,,skull ,,was ,,discovered ,,in #aiba #agf-agg ,,side ,,view ,,of ,a ,,prehistoric ,,human ,,skull ,,discovered ,,in #aiba ,,in ,,broken ,,hill ,,cave1 ,,northern ,,rhodesia #agh ,photo3 ,british ,museum 7,natural ,history74 ,a ,,cromagnon ,,man ,,or ,,cromagnard1 ,,representative ,,of ,a ,,strong ,,artistic ,,race ,,living ,,in ,,the ,,south ,,of ,,france ,,in ,,the ,,upper ,,pleistocene1 ,,perhaps #be1jjj ,,years ,,ago #agh ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,,photograph ,,showing ,a ,,narrow ,,passage ,,in ,,the ,,cavern ,,of ,,font-,,de-,,gaume ,,on ,,the ,,beune #agi ,reproduced by permission from ,osborn's ,men of the ,old ,stone ,age4 ,a ,,mammoth ,,drawn ,,on ,,the ,,wall ,,of ,,the ,,font-,,de-,,gaume ,,cavern #agi ,a ,,grazing ,,bison1 ,,delicately ,,and ,,carefully ,,drawn1 ,,engraved ,,on ,a ,,wall ,,of ,,the ,,altamira ,,cave1 ,,northern ,,spain #agi ,,photograph ,,of ,a ,,median ,,section ,,through ,,the ,,shell ,,of ,,the ,,pearly ,,nautilus #ahf ,,photograph ,,of ,,the ,,entire ,,shell ,,of ,,the ,,pearly ,,nautilus #ahf ,,nautilus #ahf ,,shoebill #ahg ,photo3 ,w4 ,s4 ,berridge4 ,,the ,,walking-,,fish ,,or ,,mud-,,skipper 7,periophthalmus71 ,,common ,,at ,,the ,,mouths ,,of ,,rivers ,,in ,,tropical ,,africa1 ,,asia1 ,,and ,,north-,,west ,,australia #aij ,,the ,,australian ,,more-,,pork ,,or ,,podargus #aij ,photo3 ,the ,times4 ,,pelican',s ,,bill1 ,,adapted ,,for ,,catching ,,and ,,storing ,,fishes #aia ,,spoonbill',s ,,bill1 ,,adapted ,,for ,,sifting ,,the ,,mud ,,and ,,catching ,,the ,,small ,,animals1 ,e4,g4 ,,fishes1 ,,crustaceans1 ,,insect ,,larv1 ,,which ,,live ,,there #aia ,,avocet',s ,,bill1 ,,adapted ,,for ,a ,,curious ,,sideways ,,scooping ,,in ,,the ,,shore-,,pools ,,and ,,catching ,,small ,,animals #aia ,,hornbill',s ,,bill1 ,,adapted ,,for ,,excavating ,a ,,nest ,,in ,a ,,tree1 ,,and ,,also ,,for ,,seizing ,,and ,,breaking ,,diverse ,,forms ,,of ,,food1 ,,from ,,mammals ,,to ,,tortoises1 ,,from ,,roots ,,to ,,fruits #aia ,,falcon',s ,,bill1 ,,adapted ,,for ,,seizing1 ,,killing1 ,,and ,,tearing ,,small ,,mammals ,,and ,,birds #aia ,,puffin',s ,,bill1 ,,adapted ,,for ,,catching ,,small ,,fishes ,,near ,,the ,,surface ,,of ,,the ,,sea1 ,,and ,,for ,,holding ,,them ,,when ,,caught ,,and ,,carrying ,,them ,,to ,,the ,,nest #aia ,,life-,,history ,,of ,a ,,frog #aib ,,hind-,,leg ,,of ,,whirligig ,,beetle ,,which ,,has ,,become ,,beautifully ,,modified ,,for ,,aquatic ,,locomotion #aib ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,the ,,big ,,robber-,,crab 7,birgus ,latro71 ,,that ,,climbs ,,the ,,coconut ,,palm ,,and ,,breaks ,,off ,,the ,,nuts #aic ,,early ,,life-,,history ,,of ,,the ,,salmon #aif ,,the ,,salmon ,,leaping ,,at ,,the ,,fall ,,is ,a ,,most ,,fascinating ,,spectacle #aig ,,diagram ,,of ,,the ,,life-,,history ,,of ,,the ,,common ,,eel 7,anguilla ,vulgaris7 #bjj ,,cassowary #bja ,photo3 ,gambier ,bolton4 ,,the ,,kiwi1 ,,another ,,flightless ,,bird1 ,,of ,,remarkable ,,appearance1 ,,habits1 ,,and ,,structure #bja ,photo3 ,gambier ,bolton4 ,,the ,,australian ,,frilled ,,lizard1 ,,which ,,is ,,at ,,present ,,trying ,,to ,,become ,a ,,biped #bjb ,a ,,carpet ,,of ,,gossamer #bjb ,,the ,,water ,,spider #bjc ,,jackdaw ,,balancing ,,on ,a ,,gatepost #bjh ,photo3 ,o4 ,j4 ,wilkinson4 ,,two ,,opossums ,,feigning ,,death #bjh ,from ,ingersoll's ,the ,wit of the ,wild4 ,,male ,,of ,,three-,,spined ,,stickleback1 ,,making ,a ,,nest ,,of ,,water-,,weed1 ,,glued ,,together ,,by ,,viscid ,,threads ,,secreted ,,from ,,the ,,kidneys ,,at ,,the ,,breeding ,,season #bji ,a ,,female ,,stickleback ,,enters ,,the ,,nest ,,which ,,the ,,male ,,has ,,made1 ,,lays ,,the ,,eggs ,,inside1 ,,and ,,then ,,departs #bji ,,homing ,,pigeon #bab ,photo3 ,imperial ,war ,museum4 ,,carrier ,,pigeon #bab ,photo3 ,imperial ,war ,museum4 ,,yellow-,,crowned ,,penguin #bac ,photo3 ,james's ,press ,agency4 ,,penguins ,,are ,a ,,peculiar ,,people #bac ,photo3 ,cagcombe ,co4 ,,harpy-,,eagle #baf ,photo3 ,w4 ,s4 ,berridge4 ,,the ,,dingo ,,or ,,wild ,,dog ,,of ,,australia1 ,,perhaps ,,an ,,indigenous ,,wild ,,species1 ,,perhaps ,a ,,domesticated ,,dog ,,that ,,has ,,gone ,,wild ,,or ,,feral #baf ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,woodpecker ,,hammering ,,at ,a ,,cotton-,,reel1 ,,attached ,,to ,a ,,tree #bag ,,the ,,beaver #bbj ,,the ,,thrush ,,at ,,its ,,anvil #bba ,photo3 ,f4 ,r4 ,hinkins ,son4 ,,alsatian ,,wolf-,,dog #bbf ,photo3 ,lafayette4 ,,the ,,polar ,,bear ,,of ,,the ,,far ,,north #bbg ,photo3 ,w4 ,s4 ,berridge4 ,,an ,,alligator ,,yawning ,,in ,,expectation ,,of ,,food #bbg ,from the ,smithsonian ,report1 #aiad4 ,,baby ,,orang #bcb ,photo3 ,w4 ,p4 ,dando4 ,,orang-,,utan #bcb ,photo3 ,gambier ,bolton4 ,,chimpanzee #bcc ,photo3 ,james's ,press ,agency4 ,,baby ,,orang-,,utan #bcc ,photo3 ,james's ,press ,agency4 ,,orang-,,utan #bcc ,photo3 ,james's ,press ,agency4 ,,baby ,,chimpanzees #bcc ,photo3 ,james's ,press ,agency4 ,,chimpanzee #bch ,photo3 ,w4 ,p4 ,dando4 ,,young ,,cheetahs1 ,,or ,,hunting ,,leopards #bch ,photo3 ,w4 ,s4 ,berridge4 ,,common ,,otter #bci ,photo3 ,c4 ,reid4 ,,sir ,,ernest ,,rutherford #bdf ,photo3 ,elliott ,fry4 ,j4 ,,clerk-,,maxwell #bdf ,photo3 ,rischgitz ,collection4 ,,sir ,,william ,,crookes #bdg ,photo3 ,ernest ,h4 ,mills4 ,,professor ,,sir ,w4 ,h4 ,,bragg #bdg ,photo3 ,photo ,press4 ,,comparative ,,sizes ,,of ,,molecules #bej ,,inconceivable ,,numbers ,,and ,,inconceivably ,,small ,,particles #bej ,,what ,,is ,a ,,million8 #bej ,,the ,,brownian ,,movement #bea ,a ,,soap ,,bubble 7,coloured ,illustration7 #beb ,reproduced from ,the ,forces of ,nature 7,messrs4 ,macmillan74 ,,detecting ,a ,,small ,,quantity ,,of ,,matter #bed ,from ,scientific ,ideas of ,to-day4 ,,this ,x-,,ray ,,photograph ,,is ,,that ,,of ,a ,,hand ,,of ,a ,,soldier ,,wounded ,,in ,,the ,,great ,,war #bed ,reproduced by permission of ,x-,rays ,ltd4 ,,an ,x-,,ray ,,photograph ,,of ,a ,,golf ,,ball1 ,,revealing ,,an ,,imperfect ,,core #bed ,photo3 ,national ,physical ,laboratory4 ,a ,,wonderful ,x-,,ray ,,photograph #bee ,reproduced by permission of ,x-,rays ,ltd4 ,,electric ,,discharge ,,in ,a ,,vacuum ,,tube #beh ,,the ,,relative ,,sizes ,,of ,,atoms ,,and ,,electrons #beh ,,electrons ,,streaming ,,from ,,the ,,sun ,,to ,,the ,,earth #bei ,,professor ,,sir ,j4 ,j4 ,,thomson #bfb ,,electrons ,,produced ,,by ,,passage ,,of ,x-,,rays ,,through ,,air #bfb ,from the ,smithsonian ,report1 #aiae4 ,,magnetic ,,deflection ,,of ,,radium ,,rays #bfc ,,professor ,r4 ,a4 ,,millikan',s ,,apparatus ,,for ,,counting ,,electrons #bfc ,reproduced by permission of ,scientific ,american4 ,,making ,,the ,,invisible ,,visible #bff ,,the ,,theory ,,of ,,electrons #bfg ,,arrangements ,,of ,,atoms ,,in ,a ,,diamond #bfg ,,disintegration ,,of ,,atoms #bgj ,,silk ,,tassel ,,electrified #bgj ,reproduced by permission from ,the ,interpretation of ,radium 7,john ,murray74 ,,silk ,,tassel ,,discharged ,,by ,,the ,,rays ,,from ,,radium #bgj ,a ,,huge ,,electric ,,spark #bga ,,electrical ,,attraction ,,between ,,common ,,objects #bga ,from ,scientific ,ideas of ,to-day4 ,,an ,,electric ,,spark #bgd ,photo3 ,leadbeater4 ,,an ,,ether ,,disturbance ,,around ,,an ,,electron ,,current #bge ,from ,scientific ,ideas of ,to-day4 ,,lightning #bgh ,photo3 ,h4 ,j4 ,shepstone4 ,,light ,,waves #bgi ,,the ,,magnetic ,,circuit ,,of ,,an ,,electric ,,current #bgi ,,the ,,magnet #bgi ,,rotating ,,disc ,,of ,,sir ,,isaac ,,newton ,,for ,,mixing ,,colours 7,coloured ,illustration7 #bhj ,,wave ,,shapes #bhb ,,the ,,power ,,of ,a ,,magnet #bhb ,,the ,,speed ,,of ,,light #bhc ,photo3 ,the ,locomotive ,publishing ,co41 ,ltd4 ,,rotating ,,disc ,,of ,,sir ,,isaac ,,newton ,,for ,,mixing ,,colours #bhc ,,niagara ,,falls #bhf ,,transformation ,,of ,,energy #bhg ,photo3 ,stephen ,cribb4 ,,boiling ,a ,,kettle ,,on ,,ice #bhg ,photo3 ,underwood ,underwood4 ,,the ,,cause ,,of ,,tides #bij ,,the ,,aegir ,,on ,,the ,,trent #bij ,photo3 ,g4 ,brocklehurst4 ,a ,,big ,,spring ,,tide1 ,,the ,,aegir ,,on ,,the ,,trent #bia ,photo3 ,g4 ,brocklehurst4 ,the ,outline of ,science ,,introduction ,there is abundant evidence of a widened and deepened interest in modern science4 ,how could it be otherwise when we think of the magnitude and the eventfulness of recent advances8 ,but the interest of the general public would be even greater than it is if the makers of new knowledge were more willing to expound their discoveries in ways that could be understanded of the people4 ,no one objects very much to technicalities in a game or on board a yacht1 and they are clearly necessary for terse and precise scientific description4 ,it is certain1 however1 that they can be reduced to a minimum without sacrificing accuracy1 when the object in view is to explain the gist of the matter4 ,so this ,,outline ,,of ,,science is meant for the general reader1 who lacks both time and opportunity for special study1 and yet would take an intelligent interest in the progress of science which is making the world always new4 ,the story of the triumphs of modern science is one of which ,man may well be proud4 ,science reads the secret of the distant star and anatomises the atom2 foretells the date of the comet's return and predicts the kinds of chickens that will hatch from a dozen eggs2 discovers the laws of the wind that bloweth where it listeth and reduces to order the disorder of disease4 ,science is always setting forth on ,columbus voyages1 discovering new worlds and conquering them by understanding4 ,for ,knowledge means ,foresight and ,foresight means ,power4 ,the idea of ,evolution has influenced all the sciences1 forcing us to think of everything as with a history behind it1 for we have travelled far since ,darwin's day4 ,the solar system1 the earth1 the mountain ranges1 and the great deeps1 the rocks and crystals1 the plants and animals1 man himself and his social institutions--all must be seen as the outcome of a long process of ,becoming4 ,there are some eighty-odd chemical elements on the earth to-day1 and it is now much more than a suggestion that these are the outcome of an inorganic evolution1 element giving rise to element1 going back and back to some primeval stuff1 from which they were all originally derived1 infinitely long ago4 ,no idea has been so powerful a tool in the fashioning of ,new ,knowledge as this simple but profound idea of ,evolution1 that the present is the child of the past and the parent of the future4 ,and with the picture of a continuity of evolution from nebula to social systems comes a promise of an increasing control--a promise that ,man will become not only a more accurate student1 but a more complete master of his world4 ,it is characteristic of modern science that the whole world is seen to be more vital than before4 ,everywhere there has been a passage from the static to the dynamic4 ,thus the new revelations of the constitution of matter1 which we owe to the discoveries of men like ,professor ,sir ,j4 ,j4 ,thomson1 ,professor ,sir ,ernest ,rutherford1 and ,professor ,frederick ,soddy1 have shown the very dust to have a complexity and an activity heretofore unimagined4 ,such phrases as dead matter and inert matter have gone by the board4 ,the new theory of the atom amounts almost to a new conception of the universe4 ,it bids fair to reveal to us many of nature's hidden secrets4 ,the atom is no longer the indivisible particle of matter it was once understood to be4 ,we know now that there is an atom within the atom--that what we thought was elementary can be dissociated and broken up4 ,the present-day theories of the atom and the constitution of matter are the outcome of the comparatively recent discovery of such things as radium1 the ,x-rays1 and the wonderful revelations of such instruments as the spectroscope and other highly perfected scientific instruments4 ,the advent of the electron theory has thrown a flood of light on what before was hidden or only dimly guessed at4 ,it has given us a new conception of the framework of the universe4 ,we are beginning to know and realise of what matter is made and what electric phenomena mean4 ,we can glimpse the vast stores of energy locked up in matter4 ,the new knowledge has much to tell us about the origin and phenomena1 not only of our own planet1 but other planets1 of the stars1 and the sun4 ,new light is thrown on the source of the sun's heat2 we can make more than guesses as to its probable age4 ,the great question to-day is3 is there one primordial substance from which all the varying forms of matter have been evolved8 ,but the discovery of electrons is only one of the revolutionary changes which give modern science an entrancing interest4 ,as in chemistry and physics1 so in the science of living creatures there have been recent advances that have changed the whole prospect4 ,a good instance is afforded by the discovery of the hormones1 or chemical messengers1 which are produced by ductless glands1 such as the thyroid1 the supra-renal1 and the pituitary1 and are distributed throughout the body by the blood4 ,the work of physiologists like ,professor ,starling and ,professor ,bayliss has shown that these chemical messengers regulate what may be called the pace of the body1 and bring about that regulated harmony and smoothness of working which we know as health4 ,it is not too much to say that the discovery of hormones has changed the whole of physiology4 ,our knowledge of the human body far surpasses that of the past generation4 ,the persistent patience of microscopists and technical improvements like the ultramicroscope have greatly increased our knowledge of the invisible world of life4 ,to the bacteria of a past generation have been added a multitude of microscopic animal microbes1 such as that which causes ,sleeping ,sickness4 ,the life-histories and the weird ways of many important parasites have been unravelled2 and here again knowledge means mastery4 ,to a degree which has almost surpassed expectations there has been a revelation of the intricacy of the stones and mortar of the house of life1 and the microscopic study of germ-cells has wonderfully supplemented the epoch-making experimental study of heredity which began with ,mendel4 ,it goes without saying that no one can call himself educated who does not understand the central and simple ideas of ,mendelism and other new departures in biology4 ,the procession of life through the ages and the factors in the sublime movement2 the peopling of the earth by plants and animals and the linking of life to life in subtle inter-relations1 such as those between flowers and their insect-visitors2 the life-histories of individual types and the extraordinary results of the new inquiry called experimental embryology--these also are among the subjects with which this ,,outline will deal4 ,the behaviour of animals is another fascinating study1 leading to a provisional picture of the dawn of mind4 ,indeed1 no branch of science surpasses in interest that which deals with the ways and habits--the truly wonderful devices1 adaptations1 and instincts--of insects1 birds1 and mammals4 ,we no longer deny a degree of intelligence to some members of the animal world--even the line between intelligence and reason is sometimes difficult to find4 ,fresh contacts between physiology and the study of man's mental life2 precise studies of the ways of children and wild peoples2 and new methods like those of the psycho-analyst must also receive the attention they deserve1 for they are giving us a ,new ,psychology and the claims of psychical research must also be recognised by the open-minded4 ,the general aim of the ,,outline is to give the reader a clear and concise view of the essentials of present-day science1 so that he may follow with intelligence the modern advance and share appreciatively in man's continued conquest of his kingdom4 ,j4 ,,arthur ,,thomson4 ,i ,,the ,,romance ,,of ,,the ,,heavens ,,the ,,scale ,,of ,,the ,,universe--,,the ,,solar ,,system #a ,the story of the triumphs of modern science naturally opens with ,astronomy4 ,the picture of the ,universe which the astronomer offers to us is imperfect2 the lines he traces are often faint and uncertain4 ,there are many problems which have been solved1 there are just as many about which there is doubt1 and notwithstanding our great increase in knowledge1 there remain just as many which are entirely unsolved4 ,the problem of the structure and duration of the universe said the great astronomer ,simon ,newcomb is the most far-reaching with which the mind has to deal4 ,its solution may be regarded as the ultimate object of stellar astronomy1 the possibility of reaching which has occupied the minds of thinkers since the beginning of civilisation4 ,before our time the problem could be considered only from the imaginative or the speculative point of view4 ,although we can to-day attack it to a limited extent by scientific methods1 it must be admitted that we have scarcely taken more than the first step toward the actual solution4444 ,what is the duration of the universe in time8 ,is it fitted to last for ever in its present form1 or does it contain within itself the seeds of dissolution8 ,must it1 in the course of time1 in we know not how many millions of ages1 be transformed into something very different from what it now is8 ,this question is intimately associated with the question whether the stars form a system4 ,if they do1 we may suppose that system to be permanent in its general features2 if not1 we must look further for our conclusions4 ,the ,heavenly ,bodies ,the heavenly bodies fall into two very distinct classes so far as their relation to our ,earth is concerned2 the one class1 a very small one1 comprises a sort of colony of which the ,earth is a member4 ,these bodies are called planets1 or wanderers4 ,there are eight of them1 including the ,earth1 and they all circle round the sun4 ,their names1 in the order of their distance from the sun1 are ,mercury1 ,venus1 ,earth1 ,mars1 ,jupiter1 ,saturn1 ,uranus1 ,neptune1 and of these ,mercury1 the nearest to the sun1 is rarely seen by the naked eye4 ,uranus is practically invisible1 and ,neptune quite so4 ,these eight planets1 together with the sun1 constitute1 as we have said1 a sort of little colony2 this colony is called the ,solar ,system4 ,the second class of heavenly bodies are those which lie outside the solar system4 ,every one of those glittering points we see on a starlit night is at an immensely greater distance from us than is any member of the ,solar ,system4 ,yet the members of this little colony of ours1 judged by terrestrial standards1 are at enormous distances from one another4 ,if a shell were shot in a straight line from one side of ,neptune's orbit to the other it would take five hundred years to complete its journey4 ,yet this distance1 the greatest in the ,solar ,system as now known 7excepting the far swing of some of the comets71 is insignificant compared to the distances of the stars4 ,one of the nearest stars to the earth that we know of is ,alpha ,centauri1 estimated to be some twenty-five million millions of miles away4 ,sirius1 the brightest star in the firmament1 is double this distance from the earth4 ,we must imagine the colony of planets to which we belong as a compact little family swimming in an immense void4 ,at distances which would take our shell1 not hundreds1 but millions of years to traverse1 we reach the stars--or rather1 a star1 for the distances between stars are as great as the distance between the nearest of them and our ,sun4 ,the ,earth1 the planet on which we live1 is a mighty globe bounded by a crust of rock many miles in thickness2 the great volumes of water which we call our oceans lie in the deeper hollows of the crust4 ,above the surface an ocean of invisible gas1 the atmosphere1 rises to a height of about three hundred miles1 getting thinner and thinner as it ascends4 ,illustration3 ,,laplace ,one of the greatest mathematical astronomers of all time and the originator of the nebular theory4 ,illustration3 ,photo3 ,royal ,astronomical ,society4 ,,professor ,j4 ,c4 ,,adams who1 anticipating the great ,french mathematician1 ,le ,verrier1 discovered the planet ,neptune by calculations based on the irregularities of the orbit of ,uranus4 ,one of the most dramatic discoveries in the history of ,science4 ,illustration3 ,photo3 ,elliott ,fry1 ,ltd4 ,,professor ,,eddington ,professor of ,astronomy at ,cambridge4 ,the most famous of the ,english disciples of ,einstein4 ,illustration3 ,,fig4 #a4--;,,diagrams ,,of ,,the ,,solar ,,system ,,the ,,comparative ,,distances ,,of ,,the ,,planets 7,drawn approximately to scale7 ,the isolation of the ,solar ,system is very great4 ,on the above scale the nearest star 7at a distance of #be trillions of miles7 would be over one half mile away4 ,the hours1 days1 and years are the measures of time as we use them2 that is3 ,jupiter's ,day 7one rotation of the planet7 is made in ten of our hours2 ,mercury's ,year 7one revolution of the planet around the ,sun7 is eighty-eight of our days4 ,mercury's ,day and ,year are the same4 ,this planet turns always the same side to the ,sun4 ,illustration3 ,,the ,,comparative ,,sizes ,,of ,,the ,,sun ,,and ,,the ,,planets 7,drawn approximately to scale7 ,on this scale the ,sun would be #ag-a_/b inches in diameter2 it is far greater than all the planets put together4 ,jupiter1 in turn1 is greater than all the other planets put together4 ,except when the winds rise to a high speed1 we seem to live in a very tranquil world4 ,at night1 when the glare of the sun passes out of our atmosphere1 the stars and planets seem to move across the heavens with a stately and solemn slowness4 ,it was one of the first discoveries of modern astronomy that this movement is only apparent4 ,the apparent creeping of the stars across the heavens at night is accounted for by the fact that the earth turns upon its axis once in every twenty-four hours4 ,when we remember the size of the earth we see that this implies a prodigious speed4 ,in addition to this the earth revolves round the sun at a speed of more than a thousand miles a minute4 ,its path round the sun1 year in year out1 measures about #ehj1jjj1jjj miles4 ,the earth is held closely to this path by the gravitational pull of the sun1 which has a mass #ccc1dcb times that of the earth4 ,if at any moment the sun ceased to exert this pull the earth would instantly fly off into space straight in the direction in which it was moving at the time1 that is to say1 at a tangent4 ,this tendency to fly off at a tangent is continuous4 ,it is the balance between it and the sun's pull which keeps the earth to her almost circular orbit4 ,in the same way the seven other planets are held to their orbits4 ,circling round the earth1 in the same way as the earth circles round the sun1 is our moon4 ,sometimes the moon passes directly between us and the sun1 and cuts off the light from us4 ,we then have a total or partial eclipse of the sun4 ,at other times the earth passes directly between the sun and the moon1 and causes an eclipse of the moon4 ,the great ball of the earth naturally trails a mighty shadow across space1 and the moon is eclipsed when it passes into this4 ,the other seven planets1 five of which have moons of their own1 circle round the sun as the earth does4 ,the sun's mass is immensely larger than that of all the planets put together1 and all of them would be drawn into it and perish if they did not travel rapidly round it in gigantic orbits4 ,so the eight planets1 spinning round on their axes1 follow their fixed paths round the sun4 ,the planets are secondary bodies1 but they are most important1 because they are the only globes in which there can be life1 as we know life4 ,if we could be transported in some magical way to an immense distance in space above the sun1 we should see our ,solar ,system as it is drawn in the accompanying diagram 7,fig4 #a71 except that the planets would be mere specks1 faintly visible in the light which they receive from the sun4 7,this diagram is drawn approximately to scale47 ,if we moved still farther away1 trillions of miles away1 the planets would fade entirely out of view1 and the sun would shrink into a point of fire1 a star4 ,and here you begin to realize the nature of the universe4 ,the sun is a star4 ,the stars are suns4 ,our sun looks big simply because of its comparative nearness to us4 ,the universe is a stupendous collection of millions of stars or suns1 many of which may have planetary families like ours4 #b ,the ,scale of the ,universe ,how many stars are there8 ,a glance at a photograph of star-clouds will tell at once that it is quite impossible to count them4 ,the fine photograph reproduced in ,figure #b represents a very small patch of that pale-white belt1 the ,milky ,way1 which spans the sky at night4 ,it is true that this is a particularly rich area of the ,milky ,way1 but the entire belt of light has been resolved in this way into masses or clouds of stars4 ,astronomers have counted the stars in typical districts here and there1 and from these partial counts we get some idea of the total number of stars4 ,there are estimated to be between two and three thousand million stars4 ,yet these stars are separated by inconceivable distances from each other1 and it is one of the greatest triumphs of modern astronomy to have mastered1 so far1 the scale of the universe4 ,for several centuries astronomers have known the relative distances from each other of the sun and the planets4 ,if they could discover the actual distance of any one planet from any other1 they could at once tell all the distances within the ,solar ,system4 ,the sun is1 on the latest measurements1 at an average distance of #ib1hcj1jjj miles from the earth1 for as the orbit of the earth is not a true circle1 this distance varies4 ,this means that in six months from now the earth will be right at the opposite side of its path round the sun1 or #ahe1jjj1jjj miles away from where it is now4 ,viewed or photographed from two positions so wide apart1 the nearest stars show a tiny shift against the background of the most distant stars1 and that is enough for the mathematician4 ,he can calculate the distance of any star near enough to show this shift4 ,we have found that the nearest star to the earth1 a recently discovered star1 is twenty-five trillion miles away4 ,only thirty stars are known to be within a hundred trillion miles of us4 ,this way of measuring does not1 however1 take us very far away in the heavens4 ,there are only a few hundred stars within five hundred trillion miles of the earth1 and at that distance the shift of a star against the background 7parallax1 the astronomer calls it7 is so minute that figures are very uncertain4 ,at this point the astronomer takes up a new method4 ,he learns the different types of stars1 and then he is able to deduce more or less accurately the distance of a star of a known type from its faintness4 ,he1 of course1 has instruments for gauging their light4 ,as a result of twenty years work in this field1 it is now known that the more distant stars of the ,milky ,way are at least a hundred thousand trillion 7#ajj1jjj1jjj1jjj1jjj1jjj7 miles away from the sun4 ,our sun is in a more or less central region of the universe1 or a few hundred trillion miles from the actual centre4 ,the remainder of the stars1 which are all outside our ,solar ,system1 are spread out1 apparently1 in an enormous disc-like collection1 so vast that even a ray of light1 which travels at the rate of #ahf1jjj miles a second1 would take #ej1jjj years to travel from one end of it to the other4 ,this1 then is what we call our universe4 ,are there other ,universes8 ,why do we say our universe8 ,why not the universe8 ,it is now believed by many of our most distinguished astronomers that our colossal family of stars is only one of many universes4 ,by a universe an astronomer means any collection of stars which are close enough to control each other's movements by gravitation2 and it is clear that there might be many universes1 in this sense1 separated from each other by profound abysses of space4 ,probably there are4 ,for a long time we have been familiar with certain strange objects in the heavens which are called spiral nebul 7,fig #d74 ,we shall see at a later stage what a nebula is1 and we shall see that some astronomers regard these spiral nebul as worlds in the making4 ,but some of the most eminent astronomers believe that they are separate universes--island-universes they call them--or great collections of millions of stars like our universe4 ,there are certain peculiarities in the structure of the ,milky ,way which lead these astronomers to think that our universe may be a spiral nebula1 and that the other spiral nebul are other universes4 ,illustration3 ,photo3 ,harvard ,college ,observatory4 ,,fig4 #b4--,,the ,,milky ,,way ,note the cloud-like effect4 ,illustration3 ,,fig4 #c--,,the ,,moon ,,entering ,,the ,,shadow ,,cast ,,by ,,the ,,earth ,the diagram shows the ,moon partially eclipsed4 ,illustration3 ,from a photograph taken at the ,yerkes ,observatory ,,fig4 #d4--,,the ,,great ,,nebula ,,in ,,andromeda1 ,,messier #ca ,vast as is the ,solar ,system1 then1 it is excessively minute in comparison with the ,stellar ,system1 the universe of the ,stars1 which is on a scale far transcending anything the human mind can apprehend4 ,,the ,,solar ,,system ,,the ,,sun #a ,but now let us turn to the ,solar ,system1 and consider the members of our own little colony4 ,within the ,solar ,system there are a large number of problems that interest us4 ,what is the size1 mass1 and distance of each of the planets8 ,what satellites1 like our ,moon1 do they possess8 ,what are their temperatures8 ,and those other1 sporadic members of our system1 comets and meteors1 what are they8 ,what are their movements8 ,how do they originate8 ,and the ,sun itself1 what is its composition1 what is the source of its heat1 how did it originate8 ,is it running down8 ,these last questions introduce us to a branch of astronomy which is concerned with the physical constitution of the stars1 a study which1 not so very many years ago1 may well have appeared inconceivable4 ,but the spectroscope enables us to answer even these questions1 and the answer opens up questions of yet greater interest4 ,we find that the stars can be arranged in an order of development--that there are stars at all stages of their life-history4 ,the main lines of the evolution of the stellar universe can be worked out4 ,in the sun and stars we have furnaces with temperatures enormously high2 it is in such conditions that substances are resolved into their simplest forms1 and it is thus we are enabled to obtain a knowledge of the most primitive forms of matter4 ,it is in this direction that the spectroscope 7which we shall refer to immediately7 has helped us so much4 ,it is to this wonderful instrument that we owe our knowledge of the composition of the sun and stars1 as we shall see4 ,that the spectroscope will detect the millionth of a milligram of matter1 and on that account has discovered new elements1 commands our admiration2 but when we find in addition that it will detect the nature of forms of matter trillions of miles away1 and moreover1 that it will measure the velocities with which these forms of matter are moving with an absurdly small per cent4 of possible error1 we can easily acquiesce in the statement that it is the greatest instrument ever devised by the brain and hand of man4 ,such are some of the questions with which modern astronomy deals4 ,to answer them requires the employment of instruments of almost incredible refinement and exactitude and also the full resources of mathematical genius4 ,whether astronomy be judged from the point of view of the phenomena studied1 the vast masses1 the immense distances1 the ons of time1 or whether it be judged as a monument of human ingenuity1 patience1 and the rarest type of genius1 it is certainly one of the grandest1 as it is also one of the oldest1 of the sciences4 ,the ,solar ,system ,in the ,solar ,system we include all those bodies dependent on the sun which circulate round it at various distances1 deriving their light and heat from the sun--the planets and their moons1 certain comets and a multitude of meteors3 in other words1 all bodies whose movements in space are determined by the gravitational pull of the sun4 ,the ,sun ,thanks to our wonderful modern instruments and the ingenious methods used by astronomers1 we have to-day a remarkable knowledge of the sun4 ,look at the figure of the sun in the frontispiece4 ,the picture represents an eclipse of the sun2 the dark body of the moon has screened the sun's shining disc and taken the glare out of our eyes2 we see a silvery halo surrounding the great orb on every side4 ,it is the sun's atmosphere1 or crown 7corona71 stretching for millions of miles into space in the form of a soft silvery-looking light2 probably much of its light is sunlight reflected from particles of dust1 although the spectroscope shows an element in the corona that has not so far been detected anywhere else in the universe and which in consequence has been named ,coronium4 ,we next notice in the illustration that at the base of the halo there are red flames peeping out from the edges of the hidden disc4 ,when one remembers that the sun is #hff1jjj miles in diameter1 one hardly needs to be told that these flames are really gigantic4 ,we shall see what they are presently4 ,regions of the ,sun ,the astronomer has divided the sun into definite concentric regions or layers4 ,these layers envelop the nucleus or central body of the sun somewhat as the atmosphere envelops our earth4 ,it is through these vapour layers that the bright white body of the sun is seen4 ,of the innermost region1 the heart or nucleus of the sun1 we know almost nothing4 ,the central body or nucleus is surrounded by a brilliantly luminous envelope or layer of vaporous matter which is what we see when we look at the sun and which the astronomer calls the photosphere4 ,above--that is1 overlying--the photosphere there is a second layer of glowing gases1 which is known as the reversing layer4 ,this layer is cooler than the underlying photosphere2 it forms a veil of smoke-like haze and is of from #ejj to #a1jjj miles in thickness4 ,a third layer or envelope immediately lying over the last one is the region known as the chromosphere4 ,the chromosphere extends from #e1jjj to #aj1jjj miles in thickness--a sea of red tumultuous surging fire4 ,chief among the glowing gases is the vapour of hydrogen4 ,the intense white heat of the photosphere beneath shines through this layer1 overpowering its brilliant redness4 ,from the uppermost portion of the chromosphere great fiery tongues of glowing hydrogen and calcium vapour shoot out for many thousands of miles1 driven outward by some prodigious expulsive force4 ,it is these red prominences which are such a notable feature in the picture of the eclipse of the sun already referred to4 ,during the solar eclipse of #aiai one of these red flames rose in less than seven hours from a height of #acj1jjj miles to more than #ejj1jjj miles above the sun's surface4 ,this immense column of red-hot gas1 four or five times the thickness of the earth1 was soaring upward at the rate of #fj1jjj miles an hour4 ,these flaming jets or prominences shooting out from the chromosphere are not to be seen every day by the naked eye2 the dazzling light of the sun obscures them1 gigantic as they are4 ,they can be observed1 however1 by the spectroscope any day1 and they are visible to us for a very short time during an eclipse of the sun4 ,some extraordinary outbursts have been witnessed4 ,thus the late ,professor ,young described one on ,september #g1 #ahga1 when he had been examining a prominence by the spectroscope3 ,it had remained unchanged since noon of the previous day--a long1 low1 quiet-looking cloud1 not very dense1 or brilliant1 or in any way remarkable except for its size4 ,at #ab3cj p4m4 the ,professor left the spectroscope for a short time1 and on returning half an hour later to his observations1 he was astonished to find the gigantic ,sun flame shattered to pieces4 ,the solar atmosphere was filled with flying debris1 and some of these portions reached a height of #ajj1jjj miles above the solar surface4 ,moving with a velocity which1 even at the distance of #ic1jjj1jjj miles1 was almost perceptible to the eye1 these fragments doubled their height in ten minutes4 ,on ,january #cj1 #ahhe1 another distinguished solar observer1 the late ,professor ,tacchini of ,rome1 observed one of the greatest prominences ever seen by man4 ,its height was no less than #adb1jjj miles--eighteen times the diameter of the earth4 ,another mighty flame was so vast that supposing the eight large planets of the solar system ranged one on top of the other1 the prominence would still tower above them4#a #a ,the ,romance of ,astronomy1 by ,h4 ,macpherson4 ,illustration3 ,,fig4 #e4--;,,diagram ,,showing ,,the ,,main ,,layers ,,of ,,the ,,sun ,compare with frontispiece4 ,illustration3 ,photo3 ,royal ,observatory1 ,greenwich4 ,,fig4 #f4--,,solar ,,prominences ,,seen ,,at ,,total ,,solar ,,eclipse1 ,may #bi1 #aiai4 ,,taken ,,at ,,sobral1 ,,brazil4 ,the small ,corona is also visible4 ,illustration3 ,,fig4 #g4--,,the ,,visible ,,surface ,,of ,,the ,,sun ,a photograph taken at the ,mount ,wilson ,observatory of the ,carnegie ,institution at ,washington4 ,illustration3 ,,fig4 #h4--,,the ,,sun ,photographed in the light of glowing hydrogen1 at the ,mount ,wilson ,observatory of the ,carnegie ,institution of ,washington3 vortex phenomena near the spots are especially prominent4 ,the fourth and uppermost layer or region is that of the corona1 of immense extent and fading away into the surrounding sky--this we have already referred to4 ,the diagram 7,fig4 #e7 shows the dispositions of these various layers of the sun4 ,it is through these several transparent layers that we see the white light body of the sun4 #b ,the ,surface of the ,sun ,here let us return to and see what more we know about the photosphere--the sun's surface4 ,it is from the photosphere that we have gained most of our knowledge of the composition of the sun1 which is believed not to be a solid body4 ,examination of the photosphere shows that the outer surface is never at rest4 ,small bright cloudlets come and go in rapid succession1 giving the surface1 through contrasts in luminosity1 a granular appearance4 ,of course1 to be visible at all at #ib1hcj1jjj miles the cloudlets cannot be small4 ,they imply enormous activity in the photosphere4 ,if we might speak picturesquely the sun's surface resembles a boiling ocean of white-hot metal vapours4 ,we have to-day a wonderful instrument1 which will be described later1 which dilutes1 as it were1 the general glare of the sun1 and enables us to observe these fiery eruptions at any hour4 ,the oceans of red-hot gas and white-hot metal vapour at the sun's surface are constantly driven by great storms4 ,some unimaginable energy streams out from the body or muscles of the sun and blows its outer layers into gigantic shreds1 as it were4 ,the actual temperature at the sun's surface1 or what appears to us to be the surface--the photosphere--is1 of course1 unknown1 but careful calculation suggests that it is from #e1jjj ,c4 to #g1jjj ,c4 ,the interior is vastly hotter4 ,we can form no conception of such temperatures as must exist there4 ,not even the most obdurate solid could resist such temperatures1 but would be converted almost instantaneously into gas4 ,but it would not be gas as we know gases on the earth4 ,the enormous pressures that exist on the sun must convert even gases into thick treacly fluids4 ,we can only infer this state of matter4 ,it is beyond our power to reproduce it4 ,sun-spots ,it is in the brilliant photosphere that the dark areas known as sun-spots appear4 ,some of these dark spots--they are dark only by contrast with the photosphere surrounding them--are of enormous size1 covering many thousands of square miles of surface4 ,what they are we cannot positively say4 ,they look like great cavities in the sun's surface4 ,some think they are giant whirlpools4 ,certainly they seem to be great whirling streams of glowing gases with vapours above them and immense upward and downward currents within them4 ,round the edges of the sun-spots rise great tongues of flame4 ,perhaps the most popularly known fact about sun-spots is that they are somehow connected with what we call magnetic storms on earth4 ,these magnetic storms manifest themselves in interruptions of our telegraphic and telephonic communications1 in violent disturbances of the mariner's compass1 and in exceptional auroral displays4 ,the connection between the two sets of phenomena cannot be doubted1 even although at times there may be a great spot on the sun without any corresponding magnetic storm effects on the earth4 ,a surprising fact about sun-spots is that they show definite periodic variations in number4 ,the best-defined period is one of about eleven years4 ,during this period the spots increase to a maximum in number and then diminish to a minimum1 the variation being more or less regular4 ,now this can only mean one thing4 ,to be periodic the spots must have some deep-seated connection with the fundamental facts of the sun's structure and activities4 ,looked at from this point of view their importance becomes great4 ,illustration3 ,reproduction from ,the ,forces of ,nature 7,messrs4 ,macmillan7 ,,the ,,aurora ,,borealis ,the aurora borealis is one of the most beautiful spectacles in the sky4 ,the colours and shape change every instant2 sometimes a fan-like cluster of rays1 at other times long golden draperies gliding one over the other4 ,blue1 green1 yellow1 red1 and white combine to give a glorious display of colour4 ,the theory of its origin is still1 in part1 obscure1 but there can be no doubt that the aurora is related to the magnetic phenomena of the earth and therefore is connected with the electrical influence of the sun4 ,it is from the study of sun-spots that we have learned that the sun's surface does not appear to rotate all at the same speed4 ,the equatorial regions are rotating quicker than regions farther north or south4 ,a point forty-five degrees from the equator seems to take about two and a half days longer to complete one rotation than a point on the equator4 ,this1 of course1 confirms our belief that the sun cannot be a solid body4 ,what is its composition8 ,we know that there are present1 in a gaseous state1 such well-known elements as sodium1 iron1 copper1 zinc1 and magnesium2 indeed1 we know that there is practically every element in the sun that we know to be in the earth4 ,how do we know8 ,it is from the photosphere1 as has been said1 that we have won most of our knowledge of the sun4 ,the instrument used for this purpose is the spectroscope2 and before proceeding to deal further with the sun and the source of its energy it will be better to describe this instrument4 ,a ,,wonderful ,,instrument ,,and ,,what ,,it ,,reveals ,the spectroscope is an instrument for analysing light4 ,so important is it in the revelations it has given us that it will be best to describe it fully4 ,every substance to be examined must first be made to glow1 made luminous2 and as nearly everything in the heavens is luminous the instrument has a great range in ,astronomy4 ,and when we speak of analysing light1 we mean that the light may be broken up into waves of different lengths4 ,what we call light is a series of minute waves in ether1 and these waves are--measuring them from crest to crest1 so to say--of various lengths4 ,each wave-length corresponds to a colour of the rainbow4 ,the shortest waves give us a sensation of violet colour1 and the largest waves cause a sensation of red4 ,the rainbow1 in fact1 is a sort of natural spectrum4 7,the meaning of the rainbow is that the moisture-laden air has sorted out these waves1 in the sun's light1 according to their length47 ,now the simplest form of spectroscope is a glass prism--a triangular-shaped piece of glass4 ,if white light 7sunlight1 for example7 passes through a glass prism1 we see a series of rainbow-tinted colours4 ,anyone can notice this effect when sunlight is shining through any kind of cut glass--the stopper of a wine decanter1 for instance4 ,if1 instead of catching with the eye the coloured lights as they emerge from the glass prism1 we allow them to fall on a screen1 we shall find that they pass1 by continuous gradations1 from red at the one end of the screen1 through orange1 yellow1 green1 blue1 and indigo1 to violet at the other end4 ,in other words1 what we call white light is composed of rays of these several colours4 ,they go to make up the effect which we call white4 ,and now just as water can be split up into its two elements1 oxygen and hydrogen1 so sunlight can be broken up into its primary colours1 which are those we have just mentioned4 ,this range of colours1 produced by the spectroscope1 we call the solar spectrum1 and these are1 from the spectroscopic point of view1 primary colours4 ,each shade of colour has its definite position in the spectrum4 ,that is to say1 the light of each shade of colour 7corresponding to its wave-length7 is reflected through a certain fixed angle on passing through the glass prism4 ,every possible kind of light has its definite position1 and is denoted by a number which gives the wave-length of the vibrations constituting that particular kind of light4 ,now1 other kinds of light besides sunlight can be analysed4 ,light from any substance which has been made incandescent may be observed with the spectroscope in the same way1 and each element can be thus separated4 ,it is found that each substance 7in the same conditions of pressure1 etc47 gives a constant spectrum of its own4 ,each metal displays its own distinctive colour4 ,it is obvious1 therefore1 that the spectrum provides the means for identifying a particular substance4 ,it was by this method that we discovered in the sun the presence of such well-known elements as sodium1 iron1 copper1 zinc1 and magnesium4 ,illustration3 ,yerkes ,observatory4 ,,fig4 #i4--,,the ,,great ,,sun-,,spot ,,of ,,july #ag1 #aije ,illustration3 ,from photographs taken at the ,yerkes ,observatory4 ,,fig4 #aj4--,,solar ,,prominences ,these are about #fj1jjj miles in height4 ,the two photographs show the vast changes occurring in ten minutes4 ,october #aj1 #aiaj4 ,illustration3 ,photo3 ,mount ,wilson ,observatory4 ,,fig4 #aa4--,,mars1 ,october #e1 #aiji ,showing the dark markings and the ,polar ,cap4 ,illustration3 ,,fig4 #ab4--;,,jupiter ,showing the belts which are probably cloud formations4 ,illustration3 ,photo3 ,professor ,e4 ,e4 ,barnard1 ,yerkes ,observatory4 ,,fig4 #ac4--,,saturn1 ,november #ai1 #aiaa ,showing the rings1 mighty swarms of meteorites4 ,every chemical element known1 then1 has a distinctive spectrum of its own when it is raised to incandescence1 and this distinctive spectrum is as reliable a means of identification for the element as a human face is for its owner4 ,whether it is a substance glowing in the laboratory or in a remote star makes no difference to the spectroscope2 if the light of any substance reaches it1 that substance will be recognised and identified by the characteristic set of waves4 ,the spectrum of a glowing mass of gas will consist in a number of bright lines of various colours1 and at various intervals2 corresponding to each kind of gas1 there will be a peculiar and distinctive arrangement of bright lines4 ,but if the light from such a mass of glowing gas be made to pass through a cool mass of the same gas it will be found that dark lines replace the bright lines in the spectrum1 the reason for this being that the cool gas absorbs the rays of light emitted by the hot gas4 ,experiments of this kind enable us to reach the important general statement that every gas1 when cold1 absorbs the same rays of light which it emits when hot4 ,crossing the solar spectrum are hundreds and hundreds of dark lines4 ,these could not at first be explained1 because this fact of discriminative absorption was not known4 ,we understand now4 ,the sun's white light comes from the photosphere1 but between us and the photosphere there is1 as we have seen1 another solar envelope of relatively cooler vapours--the reversing layer4 ,each constituent element in this outer envelope stops its own kind of light1 that is1 the kind of light made by incandescent atoms of the same element in the photosphere4 ,the stoppages register themselves in the solar spectrum as dark lines placed exactly where the corresponding bright lines would have been4 ,the explanation once attained1 dark lines became as significant as bright lines4 ,the secret of the sun's composition was out4 ,we have found practically every element in the sun that we know to be in the earth4 ,we have identified an element in the sun before we were able to isolate it on the earth4 ,we have been able even to point to the coolest places on the sun1 the centres of sun-spots1 where alone the temperature seems to have fallen sufficiently low to allow chemical compounds to form4 ,it is thus we have been able to determine what the stars1 comets1 or nebul are made of4 ,a ,unique ,discovery ,in #ahfh ,sir ,norman ,lockyer detected a light coming from the prominences of the sun which was not given by any substance known on earth1 and attributed this to an unknown gas which he called helium1 from the ,greek helios1 the sun4 ,in #ahie ,sir ,william ,ramsay discovered in certain minerals the same gas identified by the spectroscope4 ,we can say1 therefore1 that this gas was discovered in the sun nearly thirty years before it was found on earth2 this discovery of the long-lost heir is as thrilling a chapter in the detective story of science as any in the sensational stories of the day1 and makes us feel quite certain that our methods really tell us of what elements sun and stars are built up4 ,the light from the corona of the sun1 as we have mentioned indicates a gas still unknown on earth1 which has been christened ,coronium4 ,measuring the ,speed of ,light ,but this is not all2 soon a new use was found for the spectroscope4 ,we found that we could measure with it the most difficult of all speeds to measure1 speed in the line of sight4 ,movement at right angles to the direction in which one is looking is1 if there is sufficient of it1 easy to detect1 and1 if the distance of the moving body is known1 easy to measure4 ,but movement in the line of vision is both difficult to detect and difficult to measure4 ,yet1 even at the enormous distances with which astronomers have to deal1 the spectroscope can detect such movement and furnish data for its measurement4 ,if a luminous body containing1 say1 sodium is moving rapidly towards the spectroscope1 it will be found that the sodium lines in the spectrum have moved slightly from their usual definite positions towards the violet end of the spectrum1 the amount of the change of position increasing with the speed of the luminous body4 ,if the body is moving away from the spectroscope the shifting of the spectral lines will be in the opposite direction1 towards the red end of the spectrum4 ,in this way we have discovered and measured movements that otherwise would probably not have revealed themselves unmistakably to us for thousands of years4 ,in the same way we have watched1 and measured the speed of1 tremendous movements on the sun1 and so gained proof that the vast disturbances we should expect there actually do occur4 ,illustration3 ,,the ,,spectroscope ,,is ,,an ,,instrument ,,for ,,analysing ,,light2 ,,it ,,provides ,,the ,,means ,,for ,,identifying ,,different ,,substances ,this pictorial diagram illustrates the principal of ,spectrum ,analysis1 showing how sunlight is decomposed into its primary colours4 ,what we call white light is composed of seven different colours4 ,the diagram is relieved of all detail which would unduly obscure the simple process by which a ray of light is broken up by a prism into different wave-lengths4 ,the spectrum rays have been greatly magnified4 ,,is ,,the ,,sun ,,dying8 #c ,now let us return to our consideration of the sun4 ,to us on the earth the most patent and most astonishing fact about the sun is its tremendous energy4 ,heat and light in amazing quantities pour from it without ceasing4 ,where does this energy come from8 ,enormous jets of red glowing gases can be seen shooting outwards from the sun1 like flames from a fire1 for thousands of miles4 ,does this argue fire1 as we know fire on the earth8 ,on this point the scientist is sure4 ,the sun is not burning1 and combustion is not the source of its heat4 ,combustion is a chemical reaction between atoms4 ,the conditions that make it possible are known and the results are predictable and measurable4 ,but no chemical reaction of the nature of combustion as we know it will explain the sun's energy1 nor indeed will any ordinary chemical reaction of any kind4 ,if the sun were composed of combustible material throughout and the conditions of combustion as we understand them were always present1 the sun would burn itself out in some thousands of years1 with marked changes in its heat and light production as the process advanced4 ,there is no evidence of such changes4 ,there is1 instead1 strong evidence that the sun has been emitting light and heat in prodigious quantities1 not for thousands1 but for millions of years4 ,every addition to our knowledge that throws light on the sun's age seems to make for increase rather than decrease of its years4 ,this makes the wonder of its energy greater4 ,and we cannot avoid the issue of the source of the energy by saying merely that the sun is gradually radiating away an energy that originated in some unknown manner1 away back at the beginning of things4 ,reliable calculations show that the years required for the mere cooling of a globe like the sun could not possibly run to millions4 ,in other words1 the sun's energy must be subject to continuous and more or less steady renewal4 ,however it may have acquired its enormous energy in the past1 it must have some source of energy in the present4 ,the best explanation that we have to-day of this continuous accretion of energy is that it is due to shrinkage of the sun's bulk under the force of gravity4 ,gravity is one of the most mysterious forces of nature1 but it is an obvious fact that bodies behave as if they attracted one another1 and ,newton worked out the law of this attraction4 ,we may say1 without trying to go too deeply into things1 that every particle of matter attracts every other throughout the universe4 ,if the diameter of the sun were to shrink by one mile all round1 this would mean that all the millions of tons in the outer one-mile thickness would have a straight drop of one mile towards the centre4 ,and that is not all1 because obviously the layers below this outer mile would also drop inwards1 each to a less degree than the one above it4 ,what a tremendous movement of matter1 however slowly it might take place6 ,and what a tremendous energy would be involved6 ,astronomers calculate that the above shrinkage of one mile all round would require fifty years for its completion1 assuming1 reasonably1 that there is close and continuous relationship between loss of heat by radiation and shrinkage4 ,even if this were true we need not feel over-anxious on this theory2 before the sun became too cold to support life many millions of years would be required4 ,it was suggested at one time that falls of meteoric matter into the sun would account for the sun's heat4 ,this position is hardly tenable now4 ,the mere bulk of the meteoric matter required by the hypothesis1 apart from other reasons1 is against it4 ,there is undoubtedly an enormous amount of meteoric matter moving about within the bounds of the solar system1 but most of it seems to be following definite routes round the sun like the planets4 ,the stray erratic quantities destined to meet their doom by collision with the sun can hardly be sufficient to account for the sun's heat4 ,recent study of radio-active bodies has suggested another factor that may be working powerfully along with the force of gravitation to maintain the sun's store of heat4 ,in radio-active bodies certain atoms seem to be undergoing disintegration4 ,these atoms appear to be splitting up into very minute and primitive constituents4 ,but since matter may be split up into such constituents1 may it not be built up from them8 ,the question is whether these radio-active elements are undergoing disintegration1 or formation1 in the sun4 ,if they are undergoing disintegration--and the sun itself is undoubtedly radio-active--then we have another source of heat for the sun that will last indefinitely4 ,,the ,,planets ,,life ,,in ,,other ,,worlds8 #a ,it is quite clear that there cannot be life on the stars4 ,nothing solid or even liquid can exist in such furnaces as they are4 ,life exists only on planets1 and even on these its possibilities are limited4 ,whether all the stars1 or how many of them1 have planetary families like our sun1 we cannot positively say4 ,if they have1 such planets would be too faint and small to be visible tens of trillions of miles away4 ,some astronomers think that our sun may be exceptional in having planets1 but their reasons are speculative and unconvincing4 ,probably a large proportion at least of the stars have planets1 and we may therefore survey the globes of our own solar system and in a general way extend the results to the rest of the universe4 ,in considering the possibility of life as we know it we may at once rule out the most distant planets from the sun1 ,uranus and ,neptune4 ,they are probably intrinsically too hot4 ,we may also pass over the nearest planet to the sun1 ,mercury4 ,we have reason to believe that it turns on its axis in the same period as it revolves round the sun1 and it must therefore always present the same side to the sun4 ,this means that the heat on the sunlit side of ,mercury is above boiling-point1 while the cold on the other side must be between two and three hundred degrees below freezing-point4 ,the ,planet ,venus ,the planet ,venus1 the bright globe which is known to all as the morning and evening star1 seems at first sight more promising as regards the possibility of life4 ,it is of nearly the same size as the earth1 and it has a good atmosphere1 but there are many astronomers who believe that1 like ,mercury1 it always presents the same face to the sun1 and it would therefore have the same disadvantage--a broiling heat on the sunny side and the cold of space on the opposite side4 ,we are not sure4 ,the surface of ,venus is so bright--the light of the sun is reflected to us by such dense masses of cloud and dust--that it is difficult to trace any permanent markings on it1 and thus ascertain how long it takes to rotate on its axis4 ,many astronomers believe that they have succeeded1 and that the planet always turns the same face to the sun4 ,if it does1 we can hardly conceive of life on its surface1 in spite of the cloud-screen4 ,illustration3 ,,fig4 #ad4--,,the ,,moon ,showing a great plain and some typical craters4 ,there are thousands of these craters1 and some theories of their origin are explained on page #cd4 ,illustration3 ,,fig4 #ae4--,,mars #a ,drawings by ,prof4 ,lowell to accompany actual photographs of ,mars showing many of the #b canals4 ,taken in #aijg by ,mr4 ,e4 ,c4 ,slipher of the ,lowell ,observatory4 #c ,drawing by ,prof4 ,lowell made ,january #f1 #aiad4 #d ,drawing by ,prof4 ,lowell made ,january #ba1 #aiad4 ,nos4 #a and #b show the effect of the planet's rotation4 ,nos4 #c and #d depict quite different sections4 ,note the change in the polar snow-caps in the last two4 ,illustration3 ,,fig4 #af4--,,the ,,moon1 ,,at ,,nine ,,and ,,three-,,quarter ,,days ,note the mysterious rays diverging from the almost perfectly circular craters indicated by the arrows 7,tycho1 upper2 ,copernicus1 lower71 and also the mountains to the right with the lunar dawn breaking on them4 ,we turn to ,mars2 and we must first make it clear why there is so much speculation about life on ,mars1 and why it is supposed that1 if there is life on ,mars1 it must be more advanced than life on the earth4 ,is there ,life on ,mars8 ,the basis of this belief is that if1 as we saw1 all the globes in our solar system are masses of metal that are cooling down1 the smaller will have cooled down before the larger1 and will be further ahead in their development4 ,now ,mars is very much smaller than the earth1 and must have cooled at its surface millions of years before the earth did4 ,hence1 if a story of life began on ,mars at all1 it began long before the story of life on the earth4 ,we cannot guess what sort of life-forms would be evolved in a different world1 but we can confidently say that they would tend toward increasing intelligence2 and thus we are disposed to look for highly intelligent beings on ,mars4 ,but this argument supposes that the conditions of life1 namely air and water1 are found on ,mars1 and it is disputed whether they are found there in sufficient quantity4 ,the late ,professor ,percival ,lowell1 who made a lifelong study of ,mars1 maintained that there are hundreds of straight lines drawn across the surface of the planet1 and he claimed that they are beds of vegetation marking the sites of great channels or pipes by means of which the ,martians draw water from their polar ocean4 ,professor ,w4 ,h4 ,pickering1 another high authority1 thinks that the lines are long1 narrow marshes fed by moist winds from the poles4 ,there are certainly white polar caps on ,mars4 ,they seem to melt in the spring1 and the dark fringe round them grows broader4 ,other astronomers1 however1 say that they find no trace of water-vapour in the atmosphere of ,mars1 and they think that the polar caps may be simply thin sheets of hoar-frost or frozen gas4 ,they point out that1 as the atmosphere of ,mars is certainly scanty1 and the distance from the sun is so great1 it may be too cold for the fluid water to exist on the planet4 ,if one asks why our wonderful instruments cannot settle these points1 one must be reminded that ,mars is never nearer than #cd1jjj1jjj miles from the earth1 and only approaches to this distance once in fifteen or seventeen years4 ,the image of ,mars on the photographic negative taken in a big telescope is very small4 ,astronomers rely to a great extent on the eye1 which is more sensitive than the photographic plate4 ,but it is easy to have differences of opinion as to what the eye sees1 and so there is a good deal of controversy4 ,in ,august1 #aibd1 the planet will again be well placed for observation1 and we may learn more about it4 ,already a few of the much-disputed lines1 which people wrongly call canals1 have been traced on photographs4 ,astronomers who are sceptical about life on ,mars are often not fully aware of the extraordinary adaptability of life4 ,there was a time when the climate of the whole earth1 from pole to pole1 was semi-tropical for millions of years4 ,no animal could then endure the least cold1 yet now we have plenty of ,arctic plants and animals4 ,if the cold came slowly on ,mars1 as we have reason to suppose1 the population could be gradually adapted to it4 ,on the whole1 it is possible that there is advanced life on ,mars1 and it is not impossible1 in spite of the very great difficulties of a code of communication1 that our elder brothers may yet flash across space the solution of many of our problems4 #b ,jupiter and ,saturn ,next to ,mars1 going outward from the sun1 is ,jupiter4 ,between ,mars and ,jupiter1 however1 there are more than three hundred million miles of space1 and the older astronomers wondered why this was not occupied by a planet4 ,we now know that it contains about nine hundred planetoids1 or small globes of from five to five hundred miles in diameter4 ,it was at one time thought that a planet might have burst into these fragments 7a theory which is not mathematically satisfactory71 or it may be that the material which is scattered in them was prevented by the nearness of the great bulk of ,jupiter from uniting into one globe4 ,for ,jupiter is a giant planet1 and its gravitational influence must extend far over space4 ,it is #a1cjj times as large as the earth1 and has nine moons1 four of which are large1 in attendance on it4 ,it is interesting to note that the outermost moons of ,jupiter and ,saturn revolve round these planets in a direction contrary to the usual direction taken by moons round planets1 and by planets round the sun4 ,but there is no life on ,jupiter4 ,the surface which we see in photographs 7,fig4 #ab7 is a mass of cloud or steam which always envelops the body of the planet4 ,it is apparently red-hot4 ,a red tinge is seen sometimes at the edges of its cloud-belts1 and a large red region 7the red spot71 #bc1jjj miles in length1 has been visible on it for half a century4 ,there may be a liquid or solid core to the planet1 but as a whole it is a mass of seething vapours whirling round on its axis once in every ten hours4 ,as in the case of the sun1 however1 different latitudes appear to rotate at different rates4 ,the interior of ,jupiter is very hot1 but the planet is not self-luminous4 ,the planets ,venus and ,jupiter shine very brightly1 but they have no light of their own2 they reflect the sunlight4 ,saturn is in the same interesting condition4 ,the surface in the photograph 7,fig4 #ac7 is steam1 and ,saturn is so far away from the sun that the vaporisation of its oceans must necessarily be due to its own internal heat4 ,it is too hot for water to settle on its surface4 ,like ,jupiter1 the great globe turns on its axis once in ten hours--a prodigious speed--and must be a swirling1 seething mass of metallic vapours and gases4 ,it is instructive to compare ,jupiter and ,saturn in this respect with the sun4 ,they are smaller globes and have cooled down more than the central fire4 ,saturn is a beautiful object in the telescope because it has ten moons 7to include one which is disputed7 and a wonderful system of rings round it4 ,the so-called rings are a mighty swarm of meteorites--pieces of iron and stone of all sorts and sizes1 which reflect the light of the sun to us4 ,this ocean of matter is some miles deep1 and stretches from a few thousand miles from the surface of the planet to #agb1jjj miles out in space4 ,some astronomers think that this is volcanic material which has been shot out of the planet4 ,others regard it as stuff which would have combined to form an eleventh moon but was prevented by the nearness of ,saturn itself4 ,there is no evidence of life on ,saturn4 ,,the ,,moon ,mars and ,venus are therefore the only planets1 besides the earth1 on which we may look for life2 and in the case of ,venus1 the possibility is very faint4 ,but what about the moons which attend the planets8 ,they range in size from the little ten-miles-wide moons of ,mars1 to ,titan1 a moon of ,saturn1 and ,ganymede1 a satellite of ,jupiter1 which are about #c1jjj miles in diameter4 ,may there not be life on some of the larger of these moons8 ,we will take our own moon as a type of the class4 ,a ,dead ,world ,the moon is so very much nearer to us than any other heavenly body that we have a remarkable knowledge of it4 ,in ,fig4 #ad you have a photograph1 taken in one of our largest telescopes1 of part of its surface4 ,in a sense such a telescope brings the moon to within about fifty miles of us4 ,we should see a city like ,london as a dark1 sprawling blotch on the globe4 ,we could just detect a ,zeppelin or a ,diplodocus as a moving speck against the surface4 ,but we find none of these things4 ,it is true that a few astronomers believe that they see signs of some sort of feeble life or movement on the moon4 ,professor ,pickering thinks that he can trace some volcanic activity4 ,he believes that there are areas of vegetation1 probably of a low order1 and that the soil of the moon may retain a certain amount of water in it4 ,he speaks of a very thin atmosphere1 and of occasional light falls of snow4 ,he has succeeded in persuading some careful observers that there probably are slight changes of some kind taking place on the moon4 ,illustration3 ,,fig4 #ag4--;,a ,,map ,,of ,,the ,,chief ,,plains ,,and ,,craters ,,of ,,the ,,moon ,the plains were originally supposed to be seas3 hence the name ,mare4 ,illustration3 ,,fig4 #ah4--;,a ,,diagram ,,of ,a ,,stream ,,of ,,meteors ,,showing ,,the ,,earth ,,passing ,,through ,,them ,illustration3 ,photo3 ,royal ,observatory1 ,greenwich4 ,,fig4 #ai4--;,,comet1 ,september #bi1 #aijh ,notice the tendency to form a number of tails4 7,see photograph below47 ,illustration3 ,photo3 ,royal ,observatory1 ,greenwich4 ,,fig4 #bj4--;,,comet1 ,october #c1 #aijh ,the process has gone further and a number of distinct tails can now be counted4 ,but there are many things that point to absence of air on the moon4 ,even the photographs we reproduce tell the same story4 ,the edges of the shadows are all hard and black4 ,if there had been an appreciable atmosphere it would have scattered the sun's light on to the edges and produced a gradual shading off such as we see on the earth4 ,this relative absence of air must give rise to some surprising effects4 ,there will be no sounds on the moon1 because sounds are merely air waves4 ,even a meteor shattering itself to a violent end against the surface of the moon would make no noise4 ,nor would it herald its coming by glowing into a shooting star1 as it would on entering the earth's atmosphere4 ,there will be no floating dust1 no scent1 no twilight1 no blue sky1 no twinkling of the stars4 ,the sky will be always black and the stars will be clearly visible by day as by night4 ,the sun's wonderful corona1 which no man on earth1 even by seizing every opportunity during eclipses1 can hope to see for more than two hours in all in a long lifetime1 will be visible all day4 ,so will the great red flames of the sun4 ,of course1 there will be no life1 and no landscape effects and scenery effects due to vegetation4 ,the moon takes approximately twenty-seven of our days to turn once on its axis4 ,so for fourteen days there is continuous night1 when the temperature must sink away down towards the absolute cold of space4 ,this will be followed without an instant of twilight by full daylight4 ,for another fourteen days the sun's rays will bear straight down1 with no diffusion or absorption of their heat1 or light1 on the way4 ,it does not follow1 however1 that the temperature of the moon's surface must rise enormously4 ,it may not even rise to the temperature of melting ice4 ,seeing there is no air there can be no check on radiation4 ,the heat that the moon gets will radiate away immediately4 ,we know that amongst the coldest places on the earth are the tops of very high mountains1 the points that have reared themselves nearest to the sun but farthest out of the sheltering blanket of the earth's atmosphere4 ,the actual temperature of the moon's surface by day is a moot point4 ,it may be below the freezing-point or above the boiling-point of water4 ,the ,mountains of the ,moon ,the lack of air is considered by many astronomers to furnish the explanation of the enormous number of craters which pit the moon's surface4 ,there are about a hundred thousand of these strange rings1 and it is now believed by many that they are spots where very large meteorites1 or even planetoids1 splashed into the moon when its surface was still soft4 ,other astronomers think that they are the remains of gigantic bubbles which were raised in the moon's skin1 when the globe was still molten1 by volcanic gases from below4 ,a few astronomers think that they are1 as is popularly supposed1 the craters of extinct volcanoes4 ,our craters1 on the earth1 are generally deep cups1 whereas these ring-formations on the moon are more like very shallow and broad saucers4 ,clavius1 the largest of them1 is #abc miles across the interior1 yet its encircling rampart is not a mile high4 ,the mountains on the moon 7,fig4 #af7 rise to a great height1 and are extraordinarily gaunt and rugged4 ,they are like fountains of lava1 rising in places to #bf1jjj and #bg1jjj feet4 ,the lunar ,apennines have three thousand steep and weird peaks4 ,our terrestrial mountains are continually worn down by frost acting on moisture and by ice and water1 but there are none of these agencies operating on the moon4 ,its mountains are comparatively everlasting hills4 ,the moon is interesting to us precisely because it is a dead world4 ,it seems to show how the earth1 or any cooling metal globe1 will evolve in the remote future4 ,we do not know if there was ever life on the moon1 but in any case it cannot have proceeded far in development4 ,at the most we can imagine some strange lowly forms of vegetation lingering here and there in pools of heavy gas1 expanding during the blaze of the sun's long day1 and frozen rigid during the long night4 ,,meteors ,,and ,,comets ,we may conclude our survey of the solar system with a word about shooting stars1 or meteors1 and comets4 ,there are few now who do not know that the streak of fire which suddenly lights the sky overhead at night means that a piece of stone or iron has entered our atmosphere from outer space1 and has been burned up by friction4 ,it was travelling at1 perhaps1 twenty or thirty miles a second4 ,at seventy or eighty miles above our heads it began to glow1 as at that height the air is thick enough to offer serious friction and raise it to a white heat4 ,by the time the meteor reached about twenty miles or so from the earth's surface it was entirely dissipated1 as a rule in fiery vapour4 ,millions of ,meteorites ,it is estimated that between ten and a hundred million meteorites enter our atmosphere and are cremated1 every day4 ,most of them weigh only an ounce or two1 and are invisible4 ,some of them weigh a ton or more1 but even against these large masses the air acts as a kind of torpedo-net4 ,they generally burst into fragments and fall without doing damage4 ,it is clear that empty space is1 at least within the limits of our solar system1 full of these things4 ,they swarm like fishes in the seas4 ,like the fishes1 moreover1 they may be either solitary or gregarious4 ,the solitary bit of cosmic rubbish is the meteorite1 which we have just examined4 ,a social group of meteorites is the essential part of a comet4 ,the nucleus1 or bright central part1 of the head of a comet 7,fig4 #ai7 consists of a swarm1 sometimes thousands of miles wide1 of these pieces of iron or stone4 ,this swarm has come under the sun's gravitational influence1 and is forced to travel round it4 ,from some dark region of space it has moved slowly into our system4 ,it is not then a comet1 for it has no tail4 ,but as the crowded meteors approach the sun1 the speed increases4 ,they give off fine vapour-like matter and the fierce flood of light from the sun sweeps this vapour out in an ever-lengthening tail4 ,whatever way the comet is travelling1 the tail always points away from the sun4 ,a ,great ,comet ,the vapoury tail often grows to an enormous length as the comet approaches the sun4 ,the great comet of #ahdc had a tail two hundred million miles long4 ,it is1 however1 composed of the thinnest vapours imaginable4 ,twice during the nineteenth century the earth passed through the tail of a comet1 and nothing was felt4 ,the vapours of the tail are1 in fact1 so attenuated that we can hardly imagine them to be white-hot4 ,they may be lit by some electrical force4 ,however that may be1 the comet dashes round the sun1 often at three or four hundred miles a second1 then may pass gradually out of our system once more4 ,it may be a thousand years1 or it may be fifty years1 before the monarch of the system will summon it again to make its fiery journey round his throne4 ,illustration3 ,photo3 ,harvard ,college ,observatory4 ,,fig4 #ba4--,,typical ,,spectra ,six main types of stellar spectra4 ,notice the lines they have in common1 showing what elements are met with in different types of stars4 ,each of these spectra corresponds to a different set of physical and chemical conditions4 ,illustration3 ,photo3 ,mount ,wilson ,observatory4 ,,fig4 #bb4--;,a ,,nebular ,,region ,,south ,,of ,,zeta ,,orionis ,showing a great projection of dark matter cutting off the light from behind4 ,illustration3 ,photo3 ,astrophysical ,observatory1 ,victoria1 ,british ,columbia4 ,,fig4 #bc4--,,star ,,cluster ,,in ,,hercules ,a wonderful cluster of stars4 ,it has been estimated that the distance of this cluster is such that it would take light more than #ajj1jjj years to reach us4 ,,the ,,stellar ,,universe #a ,the immensity of the ,stellar ,universe1 as we have seen1 is beyond our apprehension4 ,the sun is nothing more than a very ordinary star1 perhaps an insignificant one4 ,there are stars enormously greater than the sun4 ,one such1 ,betelgeux1 has recently been measured1 and its diameter is more than #cjj times that of the sun4 ,the ,evolution of ,stars ,the proof of the similarity between our sun and the stars has come to us through the spectroscope4 ,the elements that we find by its means in the sun are also found in the same way in the stars4 ,matter1 says the spectroscope1 is essentially the same everywhere1 in the earth and the sun1 in the comet that visits us once in a thousand years1 in the star whose distance is incalculable1 and in the great clouds of fire-mist that we call nebul4 ,in considering the evolution of the stars let us keep two points clearly in mind4 ,the starting-point1 the nebula1 is no figment of the scientific imagination4 ,hundreds of thousands of nebul1 besides even vaster irregular stretches of nebulous matter1 exist in the heavens4 ,but the stages of the evolution of this stuff into stars are very largely a matter of speculation4 ,possibly there is more than one line of evolution1 and the various theories may be reconciled4 ,and this applies also to the theories of the various stages through which the stars themselves pass on their way to extinction4 ,the light of about a quarter of a million stars has been analysed in the spectroscope1 and it is found that they fall into about a dozen classes which generally correspond to stages in their evolution 7,fig4 #ba74 ,the ,age of ,stars ,in its main lines the spectrum of a star corresponds to its colour1 and we may roughly group the stars into red1 yellow1 and white4 ,this is also the order of increasing temperature1 the red stars being the coolest and the white stars the hottest4 ,we might therefore imagine that the white stars are the youngest1 and that as they grow older and cooler they become yellowish1 then red1 and finally become invisible--just as a cooling white-hot iron would do4 ,but a very interesting recent research shows that there are two kinds of red stars2 some of them are amongst the oldest stars and some are amongst the youngest4 ,the facts appear to be that when a star is first formed it is not very hot4 ,it is an immense mass of diffuse gas glowing with a dull-red heat4 ,it contracts under the mutual gravitation of its particles1 and as it does so it grows hotter4 ,it acquires a yellowish tinge4 ,as it continues to contract it grows hotter and hotter until its temperature reaches a maximum as a white star4 ,at this point the contraction process does not stop1 but the heating process does4 ,further contraction is now accompanied by cooling1 and the star goes through its colour changes again1 but this time in the inverse order4 ,it contracts and cools to yellow and finally to red4 ,but when it again becomes a red star it is enormously denser and smaller than when it began as a red star4 ,consequently the red stars are divided into two classes called1 appropriately1 ,giants and ,dwarfs4 ,this theory1 which we owe to an ,american astronomer1 ,h4 ,n4 ,russell1 has been successful in explaining a variety of phenomena1 and there is consequently good reason to suppose it to be true4 ,but the question as to how the red giant stars were formed has received less satisfactory and precise answers4 ,the most commonly accepted theory is the nebular theory4 ,,the ,,nebular ,,theory #b ,nebul are dim luminous cloud-like patches in the heavens1 more like wisps of smoke in some cases than anything else4 ,both photography and the telescope show that they are very numerous1 hundreds of thousands being already known and the number being continually added to4 ,they are not small4 ,most of them are immensely large4 ,actual dimensions cannot be given1 because to estimate these we must first know definitely the distance of the nebul from the earth4 ,the distances of some nebul are known approximately1 and we can therefore form some idea of size in these cases4 ,the results are staggering4 ,the mere visible surface of some nebul is so large that the whole stretch of the solar system would be too small to form a convenient unit for measuring it4 ,a ray of light would require to travel for years to cross from side to side of such a nebula4 ,its immensity is inconceivable to the human mind4 ,there appear to be two types of nebul1 and there is evidence suggesting that the one type is only an earlier form of the other2 but this again we do not know4 ,the more primitive nebul would seem to be composed of gas in an extremely rarified form4 ,it is difficult to convey an adequate idea of the rarity of nebular gases4 ,the residual gases in a vacuum tube are dense by comparison4 ,a cubic inch of air at ordinary pressure would contain more matter than is contained in millions of cubic inches of the gases of nebul4 ,the light of even the faintest stars does not seem to be dimmed by passing through a gaseous nebula1 although we cannot be sure on this point4 ,the most remarkable physical fact about these gases is that they are luminous4 ,whence they derive their luminosity we do not know4 ,it hardly seems possible to believe that extremely thin gases exposed to the terrific cold of space can be so hot as to be luminous and can retain their heat and their luminosity indefinitely4 ,a cold luminosity due to electrification1 like that of the aurora borealis1 would seem to fit the case better4 ,now the nebular theory is that out of great fire-mists1 such as we have described1 stars are born4 ,we do not know whether gravitation is the only or even the main force at work in a nebula1 but it is supposed that under the action of gravity the far-flung fire-mists would begin to condense round centres of greatest density1 heat being evolved in the process4 ,of course the condensation would be enormously slow1 although the sudden irruption of a swarm of meteors or some solid body might hasten matters greatly by providing large1 ready-made centres of condensation4 ,spiral ,nebul ,it is then supposed that the contracting mass of gas would begin to rotate and to throw off gigantic streamers1 which would in their turn form centres of condensation4 ,the whole structure would thus form a spiral1 having a dense region at its centre and knots or lumps of condensed matter along its spiral arms4 ,besides the formless gaseous nebul there are hundreds of thousands of spiral nebul such as we have just mentioned in the heavens4 ,they are at all stages of development1 and they are visible to us at all angles--that is to say1 some of them face directly towards us1 others are edge on1 and some are in intermediate positions4 ,it appears1 therefore1 that we have here a striking confirmation of the nebular hypothesis4 ,but we must not go so fast4 ,there is much controversy as to the nature of these spiral nebul4 ,some eminent astronomers think they are other stellar universes1 comparable in size with our own4 ,in any case they are vast structures1 and if they represent stars in process of condensation1 they must be giving birth to huge agglomerations of stars--to star clusters at least4 ,these vast and enigmatic objects do not throw much light on the origin of our own solar system4 ,the nebular hypothesis1 which was invented by ,laplace to explain the origin of our solar system1 has not yet met with universal acceptance4 ,the explanation offers grave difficulties1 and it is best while the subject is still being closely investigated1 to hold all opinions with reserve4 ,it may be taken as probable1 however1 that the universe has developed from masses of incandescent gas4 ,illustration3 ,photo3 ,yerkes ,observatory4 ,,fig4 #bd4--,,the ,,great ,,nebula ,,in ,,orion ,the most impressive nebula in the heavens4 ,it is inconceivably greater in dimensions than the whole solar system4 ,illustration3 ,photo3 ,lick ,observatory4 ,,fig4 #be--;,,giant ,,spiral ,,nebula1 ,march #bc1 #aiad ,this spiral nebula is seen full on4 ,notice the central nucleus and the two spiral arms emerging from its opposite directions4 ,is matter flowing out of the nucleus into the arms or along the arms into the nucleus8 ,in either case we should get two streams in opposite directions within the nucleus4 ,,the ,,birth ,,and ,,death ,,of ,,stars #c ,variable1 ,new1 and ,dark ,stars3 ,dying ,suns ,many astronomers believe that in variable stars we have another star1 following that of the dullest red star1 in the dying of suns4 ,the light of these stars varies periodically in so many days1 weeks1 or years4 ,it is interesting to speculate that they are slowly dying suns1 in which the molten interior periodically bursts through the shell of thick vapours that is gathering round them4 ,what we saw about our sun seems to point to some such stage in the future4 ,that is1 however1 not the received opinion about variable stars4 ,it may be that they are stars which periodically pass through a great swarm of meteors or a region of space that is rich in cosmic dust of some sort1 when1 of course1 a great illumination would take place4 ,one class of these variable stars1 which takes its name from the star ,algol1 is of special interest4 ,every third night ,algol has its light reduced for several hours4 ,modern astronomy has discovered that in this case there are really two stars1 circulating round a common centre1 and that every third night the fainter of the two comes directly between us and its companion and causes an eclipse4 ,this was until recently regarded as a most interesting case in which a dead star revealed itself to us by passing before the light of another star4 ,but astronomers have in recent years invented something1 the selenium-cell1 which is even more sensitive than the photographic plate1 and on this the supposed dead star registers itself as very much alive4 ,algol is1 however1 interesting in another way4 ,the pair of stars which we have discovered in it are hundreds of trillions of miles away from the earth1 yet we know their masses and their distances from each other4 ,the ,death and ,birth of ,stars ,we have no positive knowledge of dead stars2 which is not surprising when we reflect that a dead star means an invisible star6 ,but when we see so many individual stars tending toward death1 when we behold a vast population of all conceivable ages1 we presume that there are many already dead4 ,on the other hand1 there is no reason to suppose that the universe as a whole is running down4 ,some writers have maintained this1 but their argument implies that we know a great deal more about the universe than we actually do4 ,the scientific man does not know whether the universe is finite or infinite1 temporal or eternal2 and he declines to speculate where there are no facts to guide him4 ,he knows only that the great gaseous nebul promise myriads of worlds in the future1 and he concedes the possibility that new nebul may be forming in the ether of space4 ,the last1 and not the least interesting1 subject we have to notice is the birth of a new star4 ,this is an event which astronomers now announce every few years2 and it is a far more portentous event than the reader imagines when it is reported in his daily paper4 ,the story is much the same in all cases4 ,we say that the star appeared in #aija1 but you begin to realise the magnitude of the event when you learn that the distant blaze had really occurred about the time of the death of ,luther6 ,the light of the conflagration had been speeding toward us across space at #ahf1jjj miles a second1 yet it has taken nearly three centuries to reach us4 ,to be visible at all to us at that distance the fiery outbreak must have been stupendous4 ,if a mass of petroleum ten times the size of the earth were suddenly fired it would not be seen at such a distance4 ,the new star had increased its light many hundredfold in a few days4 ,there is a considerable fascination about the speculation that in such cases we see the resurrection of a dead world1 a means of renewing the population of the universe4 ,what happens is that in some region of the sky where no star1 or only a very faint star1 had been registered on our charts1 we almost suddenly perceive a bright star4 ,in a few days it may rise to the highest brilliancy4 ,by the spectroscope we learn that this distant blaze means a prodigious outpour of white-hot hydrogen at hundreds of miles a second4 ,but the star sinks again after a few months1 and we then find a nebula round it on every side4 ,it is natural to suppose that a dead or dying sun has somehow been reconverted in whole or in part into a nebula4 ,a few astronomers think that it may have partially collided with another star1 or approached too closely to another1 with the result we described on an earlier page4 ,the general opinion now is that a faint or dead star had rushed into one of those regions of space in which there are immense stretches of nebulous matter1 and been 7at least in part7 vaporised by the friction4 ,but the difficulties are considerable1 and some astronomers prefer to think that the blazing star may merely have lit up a dark nebula which already existed4 ,it is one of those problems on which speculation is most tempting but positive knowledge is still very incomplete4 ,we may be content1 even proud1 that already we can take a conflagration that has occurred more than a thousand trillion miles away and analyse it positively into an outflame of glowing hydrogen gas at so many miles a second4 ,,the ,,shape ,,of ,,our ,,universe #d ,our ,universe a ,spiral ,nebula ,what is the shape of our universe1 and what are its dimensions8 ,this is a tremendous question to ask4 ,it is like asking an intelligent insect1 living on a single leaf in the midst of a great ,brazilian forest1 to say what is the shape and size of the forest4 ,yet man's ingenuity has proved equal to giving an answer even to this question1 and by a method exactly similar to that which would be adopted by the insect4 ,suppose1 for instance1 that the forest was shaped as an elongated oval1 and the insect lived on a tree near the centre of the oval4 ,if the trees were approximately equally spaced from one another they would appear much denser along the length of the oval than across its width4 ,this is the simple consideration that has guided astronomers in determining the shape of our stellar universe4 ,there is one direction in the heavens along which the stars appear denser than in the directions at right angles to it4 ,that direction is the direction in which we look towards the ,milky ,way4 ,if we count the number of stars visible all over the heavens1 we find they become more and more numerous as we approach the ,milky ,way4 ,as we go farther and farther from the ,milky ,way the stars thin out until they reach a maximum sparseness in directions at right angles to the plane of the ,milky ,way4 ,we may consider the ,milky ,way to form1 as it were1 the equator of our system1 and the line at right angles to point to the north and south poles4 ,our system1 in fact1 is shaped something like a lens1 and our sun is situated near the centre of this lens4 ,in the remoter part of this lens1 near its edge1 or possibly outside it altogether1 lies the great series of star clouds which make up the ,milky ,way4 ,all the stars are in motion within this system1 but the very remarkable discovery has been made that these motions are not entirely random4 ,the great majority of the stars whose motions can be measured fall into two groups drifting past one another in opposite directions4 ,the velocity of one stream relative to the other is about twenty-five miles per second4 ,the stars forming these two groups are thoroughly well mixed2 it is not a case of an inner stream going one way and an outer stream the other4 ,but there are not quite as many stars going one way as the other4 ,for every two stars in one stream there are three in the other4 ,now1 as we have said1 some eminent astronomers hold that the spiral nebul are universes like our own1 and if we look at the two photographs 7,figs4 #be and #bf7 we see that these spirals present features which1 in the light of what we have just said about our system1 are very remarkable4 ,the nebula in ,coma ,berenices is a spiral edge-on to us1 and we see that it has precisely the lens-shaped middle and the general flattened shape that we have found in our own system4 ,the nebula in ,canes ,venatici is a spiral facing towards us1 and its shape irresistibly suggests motions along the spiral arms4 ,this motion1 whether it is towards or away from the central1 lens-shaped portion1 would cause a double streaming motion in that central portion of the kind we have found in our own system4 ,again1 and altogether apart from these considerations1 there are good reasons for supposing our ,milky ,way to possess a double-armed spiral structure4 ,and the great patches of dark absorbing matter which are known to exist in the ,milky ,way 7see ,fig4 #bb7 would give very much the mottled appearance we notice in the arms 7which we see edge-on7 of the nebula in ,coma ,berenices4 ,the hypothesis1 therefore1 that our universe is a spiral nebula has much to be said for it4 ,if it be accepted it greatly increases our estimate of the size of the material universe4 ,for our central1 lens-shaped system is calculated to extend towards the ,milky ,way for more than twenty thousand times a million million miles1 and about a third of this distance towards what we have called the poles4 ,if1 as we suppose1 each spiral nebula is an independent stellar universe comparable in size with our own1 then1 since there are hundreds of thousands of spiral nebul1 we see that the size of the whole material universe is indeed beyond our comprehension4 ,illustration3 ,photo3 ,mount ,wilson ,observatory4 ,,fig4 #bf4--;,a ,,spiral ,,nebula ,,seen ,,edge-,,on ,notice the lens-shaped formation of the nucleus and the arm stretching as a band across it4 ,see reference in the text to the resemblance between this and our stellar universe4 ,illustration3 ,photo3 ,h4 ,j4 ,shepstone4 #ajj-;,,inch ,,telescope1 ,,mount ,,wilson ,a reflecting telescope3 the largest in the world4 ,the mirror is situated at the base of the telescope4 ,illustration3 ,,the ,,solar ,,system ,,mean ,,distance ,,period ,,of ,,name ,,from ,,sun 7,,in ,,revolution ,,diameter ,,number ,,of ,,millions ,,of ,,around ,,sun 7,,in ,,miles7 ,,satellites ,,miles7 7,,in ,,years7 ,,mercury #cf4j #j4bd #cjcj #j ,,venus #fg4b #j4fb #ggjj #j ,,earth #ib4i #a4jj #giah #a ,,mars #ada4e #a4hh #dbcj #b ,,jupiter #dhc4c #aa4hf #hfejj #i ,,saturn #hhf4j #bi4df #gcjjj #aj ,,uranus #agha4i #hd4jb #caijj #d ,,neptune #biga4f #afd4gh #cdhjj #a ,,sun ------ ------ #hffdjj -- ,,moon ------ ------ #bafc -- ,,fig4 #bg ,illustration3 ,,star ,,distances ,,distance ,,in ,,star ,,light-,,years ,,polaris #gf ,,capella #di4d ,,rigel #dff ,,sirius #h4g ,,procyon #aj4e ,,regulus #ih4h ,,arcturus #dc4d ,,alpha ,,centauri #d4bi ,,vega #cd4g ,,smaller ,,magellanic ,,cloud #cb1fjj;,a ,,great ,,cluster ,,in ,,hercules #ajh1fjj;,a ,a ,,estimated ,,fig4 #bh ,the above distances are merely approximate and are subject to further revision4 ,a light-year is the distance that light1 travelling at the rate of #ahf1jjj miles per second1 would cover in one year4 ,in this simple outline we have not touched on some of the more debatable questions that engage the attention of modern astronomers4 ,many of these questions have not yet passed the controversial stage2 out of these will emerge the astronomy of the future4 ,but we have seen enough to convince us that1 whatever advances the future holds in store1 the science of the heavens constitutes one of the most important stones in the wonderful fabric of human knowledge4 ,,astronomical ,,instruments #a ,the ,telescope ,the instruments used in modern astronomy are amongst the finest triumphs of mechanical skill in the world4 ,in a great modern observatory the different instruments are to be counted by the score1 but there are two which stand out pre-eminent as the fundamental instruments of modern astronomy4 ,these instruments are the telescope and the spectroscope1 and without them astronomy1 as we know it1 could not exist4 ,there is still some dispute as to where and when the first telescope was constructed2 as an astronomical instrument1 however1 it dates from the time of the great ,italian scientist ,galileo1 who1 with a very small and imperfect telescope of his own invention1 first observed the spots on the sun1 the mountains of the moon1 and the chief four satellites of ,jupiter4 ,a good pair of modern binoculars is superior to this early instrument of ,galileo's1 and the history of telescope construction1 from that primitive instrument to the modern giant recently erected on ,mount ,wilson1 ,california1 is an exciting chapter in human progress4 ,but the early instruments have only an historic interest3 the era of modern telescopes begins in the nineteenth century4 ,during the last century telescope construction underwent an unprecedented development4 ,an immense amount of interest was taken in the construction of large telescopes1 and the different countries of the world entered on an exciting race to produce the most powerful possible instruments4 ,besides this rivalry of different countries there was a rivalry of methods4 ,the telescope developed along two different lines1 and each of these two types has its partisans at the present day4 ,these types are known as refractors and reflectors1 and it is necessary to mention1 briefly1 the principles employed in each4 ,the refractor is the ordinary1 familiar type of telescope4 ,it consists1 essentially1 of a large lens at one end of a tube1 and a small lens1 called the eye-piece1 at the other4 ,the function of the large lens is to act as a sort of gigantic eye4 ,it collects a large amount of light1 an amount proportional to its size1 and brings this light to a focus within the tube of the telescope4 ,it thus produces a small but bright image1 and the eye-piece magnifies this image4 ,in the reflector1 instead of a large lens at the top of the tube1 a large mirror is placed at the bottom4 ,this mirror is so shaped as to reflect the light that falls on it to a focus1 whence the light is again led to an eye-piece4 ,thus the refractor and the reflector differ chiefly in their manner of gathering light4 ,the powerfulness of the telescope depends on the size of the light-gatherer4 ,a telescope with a lens four inches in diameter is four times as powerful as the one with a lens two inches in diameter1 for the amount of light gathered obviously depends on the area of the lens1 and the area varies as the square of the diameter4 ,the largest telescopes at present in existence are reflectors4 ,it is much easier to construct a very large mirror than to construct a very large lens2 it is also cheaper4 ,a mirror is more likely to get out of order than is a lens1 however1 and any irregularity in the shape of a mirror produces a greater distorting effect than in a lens4 ,a refractor is also more convenient to handle than is a reflector4 ,for these reasons great refractors are still made1 but the largest of them1 the great ,yerkes' refractor1 is much smaller than the greatest reflector1 the one on ,mount ,wilson1 ,california4 ,the lens of the ,yerkes' refractor measures three feet four inches in diameter1 whereas the ,mount ,wilson reflector has a diameter of no less than eight feet four inches4 ,illustration3 ,,the ,,yerkes #dj-;,,inch ,,refractor 7,the largest refracting telescope in the world4 ,its big lens weighs #a1jjj pounds1 and its mammoth tube1 which is #fb feet long1 weighs about #ab1jjj pounds4 ,the parts to be moved weigh approximately #bb tons4 ,the great #ajj-;inch reflector of the ,mount ,wilson reflecting telescope--the largest reflecting instrument in the world--weighs nearly #i1jjj pounds and the moving parts of the telescope weigh about #ajj tons4 ,the new #gb-;inch reflector at the ,dominion ,astrophysical ,observatory1 near ,victoria1 ,b4 ,c41 weighs nearly #d1ejj pounds1 and the moving parts about #ce tons47 ,illustration3 ,photo3 ,h4 ,j4 ,shepstone4 ,,the ,,double-,,slide ,,plate ,,holder ,,on ,,yerkes #dj-;,,inch ,,refracting ,,telescope ,the smaller telescope at the top of the picture acts as a finder2 the field of view of the large telescope is so restricted that it is difficult to recognise1 as it were1 the part of the heavens being surveyed4 ,the smaller telescope takes in a larger area and enables the precise object to be examined to be easily selected4 ,illustration3 ,,modern ,,direct-,,reading ,,spectroscope 7,by ,a4 ,hilger1 ,ltd47 ,the light is brought through one telescope1 is split up by the prism1 and the resulting spectrum is observed through the other telescope4 ,but there is a device whereby the power of these giant instruments1 great as it is1 can be still further heightened4 ,that device is the simple one of allowing the photographic plate to take the place of the human eye4 ,nowadays an astronomer seldom spends the night with his eye glued to the great telescope4 ,he puts a photographic plate there4 ,the photographic plate has this advantage over the eye1 that it builds up impressions4 ,however long we stare at an object too faint to be seen1 we shall never see it4 ,with the photographic plate1 however1 faint impressions go on accumulating4 ,as hour after hour passes1 the star which was too faint to make a perceptible impression on the plate goes on affecting it until finally it makes an impression which can be made visible4 ,in this way the photographic plate reveals to us phenomena in the heavens which cannot be seen even through the most powerful telescopes4 ,telescopes of the kind we have been discussing1 telescopes for exploring the heavens1 are mounted equatorially2 that is to say1 they are mounted on an inclined pillar parallel to the axis of the earth so that1 by rotating round this pillar1 the telescope is enabled to follow the apparent motion of a star due to the rotation of the earth4 ,this motion is effected by clock-work1 so that1 once adjusted on a star1 and the clock-work started1 the telescope remains adjusted on that star for any length of time that is desired4 ,but a great official observatory1 such as ,greenwich ,observatory or the ,observatory at ,paris1 also has transit instruments1 or telescopes smaller than the equatorials and without the same facility of movement1 but which1 by a number of exquisite refinements1 are more adapted to accurate measurements4 ,it is these instruments which are chiefly used in the compilation of the ,nautical ,almanac4 ,they do not follow the apparent motions of the stars4 ,stars are allowed to drift across the field of vision1 and as each star crosses a small group of parallel wires in the eye-piece its precise time of passage is recorded4 ,owing to their relative fixity of position these instruments can be constructed to record the positions of stars with much greater accuracy than is possible to the more general and flexible mounting of equatorials4 ,the recording of transit is comparatively dry work2 the spectacular element is entirely absent2 stars are treated merely as mathematical points4 ,but these observations furnish the very basis of modern mathematical astronomy1 and without them such publications as the ,nautical ,almanac and the ,connaissance du ,temps would be robbed of the greater part of their importance4 #b ,the ,spectroscope ,we have already learnt something of the principles of the spectroscope1 the instrument which1 by making it possible to learn the actual constitution of the stars1 has added a vast new domain to astronomy4 ,in the simplest form of this instrument the analysing portion consists of a single prism4 ,unless the prism is very large1 however1 only a small degree of dispersion is obtained4 ,it is obviously desirable1 for accurate analytical work1 that the dispersion--that is1 the separation of the different parts of the spectrum--should be as great as possible4 ,the dispersion can be increased by using a large number of prisms1 the light emerging from the first prism1 entering the second1 and so on4 ,in this way each prism produces its own dispersive effect and1 when a number of prisms are employed1 the final dispersion is considerable4 ,a considerable amount of light is absorbed in this way1 however1 so that unless our primary source of light is very strong1 the final spectrum will be very feeble and hard to decipher4 ,another way of obtaining considerable dispersion is by using a diffraction grating instead of a prism4 ,this consists essentially of a piece of glass on which lines are ruled by a diamond point4 ,when the lines are sufficiently close together they split up light falling on them into its constituents and produce a spectrum4 ,the modern diffraction grating is a truly wonderful piece of work4 ,it contains several thousands of lines to the inch1 and these lines have to be spaced with the greatest accuracy4 ,but in this instrument1 again1 there is a considerable loss of light4 ,we have said that every substance has its own distinctive spectrum1 and it might be thought that1 when a list of the spectra of different substances has been prepared1 spectrum analysis would become perfectly straightforward4 ,in practice1 however1 things are not quite so simple4 ,the spectrum emitted by a substance is influenced by a variety of conditions4 ,the pressure1 the temperature1 the state of motion of the object we are observing1 all make a difference1 and one of the most laborious tasks of the modern spectroscopist is to disentangle these effects from one another4 ,simple as it is in its broad outlines1 spectroscopy is1 in reality1 one of the most intricate branches of modern science4 ,,bibliography 7,the following list of books may be useful to readers wishing to pursue further the study of ,astronomy47 ,,ball1 ,the ,story of the ,heavens4 ,,ball1 ,the ,story of the ,sun4 ,,forbes1 ,history of ,astronomy4 ,,hincks1 ,astronomy4 ,,kippax1 ,call of the ,stars4 ,,lowell1 ,mars and ,its ,canals4 ,,lowell1 ,evolution of ,worlds4 ,,mckready1 ,a ,beginner's ,star-,book4 ,,newcomb1 ,popular ,astronomy4 ,,newcomb1 ,the ,stars3 ,a ,study of the ,universe4 ,,olcott1 ,field ,book of the ,stars4 ,,price1 ,essence of ,astronomy4 ,,serviss1 ,curiosities of the ,skies4 ,,webb1 ,celestial ,objects for ,common ,telescopes4 ,,young1 ,text-,book of ,general ,astronomy4 ,,ii ,,the ,,story ,,of ,,evolution ,,introductory ,,the ,,beginning ,,of ,,the ,,earth--,,making ,a ,,home ,,for ,,life--,,the ,,first ,,living ,,creatures #a ,the ,evolution-idea is a master-key that opens many doors4 ,it is a luminous interpretation of the world1 throwing the light of the past upon the present4 ,everything is seen to be an antiquity1 with a history behind it--a natural history1 which enables us to understand in some measure how it has come to be as it is4 ,we cannot say more than understand in some measure1 for while the fact of evolution is certain1 we are only beginning to discern the factors that have been at work4 ,the evolution-idea is very old1 going back to some of the ,greek philosophers1 but it is only in modern times that it has become an essential part of our mental equipment4 ,it is now an everyday intellectual tool4 ,it was applied to the origin of the solar system and to the making of the earth before it was applied to plants and animals2 it was extended from these to man himself2 it spread to language1 to folk-ways1 to institutions4 ,within recent years the evolution-idea has been applied to the chemical elements1 for it appears that uranium may change into radium1 that radium may produce helium1 and that lead is the final stable result when the changes of uranium are complete4 ,perhaps all the elements may be the outcome of an inorganic evolution4 ,not less important is the extension of the evolution-idea to the world within as well as to the world without4 ,for alongside of the evolution of bodies and brains is the evolution of feelings and emotions1 ideas and imagination4 ,organic evolution means that the present is the child of the past and the parent of the future4 ,it is not a power or a principle2 it is a process--a process of becoming4 ,it means that the present-day animals and plants and all the subtle inter-relations between them have arisen in a natural knowable way from a preceding state of affairs on the whole somewhat simpler1 and that again from forms and inter-relations simpler still1 and so on backwards and backwards for millions of years till we lose all clues in the thick mist that hangs over life's beginnings4 ,our solar system was once represented by a nebula of some sort1 and we may speak of the evolution of the sun and the planets4 ,but since it has been the same material throughout that has changed in its distribution and forms1 it might be clearer to use some word like genesis4 ,similarly1 our human institutions were once very different from what they are now1 and we may speak of the evolution of government or of cities4 ,but ,man works with a purpose1 with ideas and ideals in some measure controlling his actions and guiding his achievements1 so that it is probably clearer to keep the good old word history for all processes of social becoming in which man has been a conscious agent4 ,now between the genesis of the solar system and the history of civilisation there comes the vast process of organic evolution4 ,the word development should be kept for the becoming of the individual1 the chick out of the egg1 for instance4 ,organic evolution is a continuous natural process of racial change1 by successive steps in a definite direction1 whereby distinctively new individualities arise1 take root1 and flourish1 sometimes alongside of1 and sometimes1 sooner or later1 in place of1 the originative stock4 ,our domesticated breeds of pigeons and poultry are the results of evolutionary change whose origins are still with us in the ,rock ,dove and the ,jungle ,fowl2 but in most cases in ,wild ,nature the ancestral stocks of present-day forms are long since extinct1 and in many cases they are unknown4 ,evolution is a long process of coming and going1 appearing and disappearing1 a long-drawn-out sublime process like a great piece of music4 ,illustration3 ,photo3 ,rischgitz ,collection4 ,,charles ,,darwin ,greatest of naturalists1 who made the idea of evolution current intellectual coin1 and in his ,origin of ,species 7#ahei7 made the whole world new4 ,illustration3 ,photo3 ,rischgitz ,collection4 ,,lord ,,kelvin ,one of the greatest physicists of the nineteenth century4 ,he estimated the age of the earth at #bj1jjj1jjj years4 ,he had not at his disposal1 however1 the knowledge of recent discoveries1 which have resulted in this estimate being very greatly increased4 ,illustration3 ,photo3 ,lick ,observatory4 ,a ,,giant ,,spiral ,,nebula ,laplace's famous theory was that the planets and the earth were formed from great whirling nebul4 ,illustration3 ,photo3 ,natural ,history ,museum4 ,,meteorite ,,which ,,fell ,,near ,,scarborough1 ,,and ,,is ,,now ,,to ,,be ,,seen ,,in ,,the ,,natural ,,history ,,museum ,it weighs about #ef lb41 and is a stony meteorite1 i4e41 an aerolite4 #b ,the ,beginning of the ,earth ,when we speak the language of science we cannot say ,in the beginning1 for we do not know of and cannot think of any condition of things that did not arise from something that went before4 ,but we may qualify the phrase1 and legitimately inquire into the beginning of the earth within the solar system4 ,if the result of this inquiry is to trace the sun and the planets back to a nebula we reach only a relative beginning4 ,the nebula has to be accounted for4 ,and even before matter there may have been a pre-material world4 ,if we say1 as was said long ago1 ,in the beginning was ,mind1 we may be expressing or trying to express a great truth1 but we have gone ,,beyond ,,science4 ,the ,nebular ,hypothesis ,one of the grandest pictures that the scientific mind has ever thrown upon the screen is that of the ,nebular ,hypothesis4 ,according to ,laplace's famous form of this theory 7#agif71 the solar system was once a gigantic glowing mass1 spinning slowly and uniformly around its centre4 ,as the incandescent world-cloud of gas cooled and its speed of rotation increased the shrinking mass gave off a separate whirling ring1 which broke up and gathered together again as the first and most distant planet4 ,the main mass gave off another ring and another till all the planets1 including the earth1 were formed4 ,the central mass persisted as the sun4 ,laplace spoke of his theory1 which ,kant had anticipated forty-one years before1 with scientific caution3 conjectures which ,i present with all the distrust which everything not the result of observation or of calculation ought to inspire4 ,subsequent research justified his distrust1 for it has been shown that the original nebula need not have been hot and need not have been gaseous4 ,moreover1 there are great difficulties in ,laplace's theory of the separation of successive rings from the main mass1 and of the condensation of a whirling gaseous ring into a planet4 ,so it has come about that the picture of a hot gaseous nebula revolving as a unit body has given place to other pictures4 ,thus ,sir ,norman ,lockyer pointed out 7#ahij7 that the earth is gathering to itself millions of meteorites every day2 this has been going on for millions of years2 in distant ages the accretion may have been vastly more rapid and voluminous2 and so the earth has grown6 ,now the meteoritic contributions are undoubted1 but they require a centre to attract them1 and the difficulty is to account for the beginning of a collecting centre or planetary nucleus4 ,moreover1 meteorites are sporadic and erratic1 scattered hither and thither rather than collecting into unit-bodies4 ,as ,professor ,chamberlin says1 meteorites have rather the characteristics of the wreckage of some earlier organisation than of the parentage of our planetary system4 ,several other theories have been propounded to account for the origin of the earth1 but the one that has found most favour in the eyes of authorities is that of ,chamberlin and ,moulton4 ,according to this theory a great nebular mass condensed to form the sun1 from which under the attraction of passing stars planet after planet1 the earth included1 was heaved off in the form of knotted spiral nebul1 like many of those now observed in the heavens4 ,of great importance were the knots1 for they served as collecting centres drawing flying matter into their clutches4 ,whatever part of the primitive bolt escaped and scattered was drawn out into independent orbits round the sun1 forming the planetesimals which behave like minute planets4 ,these planetesimals formed the food on which the knots subsequently fed4 ,the ,growth of the ,earth ,it has been calculated that the newborn earth--the earth-knot of ,chamberlin's theory--had a diameter of about #e1ejj miles4 ,but it grew by drawing planetesimals into itself until it had a diameter of over #h1ajj miles at the end of its growing period4 ,since then it has shrunk1 by periodic shrinkages which have meant the buckling up of successive series of mountains1 and it has now a diameter of #g1iah miles4 ,but during the shrinking the earth became more varied4 ,a sort of slow boiling of the internally hot earth often forced molten matter through the cold outer crust1 and there came about a gradual assortment of lighter materials nearer the surface and heavier materials deeper down4 ,the continents are built of the lighter materials1 such as granites1 while the beds of the great oceans are made of the heavier materials such as basalts4 ,in limited areas land has often become sea1 and sea has often given place to land1 but the probability is that the distinction of the areas corresponding to the great continents and oceans goes back to a very early stage4 ,the lithosphere is the more or less stable crust of the earth1 which may have been1 to begin with1 about fifty miles in thickness4 ,it seems that the young earth had no atmosphere1 and that ages passed before water began to accumulate on its surface--before1 in other words1 there was any hydrosphere4 ,the water came from the earth itself1 to begin with1 and it was long before there was any rain dissolving out saline matter from the exposed rocks and making the sea salt4 ,the weathering of the high grounds of the ancient crust by air and water furnished the material which formed the sandstones and mudstones and other sedimentary rocks1 which are said to amount to a thickness of over fifty miles in all4 #c ,making a ,home for ,life ,it is interesting to inquire how the callous1 rough-and-tumble conditions of the outer world in early days were replaced by others that allowed of the germination and growth of that tender plant we call ,,life4 ,there are very tough living creatures1 but the average organism is ill suited for violence4 ,most living creatures are adapted to mild temperatures and gentle reactions4 ,hence the fundamental importance of the early atmosphere1 heavy with planetesimal dust1 in blanketing the earth against intensities of radiance from without1 as ,chamberlin says1 and inequalities of radiance from within4 ,this was the first preparation for life1 but it was an atmosphere without free oxygen4 ,not less important was the appearance of pools and lakelets1 of lakes and seas4 ,perhaps the early waters covered the earth4 ,and water was the second preparation for life--water1 that can dissolve a larger variety of substances in greater concentration than any other liquid2 water1 that in summer does not readily evaporate altogether from a pond1 nor in winter freeze throughout its whole extent2 water1 that is such a mobile vehicle and such a subtle cleaver of substances2 water1 that forms over #hj per cent4 of living matter itself4 ,of great significance was the abundance of carbon1 hydrogen1 and oxygen 7in the form of carbonic acid and water7 in the atmosphere of the cooling earth1 for these three wonderful elements have a unique ensemble of properties--ready to enter into reactions and relations1 making great diversity and complexity possible1 favouring the formation of the plastic and permeable materials that build up living creatures4 ,we must not pursue the idea1 but it is clear that the stones and mortar of the inanimate world are such that they built a friendly home for life4 ,origin of ,living ,creatures upon the ,earth ,during the early chapters of the earth's history1 no living creature that we can imagine could possibly have lived there4 ,the temperature was too high2 there was neither atmosphere nor surface water4 ,therefore it follows that at some uncertain1 but inconceivably distant date1 living creatures appeared upon the earth4 ,no one knows how1 but it is interesting to consider possibilities4 ,illustration3 ,reproduced from the ,smithsonian ,report1 #aiae4 ,a ,,limestone ,,canyon ,many fossils of extinct animals have been found in such rock formations4 ,illustration3 ,,genealogical ,,tree ,,of ,,animals ,showing in order of evolution the general relations of the chief classes into which the world of living things is divided4 ,this scheme represents the present stage of our knowledge1 but is admittedly provisional4 ,illustration3 ,,diagram ,,of ,,amoeba 7,greatly magnified47 ,the amoeba is one of the simplest of all animals1 and gives us a hint of the original ancestors4 ,it looks like a tiny irregular speck of greyish jelly1 about #a_/ajjth of an inch in diameter4 ,it is commonly found gliding on the mud or weeds in ponds1 where it engulfs its microscopic food by means of out-flowing lobes 7,,ps74 ,the food vacuole 7,,fv7 contains ingested food4 ,from the contractile vacuole 7,,cv7 the waste matter is discharged4 ,n is the nucleus1 ,,gr1 granules4 ,from ancient times it has been a favourite answer that the dust of the earth may have become living in a way which is outside scientific description4 ,this answer forecloses the question1 and it is far too soon to do that4 ,science must often say ,ignoramus3 ,science should be slow to say ,ignorabimus4 ,a second position held by ,helmholtz1 ,lord ,kelvin1 and others1 suggests that minute living creatures may have come to the earth from elsewhere1 in the cracks of a meteorite or among cosmic dust4 ,it must be remembered that seeds can survive prolonged exposure to very low temperatures2 that spores of bacteria can survive high temperature2 that seeds of plants and germs of animals in a state of latent life can survive prolonged drought and absence of oxygen4 ,it is possible1 according to ,berthelot1 that as long as there is not molecular disintegration vital activities may be suspended for a time1 and may afterwards recommence when appropriate conditions are restored4 ,therefore1 one should be slow to say that a long journey through space is impossible4 ,the obvious limitation of ,lord ,kelvin's theory is that it only shifts the problem of the origin of organisms 7i4e4 living creatures7 from the earth to elsewhere4 ,the third answer is that living creatures of a very simple sort may have emerged on the earth's surface from not-living material1 e4g4 from some semi-fluid carbon compounds activated by ferments4 ,the tenability of this view is suggested by the achievements of the synthetic chemists1 who are able artificially to build up substances such as oxalic acid1 indigo1 salicylic acid1 caffeine1 and grape-sugar4 ,we do not know1 indeed1 what in ,nature's laboratory would take the place of the clever synthetic chemist1 but there seems to be a tendency to complexity4 ,corpuscles form atoms1 atoms form molecules1 small molecules large ones4 ,various concrete suggestions have been made in regard to the possible origin of living matter1 which will be dealt with in a later chapter4 ,so far as we know of what goes on to-day1 there is no evidence of spontaneous generation2 organisms seem always to arise from pre-existing organisms of the same kind2 where any suggestion of the contrary has been fancied1 there have been flaws in the experimenting4 ,but it is one thing to accept the verdict omne vivum e vivo as a fact to which experiment has not yet discovered an exception and another thing to maintain that this must always have been true or must always remain true4 ,if the synthetic chemists should go on surpassing themselves1 if substances like white of egg should be made artificially1 and if we should get more light on possible steps by which simple living creatures may have arisen from not-living materials1 this would not greatly affect our general outlook on life1 though it would increase our appreciation of what is often libelled as inert matter4 ,if the dust of the earth did naturally give rise very long ago to living creatures1 if they are in a real sense born of her and of the sunshine1 then the whole world becomes more continuous and more vital1 and all the inorganic groaning and travailing becomes more intelligible4 #d ,the ,first ,organisms upon the ,earth ,we cannot have more than a speculative picture of the first living creatures upon the earth or1 rather1 in the waters that covered the earth4 ,a basis for speculation is to be found1 however1 in the simplest creatures living to-day1 such as some of the bacteria and one-celled animalcules1 especially those called ,protists1 which have not taken any very definite step towards becoming either plants or animals4 ,no one can be sure1 but there is much to be said for the theory that the first creatures were microscopic globules of living matter1 not unlike the simplest bacteria of to-day1 but able to live on air1 water1 and dissolved salts4 ,from such a source may have originated a race of one-celled marine organisms which were able to manufacture chlorophyll1 or something like chlorophyll1 that is to say1 the green pigment which makes it possible for plants to utilise the energy of the sunlight in breaking up carbon dioxide and in building up 7photosynthesis7 carbon compounds like sugars and starch4 ,these little units were probably encased in a cell-wall of cellulose1 but their boxed-in energy expressed itself in the undulatory movement of a lash or flagellum1 by means of which they propelled themselves energetically through the water4 ,there are many similar organisms to-day1 mostly in water1 but some of them--simple one-celled plants--paint the tree-stems and even the paving-stones green in wet weather4 ,according to ,prof4 ,a4 ,h4 ,church there was a long chapter in the history of the earth when the sea that covered everything teemed with these green flagellates--the originators of the ,vegetable ,kingdom4 ,on another tack1 however1 there probably evolved a series of simple predatory creatures1 not able to build up organic matter from air1 water1 and salts1 but devouring their neighbours4 ,these units were not closed in with cellulose1 but remained naked1 with their living matter or protoplasm flowing out in changeful processes1 such as we see in the ,amoeb in the ditch or in our own white blood corpuscles and other amoeboid cells4 ,these were the originators of the animal kingdom4 ,thus from very simple ,protists the first animals and the first plants may have arisen4 ,all were still very minute1 and it is worth remembering that had there been any scientific spectator after our kind upon the earth during these long ages1 he would have lamented the entire absence of life1 although the seas were teeming4 ,the simplest forms of life and the protoplasm which ,huxley called the physical basis of life will be dealt with in the chapter on ,biology in a later section of this work4 ,,first ,,great ,,steps ,,in ,,evolution ,,the ,,first ,,plants--,,the ,,first ,,animals--,,beginnings ,,of ,,bodies--,,evolution ,,of ,,sex--,,beginning ,,of ,,natural ,,death #a ,the ,contrast between ,plants and ,animals ,however it may have come about1 there is no doubt at all that one of the first great steps in ,organic ,evolution was the forking of the genealogical tree into ,plants and ,animals--the most important parting of the ways in the whole history of ,nature4 ,typical plants have chlorophyll2 they are able to feed at a low chemical level on air1 water1 and salts1 using the energy of the sunlight in their photosynthesis4 ,they have their cells boxed in by cellulose walls1 so that their opportunities for motility are greatly restricted4 ,they manufacture much more nutritive material than they need1 and live far below their income4 ,they have no ready way of getting rid of any nitrogenous waste matter that they may form1 and this probably helps to keep them sluggish4 ,animals1 on the other hand1 feed at a high chemical level1 on the carbohydrates 7e4g4 starch and sugar71 fats1 and proteins 7e4g4 gluten1 albumin1 casein7 which are manufactured by other animals1 or to begin with1 by plants4 ,their cells have not cellulose walls1 nor in most cases much wall of any kind1 and motility in the majority is unrestricted4 ,animals live much more nearly up to their income4 ,if we could make for an animal and a plant of equal weight two fractions showing the ratio of the upbuilding1 constructive1 chemical processes to the down-breaking1 disruptive1 chemical processes that go on in their respective bodies1 the ratio for the plant would be much greater than the corresponding ratio for the animal4 ,in other words1 animals take the munitions which plants laboriously manufacture and explode them in locomotion and work2 and the entire system of animate nature depends upon the photosynthesis that goes on in green plants4 ,illustration3 ,from the ,smithsonian ,report1 #aiag ,a ,,piece ,,of ,a ,,reef-,,building ,,coral1 ,,built ,,up ,,by ,a ,,large ,,colony ,,of ,,small ,,sea-,,anemone-,,like ,,polyps1 ,,each ,,of ,,which ,,forms ,,from ,,the ,,salts ,,of ,,the ,,sea ,a ,,skeleton ,,or ,,shell ,,of ,,lime ,the wonderful mass of corals1 which are very beautiful1 are the skeleton remains of hundreds of these little creatures4 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,the ,,inset ,,circle ,,shows ,a ,,group ,,of ,,chalk-,,forming ,,animals1 ,,or ,,foraminifera1 ,,each ,,about ,,the ,,size ,,of ,a ,,very ,,small ,,pin',s ,,head ,they form a great part of the chalk cliffs of ,dover and similar deposits which have been raised from the floor of an ancient sea4 ,,the ,,enormously ,,enlarged ,,illustration ,,is ,,that ,,of ,a ,,common ,,foraminifer 7,,polystomella7 ,,showing ,,the ,,shell ,,in ,,the ,,centre ,,and ,,the ,,outflowing ,,network ,,of ,,living ,,matter1 ,,along ,,which ,,granules ,,are ,,continually ,,travelling1 ,,and ,,by ,,which ,,food ,,particles ,,are ,,entangled ,,and ,,drawn ,,in ,reproduced by permission of the ,natural ,history ,museum 7after ,max ,schultze74 ,as the result of much more explosive life1 animals have to deal with much in the way of nitrogenous waste products1 the ashes of the living fire1 but these are usually got rid of very effectively1 e4g4 in the kidney filters1 and do not clog the system by being deposited as crystals and the like1 as happens in plants4 ,sluggish animals like sea-squirts which have no kidneys are exceptions that prove the rule1 and it need hardly be said that the statements that have been made in regard to the contrasts between plants and animals are general statements4 ,there is often a good deal of the plant about the animal1 as in sedentary sponges1 zoophytes1 corals1 and sea-squirts1 and there is often a little of the animal about the plant1 as we see in the movements of all shoots and roots and leaves1 and occasionally in the parts of the flower4 ,but the important fact is that on the early forking of the genealogical tree1 i4e4 the divergence of plants and animals1 there depended and depends all the higher life of the animal kingdom1 not to speak of mankind4 ,the continuance of civilisation1 the upkeep of the human and animal population of the globe1 and even the supply of oxygen to the air we breathe1 depend on the silent laboratories of the green leaves1 which are able with the help of the sunlight to use carbonic acid1 water1 and salts to build up the bread of life4 #b ,the ,beginnings of ,land ,plants ,it is highly probable that for long ages the waters covered the earth1 and that all the primeval vegetation consisted of simple ,flagellates in the universal ,open ,sea4 ,but contraction of the earth's crust brought about elevations and depressions of the sea-floor1 and in places the solid substratum was brought near enough the surface to allow the floating plants to begin to settle down without getting out of the light4 ,this is how ,professor ,church pictures the beginning of a fixed vegetation--a very momentous step in evolution4 ,it was perhaps among this early vegetation that animals had their first successes4 ,as the floor of the sea in these shallow areas was raised higher and higher there was a beginning of dry land4 ,the sedentary plants already spoken of were the ancestors of the shore seaweeds1 and there is no doubt that when we go down at the lowest tide and wade cautiously out among the jungle of vegetation only exposed on such occasions we are getting a glimpse of very ancient days4 ,this is the forest primeval4 ,the ,protozoa ,animals below the level of zoophytes and sponges are called ,protozoa4 ,the word obviously means ,first ,animals1 but all that we can say is that the very simplest of them may give us some hint of the simplicity of the original first animals4 ,for it is quite certain that the vast majority of the ,protozoa to-day are far too complicated to be thought of as primitive4 ,though most of them are microscopic1 each is an animal complete in itself1 with the same fundamental bodily attributes as are manifested in ourselves4 ,they differ from animals of higher degree in not being built up of the unit areas or corpuscles called cells4 ,they have no cells1 no tissues1 no organs1 in the ordinary acceptation of these words1 but many of them show a great complexity of internal structure1 far exceeding that of the ordinary cells that build up the tissues of higher animals4 ,they are complete living creatures which have not gone in for body-making4 ,in the dim and distant past there was a time when the only animals were of the nature of ,protozoa1 and it is safe to say that one of the great steps in evolution was the establishment of three great types of ,protozoa3 7a7 ,some were very active1 the ,infusorians1 like the slipper animalcule1 the night-light 7,noctiluca71 which makes the seas phosphorescent at night1 and the deadly ,trypanosome1 which causes ,sleeping ,sickness4 7b7 ,others were very sluggish1 the parasitic ,sporozoa1 like the malaria organism which the mosquito introduces into man's body4 7c7 ,others were neither very active nor very passive1 the ,rhizopods1 with out-flowing processes of living matter4 ,this amoeboid line of evolution has been very successful2 it is represented by the ,rhizopods1 such as ,amoeb and the chalk-forming ,foraminifera and the exquisitely beautiful flint-shelled ,radiolarians of the open sea4 ,they have their counterparts in the amoeboid cells of most multicellular animals1 such as the phagocytes which migrate about in the body1 engulfing and digesting intruding bacteria1 serving as sappers and miners when something has to be broken down and built up again1 and performing other useful offices4 #c ,the ,making of a ,body ,the great naturalist ,louis ,agassiz once said that the biggest gulf in ,organic ,nature was that between the unicellular and the multicellular animals 7,protozoa and ,metazoa74 ,but the gulf was bridged very long ago when sponges1 stinging animals1 and simple worms were evolved1 and showed1 for the first time1 a body4 ,what would one not give to be able to account for the making of a body1 one of the great steps in evolution6 ,no one knows1 but the problem is not altogether obscure4 ,when an ordinary ,protozoon or one-celled animal divides into two or more1 which is its way of multiplying1 the daughter-units thus formed float apart and live independent lives4 ,but there are a few ,protozoa in which the daughter-units are not quite separated off from one another1 but remain coherent4 ,thus ,volvox1 a beautiful green ball1 found in some canals and the like1 is a colony of a thousand or even ten thousand cells4 ,it has almost formed a body6 ,but in this colony-making ,protozoon1 and in others like it1 the component cells are all of one kind1 whereas in true multicellular animals there are different kinds of cells1 showing division of labour4 ,there are some other ,protozoa in which the nucleus or kernel divides into many nuclei within the cell4 ,this is seen in the ,giant ,amoeba 7,pelomyxa71 sometimes found in duck-ponds1 or the beautiful ,opalina1 which always lives in the hind part of the frog's food-canal4 ,if a portion of the living matter of these ,protozoa should gather round each of the nuclei1 then that would be the beginning of a body4 ,it would be still nearer the beginning of a body if division of labour set in1 and if there was a setting apart of egg-cells and sperm-cells distinct from body-cells4 ,it was possibly in some such way that animals and plants with a body were first evolved4 ,two points should be noticed1 that body-making is not essentially a matter of size1 though it made large size possible4 ,for the body of a many-celled ,wheel ,animalcule or ,rotifer is no bigger than many a ,protozoon4 ,yet the ,rotifer--we are thinking of ,hydatina--has nine hundred odd cells1 whereas the ,protozoon has only one1 except in forms like ,volvox4 ,secondly1 it is a luminous fact that every many-celled animal from sponge to man that multiplies in the ordinary way begins at the beginning again as a single cell1 the fertilised egg-cell4 ,it is1 of course1 not an ordinary single cell that develops into an earthworm or a butterfly1 an eagle1 or a man2 it is a cell in which a rich inheritance1 the fruition of ages1 is somehow condensed2 but it is interesting to bear in mind the elementary fact that every many-celled creature1 reproduced in the ordinary way and not by budding or the like1 starts as a fertilised egg-cell4 ,the coherence of the daughter-cells into which the fertilised egg-cell divides is a reminiscence1 as it were1 of the primeval coherence of daughter-units that made the first body possible4 ,the ,beginning of ,sexual ,reproduction ,a freshwater ,hydra1 growing on the duckweed usually multiplies by budding4 ,it forms daughter-buds1 living images of itself2 a check comes to nutrition and these daughter-buds go free4 ,a big sea-anemone may divide in two or more parts1 which become separate animals4 ,this is asexual reproduction1 which means that the multiplication takes place by dividing into two or many portions1 and not by liberating egg-cells and sperm-cells4 ,among animals as among plants1 asexual reproduction is very common4 ,but it has great disadvantages1 for it is apt to be physiologically expensive1 and it is beset with difficulties when the body shows great division of labour1 and is very intimately bound into unity4 ,thus1 no one can think of a bee or a bird multiplying by division or by budding4 ,moreover1 if the body of the parent has suffered from injury or deterioration1 the result of this is bound to be handed on to the next generation if asexual reproduction is the only method4 ,illustration3 ,photos3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,a ,,plant-,,like ,,animal1 ,,or ,,zoophyte1 ,,called ,,obelia ,consisting of a colony of small polyps1 whose stinging tentacles are well shown greatly enlarged in the lower photograph4 ,illustration3 ,reproduced by permission of ,the ,quart4 ,journ4 ,mic4 ,sci4 ,,trypanosoma ,,gambiense 7,very highly magnified47 ,the microscopic animal ,trypanosome1 which causes ,sleeping ,sickness4 ,the study of these organisms has of late years acquired an immense importance on account of the widespread and dangerous maladies to which some of them give rise4 ,it lives in the blood of man1 who is infected by the bite of a ,tse-tse fly which carries the parasite from some other host4 ,illustration3 ,,volvox ,the ,volvox is found in some canals and the like4 ,it is one of the first animals to suggest the beginning of a body4 ,it is a colony of a thousand or even ten thousand cells1 but they are all cells of one kind4 ,in multicellular animals the cells are of different kinds with different functions4 ,each of the ordinary cells 7marked #e7 has two lashes or flagella4 ,daughter colonies inside the ,parent colony are being formed at #c1 #d1 and #b4 ,the development of germ-cells is shown at #a4 ,illustration3 ,,proterospongia ,one of the simplest multicellular animals1 illustrating the beginning of a body4 ,there is a setting apart of egg-cells and sperm-cells1 distinct from body-cells2 the collared lashed cells on the margin are different in kind from those farther in4 ,thus1 as in indubitable multicellular animals1 division of labour has begun4 ,splitting into two or many parts was the old-fashioned way of multiplying1 but one of the great steps in evolution was the discovery of a better method1 namely1 sexual reproduction4 ,the gist of this is simply that during the process of body-building 7by the development of the fertilised egg-cell7 certain units1 the germ-cells1 do not share in forming ordinary tissues or organs1 but remain apart1 continuing the full inheritance which was condensed in the fertilised egg-cell4 ,these cells kept by themselves are the originators of the future reproductive cells of the mature animal2 they give rise to the egg-cells and the sperm-cells4 ,the advantages of this method are great4 7#a7 ,the new generation is started less expensively1 for it is easier to shed germ-cells into the cradle of the water than to separate off half of the body4 7#b7 ,it is possible to start a great many new lives at once1 and this may be of vital importance when the struggle for existence is very keen1 and when parental care is impossible4 7#c7 ,the germ-cells are little likely to be prejudicially affected by disadvantageous dints impressed on the body of the parent--little likely unless the dints have peculiarly penetrating consequences1 as in the case of poisons4 7#d7 ,a further advantage is implied in the formation of two kinds of germ-cells--the ovum or egg-cell1 with a considerable amount of building material and often with a legacy of nutritive yolk2 the spermatozoon or sperm-cell1 adapted to move in fluids and to find the ovum from a distance1 thus securing change-provoking cross-fertilisation4 #d ,the ,evolution of ,sex ,another of the great steps in organic evolution was the differentiation of two different physiological types1 the male or sperm-producer and the female or egg-producer4 ,it seems to be a deep-seated difference in constitution1 which leads one egg to develop into a male1 and another1 lying beside it in the nest1 into a female4 ,in the case of pigeons it seems almost certain1 from the work of ,professor ,oscar ,riddle1 that there are two kinds of egg1 a male-producing egg and a female-producing egg1 which differ in their yolk-forming and other physiological characters4 ,in sea-urchins we often find two creatures superficially indistinguishable1 but the one is a female with large ovaries and the other is a male with equally large testes4 ,here the physiological difference does not affect the body as a whole1 but the reproductive organs or gonads only1 though more intimate physiology would doubtless discover differences in the blood or in the chemical routine 7metabolism74 ,in a large number of cases1 however1 there are marked superficial differences between the sexes1 and everyone is familiar with such contrasts as peacock and peahen1 stag and hind4 ,in such cases the physiological difference between the sperm-producer and the ovum-producer1 for this is the essential difference1 saturates through the body and expresses itself in masculine and feminine structures and modes of behaviour4 ,the expression of the masculine and feminine characters is in some cases under the control of hormones or chemical messengers which are carried by the blood from the reproductive organs throughout the body1 and pull the trigger which brings about the development of an antler or a wattle or a decorative plume or a capacity for vocal and saltatory display4 ,in some cases it is certain that the female carries in a latent state the masculine features1 but these are kept from expressing themselves by other chemical messengers from the ovary4 ,of these chemical messengers more must be said later on4 ,recent research has shown that while the difference between male and female is very deep-rooted1 corresponding to a difference in gearing1 it is not always clear-cut4 ,thus a hen-pigeon may be very masculine1 and a cock-pigeon very feminine4 ,the difference is in degree1 not in kind4 #e ,what is the meaning of the universal or almost universal inevitableness of death8 ,a ,sequoia or ,big ,tree of ,california has been known to live for over two thousand years1 but eventually it died4 ,a centenarian tortoise has been known1 and a sea-anemone sixty years of age2 but eventually they die4 ,what is the meaning of this apparently inevitable stoppage of bodily life8 ,the ,beginning of ,natural ,death ,there are three chief kinds of death1 7a7 ,the great majority of animals come to a violent end1 being devoured by others or killed by sudden and extreme changes in their surroundings4 7b7 ,when an animal enters a new habitat1 or comes into new associations with other organisms1 it may be invaded by a microbe or by some larger parasite to which it is unaccustomed and to which it can offer no resistance4 ,with many parasites a live-and-let-live compromise is arrived at1 but new parasites are apt to be fatal1 as man knows to his cost when he is bitten by a tse-tse fly which infects him with the microscopic animal 7a ,trypanosome7 that causes ,sleeping ,sickness4 ,in many animals the parasites are not troublesome as long as the host is vigorous1 but if the host is out of condition the parasites may get the upper hand1 as in the so-called grouse disease1 and become fatal4 7c7 ,but besides violent death and microbic 7or parasitic7 death1 there is natural death4 ,this is in great part to be regarded as the price paid for a body4 ,a body worth having implies complexity or division of labour1 and this implies certain internal furnishings of a more or less stable kind in which the effects of wear and tear are apt to accumulate4 ,it is not the living matter itself that grows old so much as the framework in which it works--the furnishings of the vital laboratory4 ,there are various processes of rejuvenescence1 e4g4 rest1 repair1 change1 reorganisation1 which work against the inevitable processes of senescence1 but sooner or later the victory is with ageing4 ,another deep reason for natural death is to be found in the physiological expensiveness of reproduction1 for many animals1 from worms to eels1 illustrate natural death as the nemesis of starting new lives4 ,now it is a very striking fact that to a large degree the simplest animals or ,protozoa are exempt from natural death4 ,they are so relatively simple that they can continually recuperate by rest and repair2 they do not accumulate any bad debts4 ,moreover1 their modes of multiplying1 by dividing into two or many units1 are very inexpensive physiologically4 ,it seems that in some measure this bodily immortality of the ,protozoa is shared by some simple many-celled animals like the freshwater ,hydra and ,planarian worms4 ,here is an interesting chapter in evolution1 the evolution of means of evading or staving off natural death4 ,thus there is the well-known case of the ,paloloworm of the coral-reefs where the body breaks up in liberating the germ-cells1 but the head-end remains fixed in a crevice of the coral1 and buds out a new body at leisure4 ,along with the evolution of the ways of avoiding death should be considered also the gradual establishment of the length of life best suited to the welfare of the species1 and the punctuation of the life-history to suit various conditions4 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,green ,,hydra ,a little freshwater polyp1 about half an inch long1 with a crown of tentacles round the mouth4 ,it is seen giving off a bud1 a clear illustration of asexual reproduction4 ,when a tentacle touches some small organism the latter is paralysed and drawn into the mouth4 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,earthworm ,earthworms began the profitable habit of moving with one end of the body always in front1 and from worms to man the great majority of animals have bilateral symmetry4 ,illustration3 ,,diagram ,,illustrating ,,the ,,beginning ,,of ,,individual ,,life #a4 ,an immature sperm-cell1 with #d chromosomes 7nuclear bodies7 represented as rods4 #b4 ,a mature sperm-cell1 with #b chromosomes4 #c4 ,an immature egg-cell1 with #d chromosomes represented as curved bodies4 #d4 ,a mature egg-cell1 with #b chromosomes4 #e4 ,the spermatozoon fertilises the ovum1 introducing #b chromosomes4 #f4 ,the fertilised ovum1 with #d chromosomes1 #b of paternal origin and #b of maternal origin4 #g4 ,the chromosomes lie at the equator1 and each is split longitudinally4 ,the centrosome introduced by the spermatozoon has divided into two centrosomes1 one at each pole of the nucleus4 ,these play an important part in the division or segmentation of the egg4 #h4 ,the fertilised egg has divided into two cells4 ,each cell has #b paternal and #b maternal chromosomes4 ,illustration3 ,reproduced from the ,smithsonian ,report1 #aiag4 ,,glass ,,model ,,of ,a ,,sea-,,anemone ,a long tubular sea-anemone1 with a fine crown of tentacles around the mouth4 ,the suggestion of a flower is very obvious4 ,by means of stinging lassoes on the tentacles minute animals on which it feeds are paralysed and captured for food4 ,illustration3 ,,this ,,drawing ,,shows ,,the ,,evolution ,,of ,,the ,,brain ,,from ,,fish ,,to ,,man ,the ,cerebrum1 the seat of intelligence1 increases in proportion to the other parts4 ,in mammals it becomes more and more convoluted4 ,the brain1 which lies in one plane in fishes1 becomes gradually curved on itself4 ,in birds it is more curved than the drawing shows4 #f ,great ,acquisitions ,in animals like sea-anemones and jellyfishes the general symmetry of the body is radial2 that is to say1 there is no right or left1 and the body might be halved along many planes4 ,it is a kind of symmetry well suited for sedentary or for drifting life4 ,but worms began the profitable habit of moving with one end of the body always in front1 and from worms to man the great majority of animals have bilateral symmetry4 ,they have a right and a left side1 and there is only one cut that halves the body4 ,this kind of symmetry is suited for a more strenuous life than radial animals show2 it is suited for pursuing food1 for avoiding enemies1 for chasing mates4 ,and with the establishment of bilateral symmetry must be associated the establishment of head-brains1 the beginning of which is to be found in some simple worm-types4 ,among the other great acquisitions gradually evolved we may notice3 a well-developed head with sense-organs1 the establishment of large internal surfaces such as the digestive and absorptive wall of the food-canal1 the origin of quickly contracting striped muscle and of muscular appendages1 the formation of blood as a distributing medium throughout the body1 from which all the parts take what they need and to which they also contribute4 ,another very important acquisition1 almost confined 7so far as is known7 to backboned animals1 was the evolution of what are called glands of internal secretion1 such as the thyroid and the supra-renal4 ,these manufacture subtle chemical substances which are distributed by the blood throughout the body1 and have a manifold influence in regulating and harmonising the vital processes4 ,some of these chemical messengers are called hormones1 which stimulate organs and tissues to greater activity2 others are called chalones1 which put on a brake4 ,some regulate growth and others rapidly alter the pressure and composition of the blood4 ,some of them call into active development certain parts of the body which have been1 as it were1 waiting for an appropriate trigger-pulling4 ,thus1 at the proper time1 the milk-glands of a mammalian mother are awakened from their dormancy4 ,this very interesting outcome of evolution will be dealt with in another portion of this work4 ,,the ,,inclined ,,plane ,,of ,,animal ,,behaviour #a ,before passing to a connected story of the gradual emergence of higher and higher forms of life in the course of the successive ages--the procession of life1 as it may be called--it will be useful to consider the evolution of animal behaviour4 ,evolution of ,mind ,a human being begins as a microscopic fertilised egg-cell1 within which there is condensed the long result of time--,man's inheritance4 ,the long period of nine months before birth1 with its intimate partnership between mother and offspring1 is passed as it were in sleep1 and no one can make any statement in regard to the mind of the unborn child4 ,even after birth the dawn of mind is as slow as it is wonderful4 ,to begin with1 there is in the ovum and early embryo no nervous system at all1 and it develops very gradually from simple beginnings4 ,yet as mentality cannot come in from outside1 we seem bound to conclude that the potentiality of it--whatever that means--resides in the individual from the very first4 ,the particular kind of activity known to us as thinking1 feeling1 and willing is the most intimate part of our experience1 known to us directly apart from our senses1 and the possibility of that must be implicit in the germ-cell just as the genius of ,newton was implicit in a very miserable specimen of an infant4 ,now what is true of the individual is true also of the race--there is a gradual evolution of that aspect of the living creature's activity which we call mind4 ,we cannot put our finger on any point and say3 ,before this stage there was no mind4 ,indeed1 many facts suggest the conclusion that wherever there is life there is some degree of mind--even in the plants4 ,or it might be more accurate to put the conclusion in another way1 that the activity we call life has always in some degree an inner or mental aspect4 ,illustration3 ,,okapi ,,and ,,giraffe ,the ,okapi is one of the great zological discoveries4 ,it gives a good idea of what the ,giraffe's ancestors were like4 ,the ,okapi was unknown until discovered in #aijj by ,sir ,harry ,johnston in ,central ,africa1 where these strange animals have probably lived in dense forests from time immemorial4 ,in another part of this book there is an account of the dawn of mind in backboned animals2 what we aim at here is an outline of what may be called the inclined plane of animal behaviour4 ,a very simple animal accumulates a little store of potential energy1 and it proceeds to expend this1 like an explosive1 by acting on its environment4 ,it does so in a very characteristic self-preservative fashion1 so that it burns without being consumed and explodes without being blown to bits4 ,it is characteristic of the organism that it remains a going concern for a longer or shorter period--its length of life4 ,living creatures that expended their energy ineffectively or self-destructively would be eliminated in the struggle for existence4 ,when a simple one-celled organism explores a corner of the field seen under a microscope1 behaving to all appearance very like a dog scouring a field seen through a telescope1 it seems permissible to think of something corresponding to mental endeavour associated with its activity4 ,this impression is strengthened when an amoeba pursues another amoeba1 overtakes it1 engulfs it1 loses it1 pursues it again1 recaptures it1 and so on4 ,what is quite certain is that the behaviour of the animalcule is not like that of a potassium pill fizzing about in a basin of water1 nor like the lurching movements of a gun that has got loose and taken charge on board ship4 ,another feature is that the locomotor activity of an animalcule often shows a distinct individuality3 it may swim1 for instance1 in a loose spiral4 ,but there is another side to vital activity besides acting upon the surrounding world2 the living creature is acted on by influences from without4 ,the organism acts on its environment2 that is the one side of the shield3 the environment acts upon the organism2 that is the other side4 ,if we are to see life whole we must recognise these two sides of what we call living1 and it is missing an important part of the history of animal life if we fail to see that evolution implies becoming more advantageously sensitive to the environment1 making more of its influences1 shutting out profitless stimuli1 and opening more gateways to knowledge4 ,the bird's world is a larger and finer world than an earthworm's2 the world means more to the bird than to the worm4 ,the ,trial and ,error ,method ,simple creatures act with a certain degree of spontaneity on their environment1 and they likewise react effectively to surrounding stimuli4 ,animals come to have definite answers back1 sometimes several1 sometimes only one1 as in the case of the ,slipper ,animalcule1 which reverses its cilia when it comes within the sphere of some disturbing influence1 retreats1 and1 turning upon itself tentatively1 sets off again in the same general direction as before1 but at an angle to the previous line4 ,if it misses the disturbing influence1 well and good2 if it strikes it again1 the tactics are repeated until a satisfactory way out is discovered or the stimulation proves fatal4 ,it may be said that the ,slipper ,animalcule has but one answer to every question1 but there are many ,protozoa which have several enregistered reactions4 ,when there are alternative reactions which are tried one after another1 the animal is pursuing what is called the trial-and-error method1 and a higher note is struck4 ,there is an endeavour after satisfaction1 and a trial of answers4 ,when the creature profits by experience to the extent of giving the right answer first1 there is the beginning of learning4 ,illustration3 ,,diagram ,,of ,a ,,simple ,,reflex ,,arc ,,in ,a ,,backboneless ,,animal ,,like ,,an ,,earthworm #a4 ,a sensory nerve-cell 7,s4,c47 on the surface receives a stimulus4 #b4 ,the stimulus travels along the sensatory nerve-fibre 7,s4,f47 #c4 ,the sensory nerve-fibre branches in the nerve-cord4 #d4 ,its branches come into close contact 7,,sy#a7 with those of an associative or communicating nerve-cell 7,a4,c474 #e4 ,other branches of the associative cell come into close contact 7,,sy#b7 with the branches or dendrites of a motor nerve-cell 7,m4,c474 #f4 ,an impulse or command travels along the motor nerve-fibre or axis cylinder of the motor nerve-cell4 #g4 ,the motor nerve-fibre ends on a muscle-fibre 7,m4,f47 near the surface4 ,this moves and the reflex action is complete4 ,illustration3 ,photo3 ,british ,museum 7,natural ,history74 ,,the ,,yucca ,,moth ,the ,yucca ,moth1 emerging from her cocoon1 flies at night to a ,yucca flower and collects pollen from the stamens1 holding a little ball of it in her mouth-parts4 ,she then visits another flower and lays an egg in the seed-box4 ,after this she applies the pollen to the tip of the pistil1 thus securing the fertilisation of the flower and the growth of the ovules in the pod4 ,yucca flowers in ,britain do not produce seeds because there are no ,yucca ,moths4 ,illustration3 ,,inclined ,,plane ,,of ,,animal ,,behaviour ,diagram illustrating animal behaviour4 ,the main line represents the general life of the creature4 ,on the upper side are activities implying initiative2 on the lower side actions which are almost automatic4 ,upper ,side4--,i4 ,energetic actions4 ,,ii4 ,simple tentatives4 ,,iii4 ,trial-and-error methods4 ,,iv4 ,non-intelligent experiments4 ,v4 ,experiential learning4 ,,vi4 ,associative learning4 ,,vii4 ,intelligent behaviour4 ,,viii4 ,rational conduct 7man74 ,lower ,side4--#a4 ,reactions to environment4 #b4 ,enregistered reactions4 #c4 ,simple reflex actions4 #d4 ,compound reflex actions4 #e4 ,tropisms4 #f4 ,enregistered rhythms4 #g4 ,simple instincts4 #h4 ,chain instincts4 #i4 ,instinctive activities influenced by intelligence4 #aj4 ,subconscious cerebration at a high level 7man74 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,venus' ,,fly-,,trap ,one of the most remarkable plants in the world1 which captures its prey by means of a trap formed from part of its leaf4 ,it has been induced to snap at and hold a bristle4 ,if an insect lighting on the leaf touches one of six very sensitive hairs1 which pull the trigger of the movement1 the two halves of the leaf close rapidly and the fringing teeth on the margin interlock1 preventing the insect's escape4 ,then follows an exudation of digestive juice4 ,illustration3 ,reproduced by permission from ,the ,wonders of ,instinct by ,j4 ,h4 ,fabre4 ,a ,,spider ,,sunning ,,her ,,eggs ,a kind of spider1 called ,lycosa1 lying head downwards at the edge of her nest1 and holding her silken cocoon--the bag containing the eggs--up towards the sun in her hindmost pair of legs4 ,this extraordinary proceeding is believed to assist in the hatching4 ,reflex ,actions ,among simple multicellular animals1 such as sea-anemones1 we find the beginnings of reflex actions1 and a considerable part of the behaviour of the lower animals is reflex4 ,that is to say1 there are laid down in the animal in the course of its development certain pre-arrangements of nerve-cells and muscle-cells which secure that a fit and proper answer is given to a frequently recurrent stimulus4 ,an earthworm half out of its burrow becomes aware of the light tread of a thrush's foot1 and jerks itself back into its hole before anyone can say reflex action4 ,what is it that happens8 ,certain sensory nerve-cells in the earthworm's skin are stimulated by vibrations in the earth2 the message travels down a sensory nerve-fibre from each of the stimulated cells and enters the nerve-cord4 ,the sensory fibres come into vital connection with branches of intermediary1 associative1 or communicating cells1 which are likewise connected with motor nerve-cells4 ,to these the message is thus shunted4 ,from the motor nerve-cells an impulse or command travels by motor nerve-fibres1 one from each cell1 to the muscles1 which contract4 ,if this took as long to happen as it takes to describe1 even in outline1 it would not be of much use to the earthworm4 ,but the motor answer follows the sensory stimulus almost instantaneously4 ,the great advantage of establishing or enregistering these reflex chains is that the answers are practically ready-made or inborn1 not requiring to be learned4 ,it is not necessary that the brain should be stimulated if there is a brain2 nor does the animal will to act1 though in certain cases it may by means of higher controlling nerve-centres keep the natural reflex response from being given1 as happens1 for instance1 when we control a cough or a sneeze on some solemn occasion4 ,the evolutionary method1 if we may use the expression1 has been to enregister ready-made responses2 and as we ascend the animal kingdom1 we find reflex actions becoming complicated and often linked together1 so that the occurrence of one pulls the trigger of another1 and so on in a chain4 ,the behaviour of the insectivorous plant called ,venus's fly-trap when it shuts on an insect is like a reflex action in an animal1 but plants have no definite nervous system4 ,what are ,called ,tropisms ,a somewhat higher level on the inclined plane is illustrated by what are called tropisms1 obligatory movements which the animal makes1 adjusting its whole body so that physiological equilibrium results in relation to gravity1 pressure1 currents1 moisture1 heat1 light1 electricity1 and surfaces of contact4 ,a moth is flying past a candle2 the eye next the light is more illumined than the other2 a physiological inequilibrium results1 affecting nerve-cells and muscle-cells2 the outcome is that the moth automatically adjusts its flight so that both eyes become equally illumined2 in doing this it often flies into the candle4 ,it may seem bad business that the moth should fly into the candle1 but the flame is an utterly artificial item in its environment to which no one can expect it to be adapted4 ,these tropisms play an important rle in animal behaviour4 #b ,instinctive ,behaviour ,on a higher level is instinctive behaviour1 which reaches such remarkable perfection in ants1 bees1 and wasps4 ,in its typical expression instinctive behaviour depends on inborn capacities2 it does not require to be learned2 it is independent of practice or experience1 though it may be improved by both2 it is shared equally by all members of the species of the same sex 7for the female's instincts are often different from the male's72 it refers to particular conditions of life that are of vital importance1 though they may occur only once in a lifetime4 ,the female ,yucca ,moth emerges from the cocoon when the ,yucca flower puts forth its bell-like blossoms4 ,she flies to a flower1 collects some pollen from the stamens1 kneads it into a pill-like ball1 and stows this away under her chin4 ,she flies to an older ,yucca flower and lays her eggs in some of the ovules within the seed-box1 but before she does so she has to deposit on the stigma the ball of pollen4 ,from this the pollen-tubes grow down and the pollen-nucleus of a tube fertilises the egg-cell in an ovule1 so that the possible seeds become real seeds1 for it is only a fraction of them that the ,yucca ,moth has destroyed by using them as cradles for her eggs4 ,now it is plain that the ,yucca ,moth has no individual experience of ,yucca flowers1 yet she secures the continuance of her race by a concatenation of actions which form part of her instinctive repertory4 ,from a physiological point of view instinctive behaviour is like a chain of compound reflex actions1 but in some cases1 at least1 there is reason to believe that the behaviour is suffused with awareness and backed by endeavour4 ,this is suggested in exceptional cases where the stereotyped routine is departed from to meet exceptional conditions4 ,it should also be noted that just as ants1 hive bees1 and wasps exhibit in most cases purely instinctive behaviour1 but move on occasion on the main line of trial and error or of experimental initiative1 so among birds and mammals the intelligent behaviour is sometimes replaced by instinctive routine4 ,perhaps there is no instinctive behaviour without a spice of intelligence1 and no intelligent behaviour without an instinctive element4 ,the old view that instinctive behaviour was originally intelligent1 and that instinct is lapsed intelligence1 is a tempting one1 and is suggested by the way in which habitual intelligent actions cease in the individual to require intelligent control1 but it rests on the unproved hypothesis that the acquisitions of the individual can be entailed on the race4 ,it is almost certain that instinct is on a line of evolution quite different from intelligence1 and that it is nearer to the inborn inspirations of the calculating boy or the musical genius than to the plodding methods of intelligent learning4 ,animal ,intelligence ,the higher reaches of the inclined plane of behaviour show intelligence in the strict sense4 ,they include those kinds of behaviour which cannot be described without the suggestion that the animal makes some sort of perceptual inference1 not only profiting by experience but learning by ideas4 ,such intelligent actions show great individual variability2 they are plastic and adjustable in a manner rarely hinted at in connection with instincts where routine cannot be departed from without the creature being nonplussed2 they are not bound up with particular circumstances as instinctive actions are1 but imply an appreciative awareness of relations4 ,when there is an experimenting with general ideas1 when there is conceptual as contrasted with perceptual inference1 we speak of ,reason1 but there is no evidence of this below the level of man4 ,it is not1 indeed1 always that we can credit man with rational conduct1 but he has the possibility of it ever within his reach4 ,animal instinct and intelligence will be illustrated in another part of this work4 ,we are here concerned simply with the general question of the evolution of behaviour4 ,there is a main line of tentative experimental behaviour both below and above the level of intelligence1 and it has been part of the tactics of evolution to bring about the hereditary enregistration of capacities of effective response1 the advantages being that the answers come more rapidly and that the creature is left free1 if it chooses1 for higher adventures4 ,there is no doubt as to the big fact that in the course of evolution animals have shown an increasing complexity and masterfulness of behaviour1 that they have become at once more controlled and more definitely free agents1 and that the inner aspect of the behaviour--experimenting1 learning1 thinking1 feeling1 and willing--has come to count for more and more4 #c ,evolution of ,parental ,care ,mammals furnish a crowning instance of a trend of evolution which expresses itself at many levels--the tendency to bring forth the young at a well-advanced stage and to an increase of parental care associated with a decrease in the number of offspring4 ,there is a ,british starfish called ,luidia which has two hundred millions of eggs in a year1 and there are said to be several millions of eggs in conger-eels and some other fishes4 ,these illustrate the spawning method of solving the problem of survival4 ,some animals are naturally prolific1 and the number of eggs which they sow broadcast in the waters allows for enormous infantile mortality and obviates any necessity for parental care4 ,but some other creatures1 by nature less prolific1 have found an entirely different solution of the problem4 ,they practise parental care and they secure survival with greatly economised reproduction4 ,this is a trend of evolution particularly characteristic of the higher animals4 ,so much so that ,herbert ,spencer formulated the generalisation that the size and frequency of the animal family is inverse ratio to the degree of evolution to which the animal has attained4 ,now there are many different methods of parental care which secure the safety of the young1 and one of these is called viviparity4 ,the young ones are not liberated from the parent until they are relatively well advanced and more or less able to look after themselves4 ,this gives the young a good send-off in life1 and their chances of death are greatly reduced4 ,in other words1 the animals that have varied in the direction of economised reproduction may keep their foothold in the struggle for existence if they have varied at the same time in the direction of parental care4 ,in other cases it may have worked the other way round4 ,in the interesting archaic animal called ,peripatus1 which has to face a modern world too severe for it1 one of the methods of meeting the environing difficulties is the retention of the offspring for many months within the mother1 so that it is born a fully-formed creature4 ,there are only a few offspring at a time1 and1 although there are exceptional cases like the summer green-flies1 which are very prolific though viviparous1 the general rule is that viviparity is associated with a very small family4 ,the case of flowering plants stands by itself1 for although they illustrate a kind of viviparity1 the seed being embryos1 an individual plant may have a large number of flowers and therefore a huge family4 ,viviparity naturally finds its best illustrations among terrestrial animals1 where the risks to the young life are many1 and it finds its climax among mammals4 ,now it is an interesting fact that the three lowest mammals1 the ,duckmole and two ,spiny ,ant-eaters1 lay eggs1 i4e4 are oviparous2 that the ,marsupials1 on the next grade1 bring forth their young1 as it were1 prematurely1 and in most cases stow them away in an external pouch2 while all the others--the ,placentals--show a more prolonged ante-natal life and an intimate partnership between the mother and the unborn young4 #d ,there is another way of looking at the sublime process of evolution4 ,it has implied a mastery of all the possible haunts of life2 it has been a progressive conquest of the environment4 #a4 ,it is highly probable that living organisms found their foothold in the stimulating conditions of the shore of the sea--the shallow water1 brightly illumined1 seaweed-growing shelf fringing the ,continents4 ,this littoral zone was a propitious environment where sea and fresh water1 earth and air all meet1 where there is stimulating change1 abundant oxygenation and a copious supply of nutritive material in what the streams bring down and in the rich seaweed vegetation4 ,illustration3 ,,the ,,hoatzin ,,inhabits ,,british ,,guiana ,the newly hatched bird has claws on its thumb and first finger and so is enabled to climb on the branches of trees with great dexterity until such time as the wings are strong enough to sustain it in flight4 ,illustration3 ,photograph1 from the ,british ,museum 7,natural ,history71 of a drawing by ,mr4 ,e4 ,wilson4 ,,peripatus ,a widely distributed old-fashioned type of animal1 somewhat like a permanent caterpillar4 ,it has affinities both with worms and with insects4 ,it has a velvety skin1 minute diamond-like eyes1 and short stump-like legs4 ,a defenceless1 weaponless animal1 it comes out at night1 and is said to capture small insects by squirting jets of slime from its mouth4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,rock ,,kangaroo ,,carrying ,,its ,,young ,,in ,a ,,pouch ,the young are born so helpless that they cannot even suck4 ,the mother places them in the external pouch1 and fitting their mouths on the teats injects the milk4 ,after a time the young ones go out and in as they please4 ,it is not an easy haunt of life1 but none the worse for that1 and it is tenanted to-day by representatives of practically every class of animals from infusorians to seashore birds and mammals4 ,the ,cradle of the ,open ,sea #b4 ,the open-sea or pelagic haunt includes all the brightly illumined surface waters beyond the shallow water of the shore area4 ,it is perhaps the easiest of all the haunts of life1 for there is no crowding1 there is considerable uniformity1 and an abundance of food for animals is afforded by the inexhaustible floating sea-meadows of microscopic ,alg4 ,these are reincarnated in minute animals like the open-sea crustaceans1 which again are utilised by fishes1 these in turn making life possible for higher forms like carnivorous turtles and toothed whales4 ,it is quite possible that the open sea was the original cradle of life and perhaps ,professor ,church is right in picturing a long period of pelagic life before there was any sufficiently shallow water to allow the floating plants to anchor4 ,it is rather in favour of this view that many shore animals such as crabs and starfishes1 spend their youthful stages in the relatively safe cradle of the open sea1 and only return to the more strenuous conditions of their birthplace after they have gained considerable strength of body4 ,it is probably safe to say that the honour of being the original cradle of life lies between the shore of the sea and the open sea4 ,the ,great ,deeps #c4 ,a third haunt of life is the floor of the ,deep ,sea1 the abyssal area1 which occupies more than a half of the surface of the globe4 ,it is a region of extreme cold--an eternal winter2 of utter darkness--an eternal night--relieved only by the fitful gleams of phosphorescent animals2 of enormous pressure--#b-a_/b tons on the square inch at a depth of #b1ejj fathoms2 of profound calm1 unbroken silence1 immense monotony4 ,and as there are no plants in the great abysses1 the animals must live on one another1 and1 in the long run1 on the rain of moribund animalcules which sink from the surface through the miles of water4 ,it seems a very unpromising haunt of life1 but it is abundantly tenanted1 and it gives us a glimpse of the insurgent nature of the living creature that the difficulties of the ,deep ,sea should have been so effectively conquered4 ,it is probable that the colonising of the great abysses took place in relatively recent times1 for the fauna does not include many very antique types4 ,it is practically certain that the colonisation was due to littoral animals which followed the food-dbris1 millennium after millennium1 further and further down the long slope from the shore4 ,the ,freshwaters #d4 ,a fourth haunt of life is that of the freshwaters1 including river and lake1 pond and pool1 swamp and marsh4 ,it may have been colonised by gradual migration up estuaries and rivers1 or by more direct passage from the seashore into the brackish swamp4 ,or it may have been in some cases that partially landlocked corners of ancient seas became gradually turned into freshwater basins4 ,the animal population of the freshwaters is very representative1 and is diversely adapted to meet the characteristic contingencies--the risk of being dried up1 the risk of being frozen hard in winter1 and the risk of being left high and dry after floods or of being swept down to the sea4 ,conquest of the ,dry ,land #e4 ,the terrestrial haunt has been invaded age after age by contingents from the sea or from the freshwaters4 ,we must recognise the worm invasion1 which led eventually to the making of the fertile soil1 the invasion due to air-breathing ,arthropods1 which led eventually to the important linkage between flowers and their insect visitors1 and the invasion due to air-breathing ,amphibians1 which led eventually to the higher terrestrial animals and to the development of intelligence and family affection4 ,besides these three great invasions1 there were minor ones such as that leading to land-snails1 for there has been a widespread and persistent tendency among aquatic animals to try to possess the dry land4 ,getting on to dry land had a manifold significance4 ,it implied getting into a medium with a much larger supply of oxygen than there is dissolved in the water4 ,but the oxygen of the air is more difficult to capture1 especially when the skin becomes hard or well protected1 as it is almost bound to become in animals living on dry ground4 ,thus this leads to the development of internal surfaces1 such as those of lungs1 where the oxygen taken into the body may be absorbed by the blood4 ,in most animals the blood goes to the surface of oxygen-capture2 but in insects and their relatives there is a different idea--of taking the air to the blood or in greater part to the area of oxygen-combustion1 the living tissues4 ,a system of branching air-tubes takes air into every hole and corner of the insect's body1 and this thorough aeration is doubtless in part the secret of the insect's intense activity4 ,the blood never becomes impure4 ,the conquest of the dry land also implied a predominance of that kind of locomotion which may be compared to punting1 when the body is pushed along by pressing a lever against a hard substratum4 ,and it also followed that with few exceptions the body of the terrestrial animal tended to be compact1 readily lifted off the ground by the limbs or adjusted in some other way so that there may not be too large a surface trailing on the ground4 ,an animal like a jellyfish1 easily supported in the water1 would be impossible on land4 ,such apparent exceptions as earthworms1 centipedes1 and snakes are not difficult to explain1 for the earthworm is a burrower which eats its way through the soil1 the centipede's long body is supported by numerous hard legs1 and the snake pushes itself along by means of the large ventral scales to which the lower ends of very numerous ribs are attached4 ,methods of ,mastering the ,difficulties of ,terrestrial ,life ,a great restriction attendant on the invasion of the dry land is that locomotion becomes limited to one plane1 namely1 the surface of the earth4 ,this is in great contrast to what is true in the water1 where the animal can move up or down1 to right or to left1 at any angle and in three dimensions4 ,it surely follows from this that the movements of land animals must be rapid and precise1 unless1 indeed1 safety is secured in some other way4 ,hence it is easy to understand why most land animals have very finely developed striped muscles1 and why a beetle running on the ground has far more numerous muscles than a lobster swimming in the sea4 ,land animals were also handicapped by the risks of drought and of frost1 but these were met by defences of the most diverse description1 from the hairs of woolly caterpillars to the fur of mammals1 from the carapace of tortoises to the armour of armadillos4 ,in other cases1 it is hardly necessary to say1 the difficulties may be met in other ways1 as frogs meet the winter by falling into a lethargic state in some secluded retreat4 ,another consequence of getting on to dry land is that the eggs or young can no longer be set free anyhow1 as is possible when the animal is surrounded by water1 which is in itself more or less of a cradle4 ,if the eggs were laid or the young liberated on dry ground1 the chances are many that they would be dried up or devoured4 ,so there are numerous ways in which land animals secure the safety of their young1 e4g4 by burying them in the ground1 or by hiding them in nests1 or by carrying them about for a prolonged period either before or after birth4 ,this may mean great safety for the young1 this may make it possible to have only a small family1 and this may tend to the evolution of parental care and the kindly emotions4 ,thus it may be understood that from the conquest of the land many far-reaching consequences have followed4 ,illustration3 ,photo3 ,rischgitz4 ,,professor ,,thomas ,,henry ,,huxley 7#ahbe-ie7 ,one of the most distinguished of zoologists1 with unsurpassed gifts as a teacher and expositor4 ,he did great service in gaining a place for science in ordinary education and in popular estimation4 ,no one championed ,evolutionism with more courage and skill4 ,illustration3 ,,baron ,,cuvier1 #agfi-ahcb ,one of the founders of modern ,comparative ,anatomy4 ,a man of gigantic intellect1 who came to ,paris as a youth from the provinces1 and became the director of the higher education of ,france and a peer of the ,empire4 ,he was opposed to ,evolutionist ideas1 but he had anatomical genius4 ,illustration3 ,,an ,,illustration ,,showing ,,various ,,methods ,,of ,,flying ,,and ,,swooping ,gull1 with a feather-wing1 a true flier4 ,fox-bat1 with a skin-wing1 a true flier4 ,flying ,squirrel1 with a parachute of skin1 able to swoop from tree to tree1 but not to fly4 ,flying ,fish1 with pectoral fins used as volplanes in a great leap due to the tail4 ,to some extent able to sail in albatros fashion4 ,finally1 it is worth dwelling on the risks of terrestrial life1 because they enable us better to understand why so many land animals have become burrowers and others climbers of trees1 why some have returned to the water and others have taken to the air4 ,it may be asked1 perhaps1 why the land should have been colonised at all when the risks and difficulties are so great4 ,the answer must be that necessity and curiosity are the mother and father of invention4 ,animals left the water because the pools dried up1 or because they were overcrowded1 or because of inveterate enemies1 but also because of that curiosity and spirit of adventure which1 from first to last1 has been one of the spurs of progress4 ,conquering the ,air #f4 ,the last great haunt of life is the air1 a mastery of which must be placed to the credit of insects1 ,pterodactyls1 birds1 and bats4 ,these have been the successes1 but it should be noted that there have been many brilliant failures1 which have not attained to much more than parachuting4 ,these include the ,flying ,fishes1 which take leaps from the water and are carried for many yards and to considerable heights1 holding their enlarged pectoral fins taut or with little more than a slight fluttering4 ,there is a so-called ,flying ,frog 7,rhacophorus7 that skims from branch to branch1 and the much more effective ,flying ,dragon 7,draco volans7 of the ,far ,east1 which has been mentioned already4 ,among mammals there are ,flying ,phalangers1 ,flying ,lemurs1 and more besides1 all attaining to great skill as parachutists1 and illustrating the endeavour to master the air which man has realised in a way of his own4 ,the power of flight brings obvious advantages4 ,a bird feeding on the ground is able to evade the stalking carnivore by suddenly rising into the air2 food and water can be followed rapidly and to great distances2 the eggs or the young can be placed in safe situations2 and birds in their migrations have made a brilliant conquest both of time and space4 ,many of them know no winter in their year1 and the migratory flight of the ,pacific ,golden ,plover from ,hawaii to ,alaska and back again does not stand alone4 ,,the ,,procession ,,of ,,life ,,through ,,the ,,ages #a ,the ,rock ,record ,how do we know when the various classes of animals and plants were established on the earth8 ,how do we know the order of their appearance and the succession of their advances8 ,the answer is3 by reading the ,rock ,record4 ,in the course of time the crust of the earth has been elevated into continents and depressed into ocean-troughs1 and the surface of the land has been buckled up into mountain ranges and folded in gentler hills and valleys4 ,the high places of the land have been weathered by air and water in many forms1 and the results of the weathering have been borne away by rivers and seas1 to be laid down again elsewhere as deposits which eventually formed sandstones1 mudstones1 and similar sedimentary rocks4 ,much of the material of the original crust has thus been broken down and worked up again many times over1 and if the total thickness of the sedimentary rocks is added up it amounts1 according to some geologists1 to a total of #fg miles4 ,in most cases1 however1 only a small part of this thickness is to be seen in one place1 for the deposits were usually formed in limited areas at any one time4 ,the ,use of ,fossils ,when the sediments were accumulating age after age1 it naturally came about that remains of the plants and animals living at the time were buried1 and these formed the fossils by the aid of which it is possible to read the story of the past4 ,by careful piecing together of evidence the geologist is able to determine the order in which the different sedimentary rocks were laid down1 and thus to say1 for instance1 that the ,devonian period was the time of the origin of ,amphibians4 ,in other cases the geologist utilises the fossils in his attempt to work out the order of the strata when these have been much disarranged4 ,for the simpler fossil forms of any type must be older than those that are more complex4 ,there is no vicious circle here1 for the general succession of strata is clear1 and it is quite certain that there were fishes before there were amphibians1 and amphibians before there were reptiles1 and reptiles before there were birds and mammals4 ,in certain cases1 e4g4 of fossil horses and elephants1 the actual historical succession has been clearly worked out4 ,if the successive strata contained good samples of all the plants and animals living at the time when the beds were formed1 then it would be easy to read the record of the rocks1 but many animals were too soft to become satisfactory fossils1 many were eaten or dissolved away1 many were destroyed by heat and pressure1 so that the rock record is like a library very much damaged by fire and looting and decay4 #b ,the ,geological ,time-table ,the long history of the earth and its inhabitants is conveniently divided into eras4 ,thus1 just as we speak of the ancient1 medival1 and modern history of mankind1 so we may speak of ,palozoic1 ,mesozoic and ,cenozoic eras in the history of the earth as a whole4 ,geologists cannot tell us except in an approximate way how long the process of evolution has taken4 ,one of the methods is to estimate how long has been required for the accumulation of the salts of the sea1 for all these have been dissolved out of the rocks since rain began to fall on the earth4 ,dividing the total amount of saline matter by what is contributed every year in modern times1 we get about a hundred million years as the age of the sea4 ,but as the present rate of salt-accumulation is probably much greater than it was during many of the geological periods1 the prodigious age just mentioned is in all likelihood far below the mark4 ,another method is to calculate how long it would take to form the sedimentary rocks1 like sandstones and mudstones1 which have a total thickness of over fifty miles1 though the local thickness is rarely over a mile4 ,as most of the materials have come from the weathering of the earth's crust1 and as the annual amount of weathering now going on can be estimated1 the time required for the formation of the sedimentary rocks of the world can be approximately calculated4 ,there are some other ways of trying to tell the earth's age and the length of the successive periods1 but no certainty has been reached4 ,the eras marked on the table 7page #ib7 as before the ,cambrian correspond to about thirty-two miles of thickness of strata2 and all the subsequent eras with fossil-bearing rocks to a thickness of about twenty-one miles--in itself an astounding fact4 ,perhaps thirty million years must be allotted to the ,pre-,cambrian eras1 eighteen to the ,palozoic1 nine to the ,mesozoic1 three to the ,cenozoic1 making a grand total of sixty millions4 ,the ,establishment of ,invertebrate ,stocks ,it is an astounding fact that at least half of geological time 7the ,archozoic and ,proterozoic eras7 passed before there were living creatures with parts sufficiently hard to form fossils4 ,in the latter part of the ,proterozoic era there are traces of one-celled marine animals 7,radiolarians7 with shells of flint1 and of worms that wallowed in the primal mud4 ,it is plain that as regards the most primitive creatures the rock record tells us little4 ,illustration3 ,from ,knipe's ,nebula to ,man4 ,,animals ,,of ,,the ,,cambrian ,,period e4g4 ,sponges1 ,jellyfish1 ,starfish1 ,sea-lilies1 ,water-fleas1 and ,trilobites ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,a ,,trilobite ,trilobites were ancient seashore animals1 abundant from the ,upper ,cambrian to the ,carboniferous eras4 ,they have no direct descendants to-day4 ,they were jointed-footed animals1 allied to ,crustaceans and perhaps also to ,king-crabs4 ,they were able to roll themselves up in their ring-armour4 ,illustration3 ,photo3 ,british ,museum 7,natural ,history74 ,,the ,,gambian ,,mud-,,fish1 ,,protopterus ,it can breathe oxygen dissolved in water by its gills2 it can also breathe dry air by means of its swim-bladder1 which has become a lung4 ,it is a double-breather1 showing evolution in process4 ,for seven months of the year1 the dry season1 it can remain inert in the mud1 getting air through an open pipe to the surface4 ,when water fills the pools it can use its gills again4 ,mud-nests or mud encasements with the lung-fish inside have often been brought to ,britain and the fish when liberated were quite lively4 ,illustration3 ,,the ,,arch,,opteryx 7,after ,william ,leche of ,stockholm47 ,a good restoration of the oldest known bird1 ,archopteryx 7,jurassic ,era74 ,it was about the size of a crow2 it had teeth on both jaws2 it had claws on the thumb and two fingers2 and it had a long lizard-like tail4 ,but it had feathers1 proving itself a true bird4 ,illustration3 ,,wing ,,of ,a ,,bird1 ,,showing ,,the ,,arrangement ,,of ,,the ,,feathers ,the longest feathers or primaries 7,,pr7 are borne by the two fingers 7#b and #c71 and their palm-bones 7,,cmc72 the second longest or secondaries are borne by the ulna bone 7,u7 of the fore-arm2 there is a separate tuft 7,,as7 on the thumb 7,,th74 ,the rarity of direct traces of life in the oldest rocks is partly due to the fact that the primitive animals would be of delicate build1 but it must also be remembered that the ancient rocks have been profoundly and repeatedly changed by pressure and heat1 so that the traces which did exist would be very liable to obliteration4 ,and if it be asked what right we have to suppose the presence of living creatures in the absence or extreme rarity of fossils1 we must point to great accumulations of limestone which indicate the existence of calcareous alg1 and to deposits of iron which probably indicate the activity of iron-forming ,bacteria4 ,ancient beds of graphite similarly suggest that green plants flourished in these ancient days4 #c ,the ,era of ,ancient ,life 7,palozoic7 ,the ,cambrian period was the time of the establishment of the chief stocks of backboneless animals such as sponges1 jellyfishes1 worms1 sea-cucumbers1 lamp-shells1 trilobites1 crustaceans1 and molluscs4 ,there is something very eloquent in the broad fact that the peopling of the seas had definitely begun some thirty million years ago1 for ,professor ,h4 ,f4 ,osborn points out that in the ,cambrian period there was already a colonisation of the shore of the sea1 the open sea1 and the deep waters4 ,the ,ordovician period was marked by abundant representation of the once very successful class of ,trilobites--jointed-footed1 antenna-bearing1 segmented marine animals1 with numerous appendages and a covering of chitin4 ,they died away entirely with the end of the ,palozoic era4 ,also very notable was the abundance of predatory cuttlefishes1 the bullies of the ancient seas4 ,but it was in this period that the first backboned animals made their appearance--an epoch-making step in evolution4 ,in other words1 true fishes were evolved--destined in the course of ages to replace the cuttlefishes 7which are mere molluscs7 in dominating the seas4 ,,recent ,,times ,human civilisation4 ,,pleistocene ,,or ,,glacial ,,time ,last great ,ice ,age4 ,,cenozoic ,,era ,,miocene ,,and ,,pliocene ,,times ,emergence of ,man4 ,,eocene ,,and ,,oligocene ,,times ,rise of higher mammals4 ,,cretaceous ,,period ,rise of primitive mammals1 flowering plants1 and higher insects4 ,,mesozoic ,,era ,,jurassic ,,period ,rise of birds and flying reptiles4 ,,triassic ,,period ,rise of dinosaur reptiles4 ,,permian ,,period ,rise of reptiles4 ,,carboniferous ,,period ,rise of insects4 ,,devonian ,,period ,first amphibians4 ,,pal,,ozoic ,,era ,,silurian ,,period ,land animals began4 ,,ordovician ,,period ,first fishes4 ,,cambrian ,,period ,peopling of the sea4 ,,proterozoic ,,ages ,many of the ,backboneless stocks began4 ,,arch,,ozoic ,,ages ,living creatures began to be upon the earth4 ,making of continents and ocean-basins4 ,beginnings of atmosphere and hydrosphere4 ,,formative ,,times ,cooling of the earth4 ,establishment of the solar system4 ,in the ,silurian period in which the peopling of the seas went on apace1 there was the first known attempt at colonising the dry land4 ,for in ,silurian rocks there are fossil scorpions1 and that implies ability to breathe dry air--by means of internal surfaces1 in this case known as lungbooks4 ,it was also towards the end of the ,silurian1 when a period of great aridity set in1 that fishes appeared related to our mud-fishes or double-breathers 7,dipnoi71 which have lungs as well as gills4 ,this1 again1 meant utilising dry air1 just as the present-day mud-fishes do when the water disappears from the pools in hot weather4 ,the lung-fishes or mud-fishes of to-day are but three in number1 one in ,queensland1 one in ,south ,america1 and one in ,africa1 but they are extremely interesting living fossils1 binding the class of fishes to that of amphibians4 ,it is highly probable that the first invasion of the dry land should be put to the credit of some adventurous worms1 but the second great invasion was certainly due to air-breathing ,arthropods1 like the pioneer scorpion we mentioned4 ,illustration3 ,,pictorial ,,representation ,,of ,,the ,,successive ,,strata ,,of ,,the ,,earth',s ,,crust1 ,,with ,,suggestions ,,of ,,characteristic ,,fossils ,e4g4 ,fish and ,trilobite in the ,devonian 7red71 a large ,amphibian in the ,carboniferous 7blue71 ,reptiles in ,permian 7light red71 the first ,mammal in the ,triassic 7blue71 the first ,bird in the ,jurassic 7yellow71 ,giant ,reptiles in the ,cretaceous 7white71 then follow the ,tertiary strata with progressive mammals1 and ,quaternary at the top with man and mammoth4 ,the ,devonian period1 including that of the ,old ,red ,sandstone1 was one of the most significant periods in the earth's history4 ,for it was the time of the establishment of flowering plants upon the earth and of terrestrial backboned animals4 ,one would like to have been the discoverer of the ,devonian foot-print of ,thinopus1 the first known ,amphibian foot-print--an eloquent vestige of the third great invasion of the dry land4 ,it was probably from a stock of ,devonian lung-fishes that the first ,amphibians sprang1 but it was not till the next period that they came to their own4 ,while they were still feeling their way1 there was a remarkable exuberance of shark-like and heavily armoured fishes in the ,devonian seas4 ,,evolution ,,of ,,land ,,animals #a ,giant ,amphibians and ,coal-measures ,the ,carboniferous period was marked by a mild moist climate and a luxuriant vegetation in the swampy low grounds4 ,it was a much less strenuous time than the ,devonian period2 it was like a very long summer4 ,there were no trees of the type we see now1 but there were forests of club-mosses and horsetails which grew to a gigantic size compared with their pigmy representatives of to-day4 ,in these forests the jointed-footed invaders of the dry land ran riot in the form of centipedes1 spiders1 scorpions1 and insects1 and on these the primeval ,amphibians fed4 ,the appearance of insects made possible a new linkage of far-reaching importance1 namely1 the cross-fertilisation of flowering plants by their insect visitors1 and from this time onwards it may be said that flowers and their visitors have evolved hand in hand4 ,cross-fertilisation is much surer by insects than by the wind1 and cross-fertilisation is more advantageous than self-fertilisation because it promotes both fertility and plasticity4 ,it was probably in this period that coloured flowers--attractive to insect-visitors--began to justify themselves as beauty became useful1 and began to relieve the monotonous green of the horsetail and club-moss forests1 which covered great tracts of the earth for millions of years4 ,in the ,carboniferous forests there were also land-snails1 representing one of the minor invasions of the dry land1 tending on the whole to check vegetation4 ,they1 too1 were probably preyed upon by the ,amphibians1 some of which attained a large size4 ,each age has had its giants1 and those of the ,carboniferous were ,amphibians called ,labyrinthodonts1 some of which were almost as big as donkeys4 ,it need hardly be said that it was in this period that most of the ,coal-measures were laid down by the immense accumulation of the spores and debris of the club-moss forests4 ,ages afterwards1 it was given to man to tap this great source of energy--traceable back to the sunshine of millions of years ago4 ,even then it was true that no plant or animal lives or dies to itself6 ,the ,acquisitions of ,amphibians4 ,as ,amphibians had their ,golden ,age in the ,carboniferous period we may fitly use this opportunity of indicating the advances in evolution which the emergence of ,amphibians implied4 7#a7 ,in the first place the passage from water to dry land was the beginning of a higher and more promiseful life1 taxed no doubt by increased difficulties4 ,the natural question rises why animals should have migrated from water to dry land at all when great difficulties were involved in the transition4 ,the answers must be3 7a7 that local drying up of water-basins or elevations of the land surface often made the old haunts untenable2 7b7 that there may have been great congestion and competition in the old quarters2 and 7c7 that there has been an undeniable endeavour after well-being throughout the history of animal life4 ,in the same way with mankind1 migrations were prompted by the setting in of prolonged drought1 by over-population1 and by the spirit of adventure4 7#b7 ,in ,amphibians for the first time the non-digitate paired fins of fishes were replaced by limbs with fingers and toes4 ,this implied an advantageous power of grasping1 of holding firm1 of putting food into the mouth1 of feeling things in three dimensions4 7#c7 ,we cannot be positive in regard to the soft parts of the ancient ,amphibians known only as fossils1 but if they were in a general way like the frogs and toads1 newts and salamanders of the present day1 we may say that they made among other acquisitions the following3 true ventral lungs1 a three-chambered heart1 a movable tongue1 a drum to the ear1 and lids to the eyes4 ,it is very interesting to find that though the tongue of the tadpole has some muscle-fibres in it1 they are not strong enough to effect movement1 recalling the tongue of fishes1 which has not any muscles at all4 ,gradually1 as the tadpole becomes a frog1 the muscle-fibres grow in strength1 and make it possible for the full-grown creature to shoot out its tongue upon insects4 ,this is probably a recapitulation of what was accomplished in the course of millennia in the history of the ,amphibian race4 7#d7 ,another acquisition made by ,amphibians was a voice1 due1 as in ourselves1 to the rapid passage of air over taut membranes 7vocal cords7 stretched in the larynx4 ,it is an interesting fact that for millions of years there was upon the earth no sound of life at all1 only the noise of wind and wave1 thunder and avalanche4 ,apart from the instrumental music of some insects1 perhaps beginning in the ,carboniferous1 the first vital sounds were due to ,amphibians1 and theirs certainly was the first voice--surely one of the great steps in organic evolution4 ,illustration3 ,photo3 ,british ,museum 7,natural ,history74 ,,fossil ,,of ,a ,,pterodactyl ,,or ,,extinct ,,flying ,,dragon ,the wing is made of a web of skin extended on the enormously elongated outermost finger4 ,the long tail served for balancing and steering4 ,the ,pterodactyls varied from the size of sparrows to a wing-span of fifteen feet--the largest flying creatures4 ,illustration3 ,from ,knipe's ,nebula to ,man4 ,,pariasaurus3 ,,an ,,extinct ,,vegetarian ,,triassic ,,reptile ,total length about #i feet4 7,remains found in ,cape ,colony1 ,south ,africa47 ,illustration3 ,from ,knipe's ,nebula to ,man4 ,,triceratops3 ,a ,,huge ,,extinct ,,reptile 7,from remains found in ,cretaceous strata of ,wyoming1 ,u4,s4,a47 ,this ,dinosaur1 about the size of a large rhinoceros1 had a huge three-horned skull with a remarkable bony collar over the neck4 ,but1 as in many other cases1 its brain was so small that it could have passed down the spinal canal in which the spinal cord lies4 ,perhaps this partly accounts for the extinction of giant reptiles4 ,illustration3 ,photo3 ,daily ,mail4 ,,the ,,duckmole ,,or ,,duck-,,billed ,,platypus ,,of ,,australia ,the ,duckmole or ,duck-billed ,platypus of ,australia is a survivor of the most primitive mammals4 ,it harks back to reptiles1 e4g4 in being an egg-layer1 in having comparatively large eggs1 and in being imperfectly warm-blooded4 ,it swims well and feeds on small water-animals4 ,it can also burrow4 ,evolution of the ,voice ,the first use of the voice was probably that indicated by our frogs and toads--it serves as a sex-call4 ,that is the meaning of the trumpeting with which frogs herald the spring1 and it is often only in the males that the voice is well developed4 ,but if we look forward1 past ,amphibians altogether1 we find the voice becoming a maternal call helping to secure the safety of the young--a use very obvious when young birds squat motionless at the sound of the parent's danger-note4 ,later on1 probably1 the voice became an infantile call1 as when the unhatched crocodile pipes from within the deeply buried egg1 signalling to the mother that it is time to be unearthed4 ,higher still the voice expresses emotion1 as in the song of birds1 often outside the limits of the breeding time4 ,later still1 particular sounds become words1 signifying particular things or feelings1 such as food1 danger1 home1 anger1 and joy4 ,finally words become a medium of social intercourse and as symbols help to make it possible for man to reason4 #b ,the ,early ,reptiles ,in the ,permian period reptiles appeared1 or perhaps one should say1 began to assert themselves4 ,that is to say1 there was an emergence of backboned animals which were free from water and relinquished the method of breathing by gills1 which ,amphibians retained in their young stages at least4 ,the unhatched or unborn reptile breathes by means of a vascular hood spread underneath the egg-shell and absorbing dry air from without4 ,it is an interesting point that this vascular hood1 called the allantois1 is represented in the ,amphibians by an unimportant bladder growing out from the hind end of the food-canal4 ,a great step in evolution was implied in the origin of this ante-natal hood or foetal membrane and another one--of protective significance--called the amnion1 which forms a water-bag over the delicate embryo4 ,the step meant total emancipation from the water and from gill-breathing1 and the two foetal membranes1 the amnion and the allantois1 persist not only in all reptiles but in birds and mammals as well4 ,these higher ,vertebrates are therefore called ,amniota in contrast to the ,lower ,vertebrates or ,anamnia 7the ,amphibians1 ,fishes1 and primitive types74 ,it is a suggestive fact that the embryos of all reptiles1 birds1 and mammals show gill-clefts--a tell-tale evidence of their distant aquatic ancestry4 ,but these embryonic gill-clefts are not used for respiration and show no trace of gills except in a few embryonic reptiles and birds where their dwindled vestiges have been recently discovered4 ,as to the gill-clefts1 they are of no use in higher ,vertebrates except that the first becomes the ,eustachian tube leading from the ear-passage to the back of the mouth4 ,the reason why they persist when only one is of any use1 and that in a transformed guise1 would be difficult to interpret except in terms of the ,evolution theory4 ,they illustrate the lingering influence of a long pedigree1 the living hand of the past1 the tendency that individual development has to recapitulate racial evolution4 ,in a condensed and telescoped manner1 of course1 for what took the race a million years may be recapitulated by the individual in a week6 ,in the ,permian period the warm moist climate of most of the ,carboniferous period was replaced by severe conditions1 culminating in an ,ice ,age which spread from the ,southern ,hemisphere throughout the world4 ,with this was associated a waning of the ,carboniferous flora1 and the appearance of a new one1 consisting of ferns1 conifers1 ginkgos1 and cycads1 which persisted until near the end of the ,mesozoic era4 ,the ,permian ,ice ,age lasted for millions of years1 and was most severe in the ,far ,south4 ,of course1 it was a very different world then1 for ,north ,europe was joined to ,north ,america1 ,africa to ,south ,america1 and ,australia to ,asia4 ,it was probably during the ,permian ,ice ,age that many of the insects divided their life-history into two main chapters--the feeding1 growing1 moulting1 immature1 larval stages1 e4g4 caterpillars1 and the more ascetic1 non-growing1 non-moulting1 winged phase1 adapted for reproduction4 ,between these there intervened the quiescent1 well-protected pupa stage or chrysalis1 probably adapted to begin with as a means of surviving the severe winter4 ,for it is easier for an animal to survive when the vital processes are more or less in abeyance4 ,disappearance of many ,ancient ,types ,we cannot leave the last period of the ,palozoic era and its prolonged ice age without noticing that it meant the entire cessation of a large number of ancient types1 especially among plants and backboneless animals1 which now disappear for ever4 ,it is necessary to understand that the animals of ancient days stand in three different relations to those of to-day4 7a7 ,there are ancient types that have living representatives1 sometimes few and sometimes many1 sometimes much changed and sometimes but slightly changed4 ,the lamp-shell1 ,lingulella1 of the ,cambrian and ,ordovician period has a very near relative in the ,lingula of to-day4 ,there are a few extremely conservative animals4 7b7 ,there are ancient types which have no living representatives1 except in the guise of transformed descendants1 as the ,king-crab 7,limulus7 may be said to be a transformed descendant of the otherwise quite extinct race to which ,eurypterids or ,sea-scorpions belonged4 7c7 ,there are altogether extinct types--lost races--which have left not a wrack behind4 ,for there is not any representation to-day of such races as ,graptolites and ,trilobites4 ,looking backwards over the many millions of years comprised in the ,palozoic era1 what may we emphasise as the most salient features8 ,there was in the ,cambrian the establishment of the chief classes of backboneless animals2 in the ,ordovician the first fishes and perhaps the first terrestrial plants2 in the ,silurian the emergence of air-breathing ,invertebrates and mud-fishes2 in the ,devonian the appearance of the first ,amphibians1 from which all higher land animals are descended1 and the establishment of a land flora2 in the ,carboniferous the great ,club-moss forests and an exuberance of air-breathing insects and their allies2 in the ,permian the first reptiles and a new flora4 ,,the ,,geological ,,middle ,,ages #a ,the ,mesozoic ,era ,in a broad way the ,mesozoic era corresponds with the ,golden ,age of reptiles1 and with the climax of the ,conifer and ,cycad flora1 which was established in the ,permian4 ,but among the ,conifers and ,cycads our modern flowering plants were beginning to show face tentatively1 just like birds and mammals among the great reptiles4 ,in the ,triassic period the exuberance of reptilian life which marked the ,permian was continued4 ,besides ,turtles which still persist1 there were ,ichthyosaurs1 ,plesiosaurs1 ,dinosaurs1 and ,pterosaurs1 none of which lasted beyond the ,mesozoic era4 ,of great importance was the rise of the ,dinosaurs in the ,triassic1 for it is highly probable that within the limits of this vigorous and plastic stock--some of them bipeds--we must look for the ancestors of both birds and mammals4 ,both land and water were dominated by reptiles1 some of which attained to gigantic size4 ,had there been any zoologist in those days1 he would have been very sagacious indeed if he had suspected that reptiles did not represent the climax of creation4 ,the ,flying ,dragons ,the ,jurassic period showed a continuance of the reptilian splendour4 ,they radiated in many directions1 becoming adapted to many haunts4 ,thus there were many ,fish ,lizards paddling in the seas1 many types of terrestrial dragons stalking about on land1 many swiftly gliding alligator-like forms1 and the ,flying ,dragons which began in the ,triassic attained to remarkable success and variety4 ,their wing was formed by the extension of a great fold of skin on the enormously elongated outermost finger1 and they varied from the size of a sparrow to a spread of over five feet4 ,a soldering of the dorsal vertebr as in our ,flying ,birds was an adaptation to striking the air with some force1 but as there is not more than a slight keel1 if any1 on the breast-bone1 it is unlikely that they could fly far4 ,for we know from our modern birds that the power of flight may be to some extent gauged from the degree of development of the keel1 which is simply a great ridge for the better insertion of the muscles of flight4 ,it is absent1 of course1 in the ,running ,birds1 like the ostrich1 and it has degenerated in an interesting way in the burrowing parrot 7,stringops7 and a few other birds that have gone back4 ,the ,first ,known ,bird ,but the ,jurassic is particularly memorable because its strata have yielded two fine specimens of the first known bird1 ,archopteryx4 ,these were entombed in the deposits which formed the fine-grained lithographic stones of ,bavaria1 and practically every bone in the body is preserved except the breast-bone4 ,even the feathers have left their marks with distinctness4 ,this oldest known bird--too far advanced to be the first bird--was about the size of a crow and was probably of arboreal habits4 ,of great interest are its reptilian features1 so pronounced that one cannot evade the evolutionist suggestion4 ,it had teeth in both jaws1 which no modern bird has2 it had a long lizard-like tail1 which no modern bird has2 it had claws on three fingers1 and a sort of half-made wing4 ,that is to say1 it does not show1 what all modern birds show1 a fusion of half the wrist-bones with the whole of the palm-bones1 the well-known carpo-metacarpus bone which forms a basis for the longest pinions4 ,in many reptiles1 such as ,crocodiles1 there are peculiar bones running across the abdomen beneath the skin1 the so-called abdominal ribs1 and it seems an eloquent detail to find these represented in ,archopteryx1 the earliest known bird4 ,no modern bird shows any trace of them4 ,illustration3 ,,skeleton ,,of ,,an ,,extinct ,,flightless ,,toothed ,,bird1 ,,hesperornis 7,after ,marsh47 ,the bird was five or six feet high1 something like a swimming ostrich1 with a very powerful leg but only a vestige of a wing4 ,there were sharp teeth in a groove4 ,the modern divers come nearest to this ancient type4 ,illustration3 ,,six ,,stages ,,in ,,the ,,evolution ,,of ,,the ,,horse1 ,,showing ,,gradual ,,increase ,,in ,,size 7,after ,lull and ,matthew47 #a4 ,four-toed horse1 ,eohippus1 about one foot high4 ,lower ,eocene1 ,n4 ,america4 #b4 ,another four-toed horse1 ,orohippus1 a little over a foot high4 ,middle ,eocene1 ,n4 ,america4 #c4 ,three-toed horse1 ,mesohippus1 about the size of a sheep4 ,middle ,oligocene1 ,n4 ,america4 #d4 ,three-toed horse1 ,merychippus1 ,miocene1 ,n4 ,america4 ,only one toe reaches the ground on each foot1 but the remains of two others are prominent4 #e4 ,the first one-toed horse1 ,pliohippus1 about forty inches high at the shoulder4 ,pliocene1 ,n4 ,america4 #f4 ,the modern horse1 running on the third digit of each foot4 ,there is no warrant for supposing that the flying reptiles or ,pterodactyls gave rise to birds1 for the two groups are on different lines1 and the structure of the wings is entirely different4 ,thus the long-fingered ,pterodactyl wing was a parachute wing1 while the secret of the bird's wing has its centre in the feathers4 ,it is highly probable that birds evolved from certain ,dinosaurs which had become bipeds1 and it is possible that they were for a time swift runners that took flying jumps along the ground4 ,thereafter1 perhaps1 came a period of arboreal apprenticeship during which there was much gliding from tree to tree before true flight was achieved4 ,it is an interesting fact that the problem of flight has been solved four times among animals--by insects1 by ,pterodactyls1 by birds1 and by bats2 and that the four solutions are on entirely different lines4 ,in the ,cretaceous period the outstanding events included the waning of giant reptiles1 the modernising of the flowering plants1 and the multiplication of small mammals4 ,some of the ,permian reptiles1 such as the dog-toothed ,cynodonts1 were extraordinarily mammal-like1 and it was probably from among them that definite mammals emerged in the ,triassic4 ,comparatively little is known of the early ,triassic mammals save that their back-teeth were marked by numerous tubercles on the crown1 but they were gaining strength in the late ,triassic when small arboreal insectivores1 not very distant from the modern tree-shrews 7,tupaia71 began to branch out in many directions indicative of the great divisions of modern mammals1 such as the clawed mammals1 hoofed mammals1 and the race of monkeys or ,primates4 ,in the ,upper ,cretaceous there was an exuberant radiation of mammals1 adaptive to the conquest of all sorts of haunts1 and this was vigorously continued in ,tertiary times4 ,there is no difficulty in the fact that the earliest remains of definite mammals in the ,triassic precede the first-known bird in the ,jurassic4 ,for although we usually rank mammals as higher than birds 7being mammals ourselves1 how could we do otherwise871 there are many ways in which birds are pre-eminent1 e4g4 in skeleton1 musculature1 integumentary structures1 and respiratory system4 ,the fact is that birds and mammals are on two quite different tacks of evolution1 not related to one another1 save in having a common ancestry in extinct reptiles4 ,moreover1 there is no reason to believe that the ,jurassic ,archopteryx was the first bird in any sense except that it is the first of which we have any record4 ,in any case it is safe to say that birds came to their own before mammals did4 ,looking backwards1 we may perhaps sum up what is most essential in the ,mesozoic era in ,professor ,schuchert's sentence3 ,the ,mesozoic is the ,age of ,reptiles1 and yet the little mammals and the toothed birds are storing up intelligence and strength to replace the reptiles when the cycads and conifers shall give way to the higher flowering plants4 #b ,the ,cenozoic or ,tertiary ,era ,in the ,eocene period there was a replacement of the small-brained archaic mammals by big-brained modernised types1 and with this must be associated the covering of the earth with a garment of grass and dry pasture4 ,marshes were replaced by meadows and browsing by grazing mammals4 ,in the spreading meadows an opportunity was also offered for a richer evolution of insects and birds4 ,during the ,oligocene the elevation of the land continued1 the climate became much less moist1 and the grazing herds extended their range4 ,the ,miocene was the mammalian ,golden ,age and there were crowning examples of what ,osborn calls adaptive radiation4 ,that is to say1 mammals1 like the reptiles before them1 conquer every haunt of life4 ,there are flying bats1 volplaning parachutists1 climbers in trees like sloths and squirrels1 quickly moving hoofed mammals1 burrowers like the moles1 freshwater mammals1 like duckmole and beaver1 shore-frequenting seals and manatees1 and open-sea cetaceans1 some of which dive far more than full fathoms five4 ,it is important to realise the perennial tendency of animals to conquer every corner and to fill every niche of opportunity1 and to notice that this has been done by successive sets of animals in succeeding ages4 ,most notably the mammals repeat all the experiments of reptiles on a higher turn of the spiral4 ,thus arises what is called convergence1 the superficial resemblance of unrelated types1 like whales and fishes1 the resemblance being due to the fact that the different types are similarly adapted to similar conditions of life4 ,professor ,h4 ,f4 ,osborn points out that mammals may seek any one of the twelve different habitat-zones1 and that in each of these there may be six quite different kinds of food4 ,living creatures penetrate everywhere like the overflowing waters of a great river in flood4 #c ,the ,pliocene period was a more strenuous time1 with less genial climatic conditions1 and with more intense competition4 ,old land bridges were broken and new ones made1 and the geographical distribution underwent great changes4 ,professor ,r4 ,s4 ,lull describes the ,pliocene as a period of great unrest4 ,many migrations occurred the world over1 new competitions arose1 and the weaker stocks began to show the effects of the strenuous life4 ,one momentous event seems to have occurred in the ,pliocene1 and that was the transformation of the precursor of humanity into man--the culmination of the highest line of evolution4 ,the ,pleistocene period was a time of sifting4 ,there was a continued elevation of the continental masses1 and ,ice ,ages set in1 relieved by less severe interglacial times when the ice-sheets retreated northwards for a time4 ,many types1 like the mammoth1 the woolly rhinoceros1 the sabre-toothed tiger1 the cave-lion1 and the cave-bear1 became extinct4 ,others which formerly had a wide range became restricted to the ,far ,north or were left isolated here and there on the high mountains1 like the ,snow ,mouse1 which now occurs on isolated ,alpine heights above the snow-line4 ,perhaps it was during this period that many birds of the ,northern ,hemisphere learned to evade the winter by the sublime device of migration4 ,looking backwards we may quote ,professor ,schuchert again3 ,the lands in the ,cenozoic began to bloom with more and more flowering plants and grand hardwood forests1 the atmosphere is scented with sweet odours1 a vast crowd of new kinds of insects appear1 and the places of the once dominant reptiles of the lands and seas are taken by the mammals4 ,out of these struggles there rises a greater intelligence1 seen in nearly all of the mammal stocks1 but particularly in one1 the monkey-ape-man4 ,brute man appears on the scene with the introduction of the last glacial climate1 a most trying time for all things endowed with life1 and finally there results the dominance of reasoning man over all his brute associates4 ,in man and human society the story of evolution has its climax4 ,the ,ascent of ,man ,man stands apart from animals in his power of building up general ideas and of using these in the guidance of his behaviour and the control of his conduct4 ,this is essentially wrapped up with his development of language as an instrument of thought4 ,some animals have words1 but man has language 7,logos74 ,some animals show evidence of perceptual inference1 but man often gets beyond this to conceptual inference 7,reason74 ,many animals are affectionate and brave1 self-forgetful and industrious1 but man thinks the ought1 definitely guiding his conduct in the light of ideals1 which in turn are wrapped up with the fact that he is a social person4 ,besides his big brain1 which may be three times as heavy as that of a gorilla1 man has various physical peculiarities4 ,he walks erect1 he plants the sole of his foot flat on the ground1 he has a chin and a good heel1 a big forehead and a non-protrusive face1 a relatively uniform set of teeth without conspicuous canines1 and a relatively naked body4 ,illustration3 ,,diagram ,,showing ,,seven ,,stages ,,in ,,the ,,evolution ,,of ,,the ,,fore-,,limbs ,,and ,,hind-,,limbs ,,of ,,the ,,ancestors ,,of ,,the ,,modern ,,horse1 ,,beginning ,,with ,,the ,,earliest ,,known ,,predecessors ,,of ,,the ,,horse ,,and ,,culminating ,,with ,,the ,,horse ,,of ,,to-,,day 7,after ,marsh and ,lull47 #a and #a;,a1 fore-limb and hind-limb of ,eohippus2 #b and #b;,a1 ,orohippus2 #c and #c;,a1 ,mesohippus2 #d and #d;,a1 ,hypohippus2 #e and #e;,a1 ,merychippus2 #f and #f;,a1 ,hipparion2 #g and #g;,a1 the modern horse4 ,note how the toes shorten and disappear4 ,illustration3 ,a4 ,fore-limb of ,monkey ,b4 ,fore-limb of ,whale ,,what ,,is ,,meant ,,by ,,homology8 ,,essential ,,similarity ,,of ,,architecture1 ,,though ,,the ,,appearances ,,may ,,be ,,very ,,different ,this is seen in comparing these two fore-limbs1 ,a1 of ,monkey1 ,b1 of ,whale4 ,they are as different as possible1 yet they show the same bones1 e4g4 ,,sc1 the scapula or shoulder-blade2 ,h1 the humerus or upper arm2 ,r and ,u1 the radius and ulna of the fore-arm2 ,,ca1 the wrist2 ,,mc1 the palm2 and then the fingers4 ,but in spite of man's undeniable apartness1 there is no doubt as to his solidarity with the rest of creation4 ,there is an all-pervading similitude of structure1 between man and the ,anthropoid ,apes1 though it is certain that it is not from any living form that he took his origin4 ,none of the anatomical distinctions1 except the heavy brain1 could be called momentous4 ,man's body is a veritable museum of relics 7vestigial structures7 inherited from pre-human ancestors4 ,in his everyday bodily life and in some of its disturbances1 man's pedigree is often revealed4 ,even his facial expression1 as ,darwin showed1 is not always human4 ,some fossil remains bring modern man nearer the anthropoid type4 ,it is difficult not to admit the ring of truth in the closing words of ,darwin's ,descent of ,man3 ,we must1 however1 acknowledge1 as it seems to me1 that man1 with all his noble qualities1 with sympathy which feels for the most debased1 with benevolence which extends not only to other men but to the humblest living creature1 with his ,god-like intellect which has penetrated into the movements and constitution of the solar system--with all these exalted powers--man still bears in his bodily frame the indelible stamp of his lowly origin4 ,,the ,,evolving ,,system ,,of ,,nature ,there is another side of evolution so obvious that it is often overlooked1 the tendency to link lives together in vital inter-relations4 ,thus flowers and their insect visitors are often vitally interlinked in mutual dependence4 ,many birds feed on berries and distribute the seeds4 ,the tiny freshwater snail is the host of the juvenile stages of the liver-fluke of the sheep4 ,the mosquito is the vehicle of malaria from man to man1 and the tse-tse fly spreads sleeping sickness4 ,the freshwater mussel cannot continue its race without the unconscious co-operation of the minnow1 and the freshwater fish called the bitterling cannot continue its race without the unconscious co-operation of the mussel4 ,there are numerous mutually beneficial partnerships between different kinds of creatures1 and other inter-relations where the benefit is one-sided1 as in the case of insects that make galls on plants4 ,there are also among kindred animals many forms of colonies1 communities1 and societies4 ,nutritive chains bind long series of animals together1 the cod feeding on the whelk1 the whelk on the worm1 the worm on the organic dust of the sea4 ,there is a system of successive incarnations and matter is continually passing from one embodiment to another4 ,these instances must suffice to illustrate the central biological idea of the web of life1 the interlinked ,system of ,animate ,nature4 ,linnus spoke of the ,systema ,natur1 meaning the orderly hierarchy of classes1 orders1 families1 genera1 and species2 but we owe to ,darwin in particular some knowledge of a more dynamic ,systema ,natur1 the network of vital inter-relations4 ,this has become more and more complex as evolution has continued1 and man's web is most complex of all4 ,it means making ,animate ,nature more of a unity2 it means an external method of registering steps of progress2 it means an evolving set of sieves by which new variations are sifted1 and living creatures are kept from slipping down the steep ladder of evolution4 ,parasitism ,it sometimes happens that the inter-relation established between one living creature and another works in a retrograde direction4 ,this is the case with many thoroughgoing internal parasites which have sunk into an easygoing kind of life1 utterly dependent on their host for food1 requiring no exertions1 running no risks1 and receiving no spur to effort4 ,thus we see that evolution is not necessarily progressive2 everything depends on the conditions in reference to which the living creatures have been evolved4 ,when the conditions are too easygoing1 the animal may be thoroughly well adapted to them--as a tapeworm certainly is--but it slips down the rungs of the ladder of evolution4 ,this is an interesting minor chapter in the story of evolution--the establishment of different kinds of parasites1 casual and constant1 temporary and lifelong1 external hangers-on and internal unpaying boarders1 those that live in the food-canal and depend on the host's food and those that inhabit the blood or the tissues and find their food there4 ,it seems clear that ichneumon grubs and the like which hatch inside a caterpillar and eat it alive are not so much parasites as beasts of prey working from within4 ,but there are two sides to this minor chapter3 there is the evolution of the parasite1 and there is also the evolution of counteractive measures on the part of the host4 ,thus there is the maintenance of a bodyguard of wandering amoeboid cells1 which tackle the microbes invading the body and often succeed in overpowering and digesting them4 ,thus1 again1 there is the protective capacity the blood has of making antagonistic substances or anti-bodies which counteract poisons1 including the poisons which the intruding parasites often make4 ,,the ,,evidences ,,of ,,evolution--,,how ,,it ,,came ,,about #a ,progress in ,evolution ,there has often been slipping back and degeneracy in the course of evolution1 but the big fact is that there has been progress4 ,for millions of years ,life has been slowly creeping upwards1 and if we compare the highest animals--,birds and ,mammals--with their predecessors1 we must admit that they are more controlled1 more masters of their fate1 with more mentality4 ,evolution is on the whole integrative2 that is to say1 it makes against instability and disorder1 and towards harmony and progress4 ,even in the rise of ,birds and ,mammals we can discern that the evolutionary process was making towards a fuller embodiment or expression of what ,man values most--control1 freedom1 understanding1 and love4 ,the advance of animal life through the ages has been chequered1 but on the whole it has been an advance towards increasing fullness1 freedom1 and fitness of life4 ,in the study of this advance--the central fact of ,organic ,evolution--there is assuredly much for ,man's instruction and much for his encouragement4 ,evidences of ,evolution ,in all this1 it may be said1 the fact of evolution has been taken for granted1 but what are the evidences8 ,perhaps it should be frankly answered that the idea of evolution1 that the present is the child of the past and the parent of the future1 cannot be proved as one may prove the ,law of ,gravitation4 ,all that can be done is to show that it is a key--a way of looking at things--that fits the facts4 ,there is no lock that it does not open4 ,but if the facts that the evolution theory vividly interprets be called the evidences of its validity1 there is no lack of them4 ,there is historical evidence2 and what is more eloquent than the general fact that fishes emerge before amphibians1 and these before reptiles1 and these before birds1 and so on8 ,there are wonderfully complete fossil series1 e4g4 among cuttlefishes1 in which we can almost see evolution in process4 ,the pedigree of horse and elephant and crocodile is in general very convincing1 though it is to be confessed that there are other cases in regard to which we have no light4 ,who can tell1 for instance1 how ,vertebrates arose or from what origin8 ,there is embryological evidence1 for the individual development often reads like an abbreviated recapitulation of the presumed evolution of the race4 ,the mammal's visceral clefts are tell-tale evidence of remote aquatic ancestors1 breathing by gills4 ,something is known in regard to the historical evolution of antlers in bygone ages2 the ,red ,deer of to-day recapitulates at least the general outlines of the history4 ,the individual development of an asymmetrical flat-fish1 like a plaice or sole1 which rests and swims on one side1 tells us plainly that its ancestors were symmetrical fishes4 ,there is what might be called physiological evidence1 for many plants and animals are variable before our eyes1 and evolution is going on around us to-day4 ,this is familiarly seen among domesticated animals and cultivated plants1 but there is abundant flux in ,wild ,nature4 ,it need hardly be said that some organisms are very conservative1 and that change need not be expected when a position of stable equilibrium has been secured4 ,there is also anatomical evidence of a most convincing quality4 ,in the fore-limbs of backboned animals1 say1 the paddle of a turtle1 the wing of a bird1 the flipper of a whale1 the fore-leg of a horse1 and the arm of a man2 the same essential bones and muscles are used to such diverse results6 ,what could it mean save blood relationship8 ,and as to the two sets of teeth in whalebone whales1 which never even cut the gum1 is there any alternative but to regard them as relics of useful teeth which ancestral forms possessed8 ,in short1 the evolution theory is justified by the way in which it works4 #b ,factors in ,evolution ,if it be said ,so much for the fact of evolution1 but what of the factors8 the answer is not easy4 ,for not only is the problem the greatest of all scientific problems1 but the inquiry is still very young4 ,the scientific study of evolution practically dates from the publication of ,the ,origin of ,species in #ahei4 ,heritable novelties or variations often crop up in living creatures1 and these form the raw material of evolution4 ,these variations are the outcome of expression of changes in the germ-cells that develop into organisms4 ,but why should there be changes in the constitution of the germ-cells8 ,perhaps because the living material is very complex and inherently liable to change2 perhaps because it is the vehicle of a multitude of hereditary items among which there are very likely to be reshufflings or rearrangements2 perhaps because the germ-cells have very changeful surroundings 7the blood1 the body-cavity fluid1 the sea-water72 perhaps because deeply saturating outside influences1 such as change of climate and habitat1 penetrate through the body to its germ-cells and provoke them to vary4 ,but we must be patient with the wearisome reiteration of perhaps4 ,moreover1 every many-celled organism reproduced in the usual way1 arises from an egg-cell fertilised by a sperm-cell1 and the changes involved in and preparatory to this fertilisation may make new permutations and combinations of the living items and hereditary qualities not only possible but necessary4 ,it is something like shuffling a pack of cards1 but the cards are living4 ,as to the changes wrought on the body during its lifetime by peculiarities in nurture1 habits1 and surroundings1 these dents or modifications are often very important for the individual1 but it does not follow that they are directly important for the race1 since it is not certain that they are transmissible4 ,given a crop of variations or new departures or mutations1 whatever the inborn novelties may be called1 we have then to inquire how these are sifted4 ,the sifting1 which means the elimination of the relatively less fit variations and the selection of the relatively more fit1 effected in many different ways in the course of the struggle for existence4 ,the organism plays its new card in the game of life1 and the consequences may determine survival4 ,the relatively less fit to given conditions will tend to be eliminated1 while the relatively more fit will tend to survive4 ,if the variations are hereditary and reappear1 perhaps increased in amount1 generation after generation1 and if the process of sifting continue consistently1 the result will be the evolution of the species4 ,the sifting process may be helped by various forms of isolation which lessen the range of free intercrossing between members of a species1 e4g4 by geographical barriers4 ,interbreeding of similar forms tends to make a stable stock2 out-breeding among dissimilars tends to promote variability4 ,but for an outline like this it is enough to suggest the general method of organic evolution3 ,throughout the ages organisms have been making tentatives--new departures of varying magnitude--and these tentatives have been tested4 ,the method is that of testing all things and holding fast that which is good4 ,,bibliography 7,the following short list may be useful to readers who desire to have further books recommended to them47 ,,clodd1 ,story of ,creation3 ,a ,plain ,account of ,evolution4 ,,darwin1 ,origin of ,species1 ,descent of ,man4 ,,deperet1 ,transformation of the ,animal ,world 7,internat4 ,sci4 ,series74 ,,geddes ,,and ,,thomson1 ,evolution 7,home ,university ,library74 ,,goodrich1 ,evolution 7,the ,people's ,books74 ,,headley1 ,life and ,evolution4 ,,hutchinson1 ,h4 ,,neville1 ,extinct ,monsters 7#ahib74 ,,lull1 ,organic ,evolution4 ,,mccabe1 ,a ,b ,c of ,evolution4 ,,metcalf1 ,outline of the ,theory of ,organic ,evolution4 ,,osborn1 ,h4 ,f41 ,the ,evolution of ,life 7#aiba74 ,,thomson1 ,darwinism and ,human ,life4 ,,wallace1 ,darwinism4 ,,iii ,,adaptations ,,to ,,environment ,,adaptations ,,to ,,environment ,we saw in a previous chapter how the process of evolution led to a mastery of all the haunts of life4 ,but it is necessary to return to these haunts or homes of animals in some detail1 so as to understand the peculiar circumstances of each1 and to see how in the course of ages of struggle all sorts of self-preserving and race-continuing adaptations or fitnesses have been wrought out and firmly established4 ,living creatures have spread over all the earth and in the waters under the earth2 some of them have conquered the underground world and others the air4 ,it is possible1 however1 as has been indicated1 to distinguish six great haunts of life1 each tenanted by a distinctive fauna1 namely1 the shore of the sea1 the open sea1 the depths of the sea1 the freshwaters1 the dry land1 and the air4 ,in the deep sea there are no plants at all2 in the air the only plants are floating bacteria1 though there is a sense in which a tree is very aerial1 and the orchid perched on its branches still more so2 in the other four haunts there is a flora as well as a fauna--the two working into one another's hands in interesting and often subtle inter-relations--the subject of a separate study4 ,i4 ,,the ,,shore ,,of ,,the ,,sea ,the ,seaweed ,area ,by the shore of the sea the zoologist means much more than the narrow zone between tide-marks2 he means the whole of the relatively shallow1 well-illumined1 seaweed-growing shelf around the continents and continental islands4 ,technically1 this is called the littoral area1 and it is divisible into zones1 each with its characteristic population4 ,it may be noted that the green seaweeds are highest up on the shore2 the brown ones come next2 the beautiful red ones are lowest4 ,all of them have got green chlorophyll1 which enables them to utilise the sun's rays in photosynthesis 7i4e4 building up carbon compounds from air1 water1 and salts71 but in the brown and red seaweeds the green pigment is masked by others4 ,it is maintained by some botanists that these other pigments enable their possessors to make more of the scantier light in the deeper waters4 ,however this may be1 we must always think of the shore-haunt as the seaweed-growing area4 ,directly and indirectly the life of the shore animals is closely wrapped up with the seaweeds1 which afford food and foothold1 and temper the force of the waves4 ,the minute fragments broken off from seaweeds and from the sea-grass 7a flowering plant called ,zostera7 form a sort of nutritive sea-dust which is swept slowly down the slope from the shore1 to form a very useful deposit in the quietness of deepish water4 ,it is often found in the stomachs of marine animals living a long way offshore4 ,conditions of ,shore ,life ,the littoral area as defined is not a large haunt of life2 it occupies only about #i million square miles1 a small fraction of the #aig1jjj1jjj of the whole earth's surface4 ,but it is a very long haunt1 some #aej1jjj miles1 winding in and out by bay and fiord1 estuary and creek4 ,where deep water comes close to cliffs there may be no shore at all2 in other places the relatively shallow water1 with seaweeds growing over the bottom1 may extend outwards for miles4 ,the nature of the shore varies greatly according to the nature of the rocks1 according to what the streams bring down from inland1 and according to the jetsam that is brought in by the tides4 ,the shore is a changeful place2 there is1 in the upper reaches1 a striking difference between tide in and tide out2 there are vicissitudes due to storms1 to freshwater floods1 to wind-blown sand1 and to slow changes of level1 up and down4 ,the shore is a very crowded haunt1 for it is comparatively narrow1 and every niche among the rocks may be precious4 ,illustration3 ,,an ,,eight-,,armed ,,cuttlefish ,,or ,,octopus ,,attacking ,a ,,small ,,crab ,these molluscs are particularly fond of crustaceans1 which they crunch with their parrot's beak-like jaws4 ,their salivary juice has a paralysing effect on their prey4 ,to one side1 below the eye1 may be seen the funnel through which water is very forcibly ejected in the process of locomotion4 ,illustration3 ,a ,,common ,,starfish1 ,,which ,,has ,,lost ,,three ,,arms ,,and ,,is ,,regrowing ,,them ,the lowest arm is being regrown double4 7,after ,professor ,w4 ,c4 ,mc,intosh47 ,illustration3 ,a ,,photograph ,,showing ,a ,,starfish 7,asterias ,forreri7 ,,which ,,has ,,captured ,a ,,large ,,fish ,the suctorial tube-feet are seen gripping the fish firmly4 7,after an observation on the ,californian coast47 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,the ,,paper ,,nautilus 7,,argonauta71 ,,an ,,animal ,,of ,,the ,,open ,,sea ,the delicate shell is made by the female only1 and is used as a shelter for the eggs and young ones4 ,it is secreted by two of the arms1 not by the mantle as other mollusc shells are4 ,it is a single-chambered shell1 very different from that of the ,pearly ,nautilus4 ,keen ,struggle for ,existence ,it follows that the shore must be the scene of a keen struggle for existence--which includes all the answers-back that living creatures make to environing difficulties and limitations4 ,there is struggle for food1 accentuated by the fact that small items tend to be swept away by the outgoing tide or to sink down the slope to deep water4 ,apart from direct competition1 e4g4 between hungry hermit-crabs1 it often involves hard work to get a meal4 ,this is true even of apparently sluggish creatures4 ,thus the ,crumb-of-,bread ,sponge1 or any other seashore sponge1 has to lash large quantities of water through the intricate canal system of its body before it can get a sufficient supply of the microscopic organisms and organic particles on which it feeds4 ,an index of the intensity of the struggle for food is afforded by the nutritive chains which bind animals together4 ,the shore is almost noisy with the conjugation of the verb to eat in its many tenses4 ,one pound of rock-cod requires for its formation ten pounds of whelk2 one pound of whelk requires ten pounds of sea-worms2 and one pound of worms requires ten pounds of sea-dust4 ,such is the circulation of matter1 ever passing from one embodiment or incarnation to another4 ,besides struggle for food there is struggle for foothold and for fresh air1 struggle against the scouring tide and against the pounding breakers4 ,the risk of dislodgment is often great and the fracture of limbs is a common accident4 ,of kinds of armour--the sea-urchin's hedgehog-like test1 the crab's shard1 the limpet's shell--there is great variety1 surpassed only by that of weapons--the sea-anemone's stinging-cells1 the sea-urchin's snapping-blades1 the hermit-crab's forceps1 the grappling tentacles and parrot's-beak jaws of the octopus4 ,shifts for a ,living ,we get another glimpse of the intensity of the seashore struggle for existence in the frequency of shifts for a living1 adaptations of structure or of behaviour which meet frequently recurrent vicissitudes4 ,the starfish is often in the dilemma of losing a limb or its life2 by a reflex action it jettisons the captured arm and escapes4 ,and what is lost is gradually regrown4 ,the crab gets its leg broken past all mending2 it casts off the leg across a weak breakage plane near the base1 and within a preformed bandage which prevents bleeding a new leg is formed in miniature4 ,such is the adaptive device--more reflex than reflective--which is called self-mutilation or autotomy4 ,in another part of this book there is a discussion of camouflaging and protective resemblance2 how abundantly these are illustrated on the shore6 ,but there are other shifts for a living4 ,some of the sand-hoppers and their relatives illustrate the puzzling phenomenon of feigning death1 becoming suddenly so motionless that they escape the eyes of their enemies4 ,cuttlefishes1 by discharging sepia from their ink-bags1 are able to throw dust in the eyes of their enemies4 ,some undisguised shore-animals1 e4g4 crabs1 are adepts in a hide-and-seek game2 some fishes1 like the butterfish or gunnel1 escape between stones where there seemed no opening and are almost uncatchable in their slipperiness4 ,subtlest of all1 perhaps1 is the habit some hermit-crabs have of entering into mutually beneficial partnership 7commensalism7 with sea-anemones1 which mask their bearers and also serve as mounted batteries1 getting transport as their reward and likewise crumbs from the frequently spread table4 ,but enough has been said to show that the shore-haunt exhibits an extraordinary variety of shifts for a living4 ,parental ,care on the ,shore ,according to ,darwin1 the struggle for existence1 as a big fact in the economy of ,animate ,nature1 includes not only competition but all the endeavours which secure the welfare of the offspring1 and give them a good send-off in life4 ,so it is without a jolt that we pass from struggle for food and foothold to parental care4 ,the marine leech called ,pontobdella1 an interesting greenish warty creature fond of fixing itself to skate1 places its egg-cocoons in the empty shell of a bivalve mollusc1 and guards them for weeks1 removing any mud that might injure their development4 ,we have seen a ,british starfish with its fully-formed young ones creeping about on its body1 though the usual mode of development for shore starfishes is that the young ones pass through a free-swimming larval period in the open water4 ,the father sea-spider carries about the eggs attached to two of his limbs2 the father sea-horse puts his mate's eggs into his breast pocket and carries them there in safety until they are hatched2 the father stickleback of the shore-pools makes a seaweed nest and guards the eggs which his wives are induced to lay there2 the father lumpsucker mounts guard over the bunch of pinkish eggs which his mate has laid in a nook of a rocky shore-pool1 and drives off intruders with zest4 ,he also aerates the developing eggs by frequent paddling with his pectoral fins and tail1 as the ,scots name ,cock-paidle probably suggests4 ,it is interesting that the salient examples of parental care in the shore-haunt are mostly on the male parent's side4 ,but there is maternal virtue as well4 ,illustration3 ,,ten-,,armed ,,cuttlefish ,,or ,,squid ,,in ,,the ,,act ,,of ,,capturing ,a ,,fish ,the arms bear numerous prehensile suckers1 which grip the prey4 ,in the mouth there are strong jaws shaped like a parrot's beak4 ,the cuttlefishes are molluscs and may be regarded as the highest of the backboneless or ,invertebrate animals4 ,many occur near shore1 others in the open sea1 and others in the great depths4 ,illustration3 ,,greenland ,,whale ,showing the double blowhole or nostrils on the top of the head and the whalebone plates hanging down from the roof of the mouth4 ,illustration3 ,,minute ,,transparent ,,early ,,stage ,,of ,a ,,sea-,,cucumber ,it swims in the open sea by means of girdles of microscopic cilia shown in the figure4 ,after a period of free swimming and a remarkable metamorphosis1 the animal settles down on the floor of the sea in relatively shallow water4 ,illustration3 ,photo3 ,british ,museum 7,natural ,history7 ,,an ,,intricate ,,colony ,,of ,,open-,,sea ,,animals 7,physophora ,hydrostatica7 ,,related ,,to ,,the ,,portuguese ,,man-,,of-,,war ,there is great division of labor in the colony4 ,at the top are floating and swimming persons2 the long ones below are offensive persons bearing batteries of stinging cells2 in the middle zone there are nutritive1 reproductive1 and other persons4 ,the color of the colony is a fine translucent blue4 ,swimmers and bathers are often badly stung by this strange animal and its relatives4 ,illustration3 ,a ,,scene ,,in ,,the ,,great ,,depths ,showing a deep-sea fish of large gape1 two feather-stars on the end of long stalks1 a sea-spider 7or ,pycnogon7 walking on lanky legs on the treacherous ooze1 likewise a brittle-star1 and some deep-sea corals4 ,the fauna of the shore is remarkably representative--from unicellular ,protozoa to birds like the oyster-catcher and mammals like the seals4 ,almost all the great groups of animals have apparently served an apprenticeship in the shore-haunt1 and since lessons learned for millions of years sink in and become organically enregistered1 it is justifiable to look to the shore as a great school in which were gained racial qualities of endurance1 patience1 and alertness4 ,,ii4 ,,the ,,open ,,sea ,in great contrast to the narrow1 crowded1 difficult conditions of the shore-haunt 7littoral area7 are the spacious1 bountiful1 and relatively easygoing conditions of the open sea 7pelagic area71 which means the well-lighted surface waters quite away from land4 ,many small organisms have their maximum abundance at about fifty fathoms1 so that the word surface is to be taken generously4 ,the light becomes very dim at #bej fathoms1 and the open sea1 as a zoological haunt1 stops with the light4 ,it is hardly necessary to say that the pelagic plants are more abundant near the surface1 and that below a certain depth the population consists almost exclusively of animals4 ,not a few of the animals sink and rise in the water periodically2 there are some that come near the surface by day1 and others that come near the surface by night4 ,of great interest is the habit of the extremely delicate ,ctenophores or sea-gooseberries1 which the splash of a wave would tear into shreds4 ,whenever there is any hint of a storm they sink beyond its reach1 and the ocean's surface must have remained flat as a mirror for many hours before they can be lured upwards from the calm of their deep retreat4 ,the ,floating ,sea-meadows ,to understand the vital economy of the open sea1 we must recognise the incalculable abundance of minute unicellular plants1 for they form the fundamental food-supply4 ,along with these must also be included numerous microscopic animals which have got possession of chlorophyll1 or have entered into internal partnership with unicellular ,alg 7symbiosis74 ,these green or greenish plants and animals are the producers1 using the energy of the sunlight to help them in building up carbon compounds out of air1 water1 and salts4 ,the animals which feed on the producers1 or on other animals1 are the consumers4 ,between the two come those open-sea bacteria that convert nitrogenous material1 e4g4 from dead plants or animals that other bacteria have rotted1 into forms1 e4g4 nitrates1 which plants can re-utilise4 ,the importance of these middlemen is great in keeping the circulation of matter agoing4 ,illustration3 #a4 ,,sea-,,horse ,,in ,,sargasso ,,weed4 ,in its frond-like tags of skin and in its colouring this kind of sea-horse is well concealed among the floating seaweed of the so-called ,sargasso ,sea4 #b4 ,,the ,,large ,,marine ,,lampreys 7,,petromyzon ,,marinus71 ,,which ,,may ,,be ,,as ,,long ,,as ,,one',s ,,arm1 ,,spawn ,,in ,,fresh ,,water4 ,stones and pebbles1 gripped in the suctorial mouth1 are removed from a selected spot and piled around the circumference1 so that the eggs1 which are laid within the circle1 are not easily washed away4 #c4 ,,the ,,deep-,,sea ,,fish ,,chiasmodon ,,niger ,,is ,,famous ,,for ,,its ,,voracity4 ,it sometimes manages to swallow a fish larger than itself1 which causes an extraordinary protrusion of the stomach4 #d4 ,,deep-,,sea ,,fishes4 ,two of them--,melanocetus murrayi and ,melanocetus indicus--are related to the ,angler of ,british coasts1 but adapted to life in the great abysses4 ,they are very dark in colour1 and delicately built2 they possess well-developed luminous organs4 ,the third form is called ,chauliodus1 a predatory animal with large gape and formidable teeth4 ,illustration3 ,,flinty ,,skeleton ,,of ,,venus ,,flower ,,basket 7,,euplectella71 ,a ,,japanese ,,deep-,,sea ,,sponge ,illustration3 ,,egg ,,depository ,,of ,semotilus ,atromaculatus ,in the building of this egg depository1 the male fish takes stones from the bottom of the stream1 gripping them in his mouth1 and heaps them up into the dam4 ,in the egg depository he arranges the stones so that when the eggs are deposited in the interstices they are thoroughly protected1 and cannot be washed down-stream4 #a1 dam of stones2 #b1 egg depository2 #c1 hillock of sand4 ,the arrow shows the direction of the stream4 ,upper fish1 male2 lower1 female4 ,the floating sea-meadows1 as ,sir ,john ,murray called them1 are always receiving contributions from inshore waters1 where the conditions are favourable for the prolific multiplication of unicellular ,alg1 and there is also a certain amount of non-living sea-dust always being swept out from the seaweed and sea-grass area4 ,swimmers and ,drifters ,the animals of the open sea are conveniently divided into the active swimmers 7,nekton7 and the more passive drifters 7,plankton74 ,the swimmers include whales great and small1 such birds as the storm petrel1 the fish-eating turtles and sea-snakes1 such fishes as mackerel and herring1 the winged snails or sea-butterflies on which whalebone whales largely feed1 some of the active cuttles or squids1 various open-sea prawns and their relatives1 some worms like the transparent arrow-worm1 and such active ,protozoa as ,noctiluca1 whose luminescence makes the waves sparkle in the short summer darkness4 ,very striking as an instance of the insurgence of life are the sea-skimmers 7,halobatid71 wingless insects related to the water-measurers in the ditch4 ,they are found hundreds of miles from land1 skimming on the surface of the open sea1 and diving in stormy weather4 ,they feed on floating dead animals4 ,the drifters or easygoing swimmers--for there is no hard and fast line--are represented1 for instance1 by the flinty-shelled ,radiolarians and certain of the chalk-forming animals 7,globigerinid ,foraminifera72 by jellyfishes1 swimming-bells1 and ,portuguese men-of-war2 by the comb-bearers or ,ctenophores2 by legions of minute ,crustaceans2 by strange animals called ,salps1 related to the sedentary sea-squirts2 and by some sluggish fishes like globe-fishes1 which often float idly on the surface4 ,open-sea animals tend to be delicately built1 with a specific gravity near that of the sea-water1 with adaptations1 such as projecting filaments1 which help flotation1 and with capacities of rising and sinking according to the surrounding conditions4 ,many of them are luminescent1 and many of them are very inconspicuous in the water owing to their transparency or their bluish colour4 ,in both cases the significance is obscure4 ,hunger and ,love ,hunger is often very much in evidence in the open sea1 especially in areas where the ,plankton is poor4 ,for there is great diversity in this respect1 most of the ,mediterranean1 for instance1 having a scanty ,plankton as compared with the ,north ,sea4 ,in the ,south ,pacific1 west of ,patagonia1 there is said to be an immense sea desert where there is little ,plankton1 and therefore little in the way of fishes4 ,the success of fisheries in the ,north1 e4g4 on the ,atlantic cod-banks1 is due to the richness of the floating sea-meadows and the abundance of the smaller constituents of the animal ,plankton4 ,hunger is plain enough when the ,baleen ,whale rushes through the water with open jaws1 engulfing in the huge cavern of its mouth1 where the pendent whalebone plates form a huge sieve1 incalculable millions of small fry4 ,but there is love as well as hunger in the open sea4 ,the maternal care exhibited by the whale reaches a very high level1 and the delicate shell of the female ,paper ,nautilus or ,argonaut1 in which the eggs and the young ones are sheltered1 may well be described as the most beautiful cradle in the world4 ,besides the permanent inhabitants of the open sea1 there are the larval stages of many shore-animals which are there only for a short time4 ,for there is an interesting give and take between the shore-haunt and the open sea4 ,from the shore come nutritive contributions and minute organisms which multiply quickly in the open waters4 ,but not less important is the fact that the open waters afford a safe cradle or nursery for many a delicate larva1 e4g4 of crab and starfish1 acorn-shell and sea-urchin1 which could not survive for a day in the rough-and-tumble conditions of the shore and the shallow water4 ,after undergoing radical changes and gaining strength1 the young creatures return to the shore in various ways4 ,,iii4 ,,the ,,deep ,,sea ,very different from all the other haunts are the depths of the sea1 including the floor of the abysses and the zones of water near the bottom4 ,this haunt1 forever unseen1 occupies more than a third of the earth's surface1 and it is thickly peopled4 ,it came into emphatic notice in connection with the mending of telegraph cables1 but the results of the ,challenger expedition 7#ahgc-f7 gave the first impressive picture of what was practically a new world4 ,physical ,conditions ,the average depth of the ocean is about two and a half miles2 therefore1 since many parts are relatively shallow1 there must be enormous depths4 ,a few of these1 technically called deeps1 are about six miles deep1 in which ,mount ,everest would be engulfed4 ,there is enormous pressure in such depths2 even at #b1ejj fathoms it is two and a half tons on the square inch4 ,the temperature is on and off the freezing-point of fresh water 7#bh-cd ,fahr471 due to the continual sinking down of cold water from the ,poles1 especially from the ,south4 ,apart from the fitful gleams of luminescent animals1 there is utter darkness in the deep waters4 ,the rays of sunlight are practically extinguished at #bej fathoms1 though very sensitive bromogelatine plates exposed at #ejj fathoms have shown faint indications even at that depth4 ,it is a world of absolute calm and silence1 and there is no scenery on the floor4 ,a deep1 cold1 dark1 silent1 monotonous world6 ,biological ,conditions ,while some parts of the floor of the abysses are more thickly peopled than others1 there is no depth limit to the distribution of life4 ,wherever the long arm of the dredge has reached1 animals have been found1 e4g4 ,protozoa1 sponges1 corals1 worms1 starfishes1 sea-urchins1 sea-lilies1 crustaceans1 lamp-shells1 molluscs1 ascidians1 and fishes--a very representative fauna4 ,in the absence of light there can be no chlorophyll-possessing plants1 and as the animals cannot all be eating one another there must be an extraneous source of food-supply4 ,this is found in the sinking down of minute organisms which are killed on the surface by changes of temperature and other causes4 ,what is left of them1 before or after being swallowed1 and of sea-dust and mineral particles of various kinds forms the diversified ooze of the sea-floor1 a soft muddy precipitate1 which is said to have in places the consistence of butter in summer weather4 ,there seems to be no bacteria in the abysses1 so there can be no rotting4 ,everything that sinks down1 even the huge carcase of a whale1 must be nibbled away by hungry animals and digested1 or else1 in the case of most bones1 slowly dissolved away4 ,of the whale there are left only the ear-bones1 of the shark his teeth4 ,adaptations to ,deep-sea ,life ,in adaptation to the great pressure the bodies of deep-sea animals are usually very permeable1 so that the water gets through and through them1 as in the case of ,venus' ,flower ,basket1 a flinty sponge which a child's finger would shiver4 ,but when the pressure inside is the same as that outside nothing happens4 ,in adaptation to the treacherous ooze1 so apt to smother1 many of the active deep-sea animals have very long1 stilt-like legs1 and many of the sedentary types are lifted into safety on the end of long stalks which have their bases embedded in the mud4 ,in adaptation to the darkness1 in which there is only luminescence that eyes could use1 there is a great development of tactility4 ,the interesting problem of luminescence will be discussed elsewhere4 ,as to the origin of the deep-sea fauna1 there seems no doubt that it has arisen by many contributions from the various shore-haunts4 ,following the down-drifting food1 many shore-animals have in the course of many generations reached the world of eternal night and winter1 and become adapted to its strange conditions4 ,for the animals of the deep-sea are as fit1 beautiful1 and vigorous as those elsewhere4 ,there are no slums in ,nature4 ,illustration3 ,,the ,,bitterling 7,rhodeus ,amarus7 ,a ,continental fish which lays its eggs by means of a long ovipositor inside the freshwater mussel4 ,the eggs develop inside the mollusc's gill-plates4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge4 ,,woolly ,,opossum ,,carrying ,,her ,,family ,one of the young ones is clinging to its mother and has its long prehensile tail coiled round hers4 ,illustration3 ,,surinam ,,toad 7,pipa ,americana7 ,,with ,,young ,,ones ,,hatching ,,out ,,of ,,little ,,pockets ,,on ,,her ,,back ,illustration3 ,,storm ,,petrel ,,or ,,mother ,,carey',s ,,chicken 7,procellaria ,pelagica7 ,this characteristic bird of the open sea does not come to land at all except to nest4 ,it is the smallest web-footed bird1 about four inches long4 ,the legs are long and often touch the water as the bird flies4 ,the storm petrel is at home in the ,atlantic1 and often nests on islands off the west coast of ,britain4 ,,iv4 ,,the ,,fresh ,,waters ,of the whole earth's surface the freshwaters form a very small fraction1 about a hundredth1 but they make up for their smallness by their variety4 ,we think of deep lake and shallow pond1 of the great river and the purling brook1 of lagoon and swamp1 and more besides4 ,there is a striking resemblance in the animal population of widely separated freshwater basins3 and this is partly because birds carry many small creatures on their muddy feet from one water-shed to another2 partly because some of the freshwater animals are descended from types which make their way from the sea and the seashore through estuaries and marshes1 and only certain kinds of constitution could survive the migration2 and partly because some lakes are landlocked dwindling relics of ancient seas1 and similar forms again would survive the change4 ,a typical assemblage of freshwater animals would include many ,protozoa1 like ,amoeb and the ,bell-,animalcules1 a representative of one family of sponges 7,spongillid71 the common ,hydra1 many unsegmented worms 7notably ,planarians and ,nematodes71 many ,annelids related to the earthworms1 many crustaceans1 insects1 and mites1 many bivalves and snails1 various fishes1 a newt or two1 perhaps a little mud-turtle or in warm countries a huge ,crocodilian1 various interesting birds like the water-ouzel or dipper1 and mammals like the water-vole and the water-shrew4 ,freshwater animals have to face certain difficulties1 the greatest of which are drought1 frost1 and being washed away in times of flood4 ,there is no more interesting study in the world than an inquiry into the adaptations by which freshwater animals overcome the difficulties of the situation4 ,we cannot give more than a few illustrations4 7#a7 ,drought is circumvented by the capacity that many freshwater animals have of lying low and saying nothing4 ,thus the ,african mudfish may spend half the year encased in the mud1 and many minute crustaceans can survive being dried up for years4 7#b7 ,escape from the danger of being frozen hard in the pool is largely due to the almost unique property of water that it expands as it approaches the freezing-point4 ,thus the colder water rises to the surface and forms or adds to the protecting blanket of ice4 ,the warmer water remains unfrozen at the bottom1 and the animals live on4 7#c7 ,the risk of being washed away1 e4g4 to the sea1 is lessened by all sorts of gripping1 grappling1 and anchoring structures1 and by shortening the juvenile stages when the risks are greatest4 ,v4 ,,the ,,dry ,,land ,over and over again in the history of animal life there have been attempts to get out of the water on to terra firma1 and many of these have been successful1 notably those made 7#a7 by worms1 7#b7 by air-breathing ,arthropods1 and 7#c7 by amphibians4 ,in thinking of the conquest of the dry land by animals1 we must recognise the indispensable rle of plants in preparing the way4 ,the dry ground would have proved too inhospitable had not terrestrial plants begun to establish themselves1 affording food1 shelter1 and humidity4 ,there had to be plants before there could be earthworms1 which feed on decaying leaves and the like1 but how soon was the debt repaid when the earthworms began their worldwide task of forming vegetable mould1 opening up the earth with their burrows1 circulating the soil by means of their castings1 and bruising the particles in their gizzard--certainly the most important mill in the world4 ,another important idea is that littoral haunts1 both on the seashore and in the freshwaters1 afforded the necessary apprenticeship and transitional experience for the more strenuous life on dry land4 ,much that was perfected on land had its beginnings on the shore4 ,let us inquire1 however1 what the passage from water to dry land actually implied4 ,this has been briefly discussed in a previous article 7on ,evolution71 but the subject is one of great interest and importance4 ,difficulties and ,results of the ,transition from ,water to ,land ,leaving the water for dry land implied a loss in freedom of movement1 for the terrestrial animal is primarily restricted to the surface of the earth4 ,thus it became essential that movements should be very rapid and very precise1 needs with which we may associate the acquisition of fine cross-striped1 quickly contracting muscles1 and also1 in time1 their multiplication into very numerous separate engines4 ,we exercise fifty-four muscles in the half-second that elapses between raising the heel of our foot in walking and planting it firmly on the ground again4 ,moreover1 the need for rapid precisely controlled movements implied an improved nervous system1 for the brain was a movement-controlling organ for ages before it did much in the way of thinking4 ,the transition to terra firma also involved a greater compactness of body1 so that there should not be too great friction on the surface4 ,an animal like the jellyfish is unthinkable on land1 and the elongated bodies of some land animals like centipedes and snakes are specially adapted so that they do not sprawl4 ,they are exceptions that prove the rule4 ,getting on to dry land meant entering a kingdom where the differences between day and night1 between summer and winter are more felt than in the sea4 ,this made it advantageous to have protections against evaporation and loss of heat and other such dangers4 ,hence a variety of ways in which the surface of the body acquired a thickened skin1 or a dead cuticle1 or a shell1 or a growth of hair1 and so forth4 ,in many cases there is an increase of the protection before the winter sets in1 e4g4 by growing thicker fur or by accumulating a layer of fat below the skin4 ,but the thickening or protection of the skin involved a partial or total loss of the skin as a respiratory surface4 ,there is more oxygen available on dry land than in the water1 but it is not so readily captured4 ,thus we see the importance of moist internal surfaces for capturing the oxygen which has been drawn into the interior of the body into some sort of lung4 ,a unique solution was offered by ,tracheate ,arthropods1 such as ,peripatus1 ,centipedes1 ,millipedes1 and ,insects1 where the air is carried to every hole and corner of the body by a ramifying system of air-tubes or trache4 ,in most animals the blood goes to the air1 in insects the air goes to the blood4 ,in the ,robber-,crab1 which has migrated from the shore inland1 the dry air is absorbed by vascular tufts growing under the shelter of the gill-cover4 ,the problem of disposing of eggs or young ones is obviously much more difficult on land than in the water4 ,for the water offers an immediate cradle1 whereas on the dry land there were many dangers1 e4g4 of drought1 extremes of temperature1 and hungry sharp-eyed enemies1 which had to be circumvented4 ,so we find all manner of ways in which land animals hide their eggs or their young ones in holes and nests1 on herbs and on trees4 ,some carry their young ones about after they are born1 like the ,surinam toad and the kangaroo1 while others have prolonged the period of ante-natal life during which the young ones develop in safety within their mother1 and in very intimate partnership with her in the case of the placental mammals4 ,it is very interesting to find that the pioneer animal called ,peripatus1 which bridges the gap between worms and insects1 carries its young for almost a year before birth4 ,enough has been said to show that the successive conquests of the dry land had great evolutionary results4 ,it is hardly too much to say that the invasion which the ,amphibians led was the beginning of better brains1 more controlled activities1 and higher expressions of family life4 ,illustration3 ,,albatross3 ,a ,,characteristic ,,pelagic ,,bird ,,of ,,the ,,southern ,,sea ,it may have a spread of wing of over #aa feet from tip to tip4 ,it is famous for its extraordinary power of sailing round the ship without any apparent strokes of its wings4 ,,vi4 ,,the ,,air ,there are no animals thoroughly aerial1 but many insects spend much of their adult life in the free air1 and the swift hardly pauses in its flight from dawn to dusk of the long summer day1 alighting only for brief moments at the nest to deliver insects to the young4 ,all the active life of bats certainly deserves to be called aerial4 ,the air was the last haunt of life to be conquered1 and it is interesting to inquire what the conquest implied4 7#a7 ,it meant transcending the radical difficulty of terrestrial life which confines the creatures of the dry land to moving on one plane1 the surface of the earth4 ,but the power of flight brought its possessors back to the universal freedom of movement which water animals enjoy4 ,when we watch a sparrow rise into the air just as the cat has completed her stealthy stalking1 we see that flight implies an enormous increase of safety4 7#b7 ,the power of flight also opened up new possibilities of following the prey1 of exploring new territories1 of prospecting for water4 7#c7 ,of great importance too was the practicability of placing the eggs and the young1 perhaps in a nest1 in some place inaccessible to most enemies4 ,when one thinks of it1 the rooks' nests swaying on the tree-tops express the climax of a brilliant experiment4 7#d7 ,the crowning advantage was the possibility of migrating1 of conquering time 7by circumventing the arid summer and the severe winter7 and of conquering space 7by passing quickly from one country to another and sometimes almost girdling the globe74 ,there are not many acquisitions that have meant more to their possessors than the power of flight4 ,it was a key opening the doors of a new freedom4 ,the problem of flight1 as has been said in a previous chapter1 has been solved four times1 and the solution has been different in each case4 ,the four solutions are those offered by insects1 extinct ,pterodactyls1 birds1 and bats4 ,moreover1 as has been pointed out1 there have been numerous attempts at flight which remain glorious failures1 notably the flying fishes1 which take a great leap and hold their pectoral fins taut2 the ,flying ,tree-,toad1 whose webbed fingers and toes form a parachute2 the ,flying ,lizard 7,draco volans71 which has its skin pushed out on five or six greatly elongated mobile ribs2 and various flying mammals1 e4g4 ,flying ,phalangers and ,flying ,squirrels1 which take great swooping leaps from tree to tree4 ,the wings of an insect are hollow flattened sacs which grow out from the upper parts of the sides of the second and third rings of the region called the thorax4 ,they are worked by powerful muscles1 and are supported1 like a fan1 by ribs of chitin1 which may be accompanied by air-tubes1 blood-channels1 and nerves4 ,the insect's body is lightly built and very perfectly aerated1 and the principle of the insect's flight is the extremely rapid striking of the air by means of the lightly built elastic wings4 ,many an insect has over two hundred strokes of its wings in one second4 ,hence1 in many cases1 the familiar hum1 comparable on a small scale to that produced by the rapidly revolving blades of an aeroplane's propeller4 ,for a short distance a bee can outfly a pigeon1 but few insects can fly far1 and they are easily blown away or blown back by the wind4 ,dragon-flies and bees may be cited as examples of insects that often fly for two or three miles4 ,but this is exceptional1 and the usual shortness of insect flight is an important fact for man since it limits the range of insects like house-flies and mosquitoes which are vehicles of typhoid fever and malaria respectively4 ,the most primitive insects 7spring-tails and bristle-tails7 show no trace of wings1 while fleas and lice have become secondarily wingless4 ,it is interesting to notice that some insects only fly once in their lifetime1 namely1 in connection with mating4 ,the evolution of the insect's wing remains quite obscure1 but it is probable that insects could run1 leap1 and parachute before they could actually fly4 ,the extinct ,flying ,dragons or ,pterodactyls had their golden age in the ,cretaceous era1 after which they disappeared1 leaving no descendants4 ,a fold of skin was spread out from the sides of the body by the enormously elongated outermost finger 7usually regarded as corresponding to our little finger72 it was continued to the hind-legs and thence to the tail4 ,it is unlikely that the ,pterodactyls could fly far1 for they have at most a weak keel on their breast-bone2 on the other hand1 some of them show a marked fusion of dorsal vertebr1 which1 as in flying birds1 must have served as a firm fulcrum for the stroke of the wings4 ,the quaint creatures varied from the size of a sparrow up to a magnificent spread of #ae-bj feet from tip to tip of the wings4 ,they were the largest of all flying creatures4 ,the bird's solution of the problem of flight1 which will be discussed separately1 is centred in the feather1 which forms a coherent vane for striking the air4 ,in ,pterodactyl and bat the wing is a web-wing or patagium1 and a small web is to be seen on the front side of the bird's wing4 ,but the bird's patagium is unimportant1 and the bird's wing is on an evolutionary tack of its own--a fore-limb transformed for bearing the feathers of flight4 ,feathers are in a general way comparable to the scales of reptiles1 but only in a general way1 and no transition stage is known between the two4 ,birds evolved from a bipedal ,dinosaur stock1 as has been noticed already1 and it is highly probable that they began their ascent by taking running leaps along the ground1 flapping their scaly fore-limbs1 and balancing themselves in kangaroo-like fashion with an extended tail4 ,a second chapter was probably an arboreal apprenticeship1 during which they made a fine art of parachuting--a persistence of which is to be seen in the pigeon gliding from the dovecot to the ground4 ,it is in birds that the mastery of the air reaches its climax1 and the mysterious sailing of the albatross and the vulture is surely the most remarkable locomotor triumph that has ever been achieved4 ,without any apparent stroke of the wings1 the bird sails for half an hour at a time with the wind and against the wind1 around the ship and in majestic spirals in the sky1 probably taking advantage of currents of air of different velocities1 and continually changing energy of position into energy of motion as it sinks1 and energy of motion into energy of position as it rises4 ,it is interesting to know that some dragon-flies are also able to sail4 ,the web-wing of bats involves much more than the fore-arm4 ,the double fold of skin begins on the side of the neck1 passes along the front of the arm1 skips the thumb1 and is continued over the elongated palm-bones and fingers to the sides of the body again1 and to the hind-legs1 and to the tail if there is a tail4 ,it is interesting to find that the bones of the bat's skeleton tend to be lightly built as in birds1 that the breast-bone has likewise a keel for the better insertion of the pectoral muscles1 and that there is a solidifying of the vertebr of the back1 affording as in birds a firm basis for the wing action4 ,such similar adaptations to similar needs1 occurring in animals not nearly related to one another1 are called convergences1 and form a very interesting study4 ,in addition to adaptations which the bat shares with the flying bird1 it has many of its own4 ,there are so many nerve-endings on the wing1 and often also on special skin-leaves about the ears and nose1 that the bat flying in the dusk does not knock against branches or other obstacles4 ,some say that it is helped by the echoes of its high-pitched voice1 but there is no doubt as to its exquisite tactility4 ,that it usually produces only a single young one at a time is a clear adaptation to flight1 and similarly the sharp1 mountain-top-like cusps on the back teeth are adapted in insectivorous bats for crunching insects4 ,whether we think of the triumphant flight of birds1 reaching a climax in migration1 or of the marvel that a creature of the earth--as a mammal essentially is--should evolve such a mastery of the air as we see in bats1 or even of the repeated but splendid failures which parachuting animals illustrate1 we gain an impression of the insurgence of living creatures in their characteristic endeavour after fuller well-being4 ,we have said enough to show how well adapted many animals are to meet the particular difficulties of the haunt which they tenant4 ,but difficulties and limitations are ever arising afresh1 and so one fitness follows on another4 ,it is natural1 therefore1 to pass to the frequent occurrence of protective resemblance1 camouflage1 and mimicry--the subject of the next article4 ,,bibliography ,,elmhirst1 ,r41 ,animals of the ,shore4 ,,flattely ,,and ,,walton1 ,the ,biology of the ,shore 7#aiba74 ,,furneaux1 ,life of ,ponds and ,streams4 ,,hickson1 ,s4 ,j41 ,story of ,life in the ,seas and ,fauna of the ,deep ,sea4 ,,johnstone1 ,j41 ,life in the ,sea 7,cambridge ,manual of ,science74 ,,miall1 ,l4 ,c41 ,aquatic ,insects4 ,,murray1 ,,sir ,,john1 ,the ,ocean 7,home ,university ,library74 ,,murray1 ,,sir ,,john ,,and ,,hjort1 ,,dr4 ,j41 ,the ,depths of the ,ocean4 ,,newbigin1 ,m4 ,i41 ,life by the ,sea ,shore4 ,,pycraft1 ,w4 ,p41 ,history of ,birds4 ,,scharff1 ,r4 ,f41 ,history of the ,european ,fauna 7,contemp4 ,sci4 ,series74 ,,thomson1 ,j4 ,,arthur1 ,the ,wonder of ,life 7#aiad7 and ,the ,haunts of ,life 7#aiba74 ,,iv ,,the ,,struggle ,,for ,,existence ,,animal ,,and ,,bird ,,mimicry ,,and ,,disguise #a ,for every animal one discovers when observing carefully1 there must be ten unseen4 ,this is partly because many animals burrow in the ground or get in underneath things and into dark corners1 being what is called cryptozoic or elusive4 ,but it is partly because many animals put on disguise or have in some way acquired a garment of invisibility4 ,this is very common among animals1 and it occurs in many forms and degrees4 ,the reason why it is so common is because the struggle for existence is often very keen1 and the reasons why the struggle for existence is keen are four4 ,first1 there is the tendency to over-population in many animals1 especially those of low degree4 ,second1 there is the fact that the scheme of nature involves nutritive chains or successive incarnations1 one animal depending upon another for food1 and all in the long run on plants2 thirdly1 every vigorous animal is a bit of a hustler1 given to insurgence and sticking out his elbows4 ,there is a fourth great reason for the struggle for existence1 namely1 the frequent changefulness of the physical environment1 which forces animals to answer back or die2 but the first three reasons have most to do with the very common assumption of some sort of disguise4 ,even when an animal is in no sense a weakling1 it may be very advantageous for it to be inconspicuous when it is resting or when it is taking care of its young4 ,our problem is the evolution of elusiveness1 so far at least as that depends on likeness to surroundings1 on protective resemblance to other objects1 and in its highest reaches on true mimicry4 ,colour ,permanently ,like ,that of ,surroundings ,many animals living on sandy places have a light-brown colour1 as is seen in some lizards and snakes4 ,the green lizard is like the grass and the green tree-snake is inconspicuous among the branches4 ,the spotted leopard is suited to the interrupted light of the forest1 and it is sometimes hard to tell where the jungle ends and the striped tiger begins4 ,there is no better case than the hare or the partridge sitting a few yards off on the ploughed field4 ,even a donkey grazing in the dusk is much more readily heard than seen4 ,the experiment has been made of tethering the green variety of ,praying ,mantis on green herbage1 fastening them with silk threads4 ,they escape the notice of birds4 ,the same is true when the brown variety is tethered on withered herbage4 ,but if the green ones are put on brown plants1 or the brown ones on green plants1 the birds pick them off4 ,similarly1 out of #cjj chickens in a field1 #bdj white or black and therefore conspicuous1 #fj spotted and inconspicuous1 #bd were soon picked off by crows1 but only one of these was spotted4 ,this was not the proportion that there should have been if the mortality had been fortuitous4 ,there is no doubt that it often pays an animal to be like its habitual surroundings1 like a little piece of scenery if the animal is not moving4 ,it is safe to say that in process of time wide departures from the safest coloration will be wiped out in the course of ,nature's ceaseless sifting4 ,but we must not be credulous1 and there are three cautions to be borne in mind4 7#a7 ,an animal may be very like its surroundings without there being any protection implied4 ,the arrow-worms in the sea are as clear as glass1 and so are many open-sea animals4 ,but this is because their tissues are so watery1 with a specific gravity near that of the salt water4 ,and the invisibility does not save them1 always or often1 from being swallowed by larger animals that gather the harvest of the sea4 7#b7 ,among the cleverer animals it looks as if the creature sometimes sought out a spot where it was most inconspicuous4 ,a spider may place itself in the middle of a little patch of lichen1 where its self-effacement is complete4 ,perhaps it is more comfortable as well as safer to rest in surroundings the general colour of which is like that of the animal's body4 7#c7 ,the fishes that live among the coral-reefs are startling in their brilliant coloration1 and there are many different patterns4 ,to explain this it has been suggested that these fishes are so safe among the mazy passages and endless nooks of the reefs1 that they can well afford to wear any colour that suits their constitution4 ,in some cases this may be true1 but naturalists who have put on a diving suit and walked about among the coral have told us that each kind of fish is particularly suited to some particular place1 and that some are suited for midday work and others for evening work4 ,sometimes there is a sort of ,box and ,cox arrangement by which two different fishes utilise the same corner at different times4 ,illustration3 ,,the ,,praying ,,mantis 7,mantis ,religiosa7 ,a very voracious insect with a quiet1 unobtrusive appearance4 ,it holds its formidable forelegs as if in the attitude of prayer2 its movements are very slow and stealthy2 and there is a suggestion of a leaf in the forewing4 ,but there is no reason to credit the creature with conscious guile6 ,illustration3 ,,protective ,,coloration3 ,a ,,winter ,,scene ,,in ,,north ,,scandinavia ,showing ,variable ,hare1 ,willow ,grouse1 and ,arctic ,fox1 all white in winter and inconspicuous against the snow4 ,but the white dress is also the dress that is physiologically best1 for it loses least of the animal heat4 ,illustration3 ,,the ,,variable ,,monitor 7,varanus7 ,the monitors are the largest of existing lizards1 the ,australian species represented in the photograph attaining a length of four feet4 ,it has a brown colour with yellow spots1 and in spite of its size it is not conspicuous against certain backgrounds1 such as the bark of a tree4 #b ,gradual ,change of ,colour ,the common shore-crab shows many different colours and mottlings1 especially when it is young4 ,it may be green or grey1 red or brown1 and so forth1 and it is often in admirable adjustment to the colour of the rock-pool where it is living4 ,experiments1 which require extension1 have shown that when the crab has moulted1 which it has to do very often when it is young1 the colour of the new shell tends to harmonise with the general colour of the rocks and seaweed4 ,how this is brought about1 we do not know4 ,the colour does not seem to change till the next moult1 and not then unless there is some reason for it4 ,a full-grown shore-crab is well able to look after itself1 and it is of interest to notice1 therefore1 that the variety of coloration is mainly among the small individuals1 who have1 of course1 a much less secure position4 ,it is possible1 moreover1 that the resemblance to the surroundings admits of more successful hunting1 enabling the small crab to take its victim unawares4 ,professor ,poulton's experiments with the caterpillars of the small tortoise-shell butterfly showed that in black surroundings the pup tend to be darker1 in white surroundings lighter1 in gilded boxes golden2 and the same is true in other cases4 ,it appears that the surrounding colour affects the caterpillars through the skin during a sensitive period--the twenty hours immediately preceding the last twelve hours of the larval state4 ,the result will tend to make the quiescent pup less conspicuous during the critical time of metamorphosis4 ,the physiology of this sympathetic colouring remains obscure4 ,seasonal ,change of ,colouring ,the ptarmigan moults three times in the year4 ,its summer plumage is rather grouselike above1 with a good deal of rufous brown2 the back becomes much more grey in autumn2 almost all the feathers of the winter plumage are white4 ,that is to say1 they develop without any pigment and with numerous gas-bubbles in their cells4 ,now there can be no doubt that this white winter plumage makes the ptarmigan very inconspicuous amidst the snow4 ,sometimes one comes within a few feet of the crouching bird without seeing it1 and this garment of invisibility may save it from the hungry eyes of golden eagles4 ,similarly the brown stoat becomes the white ermine1 mainly by the growth1 of a new suit of white fur1 and the same is true of the mountain hare4 ,the ermine is all white except the black tip of its tail2 the mountain hare in its winter dress is all white save the black tips of its ears4 ,in some cases1 especially in the mountain hare1 it seems that individual hairs may turn white1 by a loss of pigment1 as may occur in man4 ,according to ,metchnikoff1 the wandering amoeboid cells of the body1 called phagocytes1 may creep up into the hairs and come back again with microscopic burdens of pigment4 ,the place of the pigment is taken by gas-bubbles1 and that is what causes the whiteness4 ,in no animals is there any white pigment2 the white colour is like that of snow or foam1 it is due to the complete reflection of the light from innumerable minute surfaces of crystals or bubbles4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,banded ,,krait3 ,a ,,very ,,poisonous ,,snake ,,with ,,alternating ,,yellow ,,and ,,dark ,,bands ,it is very conspicuous and may serve as an illustration of warning coloration4 ,perhaps1 that is to say1 its striking coloration serves as an advertisement1 impressing other creatures with the fact that the ,banded ,krait should be left alone4 ,it is very unprofitable for a snake to waste its venom on creatures it does not want4 ,illustration3 ,photos3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,the ,,warty ,,chameleon ,the upper photograph shows the ,warty ,chameleon inflated and conspicuous4 ,at another time1 however1 with compressed body and adjusted coloration1 the animal is very inconspicuous4 ,the lower photograph shows the sudden protrusion of the very long tongue on a fly4 ,illustration3 ,,seasonal ,,colour-,,change3 ,a ,,summer ,,scene ,,in ,,north ,,scandinavia ,showing a brown ,variable ,hare1 ,willow ,grouse1 and ,arctic ,fox1 all inconspicuous in their coloration when seen in their natural surroundings4 ,the mountain hare may escape the fox the more readily because its whiteness makes it so inconspicuous against a background of snow2 and yet1 at other times1 we have seen the creature standing out like a target on the dark moorland4 ,so it cuts both ways4 ,the ermine has almost no enemies except the gamekeeper1 but its winter whiteness may help it to sneak upon its victims1 such as grouse or rabbit1 when there is snow upon the ground4 ,in both cases1 however1 the probability is that the constitutional rhythm which leads to white hair in winter has been fostered and fixed for a reason quite apart from protection4 ,the fact is that for a warm-blooded creature1 whether bird or mammal1 the physiologically best dress is a white one1 for there is less radiation of the precious animal heat from white plumage or white pelage than from any other colour4 ,the quality of warm-bloodedness is a prerogative of birds and mammals1 and it means that the body keeps an almost constant temperature1 day and night1 year in and year out4 ,this is effected by automatic internal adjustments which regulate the supply of heat1 chiefly from the muscles1 to the loss of heat1 chiefly through the skin and from the lungs4 ,the chief importance of this internal heat is that it facilitates the smooth continuance of the chemical processes on which life depends4 ,if the temperature falls1 as in hibernating mammals 7whose warm-bloodedness is imperfect71 the rate of the vital process is slowed down--sometimes dangerously4 ,thus we see how the white coat helps the life of the creature4 #c ,rapid ,colour-change ,bony flat-fishes1 like plaice and sole1 have a remarkable power of adjusting their hue and pattern to the surrounding gravel and sand1 so that it is difficult to find them even when we know that they are there4 ,it must be admitted that they are also very quick to get a sprinkling of sand over their upturned side1 so that only the eyes are left showing4 ,but there is no doubt as to the exactness with which they often adjust themselves to be like a little piece of the substratum on which they lie2 they will do this within limits in experimental conditions when they are placed on a quite artificial floor4 ,as these fishes are very palatable and are much sought after by such enemies as cormorants and otters1 it is highly probably that their power of self-effacement often saves their life4 ,and it may be effected within a few minutes1 in some cases within a minute4 ,in these self-effacing flat-fishes we know with some precision what happens4 ,the adjustment of colour and pattern is due to changes in the size1 shape1 and position of mobile pigment-cells 7chromatophores7 and the skin4 ,but what makes the pigment-cells change8 ,the fact that a blind flat-fish does not change its colour gives us the first part of the answer4 ,the colour and the pattern of the surroundings must affect the eye4 ,the message travels by the optic nerve to the brain2 from the brain1 instead of passing down the spinal cord1 the message travels down the chain of sympathetic ganglia4 ,from these it passes along the nerves which comes out of the spinal cord and control the skin4 ,thus the message reaches the colour-cells in the skin1 and before you have carefully read these lines the flat-fish has slipped on its ,gyges ring and become invisible4 ,the same power of rapid colour-change is seen in cuttlefishes1 where it is often an expression of nervous excitement1 though it sometimes helps to conceal4 ,it occurs with much subtlety in the sop prawn1 ,hippolyte1 which may be brown on a brown seaweed1 green on sea-lettuce or sea-grass1 red on red seaweed1 and so on through an extensive repertory4 ,according to the nature of the background1 ,professor ,gamble writes so is the mixture of the pigments compounded so as to form a close reproduction both of its colour and its pattern4 ,a sweep of the shrimp net detaches a battalion of these sleeping prawns1 and if we turn the motley into a dish and give a choice of seaweed1 each variety after its kind will select the one with which it agrees in colour1 and vanish4 ,both when young and when full-grown1 the sop prawn takes on the colour of its immediate surroundings4 ,at nightfall ,hippolyte1 of whatever colour1 changes to a transparent azure blue3 its stolidity gives place to a nervous restlessness2 at the least tremor it leaps violently1 and often swims actively from one food-plant to another4 ,this blue fit lasts till daybreak1 and is then succeeded by the prawn's diurnal tint4 ,thus1 ,professor ,gamble continues1 the colour of an animal may express a nervous rhythm4 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,protective ,,resemblance ,hawk ,moth1 settled down on a branch1 and very difficult to detect as long as it remains stationary4 ,note its remarkable sucking tongue1 which is about twice the length of its body4 ,the tongue can be quickly coiled up and put safely away beneath the lower part of the head4 ,illustration3 ,,when ,,only ,a ,,few ,,days ,,old1 ,,young ,,bittern ,,begin ,,to ,,strike ,,the ,,same ,,attitude ,,as ,,their ,,parents ,,thrusting ,,their ,,bills ,,upwards ,,and ,,drawing ,,their ,,bodies ,,up ,,so ,,that ,,they ,,resemble ,a ,,bunch ,,of ,,reeds ,the soft browns and blue-greens harmonise with the dull sheaths of the young reeds2 the nestling bittern is thus completely camouflaged4 ,the ,case of ,chameleons ,the highest level at which rapid colour-change occurs is among lizards1 and the finest exhibition of it is among the chameleons4 ,these quaint creatures are characteristic of ,africa2 but they occur also in ,andalusia1 ,arabia1 ,ceylon1 and ,southern ,india4 ,they are adapted for life on trees1 where they hunt insects with great deliberateness and success4 ,the protrusible tongue1 ending in a sticky club1 can be shot out for about seven inches in the common chameleon4 ,their hands and feet are split so that they grip the branches firmly1 and the prehensile tail rivals a monkey's4 ,when they wish they can make themselves very slim1 contracting the body from side to side1 so that they are not very readily seen4 ,in other circumstances1 however1 they do not practise self-effacement1 but the very reverse4 ,they inflate their bodies1 having not only large lungs1 but air-sacs in connection with them4 ,the throat bulges2 the body sways from side to side2 and the creature expresses its sentiments in a hiss4 ,the power of colour-change is very remarkable1 and depends partly on the contraction and expansion of the colour-cells 7chromatophores7 in the under-skin 7or dermis7 and partly on close-packed refractive granules and crystals of a waste-product called guanin4 ,the repertory of possible colours in the common chameleon is greater than in any other animal except the sop prawn4 ,there is a legend of a chameleon which was brown in a brown box1 green in a green box1 and blue in a blue box1 and died when put into one lined with tartan2 and there is no doubt that one and the same animal has a wide range of colours4 ,the so-called chameleon 7,anolis7 of ,north ,america is so sensitive that a passing cloud makes it change its emerald hue4 ,there is no doubt that a chameleon may make itself more inconspicuous by changing its colour1 being affected by the play of light on its eyes4 ,a bright-green hue is often seen on those that are sitting among strongly illumined green leaves4 ,but the colour also changes with the time of day and with the animal's moods4 ,a sudden irritation may bring about a rapid change2 in other cases the transformation comes about very gradually4 ,when the colour-change expresses the chameleon's feelings it might be compared to blushing1 but that is due to an expansion of the arteries of the face1 allowing more blood to get into the capillaries of the under-skin4 ,the case of the chameleon is peculiarly interesting because the animal has two kinds of tactics--self-effacement on the one hand and bluffing on the other4 ,there can be little doubt that the power of colour-change sometimes justifies itself by driving off intruders4 ,dr4 ,cyril ,crossland observed that a chameleon attacked by a fox-terrier turned round and opened its great pink mouth in the face of the advancing dog1 at the same time rapidly changing colour1 becoming almost black4 ,this ruse succeeded every time1 the dog turning off at once4 ,in natural leafy surroundings the startling effect would be much greater--a sudden throwing off of the mantle of invisibility and the exposure of a conspicuous black body with a large red mouth4 #d ,likeness to ,other ,things ,dr4 ,h4 ,o4 ,forbes tells of a flat spider which presents a striking resemblance to a bird's dropping on a leaf4 ,years after he first found it he was watching in a forest in the ,far ,east when his eye fell on a leaf before him which had been blotched by a bird4 ,he wondered idly why he had not seen for so long another specimen of the bird-dropping spider 7,ornithoscatoides decipiens71 and drew the leaf towards him4 ,instantaneously he got a characteristic sharp nip2 it was the spider after all6 ,here the colour-resemblance was enhanced by a form-resemblance4 ,illustration3 ,a4 ,,protective ,,coloration ,,or ,,camouflaging1 ,,giving ,,animals ,a ,,garment ,,of ,,invisibility ,at the foot of the plate is a ,nightjar1 with plumage like bark and withering leaves2 to the right1 resting on a branch1 is shown a ,chameleon in a green phase amid green surroundings2 the insects on the reeds are ,locusts2 while a green ,frog1 merged into its surroundings1 rests on a leaf near the centre at the top of the picture4 ,b4 ,,another ,,example ,,of ,,protective ,,coloration ,,or ,,camouflage ,a shore scene showing ,trout in the pool almost invisible against their background4 ,the ,stone ,curlews1 both adult and young1 are very inconspicuous among the stones on the beach4 ,but why should it profit a spider to be like a bird-dropping8 ,perhaps because it thereby escapes attention2 but there is another possibility4 ,it seems that some butterflies1 allied to our ,blues1 are often attracted to excrementitious material1 and the spider ,dr4 ,forbes observed had actually caught its victim4 ,this is borne out by a recent observation by ,dr4 ,d4 ,g4 ,h4 ,carpenter1 who found a ,uganda bug closely resembling a bird-dropping on sand4 ,the bug actually settled down on a bird-dropping on sand1 and caught a blue butterfly which came to feed there6 ,some of the walking-stick insects1 belonging to the order of crickets and grasshoppers 7,orthoptera71 have their body elongated and narrow1 like a thin dry branch1 and they have a way of sticking out their limbs at abrupt and diverse angles1 which makes the resemblance to twigs very close indeed4 ,some of these quaint insects rest through the day and have the remarkable habit of putting themselves into a sort of kataleptic state4 ,many creatures turn stiff when they get a shock1 or pass suddenly into new surroundings1 like some of the sand-hoppers when we lay them on the palm of our hand2 but these twig-insects put themselves into this strange state4 ,the body is rocked from side to side for a short time1 and then it stiffens4 ,an advantage may be that even if they were surprised by a bird or a lizard1 they will not be able to betray themselves by even a tremor4 ,disguise is perfected by a remarkable habit1 a habit which leads us to think of a whole series of different ways of lying low and saying nothing which are often of life-preserving value4 ,the top end of the series is seen when a fox plays 'possum4 ,the leaf-butterfly ,kallima1 conspicuously coloured on its upper surface1 is like a withered leaf when it settles down and shows the under side of its wings4 ,here1 again1 there is precise form-resemblance1 for the nervures on the wings are like the mid-rib and side veins on a leaf1 and the touch of perfection is given in the presence of whitish spots which look exactly like the discolorations produced by lichens on leaves4 ,an old entomologist1 ,mr4 ,jenner ,weir1 confessed that he repeatedly pruned off a caterpillar on a bush in mistake for a superfluous twig1 for many brownish caterpillars fasten themselves by their posterior claspers and by an invisible thread of silk from their mouth1 and project from the branch at a twig-like angle4 ,an insect may be the very image of a sharp prickle or a piece of soft moss2 a spider may look precisely like a tiny knob on a branch or a fragment of lichen2 one of the sea-horses 7,phyllopteryx7 has frond-like tassels on various parts of its body1 so that it looks extraordinarily like the seaweeds among which it lives4 ,in a few cases1 e4g4 among spiders1 it has been shown that animals with a special protective resemblance to something else seek out a position where this resemblance tells1 and there is urgent need for observations bearing on this selection of environment4 #e ,mimicry in the ,true ,sense ,it sometimes happens that in one and the same place there are two groups of animals not very nearly related which are doubles of one another4 ,investigation shows that the members of the one group1 always in the majority1 are in some way specially protected1 e4g4 by being unpalatable4 ,they are the mimicked4 ,the members of the other group1 always in the minority1 have not got the special protection possessed by the others4 ,they are the mimickers1 though the resemblance is not1 of course1 associated with any conscious imitation4 ,the theory is that the mimickers live on the reputation of the mimicked4 ,if the mimicked are left alone by birds because they have a reputation for unpalatability1 or because they are able to sting1 the mimickers survive--although they are palatable and stingless4 ,they succeed1 not through any virtue of their own1 but because of their resemblance to the mimicked1 for whom they are mistaken4 ,there are many cases of mimetic resemblance so striking and so subtle that it seems impossible to doubt that the thing works2 there are other cases which are rather far-fetched1 and may be somewhat of the nature of coincidences4 ,thus although ,mr4 ,bates tells us that he repeatedly shot humming-bird moths in mistake for humming-birds1 we cannot think that this is a good illustration of mimicry4 ,what is needed for many cases is what is forthcoming for some1 namely1 experimental evidence1 e4g4 that the unpalatable mimicked butterflies are left in relative peace while similar palatable butterflies are persecuted4 ,it is also necessary to show that the mimickers do actually consort with the mimicked4 ,some beetles and moths are curiously wasplike1 which may be a great advantage2 the common drone-fly is superficially like a small bee2 some harmless snakes are very like poisonous species2 and ,mr4 ,wallace maintained that the powerful friar-birds of the ,far ,east are mimicked by the weak and timid orioles4 ,when the model is unpalatable or repulsive or dangerous1 and the mimic the reverse1 the mimicry is called ,batesian 7after ,mr4 ,bates71 but there is another kind of mimicry called ,mllerian 7after ,fritz ,mller7 where the mimic is also unpalatable4 ,the theory in this case is that the mimicry serves as mutual assurance1 the members of the ring getting on better by consistently presenting the same appearance1 which has come to mean to possible enemies a signal1 ,noli me tangere 7,leave me alone74 ,there is nothing out of the question in this theory1 but it requires to be taken in a critical spirit4 ,it leads us to think of warning colours1 which are the very opposite of the disguises which we are now studying4 ,some creatures like skunks1 magpies1 coral-snakes1 cobras1 brightly coloured tree-frogs are obtrusive rather than elusive1 and the theory of ,alfred ,russel ,wallace was that the flaunting conspicuousness serves as a useful advertisement1 impressing itself on the memories of inexperienced enemies1 who soon learn to leave creatures with warning colours alone4 ,in any case it is plain that an animal which is as safe as a wasp or a coral-snake can afford to wear any suit of clothes it likes4 ,illustration3 ,,dead-,,leaf ,,butterfly 7,kallima ,inachis7 ,,from ,,india ,it is conspicuous on its upper surface1 but when it settles down on a twig and shows the underside of its wings it is practically invisible4 ,the colouring of the under surface of the wings is like that of the withering leaf2 there are spots like fungas spots2 and the venation of the wings suggests the mid-rib and veins of the leaf4 ,a1 showing upper surface2 ,b1 showing under surface2 ,c1 a leaf4 ,illustration3 ,,protective ,,resemblance ,,between ,a ,,small ,,spider 7to the left7 ,,and ,,an ,,ant 7to the right7 ,as ants are much dreaded1 it is probably profitable to the spider to be like an ant4 ,it will be noted that the spider has four pairs of legs and no feelers1 whereas the ant has three pairs of legs and a pair of feelers4 ,illustration3 ,photo3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,,the ,,wasp ,,beetle1 ,,which1 ,,when ,,moving ,,amongst ,,the ,,branches ,,gives ,a ,,wasp-,,like ,,impression ,illustration3 ,,hermit-,,crab ,,with ,,partner ,,sea-,,anemones ,hermit-crabs hide their soft tail in the shell of a whelk or some other sea-snail4 ,but some hermit-crabs place sea-anemones on the back of their borrowed shell4 ,the sea-anemones mask the hermit-crab and their tentacles can sting4 ,as for the sea-anemones1 they are carried about by the hermit-crab and they get crumbs from its table4 ,this kind of mutually beneficial external partnership is called commensalism1 i4e4 eating at the same table4 ,illustration3 ,photo3 ,g4 ,p4 ,duffus4 ,,cuckoo-,,spit ,the white mass in the centre of the picture is a soapy froth which the young frog-hopper makes1 and within which it lies safe both from the heat of the sun and almost all enemies4 ,after sojourning for a time in the cuckoo-spit1 the frog-hopper becomes a winged insect4 ,masking ,the episode in ,scottish history called ,the ,walking ,wood of ,birnam1 when the advancing troop masked their approach by cutting down branches of the trees1 has had its counterpart in many countries4 ,but it is also enacted on the seashore4 ,there are many kinds of crabs that put on disguise with what looks like deliberateness4 ,the sand-crab takes a piece of seaweed1 nibbles at the end of it1 and then rubs it on the back of the carapace or on the legs so that it fixes to the bristles4 ,as the seaweed continues to live1 the crab soon has a little garden on its back which masks the crab's real nature4 ,it is most effective camouflaging1 but if the crab continues to grow it has to moult1 and that means losing the disguise4 ,it is then necessary to make a new one4 ,the crab must have on the shore something corresponding to a reputation2 that is to say1 other animals are clearly or dimly aware that the crab is a voracious and combative creature4 ,how useful to the crab1 then1 to have its appearance cloaked by a growth of innocent seaweed1 or sponge1 or zoophyte4 ,it will enable the creature to sneak upon its victims or to escape the attention of its own enemies4 ,if a narrow-beaked crab is cleaned artificially it will proceed to clothe itself again1 the habit has become instinctive2 and it must be admitted that while a particular crab prefers a particular kind of seaweed for its dress1 it will cover itself with unsuitable and even conspicuous material1 such as pieces of coloured cloth1 if nothing better is available4 ,the disguise differs greatly1 for one crab is masked by a brightly coloured and unpalatable sponge densely packed with flinty needles2 another cuts off the tunic of a sea-squirt and throws it over its shoulders2 another trundles about a bivalve shell4 ,the facts recall the familiar case of the hermit-crab1 which protects its soft tail by tucking it into the empty shell of a periwinkle or a whelk or some other sea-snail1 and that case leads on to the elaboration known as commensalism1 where the hermit-crab fixes sea-anemones on the back of its borrowed house4 ,the advantage here is beyond that of masking1 for the sea-anemone can sting1 which is a useful quality in a partner4 ,that this second advantage may become the main one is evident in several cases where the sea-anemone is borne1 just like a weapon1 on each of the crustacean's great claws4 ,moreover1 as the term commensalism 7eating at the same table7 suggests1 the partnership is mutually beneficial4 ,for the sea-anemone is carried about by the hermit-crab1 and it doubtless gets its share of crumbs from its partner's frequent meals4 ,there is a very interesting sidelight on the mutual benefit in the case of a dislodged sea-anemone which sulked for a while and then waited in a state of preparedness until a hermit-crab passed by and touched it4 ,whereupon the sea-anemone gripped and slowly worked itself up on to the back of the shell4 #f ,other ,kinds of ,elusiveness ,there are various kinds of disguise which are not readily classified4 ,a troop of cuttlefish swimming in the sea is a beautiful sight4 ,they keep time with one another in their movements and they show the same change of colour almost at the same moment4 ,they are suddenly attacked1 however1 by a small shark1 and then comes a simultaneous discharge of sepia from their ink-bags4 ,there are clouds of ink in the clear water1 for1 as ,professor ,hickson puts it1 the cuttlefishes have thrown dust in the eyes of their enemies4 ,one can see a newborn cuttlefish do this a minute after it escapes from the egg4 ,very beautiful is the way in which many birds1 like our common chaffinch1 disguise the outside of their nest with moss and lichen and other trifles felted together1 so that the cradle is as inconspicuous as possible4 ,there seems to be a touch of art in fastening pieces of spider's web on the outside of a nest6 ,how curious is the case of the tree-sloth of ,south ,american forests1 that walks slowly1 back downwards1 along the undersides of the branches1 hanging on by its long1 curved fingers and toes4 ,it is a nocturnal animal1 and therefore not in special danger1 but when resting during the day it is almost invisible because its shaggy hair is so like certain lichens and other growths on the branches4 ,but the protective resemblance is enhanced by the presence of a green alga1 which actually lives on the surface of the sloth's hairs--an alga like the one that makes tree-stems and gate-posts green in damp weather4 ,there is no commoner sight in the early summer than the cuckoo-spit on the grasses and herbage by the wayside4 ,it is conspicuous and yet it is said to be left severely alone by almost all creatures4 ,in some way it must be a disguise4 ,it is a sort of soap made by the activity of small frog-hoppers while they are still in the wingless larval stage1 before they begin to hop4 ,the insect pierces with its sharp mouth-parts the skin of the plant and sucks in sweet sap which by and by overflows over its body4 ,it works its body up and down many times1 whipping in air1 which mixes with the sugary sap1 reminding one of how whipped egg is made4 ,but along with the sugary sap and the air1 there is a little ferment from the food-canal and a little wax from glands on the skin1 and the four things mixed together make a kind of soap which lasts through the heat of the day4 ,there are many other modes of disguise besides those which we have been able to illustrate4 ,indeed1 the biggest fact is that there are so many1 for it brings us back to the idea that life is not an easy business4 ,it is true1 as ,walt ,whitman says1 that animals do not sweat and whine about their condition2 perhaps it is true1 as he says1 that not one is unhappy over the whole earth4 ,but there is another truth1 that this world is not a place for the unlit lamp and the ungirt loin1 and that when a creature has not armour or weapons or cleverness it must find some path of safety or go back4 ,one of these paths of safety is disguise1 and we have illustrated its evolution4 ,v ,,the ,,ascent ,,of ,,man ,,the ,,ascent ,,of ,,man #a ,no one thinks less of ,sir ,isaac ,newton because he was born as a very puny infant1 and no one should think less of the human race because it sprang from a stock of arboreal mammals4 ,there is no doubt as to man's apartness from the rest of creation when he is seen at his best--a little lower than the angels1 crowned with glory and honour4 ,what a piece of work is a man6 ,how noble in reason6 ,how infinite in faculty6 in form and moving how express and admirable6 in action how like an angel6 in apprehension so like a ,god4 ,nevertheless1 all the facts point to his affiliation to the stock to which monkeys and apes also belong4 ,not1 indeed1 that man is descended from any living ape or monkey2 it is rather that he and they have sprung from a common ancestry--are branches of the same stem4 ,this conclusion is so momentous that the reasons for accepting it must be carefully considered4 ,they were expounded with masterly skill in ,darwin's ,descent of ,man in #ahga--;a book which was but an expansion of a chapter in ,the ,origin of ,species 7#ahei74 ,anatomical ,proof of ,man's ,relationship with a ,simian ,stock ,the anatomical structure of man is closely similar to that of the anthropoid apes--the gorilla1 the orang1 the chimpanzee1 and the gibbon4 ,bone for bone1 muscle for muscle1 blood-vessel for blood-vessel1 nerve for nerve1 man and ape agree4 ,as the conservative anatomist1 ,sir ,richard ,owen1 said1 there is between them an all-pervading similitude of structure4 ,differences1 of course1 there are1 but they are not momentous except man's big brain1 which may be three times as heavy as that of a gorilla4 ,the average human brain weighs about #dh ounces2 the gorilla brain does not exceed #bj ounces at its best4 ,the capacity of the human skull is never less than #ee cubic inches2 in the orang and the chimpanzee the figures are #bf and #bg-a_/b respectively4 ,we are not suggesting that the most distinctive features of man are such as can be measured and weighed1 but it is important to notice that the main seat of his mental powers is physically far ahead of that of the highest of the anthropoid apes4 ,man alone is thoroughly erect after his infancy is past2 his head weighted with the heavy brain does not droop forward as the ape's does2 with his erect attitude there is perhaps to be associated his more highly developed vocal organs4 ,compared with an anthropoid ape1 man has a bigger and more upright forehead1 a less protrusive face region1 smaller cheek-bones and eyebrow ridges1 and more uniform teeth4 ,he is almost unique in having a chin4 ,man plants the sole of his foot flat on the ground1 his big toe is usually in a line with the other toes1 and he has a better heel than any monkey has4 ,the change in the shape of the head is to be thought of in connection with the enlargement of the brain1 and also in connection with the natural reduction of the muzzle region when the hand was freed from being an organ of support and became suited for grasping the food and conveying it to the mouth4 ,everyone is familiar in man's clothing with traces of the past persisting in the present1 though their use has long since disappeared4 ,there are buttons on the back of the waist of the morning coat to which the tails of the coat used to be fastened up1 and there are buttons1 occasionally with buttonholes1 at the wrist which were once useful in turning up the sleeve4 ,the same is true of man's body1 which is a veritable museum of relics4 ,some anatomists have made out a list of over a hundred of these vestigial structures1 and though this number is perhaps too high1 there is no doubt that the list is long4 ,in the inner upper corner of the eye there is a minute tag--but larger in some races than in others--which is the last dwindling relic of the third eyelid1 used in cleaning the front of the eye1 which most mammals possess in a large and well-developed form4 ,it can be easily seen1 for instance1 in ox and rabbit4 ,in man and in monkeys it has become a useless vestige1 and the dwindling must be associated with the fact that the upper eyelid is much more mobile in man and monkeys than in the other mammals4 ,the vestigial third eyelid in man is enough of itself to prove his relationship with the mammals1 but it is only one example out of many4 ,some of these are discussed in the article dealing with the human body1 but we may mention the vestigial muscles going to the ear-trumpet1 man's dwindling counterpart of the skin-twitching muscle which we see a horse use when he jerks a fly off his flanks1 and the short tail which in the seven-weeks-old human embryo is actually longer than the leg4 ,without committing ourselves to a belief in the entire uselessness of the vermiform appendix1 which grows out as a blind alley at the junction of the small intestine with the large1 we are safe in saying that it is a dwindling structure--the remains of a blind gut which must have been capacious and useful in ancestral forms4 ,in some mammals1 like the rabbit1 the blind gut is the bulkiest structure in the body1 and bears the vermiform appendix at its far end4 ,in man the appendix alone is left1 and it tells its tale4 ,it is interesting to notice that it is usually longer in the orang than in man1 and that it is very variable1 as dwindling structures tend to be4 ,one of the unpleasant expressions of this variability is the liability to go wrong3 hence appendicitis4 ,now these vestigial structures are1 as ,darwin said1 like the unsounded1 i4e4 functionless1 letters in words1 such as the o in leopard1 the b in doubt1 the g in reign4 ,they are of no use1 but they tell us something of the history of the words4 ,so do man's vestigial structures reveal his pedigree4 ,they must have an historical or evolutionary significance4 ,no other interpretation is possible4 ,illustration3 ,photo3 ,new ,york ,zoological ,park4 ,,chimpanzee1 ,,sitting ,the head shows certain facial characteristics1 e4g4 the beetling eyebrow ridges1 which were marked in the ,neanderthal race of men4 ,note the shortening of the thumb and the enlargement of the big toe4 ,illustration3 ,photo3 ,new ,york ,zoological ,park4 ,,chimpanzee1 ,,illustrating ,,walking ,,powers ,note the great length of the arms and the relative shortness of the legs4 ,illustration3 ,,surface ,,view ,,of ,,the ,,brains ,,of ,,man 7#a7 ,,and ,,chimpanzee 7#b7 ,the human brain is much larger and heavier1 more dome-like1 and with much more numerous and complicated convolutions4 ,illustration3 ,photo3 ,new ,york ,zoological ,park4 ,,side-,,view ,,of ,,chimpanzee',s ,,head4 7,compare with opposite picture47 ,illustration3 ,after a model by ,j4 ,h4 ,mc,gregor4 ,,profile ,,view ,,of ,,head ,,of ,,pithecanthropus1 ,,the ,,java ,,ape ,,man1 ,,reconstructed ,,from ,,the ,,skull-,,cap4 ,illustration3 ,,the ,,flipper ,,of ,a ,,whale ,,and ,,the ,,hand ,,of ,a ,,man ,in the bones and in their arrangement there is a close resemblance in the two cases1 yet the outcome is very different4 ,the multiplication of finger joints in the whale is a striking feature4 ,some men1 oftener than women1 show on the inturned margin of the ear-trumpet or pinna1 a little conical projection of great interest4 ,it is a vestige of the tip of the pointed ear of lower mammals1 and it is well named ,darwin's point4 ,it was he who described it as a surviving symbol of the stirring times and dangerous days of man's animal youth4 #b ,physiological ,proof of ,man's ,relationship with a ,simian ,stock ,the everyday functions of the human body are practically the same as those of the anthropoid ape1 and similar disorders are common to both4 ,monkeys may be infected with certain microbes to which man is peculiarly liable1 such as the bacillus of tuberculosis4 ,darwin showed that various human gestures and facial expressions have their counterparts in monkeys4 ,the sneering curl of the upper lip1 which tends to expose the canine tooth1 is a case in point1 though it may be seen in many other mammals besides monkeys--in dogs1 for instance1 which are at some considerable distance from the simian branch to which man's ancestors belonged4 ,when human blood is transfused into a dog or even a monkey1 it behaves in a hostile way to the other blood1 bringing about a destruction of the red blood corpuscles4 ,but when it is transfused into a chimpanzee there is an harmonious mingling of the two4 ,this is a very literal demonstration of man's blood-relationship with the higher apes4 ,but there is a finer form of the same experiment4 ,when the blood-fluid 7or serum7 of a rabbit1 which has had human blood injected into it1 is mingled with human blood1 it forms a cloudy precipitate4 ,it forms almost as marked a precipitate when it is mingled with the blood of an anthropoid ape4 ,but when it is mingled with the blood of an ,american monkey there is only a slight clouding after a considerable time and no actual precipitate4 ,when it is added to the blood of one of the distantly related half-monkeys or lemurs there is no reaction or only a very weak one4 ,with the blood of mammals off the simian line altogether there is no reaction at all4 ,thus1 as a distinguished anthropologist1 ,professor ,schwalbe1 has said3 ,we have in this not only a proof of the literal blood-relationship between man and apes1 but the degree of relationship with the different main groups of apes can be determined beyond possibility of mistake4 ,we can imagine how this modern line of experiment would have delighted ,darwin4 ,illustration3 ,,the ,,gorilla1 ,,inhabiting ,,the ,,forest ,,tract ,,of ,,the ,,gaboon ,,in ,,africa ,a full-grown individual stands about #e feet high4 ,the gait is shuffling1 the strength enormous1 the diet mainly vegetarian1 the temper rather ferocious4 ,embryological ,proof of ,man's ,relationship with a ,simian ,stock ,in his individual development1 man does in some measure climb up his own genealogical tree4 ,stages in the development of the body during its nine months of ante-natal life are closely similar to stages in the development of the anthropoid embryo4 ,babies born in times of famine or siege are sometimes1 as it were1 imperfectly finished1 and sometimes have what may be described as monkeyish features and ways4 ,a visit to an institution for the care of children who show arrested1 defective1 or disturbed development leaves one sadly impressed with the risk of slipping down the rungs of the steep ladder of evolution2 and even in adults the occurrence of serious nervous disturbance1 such as shell-shock1 is sometimes marked by relapses to animal ways4 ,it is a familiar fact that a normal baby reveals the past in its surprising power of grip1 and the careful experiments of ,dr4 ,louis ,robinson showed that an infant three weeks old could support its own weight for over two minutes1 holding on to a horizontal bar4 ,in many cases no sign of distress is evinced and no cry uttered1 until the grasp begins to give way4 ,this persistent grasp probably points back to the time when the baby had to cling to its arboreal mother4 ,the human tail is represented in the adult by a fusion of four or five vertebr forming the coccyx at the end of the backbone1 and is normally concealed beneath the flesh1 but in the embryo the tail projects freely and is movable4 ,up to the sixth month of the ante-natal sleep the body is covered1 all but the palms and soles1 with longish hair 7the lanugo71 which usually disappears before birth4 ,this is a stage in the normal development1 which is reasonably interpreted as a recapitulation of a stage in the racial evolution4 ,we draw this inference when we find that the unborn offspring of an almost hairless whale has an abundant representation of hairs2 we must draw a similar inference in the case of man4 ,it must be noticed that there are two serious errors in the careless statement often made that man in his development is at one time like a little fish1 at a later stage like a little reptile1 at a later stage like a little primitive mammal1 and eventually like a little monkey4 ,the first error here is that the comparison should be made with embryo-fish1 embryo-reptile1 embryo-mammal1 and so on4 ,it is in the making of the embryos that the great resemblance lies4 ,when the human embryo shows the laying down of the essential vertebrate characters1 such as brain and spinal cord1 then it is closely comparable to the embryo of a lower vertebrate at a similar stage4 ,when1 at a subsequent stage1 its heart1 for instance1 is about to become a four-chambered mammalian heart1 it is closely comparable to the heart of1 let us say1 a turtle1 which never becomes more than three-chambered4 ,the point is that in the making of the organs of the body1 say brain and kidneys1 the embryo of man pursues a path closely corresponding to the path followed by the embryos of other backboned animals lower in the scale1 but at successive stages it parts company with these1 with the lowest first and so on in succession4 ,a human embryo is never like a little reptile1 but the developing organs pass through stages which very closely resemble the corresponding stages in lower types which are in a general way ancestral4 ,the second error is that every kind of animal1 man included1 has from the first a certain individuality1 with peculiar characteristics which are all its own4 ,this is expressed by the somewhat difficult word specificity1 which just means that every species is itself and no other4 ,so in the development of the human embryo1 while there are close resemblances to the embryos of apes1 monkeys1 other mammals1 and even1 at earlier stages still1 to the embryos of reptile and fish1 it has to be admitted that we are dealing from first to last with a human embryo with peculiarities of its own4 ,illustration3 ,,darwin',s ,,point ,,on ,,human ,,ear 7,,marked ,d4,p47 ,it corresponds to the tip 7,t7 of the ear of an ordinary mammal1 as shown in the hare's ear below4 ,in the young orang the part corresponding to ,darwin's point is still at the tip of the ear4 ,illustration3 ,photo3 ,j4 ,russell ,sons4 ,,professor ,,sir ,,arthur ,,keith1 ,m4,d41 ,,ll4,d41 ,f4,r4,s4 ,conservator of the ,museum and ,hunterian ,professor1 ,royal ,college of ,surgeons of ,england4 ,one of the foremost living anthropologists and a leading authority on the antiquity of man4 ,illustration3 ,after ,t4 ,h4 ,huxley 7by permission of ,messrs4 ,macmillan74 ,,skeletons ,,of ,,the ,,gibbon1 ,,orang1 ,,chimpanzee1 ,,gorilla1 ,,man ,photographically reduced from diagrams of the natural size 7except that of the gibbon1 which was twice as large as nature7 drawn by ,mr4 ,waterhouse ,hawkins from specimens in the ,museum of the ,royal ,college of ,surgeons4 ,every human being begins his or her life as a single cell--a fertilised egg-cell1 a treasure-house of all the ages4 ,for in this living microcosm1 only a small fraction 7#a_/abe7 of an inch in diameter1 there is condensed--who can imagine how8--all the natural inheritance of man1 all the legacy of his parentage1 of his ancestry1 of his long pre-human pedigree4 ,darwin called the pinhead brain of the ant the most marvellous atom of matter in the world1 but the human ovum is more marvellous still4 ,it has more possibilities in it than any other thing1 yet without fertilisation it will die4 ,the fertilised ovum divides and redivides2 there results a ball of cells and a sack of cells2 gradually division of labour becomes the rule2 there is a laying down of nervous system and food-canal1 muscular system and skeleton1 and so proceeds what is learnedly called differentiation4 ,out of the apparently simple there emerges the obviously complex4 ,as ,aristotle observed more than two thousand years ago1 in the developing egg of the hen there soon appears the beating heart6 ,there is nothing like this in the non-living world4 ,but to return to the developing human embryo1 there is formed from and above the embryonic food-canal a skeletal rod1 which is called the notochord4 ,it thrills the imagination to learn that this is the only supporting axis that the lower orders of the backboned race possess4 ,the curious thing is that it does not become the backbone1 which is certainly one of the essential features of the vertebrate race4 ,the notochord is the supporting axis of the pioneer backboned animals1 namely the ,lancelets and the ,round-mouths 7,cyclostomes71 such as the ,lamprey4 ,they have no backbone in the strict sense1 but they have this notochord4 ,it can easily be dissected out in the lamprey--a long gristly rod4 ,it is surrounded by a sheath which becomes the backbone of most fishes and of all higher animals4 ,the interesting point is that although the notochord is only a vestige in the adults of these types1 it is never absent from the embryo4 ,it occurs even in man1 a short-lived relic of the primeval supporting axis of the body4 ,it comes and then it goes1 leaving only minute traces in the adult4 ,we cannot say that it is of any use1 unless it serves as a stimulus to the development of its substitute1 the backbone4 ,it is only a piece of preliminary scaffolding1 but there is no more eloquent instance of the living hand of the past4 ,one other instance must suffice of what ,professor ,lull calls the wonderful changes wrought in the dark of the ante-natal period1 which recapitulate in rapid abbreviation the great evolutionary steps which were taken by man's ancestors during the long night of the geological past4 ,on the sides of the neck of the human embryo there are four pairs of slits1 the visceral clefts1 openings from the beginning of the food-canals to the surface4 ,there is no doubt as to their significance4 ,they correspond to the gill-slits of fishes and tadpoles4 ,yet in reptiles1 birds1 and mammals they have no connection with breathing1 which is their function in fishes and amphibians4 ,indeed1 they are not of any use at all1 except that the first becomes the ,eustachian tube bringing the ear-passage into connection with the back of the mouth1 and that the second and third have to do with the development of a curious organ called the thymus gland4 ,persistent1 nevertheless1 these gill-slits are1 recalling even in man an aquatic ancestry of many millions of years ago4 ,when all these lines of evidence are considered1 they are seen to converge in the conclusion that man is derived from a simian stock of mammals4 ,he is solidary with the rest of creation4 ,to quote the closing words of ,darwin's ,descent of ,man3 ,we must1 however1 acknowledge1 as it seems to me1 that man with all his noble qualities1 with sympathy which feels for the most debased1 with benevolence which extends not only to other men but to the humblest living creature1 with his ,god-like intellect1 which has penetrated into the movements and constitution of the solar system--with all these exalted powers--man still bears in his bodily frame the indelible stamp of his lowly origin4 ,we should be clear that this view does not say more than that man sprang from a stock common to him and to the higher apes4 ,those who are repelled by the idea of man's derivation from a simian type should remember that the theory implies rather more than this1 namely1 that man is the outcome of a genealogy which has implied many millions of years of experimenting and sifting--the groaning and travailing of a whole creation4 ,speaking of man's mental qualities1 ,sir ,ray ,lankester says3 ,they justify the view that man forms a new departure in the gradual unfolding of ,nature's predestined plan4 ,in any case1 we have to try to square our views with the facts1 not the facts with our views1 and while one of the facts is that man stands unique and apart1 the other is that man is a scion of a progressive simian stock4 ,naturalists have exposed the pit whence man has been digged and the rock whence he has been hewn1 but it is surely a heartening encouragement to know that it is an ascent1 not a descent1 that we have behind us4 ,there is wisdom in ,pascal's maxim3 ,it is dangerous to show man too plainly how like he is to the animals1 without1 at the same time1 reminding him of his greatness4 ,it is equally unwise to impress him with his greatness and not with his lowliness4 ,it is worse to leave him in ignorance of both4 ,but it is very profitable to recognise the two facts4 #c ,man's ,pedigree ,the facts of anatomy1 physiology1 and embryology1 of which we have given illustrations1 all point to man's affiliation with the order of monkeys and apes4 ,to this order is given the name ,primates1 and our first and second question must be when and whence the ,primates began4 ,the rock record answers the first question3 the ,primates emerged about the dawn of the ,eocene era1 when grass was beginning to cover the earth with a garment4 ,their ancestral home was in the north in both hemispheres1 and then they migrated to ,africa1 ,india1 ,malay1 and ,south ,america4 ,in ,north ,america the ,primates soon became extinct1 and the same thing happened later on in ,europe4 ,in this case1 however1 there was a repeopling from the ,south 7in the ,lower ,miocene7 and then a second extinction 7in the ,upper ,pliocene7 before man appeared4 ,there is considerable evidence in support of ,professor ,r4 ,s4 ,lull's conclusion1 that in ,southern ,asia1 ,africa1 and ,south ,america the evolution of ,primates was continuous since the first great southward migration1 and there is1 of course1 an abundant modern representation of ,primates in these regions to-day4 ,as to the second question3 ,whence the ,primates sprang1 the answer must be more conjectural4 ,but it is a reasonable view that ,carnivores and ,primates sprang from a common ,insectivore stock1 the one order diverging towards flesh-eating and hunting on the ground1 the other order diverging towards fruit-eating and arboreal habits4 ,there is no doubt that the ,insectivores 7including shrews1 tree-shrews1 hedgehog1 mole1 and the like7 were very plastic and progressive mammals4 ,what followed in the course of ages was the divergence of branch after branch from the main ,primate stem4 ,first there diverged the ,south ,american monkeys on a line of their own1 and then the ,old ,world monkeys1 such as the macaques and baboons4 ,ages passed and the main stems gave off 7in the ,oligocene period7 the branch now represented by the small anthropoid apes--the gibbon and the siamang4 ,distinctly later there diverged the branch of the large anthropoid apes--the gorilla1 the chimpanzee1 and the orang4 ,that left a generalised humanoid stock separated off from all monkeys and apes1 and including the immediate precursors of man4 ,when this sifting out of a generalised humanoid stock took place remains very uncertain1 some authorities referring it to the ,miocene1 others to the early ,pliocene4 ,some would estimate its date at half a million years ago1 others at two millions6 ,the fact is that questions of chronology do not as yet admit of scientific statement4 ,illustration3 ,,side-,,view ,,of ,,skull ,,of ,,man 7,m7 ,,and ,,gorilla 7,g7 ,notice in the gorilla's skull the protrusive face region1 the big eyebrow ridges1 the much less domed cranial cavity1 the massive lower jaw1 the big canine teeth4 ,notice in man's skull the well-developed forehead1 the domed and spacious cranial cavity1 the absence of any snout1 the chin process1 and many other marked differences separating the human skull from the ape's4 ,illustration3 ,,the ,,skull ,,and ,,brain-,,case ,,of ,,pithecanthropus1 ,,the ,,java ,,ape-,,man1 ,,as ,,restored4 ,,by ,j4 ,h4 ,mc,g,r,e,g,o,r ,,from ,,the ,,scanty ,,remains ,the restoration shows the low1 retreating forehead and the prominent eyebrow ridges4 ,illustration3 ,,suggested ,,genealogical ,,tree ,,of ,,man ,,and ,,anthropoid ,,apes ,from ,sir ,arthur ,keith2 the lettering to the right has been slightly simplified4 ,we are on firmer1 though still uncertain1 ground when we state the probability that it was in ,asia that the precursors of man were separated off from monkeys and apes1 and began to be terrestrial rather than arboreal4 ,professor ,lull points out that ,asia is nearest to the oldest known human remains 7in ,java71 and that ,asia was the seat of the most ancient civilisations and the original home of many domesticated animals and cultivated plants4 ,the probability is that the cradle of the human race was in ,asia4 ,man's ,arboreal ,apprenticeship ,at this point it will be useful to consider man's arboreal apprenticeship and how he became a terrestrial journeyman4 ,professor ,wood ,jones has worked out very convincingly the thesis that man had no direct four-footed ancestry1 but that the ,primate stock to which he belongs was from its first divergence arboreal4 ,he maintains that the leading peculiarities of the immediate precursors of man were wrought out during a long arboreal apprenticeship4 ,the first great gain of arboreal life on bipedal erect lines 7not after the quadrupedal fashion of tree-sloths1 for instance7 was the emancipation of the hand4 ,the foot became the supporting and branch-gripping member1 and the hand was set free to reach upward1 to hang on by1 to seize the fruit1 to lift it and hold it to the mouth1 and to hug the young one close to the breast4 ,the hand thus set free has remained plastic--a generalised1 not a specialised member4 ,much has followed from man's handiness4 ,the arboreal life had many other consequences4 ,it led to an increased freedom of movement of the thigh on the hip joint1 to muscular arrangements for balancing the body on the leg1 to making the backbone a supple yet stable curved pillar1 to a strongly developed collar-bone which is only found well-formed when the fore-limb is used for more than support1 and to a power of opposing the thumb and the big toe to the other digits of the hand and foot--an obvious advantage for branch-gripping4 ,but the evolution of a free hand made it possible to dispense with protrusive lips and gripping teeth4 ,thus began the recession of the snout region1 the associated enlargement of the brain-box1 and the bringing of the eyes to the front4 ,the overcrowding of the teeth that followed the shortening of the snout was one of the taxes on progress of which modern man is often reminded in his dental troubles4 ,another acquisition associated with arboreal life was a greatly increased power of turning the head from side to side--a mobility very important in locating sounds and in exploring with the eyes4 ,furthermore1 there came about a flattening of the chest and of the back1 and the movements of the midriff 7or diaphragm7 came to count for more in respiration than the movements of the ribs4 ,the sense of touch came to be of more importance and the sense of smell of less2 the part of the brain receiving tidings from hand and eye and ear came to predominate over the part for receiving olfactory messages4 ,finally1 the need for carrying the infant about among the branches must surely have implied an intensification of family relations1 and favoured the evolution of gentleness4 ,illustration3 ,photo3 ,new ,york ,zoological ,park4 ,,the ,,gibbon ,,is ,,lower ,,than ,,the ,,other ,,apes ,,as ,,regards ,,its ,,skull ,,and ,,dentition1 ,,but ,,it ,,is ,,highly ,,specialized ,,in ,,the ,,adaptation ,,of ,,its ,,limbs ,,to ,,arboreal ,,life ,illustration3 ,photo3 ,new ,york ,zoological ,park4 ,,the ,,orang ,,has ,a ,,high ,,rounded ,,skull ,,and ,a ,,long ,,face ,illustration3 ,photo3 ,british ,museum 7,natural ,history74 ,,comparisons ,,of ,,the ,,skeletons ,,of ,,horse ,,and ,,man ,bone for bone1 the two skeletons are like one another1 though man is a biped and the horse a quadruped4 ,the backbone in man is mainly vertical2 the backbone in the horse is horizontal except in the neck and the tail4 ,man's skull is mainly in a line with the backbone2 the horse's at an angle to it4 ,both man and horse have seven neck vertebr4 ,man has five digits on each limb2 the horse has only one digit well developed on each limb4 ,it may be urged that we are attaching too much importance to the arboreal apprenticeship1 since many tree-loving animals remain to-day very innocent creatures4 ,to this reasonable objection there are two answers1 first that in its many acquisitions the arboreal evolution of the humanoid precursors of man prepared the way for the survival of a human type marked by a great step in brain-development2 and second that the passage from the humanoid to the human was probably associated with a return to mother earth4 ,according to ,professor ,lull1 to whose fine textbook1 ,organic ,evolution 7#aiag71 we are much indebted1 climatic conditions in ,asia in the ,miocene or early ,pliocene were such as to compel the descent of the pre-human ancestor from the trees1 a step which was absolutely essential to further human development4 ,continental elevation and consequent aridity led to a dwindling of the forests1 and forced the ape-man to come to earth4 ,and at the last arose the man4 ,according to ,lull1 the descent from the trees was associated with the assumption of a more erect posture1 with increased liberation and plasticity of the hand1 with becoming a hunter1 with experiments towards clothing and shelter1 with an exploring habit1 and with the beginning of communal life4 ,it is a plausible view that the transition from the humanoid to the human was effected by a discontinuous variation of considerable magnitude1 what is nowadays called a mutation1 and that it had mainly to do with the brain and the vocal organs4 ,but given the gains of the arboreal apprenticeship1 the stimulus of an enforced descent to terra firma1 and an evolving brain and voice1 we can recognise accessory factors which helped success to succeed4 ,perhaps the absence of great physical strength prompted reliance on wits2 the prolongation of infancy would help to educate the parents in gentleness2 the strengthening of the feeling of kinship would favour the evolution of family and social life--of which there are many anticipations at lower levels4 ,there is much truth in the saying3 ,man did not make society1 society made man4 ,a continuation of the story will deal with the emergence of the primitive types of man and the gradual ascent of the modern species4 #d ,tentative ,men ,so far the story has been that of the sifting out of a humanoid stock and of the transition to human kind1 from the ancestors of apes and men to the man-ape1 and from the man-ape to man4 ,it looks as if the sifting-out process had proceeded further1 for there were several human branches that did not lead on to the modern type of man4 #a4 ,the first of these is represented by the scanty fossil remains known as ,pithecanthropus erectus1 found in ,java in fossiliferous beds which date from the end of the ,pliocene or the beginning of the ,pleistocene era4 ,perhaps this means half a million years ago1 and the remains occurred along with those of some mammals which are now extinct4 ,unfortunately the remains of ,pithecanthropus the ,erect consisted only of a skull-cap1 a thigh-bone1 and two back teeth1 so it is not surprising that experts should differ considerably in their interpretation of what was found4 ,some have regarded the remains as those of a large gibbon1 others as those of a pre-human ape-man1 and others as those of a primitive man off the main line of ascent4 ,according to ,sir ,arthur ,keith1 ,pithecanthropus was a being human in stature1 human in gait1 human in all its parts1 save its brain4 ,the thigh-bone indicates a height of about #e feet #g inches1 one inch less than the average height of the men of to-day4 ,the skull-cap indicates a low1 flat forehead1 beetling brows1 and a capacity about two-thirds of the modern size4 ,the remains were found by ,dubois1 in #ahid1 in ,trinil in ,central ,java4 #b4 ,the next offshoot is represented by the ,heidelberg man 7,homo heidelbergensis71 discovered near ,heidelberg in #aijg by ,dr4 ,schoetensack4 ,but the remains consisted only of a lower jaw and its teeth4 ,along with this relic were bones of various mammals1 including some long since extinct in ,europe1 such as elephant1 rhinoceros1 bison1 and lion4 ,the circumstances indicate an age of perhaps #cjj1jjj years ago4 ,there were also very crude flint implements 7or eoliths74 ,but the teeth are human teeth1 and the jaw seems transitional between that of an anthropoid ape and that of man4 ,thus there was no chin4 ,according to most authorities the lower jaw from the ,heidelberg sand-pit must be regarded as a relic of a primitive type off the main line of human ascent4 ,illustration3 ,a ,,reconstruction ,,of ,,the ,,java ,,man 7,pithecanthropus erectus47 #c4 ,it was in all probability in the ,pliocene that there took origin the ,neanderthal species of man1 ,homo neanderthalensis1 first known from remains found in #ahef in the ,neanderthal ravine near ,dsseldorf4 ,according to some authorities ,neanderthal man was living in ,europe a quarter of a million years ago4 ,other specimens were afterwards found elsewhere1 e4g4 in ,belgium 7the men of ,spy71 in ,france1 in ,croatia1 and at ,gibraltar1 so that a good deal is known of ,neanderthal man4 ,he was a loose-limbed fellow1 short of stature and of slouching gait1 but a skilful artificer1 fashioning beautifully worked flints with a characteristic style4 ,he used fire2 he buried his dead reverently and furnished them with an outfit for a long journey2 and he had a big brain4 ,but he had great beetling1 ape-like eyebrow ridges and massive jaws1 and he showed simian characters swarming in the details of his structure4 ,in most of the points in which he differs from modern man he approaches the anthropoid apes1 and he must be regarded as a low type of man off the main line4 ,huxley regarded the ,neanderthal man as a low form of the modern type1 but expert opinion seems to agree rather with the view maintained in #ahfd by ,professor ,william ,king of ,galway1 that the ,neanderthal man represents a distinct species off the main line of ascent4 ,he disappeared with apparent suddenness 7like some aboriginal races to-day7 about the end of the ,fourth ,great ,ice ,age2 but there is evidence that before he ceased to be there had emerged a successor rather than a descendant--the modern man4 #d4 ,another offshoot from the main line is probably represented by the ,piltdown man1 found in ,sussex in #aiab4 ,the remains consisted of the walls of the skull1 which indicate a large brain1 and a high forehead without the beetling eyebrows of the ,neanderthal man and ,pithecanthropus4 ,the find included a tooth and part of a lower jaw1 but these perhaps belong to some ape1 for they are very discrepant4 ,the ,piltdown skull represents the most ancient human remains as yet found in ,britain1 and ,dr4 ,smith ,woodward's establishment of a separate genus ,eoanthropus expresses his conviction that the ,piltdown man was off the line of the evolution of the modern type4 ,if the tooth and piece of lower jaw belong to the ,piltdown skull1 then there was a remarkable combination of ape-like and human characters4 ,as regards the brain1 inferred from the skull-walls1 ,sir ,arthur ,keith says3 ,all the essential features of the brain of modern man are to be seen in the brain cast4 ,there are some which must be regarded as primitive4 ,there can be no doubt that it is built on exactly the same lines as our modern brains4 ,a few minor alterations would make it in all respects a modern brain4444 ,although our knowledge of the human brain is limited--there are large areas to which we can assign no definite function--we may rest assured that a brain which was shaped in a mould so similar to our own was one which responded to the outside world as ours does4 ,piltdown man saw1 heard1 felt1 thought1 and dreamt much as we do still4 ,and this was #aej1jjj years ago at a modern estimate1 and some would say half a million4 ,there is neither agreement nor certainty as to the antiquity of man1 except that the modern type was distinguishable from its collaterals hundreds of thousands of years ago4 ,the general impression left is very grand4 ,in remote antiquity the ,primate stem diverged from the other orders of mammals2 it sent forth its tentative branches1 and the result was a tangle of monkeys2 ages passed and the monkeys were left behind1 while the main stem1 still probing its way1 gave off the ,anthropoid apes1 both small and large4 ,but they too were left behind1 and the main line gave off other experiments--indications of which we know in ,java1 at ,heidelberg1 in the ,neanderthal1 and at ,piltdown4 ,none of these lasted or was made perfect4 ,they represent tentative men who had their day and ceased to be1 our predecessors rather than our ancestors4 ,still1 the main stem goes on evolving1 and who will be bold enough to say what fruit it has yet to bear6 ,illustration3 ,after a model by ,j4 ,h4 ,mc,gregor4 ,,profile ,,view ,,of ,,the ,,head ,,of ,,pithecanthropus1 ,,the ,,java ,,ape-,,man--,,an ,,early ,,offshoot ,,from ,,the ,,main ,,line ,,of ,,man',s ,,ascent ,the animal remains found along with the skull-cap1 thigh-bone1 and two teeth of ,pithecanthropus seem to indicate the lowest ,pleistocene period1 perhaps #ejj1jjj years ago4 ,illustration3 ,from the reconstruction by ,j4 ,h4 ,mc,gregor4 ,,piltdown ,,skull4 ,,the ,,dark ,,parts ,,only ,,are ,,preserved1 ,,namely ,,portions ,,of ,,the ,,cranial ,,walls ,,and ,,the ,,nasal ,,bones ,some authorities include a canine tooth and part of the lower jaw which were found close by4 ,the remains were found in #aiab in ,thames gravels in ,sussex1 and are usually regarded as vastly more ancient than those of ,neanderthal ,man4 ,it has been suggested that ,piltdown ,man lived #ajj1jjj to #aej1jjj years ago1 in the ,third ,interglacial period4 ,illustration3 ,reproduced by permission from ,osborn's ,men of the ,old ,stone ,age4 ,,sand-,,pit ,,at ,,mauer1 ,,near ,,heidelberg3 ,,discovery ,,site ,,of ,,the ,,jaw ,,of ,,heidelberg ,,man a-b4 ,newer loess1 either of ,third ,interglacial or of ,postglacial times4 b-c4 ,older loess 7sandy loess71 of the close of ,second ,interglacial times4 c-f4 ,the sands of ,mauer4 d-e4 ,an intermediate layer of clay4 ,the white cross 7,x7 indicates the spot at the base of the sands of ,mauer at which the jaw of ,heidelberg was discovered4 ,primitive ,men ,ancient skeletons of men of the modern type have been found in many places1 e4g4 ,combe ,capelle in ,dordogne1 ,galley ,hill in ,kent1 ,cro-,magnon in ,prigord1 ,mentone on the ,riviera2 and they are often referred to as ,cave-men or men of the ,early ,stone ,age4 ,they had large skulls1 high foreheads1 well-marked chins1 and other features such as modern man possesses4 ,they were true men at last--that is to say1 like ourselves6 ,the spirited pictures they made on the walls of caves in ,france and ,spain show artistic sense and skill4 ,well-finished statuettes representing nude female figures are also known4 ,the elaborate burial customs point to a belief in life after death4 ,they made stone implements--knives1 scrapers1 gravers1 and the like1 of the type known as ,palolithic1 and these show interesting gradations of skill and peculiarities of style4 ,the ,cave-men lived between the third and fourth ,ice ,ages1 along with cave-bear1 cave-lion1 cave-hyna1 mammoth1 woolly rhinoceros1 ,irish elk1 and other mammals now extinct--taking us back to #cj1jjj-ej1jjj years ago1 and many would say much more4 ,some of the big-brained skulls of these ,palolithic cave-men show not a single feature that could be called primitive4 ,they show teeth which in size and form are exactly the same as those of a thousand generations afterwards--and suffering from gumboil too6 ,there seems little doubt that these vigorous ,palolithic ,cave-men of ,europe were living for a while contemporaneously with the men of ,neanderthal1 and it is possible that they directly or indirectly hastened the disappearance of their more primitive collaterals4 ,curiously enough1 however1 they had not themselves adequate lasting power in ,europe1 for they seem for the most part to have dwindled away1 leaving perhaps stray present-day survivors in isolated districts4 ,the probability is that after their decline ,europe was repeopled by immigrants from ,asia4 ,it cannot be said that there is any inherent biological necessity for the decline of a vigorous race--many animal races go back for millions of years--but in mankind the historical fact is that a period of great racial vigour and success is often followed by a period of decline1 sometimes leading to practical disappearance as a definite race4 ,the causes of this waning remain very obscure--sometimes environmental1 sometimes constitutional1 sometimes competitive4 ,sometimes the introduction of a new parasite1 like the malaria organism1 may have been to blame4 ,after the ,ice ,ages had passed1 perhaps #be1jjj years ago1 the ,palolithic culture gave place to the ,neolithic4 ,the men who made rudely dressed but often beautiful stone implements were succeeded or replaced by men who made polished stone implements4 ,the earliest inhabitants of ,scotland were of this ,neolithic culture1 migrating from the ,continent when the ice-fields of the ,great ,glaciation had disappeared4 ,their remains are often associated with the ,fifty-foot ,beach which1 though now high and dry1 was the seashore in early ,neolithic days4 ,much is known about these men of the polished stones4 ,they were hunters1 fowlers1 and fishermen2 without domesticated animals or agriculture2 short folk1 two or three inches below the present standard2 living an active strenuous life4 ,similarly1 for the south1 ,sir ,arthur ,keith pictures for us a ,neolithic community at ,coldrum in ,kent1 dating from about #d1jjj years ago--a few ticks of the geological clock4 ,it consisted1 in this case1 of agricultural pioneers1 men with large heads and big brains1 about two inches shorter in stature than the modern ,british average 7#e ft4 #h in471 with better teeth and broader palates than men have in these days of soft food1 with beliefs concerning life and death similar to those that swayed their contemporaries in ,western and ,southern ,europe4 ,very interesting is the manipulative skill they showed on a large scale in erecting standing stones 7probably connected with calendar-keeping and with worship71 and on a small scale in making daring operations on the skull4 ,four thousand years ago is given as a probable date for that early community in ,kent1 but evidences of ,neolithic man occur in situations which demand a much greater antiquity--perhaps #cj1jjj years4 ,and man was not young then6 ,illustration3 ,,paintings ,,on ,,the ,,roof ,,of ,,the ,,altamira ,,cave ,,in ,,northern ,,spain1 ,,showing ,a ,,bison ,,above ,,and ,a ,,galloping ,,boar ,,below ,the artistic drawings1 over #b feet in length1 were made by the ,reindeer ,men or ,cromagnards in the time of the ,upper or ,post-,glacial ,pleistocene1 before the appearance of the ,neolithic men4 ,we must open one more chapter in the thrilling story of the ,ascent of ,man--the ,metal ,ages1 which are in a sense still continuing4 ,metals began to be used in the late ,polished ,stone 7,neolithic7 times1 for there were always overlappings4 ,copper came first1 ,bronze second1 and ,iron last4 ,the working of copper in the ,east has been traced back to the fourth millennium ,b4,c41 and there was also a very ancient ,copper ,age in the ,new ,world4 ,it need hardly be said that where copper is scarce1 as in ,britain1 we cannot expect to find much trace of a ,copper ,age4 ,the ores of different metals seem to have been smelted together in an experimental way by many prehistoric metallurgists1 and bronze was the alloy that rewarded the combination of tin with copper4 ,there is evidence of a more or less definite ,bronze ,age in ,egypt and ,babylonia1 ,greece and ,europe4 ,it is not clear why iron should not have been the earliest metal to be used by man1 but the ,iron ,age dates from about the middle of the second millennium ,b4,c4 ,from ,egypt the usage spread through the ,mediterranean region to ,north ,europe1 or it may have been that discoveries made in ,central ,europe1 so rich in iron-mines1 saturated southwards1 following for instance1 the route of the amber trade from the ,baltic4 ,compared with stone1 the metals afforded much greater possibilities of implements1 instruments1 and weapons1 and their discovery and usage had undoubtedly great influence on the ,ascent of ,man4 ,occasionally1 however1 on his descent4 ,retrospect ,looking backwards1 we discern the following stages3 7#a7 ,the setting apart of a ,primate stock1 marked off from other mammals by a tendency to big brains1 a free hand1 gregariousness1 and good-humoured talkativeness4 7#b7 ,the divergence of marmosets and ,new ,world monkeys and ,old ,world monkeys1 leaving a stock--an anthropoid stock--common to the present-day and extinct apes and to mankind4 7#c7 ,from this common stock the ,anthropoid apes diverged1 far from ignoble creatures1 and a humanoid stock was set apart4 7#d7 ,from the latter 7we follow ,sir ,arthur ,keith and other authorities7 there arose what may be called1 without disparagement1 tentative or experimental men1 indicated by ,pithecanthropus the ,erect1 the ,heidelberg man1 the ,neanderthalers1 and1 best of all1 the early men of the ,sussex ,weald--hinted at by the ,piltdown skull4 ,it matters little whether particular items are corroborated or disproved--e4g4 whether the ,heidelberg man came before or after the ,neanderthalers--the general trend of evolution remains clear4 7#e7 ,in any case1 the result was the evolution of ,homo sapiens1 the man we are--a quite different fellow from the ,neanderthaler4 7#f7 ,then arose various stocks of primitive men1 proving everything and holding fast to that which is good4 ,there were the ,palolithic peoples1 with rude stone implements1 a strong vigorous race1 but probably1 in most cases1 supplanted by fresh experiments4 ,these may have arisen as shoots from the growing point of the old race1 or as a fresh offshoot from more generalised members at a lower level4 ,this is the eternal possible victory alike of aristocracy and democracy4 7#g7 ,palolithic men were involved in the succession of four ,great ,ice ,ages or ,glaciations1 and it may be that the human race owes much to the alternation of hard times and easy times--glacial and interglacial4 ,when the ice-fields cleared off ,neolithic man had his innings4 7#h7 ,and we have closed the story1 in the meantime1 with the ,metal ,ages4 ,illustration3 ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,,piltdown ,,man1 ,,preceding ,,neanderthal ,,man1 ,,perhaps #ajj1jjj ,,to #aej1jjj ,,years ,,ago ,illustration3 ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,,the ,,neanderthal ,,man ,,of ,,la ,,chapelle-,,aux-,,saints ,the men of this race lived in ,europe from the ,third ,interglacial period through the ,fourth ,glacial4 ,they disappeared somewhat suddenly1 being replaced by the ,modern ,man type1 such as the ,cromagnards4 ,many regard the ,neanderthal ,men as a distinct species4 ,it seems not unfitting that we should at this point sound another note--that of the man of feeling4 ,it is clear in ,william ,james's words3 ,bone of our bone1 and flesh of our flesh1 are these half-brutish prehistoric brothers4 ,girdled about with the immense darkness of this mysterious universe even as we are1 they were born and died1 suffered and struggled4 ,given over to fearful crime and passion1 plunged in the blackest ignorance1 preyed upon by hideous and grotesque delusions1 yet steadfastly serving the profoundest of ideals in their fixed faith that existence in any form is better than non-existence1 they ever rescued triumphantly from the jaws of ever imminent destruction the torch of life which1 thanks to them1 now lights the world for us4 ,races of ,mankind ,given a variable stock spreading over diverse territory1 we expect to find it splitting up into varieties which may become steadied into races or incipient species4 ,thus we have races of hive-bees1 ,italians1 ,punics1 and so forth2 and thus there arose races of men4 ,certain types suited certain areas1 and periods of in-breeding tended to make the distinctive peculiarities of each incipient race well-defined and stable4 ,when the original peculiarities1 say1 of negro and ,mongol1 ,australian and ,caucasian1 arose as brusque variations or mutations1 then they would have great staying power from generation to generation4 ,they would not be readily swamped by intercrossing or averaged off4 ,peculiarities and changes of climate and surroundings1 not to speak of other change-producing factors1 would provoke new departures from age to age1 and so fresh racial ventures were made4 ,moreover1 the occurrence of out-breeding when two races met1 in peace or in war1 would certainly serve to induce fresh starts4 ,very important in the evolution of human races must have been the alternating occurrence of periods of in-breeding 7endogamy71 tending to stability and sameness1 and periods of out-breeding 7exogamy71 tending to changefulness and diversity4 ,thus we may distinguish several more or less clearly defined primitive races of mankind--notably the ,african1 the ,australian1 the ,mongolian1 and the ,caucasian4 ,the woolly-haired ,african race includes the negroes and the very primitive bushmen4 ,the wavy-to curly-haired ,australian race includes the ,jungle ,tribes of the ,deccan1 the ,vedda of ,ceylon1 the ,jungle ,folk or ,semang1 and the natives of unsettled parts of ,australia--all sometimes slumped together as ,pre-,dravidians4 ,the straight-haired ,mongols include those of ,tibet1 ,indo-,china1 ,china1 and ,formosa1 those of many oceanic islands1 and of the north from ,japan to ,lapland4 ,the ,caucasians include ,mediterraneans1 ,semites1 ,nordics1 ,afghans1 ,alpines1 and many more4 ,there are very few corners of knowledge more difficult than that of the ,races of ,men1 the chief reason being that there has been so much movement and migration in the course of the ages4 ,one physical type has mingled with another1 inducing strange amalgams and novelties4 ,if we start with what might be called zoological races or strains differing1 for instance1 in their hair 7woolly-haired ,africans1 straight-haired ,mongols1 curly-or wavy-haired ,pre-,dravidians and ,caucasians71 we find these replaced by peoples who are mixtures of various races1 brethren by civilisation more than by blood4 ,as ,professor ,flinders ,petrie has said1 the only meaning the term race now can have is that of a group of human beings whose type has been unified by their rate of assimilation exceeding the rate of change produced by the infiltration of foreign elements4 ,it is probable1 however1 that the progress of precise anthropology will make it possible to distinguish the various racial strains that make up any people4 ,for the human sense of race is so strong that it convinces us of reality even when scientific definition is impossible4 ,it was this the ,british sailor expressed in his answer to the question ,what is a ,dago8 ,dagoes1 he replied1 is anything wot isn't our sort of chaps4 ,illustration3 ,,restoration ,,by ,a4 ,,forestier ,,of ,,the ,,rhodesian ,,man ,,whose ,,skull ,,was ,,discovered ,,in #aiba ,attention may be drawn to the beetling eyebrow ridges1 the projecting upper lip1 the large eye-sockets1 the well-poised head1 the strong shoulders4 ,the squatting figure is crushing seeds with a stone1 and a crusher is lying on the rock to his right4 ,illustration3 ,,restoration ,,by ,a4 ,,forestier ,,of ,,the ,,rhodesian ,,man ,,whose ,,skull ,,was ,,discovered ,,in #aiba ,the figure in the foreground1 holding a staff1 shows the erect attitude and the straight legs4 ,his left hand holds a flint implement4 ,on the left1 behind the sitting figure1 is seen the entrance to the cave4 ,this new ,rhodesian cave-man may be regarded as a southern representative of a ,neanderthal race1 or as an extinct type intermediate between the ,neanderthal ,men and the ,modern ,man type4 ,steps in ,human ,evolution ,real men arose1 we believe1 by variational uplifts of considerable magnitude which led to big and complex brains and to the power of reasoned discourse4 ,in some other lines of mammalian evolution there were from time to time great advances in the size and complexity of the brain1 as is clear1 for instance1 in the case of horses and elephants4 ,the same is true of birds as compared with reptiles1 and everyone recognises the high level of excellence that has been attained by their vocal powers4 ,how these great cerebral advances came about we do not know1 but it has been one of the main trends of animal evolution to improve the nervous system4 ,two suggestions may be made4 ,first1 the prolongation of the period of ante-natal life1 in intimate physiological partnership with the mother1 may have made it practicable to start the higher mammal with a much better brain than in the lower orders1 like ,insectivores and ,rodents1 and still more ,marsupials1 where the period before birth 7gestation7 is short4 ,second1 we know that the individual development of the brain is profoundly influenced by the internal secretions of certain ductless glands notably the thyroid4 ,when this organ is not functioning properly the child's brain development is arrested4 ,it may be that increased production of certain hormones--itself1 of course1 to be accounted for--may have stimulated brain development in man's remote ancestors4 ,given variability along the line of better brains and given a process of discriminate sifting which would consistently offer rewards to alertness and foresight1 to kin-sympathy and parental care1 there seems no great difficulty in imagining how ,man would evolve4 ,we must not think of an ,aristotle or a ,newton except as fine results which justify all the groaning and travailing2 we must think of average men1 of primitive peoples to-day1 and of our forbears long ago4 ,we must remember how much of man's advance is dependent on the external registration of the social heritage1 not on the slowly changing natural inheritance4 ,looking backwards it is impossible1 we think1 to fail to recognise progress4 ,there is a ring of truth in the fine description schylus gave of primitive men that-- first1 beholding they beheld in vain1 and1 hearing1 heard not1 but1 like shapes in dreams1 mixed all things wildly down the tedious time1 nor knew to build a house against the sun with wicketed sides1 nor any woodwork knew1 but lived like silly ants1 beneath the ground1 in hollow caves unsunned4 ,there came to them no steadfast sign of winter1 nor of spring flower-perfumed1 nor of summer full of fruit1 but blindly and lawlessly they did all things4 ,contrast this picture with the position of man to-day4 ,he has mastered the forces of ,nature and is learning to use their resources more and more economically2 he has harnessed electricity to his chariot and he has made the ether carry his messages4 ,he tapped supplies of material which seemed for centuries unavailable1 having learned1 for instance1 how to capture and utilise the free nitrogen of the air4 ,with his telegraph and wireless he has annihilated distance1 and he has added to his navigable kingdom the depths of the sea and the heights of the air4 ,he has conquered one disease after another1 and the young science of heredity is showing him how to control in his domesticated animals and cultivated plants the nature of the generations yet unborn4 ,with all his faults he has his ethical face set in the right direction4 ,the main line of movement is towards the fuller embodiment of the true1 the beautiful1 and the good in healthy lives which are increasingly a satisfaction in themselves4 ,illustration3 ,photo3 ,british ,museum 7,natural ,history74 ,,side-,,view ,,of ,a ,,prehistoric ,,human ,,skull ,,discovered ,,in #aiba ,,in ,,broken ,,hill ,,cave1 ,,northern ,,rhodesia ,very striking are the prominent eyebrow ridges and the broad massive face4 ,the skull looks less domed than that of modern man1 but its cranial capacity is far above the lowest human limit4 ,the teeth are interesting in showing marked rotting or caries1 hitherto unknown in prehistoric skulls4 ,in all probability the ,rhodesian man was an ,african representative of the extinct ,neanderthal species hitherto known only from ,europe4 ,illustration3 ,after the restoration modelled by ,j4 ,h4 ,mc,gregor4 ,a ,,cromagnon ,,man ,,or ,,cromagnard1 ,,representative ,,of ,a ,,strong ,,artistic ,,race ,,living ,,in ,,the ,,south ,,of ,,france ,,in ,,the ,,upper ,,pleistocene1 ,,perhaps #be1jjj ,,years ,,ago ,they seemed to have lived for a while contemporaneously with the ,neanderthal ,men1 and there may have been interbreeding4 ,some ,cromagnards probably survive1 but the race as a whole declined1 and there was repopulation of ,europe from the ,east4 ,illustration3 ,reproduced by permission from ,osborn's ,men of the ,old ,stone ,age4 ,,photograph ,,showing ,a ,,narrow ,,passage ,,in ,,the ,,cavern ,,of ,,font-,,de-,,gaume ,,on ,,the ,,beune ,throughout the cavern the walls are crowded with engravings2 on the left wall1 shown in the photograph1 are two painted bison4 ,in the great gallery there may be found not less than eighty figures--bison1 reindeer1 and mammoths4 ,a specimen of the last is reproduced below4 ,illustration3 ,a ,,mammoth ,,drawn ,,on ,,the ,,wall ,,of ,,the ,,font-,,de-,,gaume ,,cavern ,the mammoth age was in the ,middle ,pleistocene1 while ,neanderthal ,men still flourished1 probably far over #cj1jjj years ago4 ,illustration3 ,a ,,grazing ,,bison1 ,,delicately ,,and ,,carefully ,,drawn1 ,,engraved ,,on ,a ,,wall ,,of ,,the ,,altamira ,,cave1 ,,northern ,,spain ,this was the work of a ,reindeer ,man or ,cromagnard1 in the ,upper or ,post-,glacial ,pleistocene1 perhaps #be1jjj years ago4 ,firelight must have been used in making these cave drawings and engravings4 ,factors in ,human ,progress ,many1 we believe1 were the gains that rewarded the arboreal apprenticeship of man's ancestors4 ,many1 likewise1 were the results of leaving the trees and coming down to the solid earth--a transition which marked the emergence of more than tentative men4 ,what great steps followed8 ,some of the greatest were--the working out of a spoken language and of external methods of registration2 the invention of tools2 the discovery of the use of fire2 the utilisation of iron and other metals2 the taming of wild animals such as dog and sheep1 horses and cattle2 the cultivation of wild plants such as wheat and rice2 and the irrigation of fields4 ,all through the ages necessity has been the mother of invention and curiosity its father2 but perhaps we miss the heart of the matter if we forget the importance of some leisure time--wherein to observe and think4 ,if our earth had been so clouded that the stars were hidden from men's eyes the whole history of our race would have been different4 ,for it was through his leisure-time observations of the stars that early man discovered the regularity of the year and got his fundamental impressions of the order of ,nature--on which all his science is founded4 ,if we are to think clearly of the factors of human progress we must recall the three great biological ideas--the living organism1 its environment1 and its functioning4 ,for man these mean 7#a7 the living creature1 the outcome of parents and ancestors1 a fresh expression of a bodily and mental inheritance2 7#b7 the surroundings1 including climate and soil1 the plants and animals these allow2 and 7#c7 the activities of all sorts1 occupations and habits1 all the actions and reactions between man and his milieu4 ,in short1 we have to deal with ,,folk1 ,,place1 ,,work2 the ,famille1 ,lieu1 ,travail of the ,le,play school4 ,as to ,,folk1 human progress depends on intrinsic racial qualities--notably health and vigour of body1 clearness and alertness of mind1 and an indispensable sociality4 ,the most powerful factors in the world are clear ideas in the minds of energetic men of good will4 ,the differences in bodily and mental health which mark races1 and stocks within a people1 just as they mark individuals1 are themselves traceable back to germinal variations or mutations1 and to the kind of sifting to which the race or stock has been subjected4 ,easygoing conditions are not only without stimulus to new departures1 they are without the sifting which progress demands4 ,as to ,,place1 it is plain that different areas differ greatly in their material resources and in the availability of these4 ,moreover1 even when abundant material resources are present1 they will not make for much progress unless the climate is such that they can be readily utilised4 ,indeed1 climate has been one of the great factors in civilisation1 here stimulating and there depressing energy1 in one place favouring certain plants and animals important to man1 in another place preventing their presence4 ,moreover1 climate has slowly changed from age to age4 ,as to ,,work1 the form of a civilisation is in some measure dependent on the primary occupations1 whether hunting or fishing1 farming or shepherding2 and on the industries of later ages which have a profound moulding effect on the individual at least4 ,we cannot1 however1 say more than that the factors of human progress have always had these three aspects1 ,folk1 ,place1 ,work1 and that if progress is to continue on stable lines it must always recognise the essential correlation of fitter folk in body and mind3 improved habits and functions1 alike in work and leisure2 and bettered surroundings in the widest and deepest sense4 ,,bibliography ,,darwin1 ,,charles1 ,descent of ,man4 ,,haddon1 ,a4 ,c41 ,races of ,men4 ,,haddon1 ,a4 ,c41 ,history of ,anthropology4 ,,keane1 ,a4 ,h41 ,man ,past and ,present4 ,,keith1 ,,arthur1 ,antiquity of ,man4 ,,lull1 ,r4 ,s41 ,organic ,evolution4 ,,mccabe1 ,,joseph1 ,evolution of ,civilization4 ,,marett1 ,r4 ,r41 ,anthropology 7,home ,university ,library74 ,,osborn1 ,h4 ,f41 ,men of the ,early ,stone ,age4 ,,sollas1 ,w4 ,j41 ,ancient ,hunters and their ,modern ,representatives4 ,,tylor1 ,e4 ,b41 ,anthropology and ,primitive ,culture4 ,,vi ,,evolution ,,going ,,on ,,evolution ,,going ,,on ,evolution1 as we have seen in a previous chapter1 is another word for race-history4 ,it means the ceaseless process of ,becoming1 linking generation to generation of living creatures4 ,the ,doctrine of ,evolution states the fact that the present is the child of the past and the parent of the future4 ,it comes to this1 that the living plants and animals we know are descended from ancestors on the whole simpler1 and these from others likewise simpler1 and so on1 back and back--till we reach the first living creatures1 of which1 unfortunately1 we know nothing4 ,evolution is a process of racial change in a definite direction1 whereby new forms arise1 take root1 and flourish1 alongside of or in the place of their ancestors1 which were in most cases rather simpler in structure and behaviour4 ,the rock-record1 which cannot be wrong1 though we may read it wrongly1 shows clearly that there was once a time in the history of the ,earth when the only backboned animals were ,fishes4 ,ages passed1 and there evolved ,amphibians1 with fingers and toes1 scrambling on to dry land4 ,ages passed1 and there evolved ,reptiles1 in bewildering profusion4 ,there were fish-lizards and sea-serpents1 terrestrial dragons and flying dragons1 a prolific and varied stock4 ,from the terrestrial ,dinosaurs it seems that ,birds and ,mammals arose4 ,in succeeding ages there evolved all the variety of ,birds and all the variety of ,mammals4 ,until at last arose the ,man4 ,the question is whether similar processes of evolution are still going on4 ,we are so keenly aware of rapid changes in mankind1 though these concern the social heritage much more than the flesh-and-blood natural inheritance1 that we find no difficulty in the idea that evolution is going on in mankind4 ,we know the contrast between modern man and primitive man1 and we are convinced that in the past1 at least1 progress has been a reality4 ,that degeneration may set in is an awful possibility--involution rather than evolution--but even if going back became for a time the rule1 we cannot give up the hope that the race would recover itself and begin afresh to go forward4 ,for although there have been retrogressions in the history of life1 continued through unthinkably long ages1 and although great races1 the ,flying ,dragons for instance1 have become utterly extinct1 leaving no successors whatsoever1 we feel sure that there has been on the whole a progress towards nobler1 more masterful1 more emancipated1 more intelligent1 and better forms of life--a progress towards what mankind at its best has always regarded as best1 i4e4 affording most enduring satisfaction4 ,so we think of evolution going on in mankind1 evolution chequered by involution1 but on the whole progressive evolution4 ,evolutionary ,prospect for ,man ,it is not likely that man's body will admit of great change1 but there is room for some improvement1 e4g4 in the superfluous length of the food-canal and the overcrowding of the teeth4 ,it is likely1 however1 that there will be constitutional changes1 e4g4 of prolonged youthfulness1 a higher standard of healthfulness1 and a greater resistance to disease4 ,it is justifiable to look forward to great improvements in intelligence and in control4 ,the potentialities of the human brain1 as it is1 are far from being utilised to the full1 and new departures of promise are of continual occurrence4 ,what is of great importance is that the new departures or variations which emerge in fine children should be fostered1 not nipped in the bud1 by the social environment1 education included4 ,the evolutionary prospect for man is promising4 ,illustration3 ,,photograph ,,of ,a ,,median ,,section ,,through ,,the ,,shell ,,of ,,the ,,pearly ,,nautilus ,it is only the large terminal chamber that is occupied by the animal4 ,illustration3 ,,photograph ,,of ,,the ,,entire ,,shell ,,of ,,the ,,pearly ,,nautilus ,the headquarters of the ,nautilus are in the ,indian and ,pacific ,oceans4 ,they sometimes swim at the surface of the sea1 but they usually creep slowly about on the floor of comparatively shallow water4 ,illustration3 ,,nautilus ,a section through the ,pearly ,nautilus1 ,nautilus pompilius1 common from ,malay to ,fiji4 ,the shell is often about #i inches long4 ,the animal lives in the last chamber only1 but a tube 7,s7 runs through the empty chambers1 perforating the partitions 7,,se74 ,the bulk of the animal is marked ,,vm2 the eye is shown at ,e2 a hood is marked ,h2 round the mouth there are numerous lobes 7,l7 bearing protrusible tentacles1 some of which are shown4 ,when the animal is swimming near the surface the tentacles radiate out in all directions1 and it has been described as a shell with something like a cauliflower sticking out of it4 ,the ,pearly ,nautilus is a good example of a conservative type1 for it began in the ,triassic ,era4 ,but the family of ,nautiloids to which it belongs illustrates very vividly what is meant by a dwindling race4 ,the ,nautiloids began in the ,cambrian1 reached their golden age in the ,silurian1 and began to decline markedly in the ,carboniferous4 ,there are #b1ejj extinct or fossil species of ,nautiloids1 and only #d living to-day4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge4 ,,shoebill ,a bird of a savage nature1 never mixing with other marsh birds4 ,according to ,dr4 ,chalmers ,mitchell1 it shows affinities to herons1 storks1 pelicans1 and gannets1 and is a representative of a type equal to both herons and storks and falling between the two4 ,but it is very important to realise that among plant and animals likewise1 ,evolution is going on4 ,the ,fountain of ,change3 ,variability ,on an ordinary big clock we do not readily see that even the minute hand is moving1 and if the clock struck only once in a hundred years we can conceive of people arguing whether the hands did really move at all4 ,so it often is with the changes that go on from generation to generation in living creatures4 ,the flux is so slow1 like the flowing of a glacier1 that some people fail to be convinced of its reality4 ,and it must1 of course1 be admitted that some kinds of living creatures1 like the ,lamp-shell ,ligula or the ,pearly ,nautilus1 hardly change from age to age1 whereas others1 like some of the birds and butterflies1 are always giving rise to something new4 ,the ,evening ,primrose among plants1 and the ,fruit-fly1 ,drosophila1 among animals1 are well-known examples of organisms which are at present in a sporting or mutating mood4 ,certain dark varieties of moth1 e4g4 of the ,peppered ,moth1 are taking the place of the paler type in some parts of ,england1 and the same is true of some dark forms of ,sugar-bird in the ,west ,indian islands4 ,very important is the piece of statistics worked out by ,professor ,r4 ,c4 ,punnett1 that if a population contains 4#jja per cent of a new variety1 and if that variety has even a #e per cent selection advantage over the original form1 the latter will almost completely disappear in less than a hundred generations4 ,this sort of thing has been going on all over the world for untold ages1 and the face of animate nature has consequently changed4 ,we are impressed by striking novelties that crop up--a clever dwarf1 a musical genius1 a calculating boy1 a cock with a #aj ft4 tail1 a wonder-horse with a mane reaching to the ground1 a tailless cat1 a white blackbird1 a copper beech1 a ,greater ,celandine with much cut up leaves2 but this sort of mutation is common1 and smaller1 less brusque variations are commoner still4 ,they form the raw materials of possible evolution4 ,we are actually standing before an apparently inexhaustible fountain of change4 ,this is evolution going on4 ,the ,sporting ,jellyfish ,it is of interest to consider a common animal like the jellyfish ,aurelia4 ,it is admirably suited for a leisurely life in the open sea1 where it swims about by contracting its saucer-shaped body1 thus driving water out from its concavity4 ,by means of millions of stinging cells on its four frilled lips and on its marginal tentacles it is able to paralyse and lasso minute crustaceans and the like1 which it then wafts into its mouth4 ,it has a very eventful life-history1 for it has in its early youth to pass through a fixed stage1 fastened to rock or seaweed1 but it is a successful animal1 well suited for its habitat1 and practically cosmopolitan in its distribution4 ,it is certainly an old-established creature4 ,yet it is very variable in colour and in size1 and even in internal structure4 ,very often it is the size of a saucer or a soup-plate1 but giants over two feet in diameter are well known4 ,much more important1 however1 than variation in colour and size are the inborn changes in structure4 ,normally a jellyfish has its parts in four or multiples of four4 ,thus it has four frilled lips1 four tufts of digestive filaments in its stomach1 and four brightly coloured reproductive organs4 ,it has eight sense-organs round the margin of its disc1 eight branched and eight unbranched radial canals running from the central stomach to a canal round the circumference4 ,the point of giving these details is just this1 that every now and then we find a jellyfish with its parts in sixes1 fives1 or threes1 and with a multitude of minor idiosyncrasies4 ,even in the well-established jellyfish there is a fountain of change4 #a ,evolution of ,plants ,it is instructive to look at the various kinds of cabbages1 such as cauliflower and ,brussels sprouts1 kale and curly greens1 and remember that they are all scions of the not very promising wild cabbage found on our shores4 ,and are not all the aristocrat apple-trees of our orchards descended from the plebeian crab-apple of the roadside8 ,we know far too little about the precise origin of our cultivated plants1 but there is no doubt that after man got a hold of them he took advantage of their variability to establish race after race1 say1 of rose and chrysanthemum1 of potato and cereal4 ,the evolution of cultivated plants is continuing before our eyes1 and the creations of ,mr4 ,luther ,burbank1 such as the stoneless plum and the primus berry1 the spineless cactus and the ,shasta daisy1 are merely striking instances of what is always going on4 ,there is reason to believe that the domestic dog has risen three times1 from three distinct ancestors--a wolf1 a jackal1 and a coyote4 ,so a multiple pedigree must be allowed for in the case of the dog1 and the same is true in regard to some other domesticated animals4 ,but the big fact is the great variety of breeds that man has been able to fix1 after he once got started with a domesticated type4 ,there are over #bjj well-marked breeds of domestic pigeons1 and there is very strong evidence that all are descended from the wild rock-dove1 just as the numerous kinds of poultry are descended from the jungle-fowl of some parts of ,india and the ,malay ,islands4 ,even more familiar is the way in which man has1 so to speak1 unpacked the complex fur of the wild rabbit1 and established all the numerous colour-varieties which we see among domestic rabbits4 ,and apart from colour-varieties there are long-haired ,angoras and quaint lop-eared forms1 and many more besides4 ,all this points to evolution going on4 ,the ,romance of the ,wheat ,it is well-known that ,neolithic man grew wheat1 and some authorities have put the date of the first wheat harvest at between fifteen thousand and ten thousand years ago4 ,the ancient civilisations of ,babylonia1 ,egypt1 ,crete1 ,greece1 and ,rome were largely based on wheat1 and it is highly probable that the first great wheatfields were in the fertile land between the ,tigris and the ,euphrates4 ,the oldest ,egyptian tombs that contain wheat1 which1 by the way1 never germinates after its millennia of rest1 belong to the ,first ,dynasty1 and are about six thousand years old4 ,but there must have been a long history of wheat before that4 ,now it is a very interesting fact that the almost certain ancestor of the cultivated wheat is at present living on the arid and rocky slopes of ,mount ,hermon4 ,it is called ,triticum hermonis1 and it is varying notably to-day1 as it did long ago when it gave rise to the emmer1 which was cultivated in the ,neolithic ,age and is the ancestor of all our ordinary wheats4 ,we must think of ,neolithic man noticing the big seeds of this ,hermon grass1 gathering some of the heads1 breaking the brittle spikelet-bearing axis in his fingers1 knocking off the rough awns or bruising the spikelets in his hand till the glumes or chaff separated off and could be blown away1 chewing a mouthful of the seeds--and resolving to sow and sow again4 ,that was the beginning of a long story1 in the course of which man took advantage of the numerous variations that cropped up in this sporting stock and established one successful race after another on his fields4 ,virgil refers in the ,georgics to the gathering of the largest and fullest ears of wheat in order to get good seed for another sowing1 but it was not till the first quarter of the nineteenth century that the great step was taken1 by men like ,patrick ,sheriff of ,haddington1 of deliberately selecting individual ears of great excellence and segregating their progeny from mingling with mediocre stock4 ,this is the method which has been followed with remarkable success in modern times4 ,one of the factors that assisted the ,allies in overcoming the food crisis in the darkest period of the war was the virtue of ,marquis ,wheat1 a very prolific1 early ripening1 hard red spring wheat with excellent milling and baking qualities4 ,it is now the dominant spring wheat in ,canada and the ,united ,states1 and it has enormously increased the real wealth of the world in the last ten years 7#aiba74 ,now our point is simply that this ,marquis ,wheat is a fine example of evolution going on4 ,in #aiag upwards of #bej1jjj1jjj bushels of this wheat were raised in ,north ,america1 and in #aiah upwards of #cjj1jjj1jjj bushels2 yet the whole originated from a single grain planted in an experimental plot at ,ottawa by ,dr4 ,charles ,e4 ,saunders so recently as the spring of #aijc4 ,illustration3 ,,the ,,walking-,,fish ,,or ,,mud-,,skipper 7,,periophthalmus71 ,,common ,,at ,,the ,,mouths ,,of ,,rivers ,,in ,,tropical ,,africa1 ,,asia1 ,,and ,,north-,,west ,,australia ,it skips about by means of its strong pectoral fins on the mud-flats2 it jumps from stone to stone hunting small shore-animals2 it climbs up the roots of the mangrove-trees4 ,the close-set eyes protrude greatly and are very mobile4 ,the tail seems to help in respiration4 ,illustration3 ,photo3 ,the ,times4 ,,the ,,australian ,,more-,,pork ,,or ,,podargus ,a bird with a frog-like mouth1 allied to the ,british ,nightjar4 ,now in the ,london ,zoological ,gardens4 ,the capacious mouth is well suited for engulfing large insects such as locusts and mantises1 which are mostly caught on the trees4 ,during the day the ,more-pork or ,frog-mouth sleeps upright on a branch1 and its mottled brown plumage makes it almost invisible4 ,illustration3 ,,pelican',s ,,bill1 ,,adapted ,,for ,,catching ,,and ,,storing ,,fishes ,there is an enormous dilatable sac beneath the lower jaw4 ,illustration3 ,,hornbill',s ,,bill1 ,,adapted ,,for ,,excavating ,a ,,nest ,,in ,a ,,tree1 ,,and ,,also ,,for ,,seizing ,,and ,,breaking ,,diverse ,,forms ,,of ,,food1 ,,from ,,mammals ,,to ,,tortoises1 ,,from ,,roots ,,to ,,fruits ,the use of the helmet or casque is obscure4 ,illustration3 ,,spoonbill',s ,,bill1 ,,adapted ,,for ,,sifting ,,the ,,mud ,,and ,,catching ,,the ,,small ,,animals1 ,e4,g4 ,,fishes1 ,,crustaceans1 ,,insect ,,larv1 ,,which ,,live ,,there ,illustration3 ,,falcon',s ,,bill1 ,,adapted ,,for ,,seizing1 ,,killing1 ,,and ,,tearing ,,small ,,mammals ,,and ,,birds ,illustration3 ,,avocet',s ,,bill1 ,,adapted ,,for ,a ,,curious ,,sideways ,,scooping ,,in ,,the ,,shore-,,pools ,,and ,,catching ,,small ,,animals ,illustration3 ,,puffin',s ,,bill1 ,,adapted ,,for ,,catching ,,small ,,fishes ,,near ,,the ,,surface ,,of ,,the ,,sea1 ,,and ,,for ,,holding ,,them ,,when ,,caught ,,and ,,carrying ,,them ,,to ,,the ,,nest ,the scaly covering is moulted in the autumn4 ,we must not dwell too long on this particular instance of evolution1 though it has meant much to our race4 ,we wish1 however1 following ,professor ,buller's ,essays on ,wheat 7#aiai71 to explain the method by which this good seed was discovered4 ,from one we may learn all4 ,the parent of ,marquis ,wheat on the male side was the mid-,europe ,red ,fife--a first-class cereal4 ,the parent on the female side was less promising1 a rather nondescript1 not pure-bred wheat1 called ,red ,calcutta1 which was imported from ,india into ,canada about thirty years ago4 ,the father was part of a cargo that came from the ,baltic to ,glasgow1 and was happily included in a sample sent on to ,david ,fife in ,ontario about #ahdb4 ,from one kernel of this sample ,david ,fife started his stock of ,red ,fife1 which was crossed by ,dr4 ,saunders with ,hard ,red ,calcutta4 ,the result of the cross was a medley of types1 nearly a hundred varieties altogether1 and it was in scrutinising these that ,dr4 ,saunders hit upon ,marquis4 ,he worked steadily through the material1 studying head after head of what resulted from sowing1 and selecting out those that gave most promise4 ,each of the heads selected was propagated2 most of the results were rejected2 the elect were sifted again and yet again1 and finally ,marquis ,wheat emerged1 rich in constructive possibilities1 probably the most valuable food-plant in the world4 ,it is like a romance to read that the first crop of the wheat that was destined within a dozen years to overtax the mightiest elevators in the land was stored away in the winter of #aijd-e in a paper packet no larger than an envelope4 ,thus from the ,wild ,wheat of ,mount ,hermon there evolved one of the most important food-plants of the world4 ,this surely is ,evolution going on4 #b ,changes in the ,animal ,life of a ,country ,nothing gives us a more convincing impression of evolution in being than a succession of pictures of the animal life of a country in different ages4 ,dr4 ,james ,ritchie1 a naturalist of distinction1 has written a masterly book1 ,the ,influence of ,man on ,animal ,life in ,scotland 7#aibj71 in which we get this succession of pictures4 ,within itself1 he says1 a fauna is in a constant state of uneasy restlessness1 an assemblage of creatures which in its parts ebbs and flows as one local influence or another plays upon it4 ,there are temporary and local changes1 endless disturbances and readjustments of the balance of nature4 ,one year there is a plague of field-voles1 perhaps next year grouse disease is rife2 in one place there is huge increase of starlings1 in another place of rabbits2 here cockchafers are in the ascendant1 and there the moles are spoiling the pasture4 ,but while the parts fluctuate1 the fauna as a whole follows a path of its own4 ,as well as internal tides which swing to and fro about an average level1 there is a drift which carries the fauna bodily along an 'irretraceable course4' ,this is partly due to considerable changes of climate1 for climate calls the tune to which living creatures dance1 but it is also due to new departures among the animals themselves4 ,we need not go back to the extinct animals and lost faunas of past ages--for ,britain has plenty of relics of these--which illustrate the reality of the faunal drift1 but it may be very useful1 in illustration of evolution in being1 to notice what has happened in ,scotland since the end of the ,great ,ice ,age4 ,some nine thousand years ago or more1 certain long-headed1 square-jawed1 short-limbed1 but agile hunters and fishermen1 whom we call ,neolithic ,man1 established themselves in ,scotland4 ,what was the state of the country then8 ,it was a country of swamps1 low forests of birch1 alder1 and willow1 fertile meadows1 and snow-capped mountains4 ,its estuaries penetrated further inland than they now do1 and the sea stood at the level of the ,fifty-,foot ,beach4 ,on its plains and in its forests roamed many creatures which are strange to the fauna of to-day--the ,elk and the ,reindeer1 ,wild ,cattle1 the ,wild ,boar and perhaps ,wild ,horses1 a fauna of large animals which paid toll to the ,european ,lynx1 the ,brown ,bear and the ,wolf4 ,in all likelihood1 the marshes resounded to the boom of the ,bittern and the plains to the breeding calls of the ,crane and the ,great ,bustard4 ,such is ,dr4 ,ritchie's initial picture4 ,illustration3 ,,life-,,history ,,of ,a ,,frog #a1 ,before hatching2 #b1 newly hatched larv hanging on to water-weed2 #c1 with external gills2 #d1 external gills are covered over and are absorbed2 #e1 limbless larva about a month old with internal gills2 #f1 tadpole with hind-legs1 about two months old2 #g1 with the fore-limbs emerging2 #h1 with all four legs free2 #i1 a young frog1 about three months old1 showing the almost complete absorption of the tail and the change of the tadpole mouth into a frog mouth4 ,illustration3 ,photo3 ,j4 ,j4 ,ward4 ,f4,e4,s4 ,,hind-,,leg ,,of ,,whirligig ,,beetle ,,which ,,has ,,become ,,beautifully ,,modified ,,for ,,aquatic ,,locomotion ,the flattened tips form an expanding fan or paddle1 which opens and closes with astonishing rapidity4 ,the closing of the fan1 like the feathering of an oar1 reduces friction when the leg is being moved forwards for the next stroke4 ,illustration3 ,,the ,,big ,,robber-,,crab 7,birgus ,latro71 ,,that ,,climbs ,,the ,,coco-,,nut ,,palm ,,and ,,breaks ,,off ,,the ,,nuts ,it occurs on islands in the ,indian ,ocean and ,pacific1 and is often found far above sea-level4 ,it is able to breathe dry air4 ,one is seen emerging from its burrow1 which is often lined with coco-nut fibre4 ,the empty coco-nut shell is sometimes used by the ,robber-,crab for the protection of its tail4 ,now what happened in this kingdom of ,caledonia which ,neolithic ,man had found8 ,he began to introduce domesticated animals1 and that meant a thinning of the ranks of predacious creatures4 ,safety first was the dangerous motto in obedience to which man exterminated the lynx1 the brown bear1 and the wolf4 ,other creatures1 such as the great auk1 were destroyed for food1 and others like the marten for their furs4 ,small pests were destroyed to protect the beginnings of agriculture2 larger animals like the boar were hunted out of existence2 others1 like the pearl-bearing river-mussels1 yielded to subtler demands4 ,no doubt there was protection also--protection for sport1 for utility1 for sthetic reasons1 and because of humane sentiments2 even wholesome superstitions have safeguarded the robin redbreast and the wren4 ,there were introductions too--the rabbit for utility1 the pheasant for sport1 and the peacock for amenity4 ,and every introduction1 every protection1 every killing out had its far-reaching influences4 ,but if we are to picture the evolution going on1 we must think also of man's indirect interference with animal life4 ,he destroyed the forests1 he cultivated the wild1 he made bridges1 he allowed aliens1 like rats and cockroaches1 to get in unawares4 ,of course1 he often did good1 as when he drained swamps and got rid of the mosquitoes which once made malaria rife in ,scotland4 ,what has been the net result8 ,not1 as one might think for a moment1 a reduction in the number of different kinds of animals4 ,fourteen or so species of birds and beasts have been banished from ,scotland since man interfered1 but as far as numbers go they have been more than replaced by deliberate introductions like fallow deer1 rabbit1 squirrel1 and pheasant1 and by accidental introductions like rats and cockroaches4 ,but the change is rather in quality than in quantity2 the smaller have taken the place of the larger1 rather paltry pigmies of noble giants4 ,thus we get a vivid idea that evolution1 especially when man interferes1 is not necessarily progressive4 ,that depends on the nature of the sieves with which the living materials are sifted4 ,as ,dr4 ,ritchie well says1 the standard of the wild fauna as regards size has fallen and is falling1 and it is not in size only that there is loss1 there is a deterioration of quality4 ,for how can the increase of ,rabbits and ,sparrows and ,earthworms and ,caterpillars1 and the addition of millions of ,rats and ,cochroaches and ,crickets and ,bugs1 ever take the place of those fine creatures round the memories of which the glamour of ,scotland's past still plays--the ,reindeer and the ,elk1 the ,wolf1 the ,brown ,bear1 the ,lynx1 and the ,beaver1 the ,bustard1 the ,crane1 the ,bumbling ,bittern1 and many another1 lost or disappearing4 ,thus we see again that evolution is going on4 #c ,the ,adventurers ,all through the millions of years during which animals have tenanted the earth and the waters under the earth1 there has been a search for new kingdoms to conquer1 for new corners in which to make a home4 ,and this still goes on4 ,it has been and is one of the methods of evolution to fill every niche of opportunity4 ,there is a spider that lives inside a pitcher-plant1 catching some of the inquisitive insects which slip down the treacherous internal surface of the trap4 ,there is another that makes its home in crevices among the rocks on the shore of the ,mediterranean1 or even in empty tubular shells1 keeping the water out1 more or less successfully1 by spinning threads of silk across the entrance to its retreat4 ,the beautiful brine-shrimp1 ,artemia salina1 that used to occur in ,british salterns has found a home in the dense waters of the ,great ,salt ,lake of ,utah4 ,several kinds of earthworms have been found up trees1 and there is a fish1 ,arges1 that climbs on the stones of steep mountain torrents of the ,andes4 ,the intrepid explorers of the ,scotia voyage found quite a number of ,arctic terns spending our winter within the summer of the ,antarctic ,circle--which means girdling the globe from pole to pole2 and every now and then there are incursions of rare birds1 like ,pallas's ,sand-grouse1 into ,britain1 just as if they were prospecting in search of a promised land4 ,twice or thrice the distinctively ,north ,american ,killdeer ,plover has been found in ,britain1 having somehow or other got across the ,atlantic4 ,we miss part of the meaning of evolution if we do not catch this note of insurgence and adventure1 which some animal or other never ceases to sound1 though many establish themselves in a security not easily disturbed1 and though a small minority give up the struggle against the stream and are content to acquiesce1 as parasites or rottenness eaters1 in a drifting life of ease4 ,more important than very peculiar cases is the broad fact that over and over again in different groups of animals there have been attempts to master different kinds of haunts--such as the underground world1 the trees1 the freshwaters1 and the air4 ,there are burrowing amphibians1 burrowing reptiles1 burrowing birds1 and burrowing mammals2 there are tree-toads1 tree-snakes1 tree-lizards1 tree-kangaroos1 tree-sloths1 tree-shrews1 tree-mice1 tree-porcupines1 and so on2 enough of a list to show1 without mentioning birds1 how many different kinds of animals have entered upon an arboreal apprenticeship--an apprenticeship often with far-reaching consequences4 ,what the freeing of the hand from being an organ of terrestrial support has meant in the evolution of monkeys is a question that gives a spur to our imagination4 ,the ,case of the ,robber ,crab ,on some of the coral islands of the ,indian and ,pacific ,oceans there lives a land-crab1 ,birgus1 which has learned to breathe on land4 ,it breathes dry air by means of curious blood-containing tufts in the upper part of its gill-cavity1 and it has also rudimentary gills4 ,it is often about a foot long1 and it has very heavy great claws1 especially on the left-hand side4 ,with this great claw it hammers on the eye-hole of a coconut1 from which it has torn off the fibrous husk4 ,it hammers until a hole is made by which it can get at the pulp4 ,part of the shell is sometimes used as a protection for the soft abdomen--for the robber-crab1 as it is called1 is an offshoot from the hermit-crab stock4 ,every year this quaint explorer1 which may go far up the hills and climb the coco-palms1 has to go back to the sea to spawn4 ,the young ones are hatched in the same state as in our common shore-crab4 ,that is to say1 they are free-swimming larv which pass through an open-water period before they settle down on the shore1 and eventually creep up on to dry land4 ,just as open-water turtles lay their eggs on sandy shores1 going back to their old terrestrial haunt1 so the robber-crab1 which has almost conquered the dry land1 has to return to the seashore to breed4 ,there is a peculiar interest in the association of the robber-crab with the coco-palm1 for that tree is not a native of these coral islands1 but has been introduced1 perhaps from ,mexico1 by the ,polynesian mariners before the discovery of ,america by ,columbus4 ,so the learning to deal with coconuts is a recent achievement1 and we are face to face with a very good example of evolution going on4 ,illustration3 ,,early ,,life-,,history ,,of ,,the ,,salmon #a4 ,the fertilised egg1 shed in the gravelly bed of the river4 #b4 ,the embryo within the egg1 just before hatching4 ,the embryo has been constricted off from the yolk-laden portion of the egg4 #c4 ,the newly hatched salmon1 or alevin1 encumbered with its legacy of yolk 7,y4,s474 #d and #e4 ,the larval salmon1 still being nourished from the yolk-sac 7,y4,s471 which is diminishing in size as the fish grows larger4 #f4 ,the salmon fry about six weeks old1 with the yolk fully absorbed1 so that the young fish has now to feed for itself4 ,the fry become parr1 which go to the sea as smolts1 and return as grilse4 ,in all cases the small figures to the right indicate the natural size4 ,illustration3 ,,the ,,salmon ,,leaping ,,at ,,the ,,fall ,,is ,a ,,most ,,fascinating ,,spectacle ,again and again we see them jumping out of the seething foam beneath the fall1 casting themselves into the curtain of the down-rushing water1 only to be carried back by it into the depths whence they have risen4 ,one here and another there makes its effort good1 touches the upper lip of the cataract1 gives a swift stroke of its tail1 and rushes on towards those upper reaches which are the immemorial spawning beds of its race4 ,the ,story of the ,salmon ,in late autumn or in winter the salmon spawn in the rivers4 ,the female makes a shallow trough in the gravel by moving her tail from side to side1 and therein lays many eggs4 ,the male1 who is in attendance1 fertilises these with the milt1 and then the female covers them deeply with gravel4 ,the process is repeated over and over again for a week or more till all the eggs are shed4 ,for three to four months the eggs develop1 and eventually there emerge the larv or alevins1 which lurk among the pebbles4 ,they cannot swim much1 for they are encumbered by a big legacy of yolk4 ,in a few weeks1 perhaps eight1 the protruding bag of yolk has disappeared and the fry1 about an inch long1 begin to move about more actively and to fend for themselves4 ,by the end of the year they have grown to be rather trout-like parr1 about four inches long4 ,in two years these are double that length4 ,usually in the second year1 but it may be earlier or later1 the parr become silvery smolts1 which go out to sea1 usually about the month of ,may4 ,they feed on young herring and the like and grow large and strong4 ,when they are about three and a half years old they come up the rivers as grilse and may spawn4 ,or they may pass through the whole grilse stage in the sea and come up the rivers with all the characters of the full-grown fish4 ,in many cases the salmon spawn only once1 and some 7they are called kelts after spawning7 are so much exhausted by starting a new generation that they die or fall a victim to otters and other enemies4 ,in the case of the salmon of the ,north ,pacific 7in the genus ,oncorhynchus1 not ,salmo7 all the individuals die after spawning1 none being able to return to the sea4 ,it must be remembered that full-grown salmon do not as a rule feed in fresh water1 though they may be unable to resist snapping at the angler's strange creations4 ,a very interesting fact is that the salmon keeps as it were a diary of its movements1 which vary a good deal in different rivers4 ,this diary is written in the scales1 and a careful reading of the concentric lines on the scales shows the age of the fish1 and when it went out to sea1 and whether it has spawned or not1 and more besides4 ,interpretation of the ,salmon's ,story ,when an animal frequents two different haunts1 in one of which it breeds1 it is very often safe to say that the breeding-place represents the original home4 ,the flounder is quite comfortable far up the rivers1 but it has to go to the shore-waters to spawn1 and there is no doubt that the flounder is a marine fish which has recently learned to colonise the fresh waters4 ,its relatives1 like plaice and sole1 are strictly marine4 ,but it is impossible to make a dogma of the rule that the breeding-place corresponds to the original home4 ,thus some kinds of bass1 which belong to the marine family of sea-perches1 live in the sea or in estuaries1 while two have become permanent residents in fresh water4 ,or1 again1 the members of the herring family are very distinctively marine1 but the shad1 which belong to this family1 spawn in rivers and may spend their lives there4 ,so there are two different ways of interpreting the life-history of the salmon4 ,some authorities regard the salmon as a marine fish which is establishing itself in fresh water4 ,but others read the story the other way and regard the salmon as a member of a freshwater race1 that has taken to the sea for feeding purposes4 ,in regard to trout1 we know that the ranks of those in rivers and lakes are continually being reinforced by migrants from the sea1 and that some trout go down to the sea while others remain in the freshwater4 ,we know also in regard to a related fish1 the char1 that while the great majority of kinds are now permanent residents in cold and deep1 isolated northern lakes1 there are ,arctic forms which live in the sea but enter the rivers to spawn4 ,these facts favour the view that the salmon was originally a marine fish4 ,but there are arguments on both sides1 and1 for our present purpose1 the important fact is that the salmon is conquering two haunts4 ,its evolution is going on4 ,the ,romance of the ,eel ,early in summer1 at dates varying with the distance of the rivers from the open ,atlantic1 crowds of young eels or elvers come up-stream4 ,sometimes the procession or eel-fare includes thousands of individuals1 each about the length of our first finger1 and as thick as a stout knitting needle4 ,they obey an inborn impulse to swim against the stream1 seeking automatically to have both sides of their body equally stimulated by the current4 ,so they go straight ahead4 ,the obligation works only during the day1 for when the sun goes down behind the hills the elvers snuggle under stones or beneath the bank and rest till dawn4 ,in the course of time they reach the quiet upper reaches of the river or go up rivulets and drainpipes to the isolated ponds4 ,their impulse to go on must be very imperious1 for they may wriggle up the wet moss by the side of a waterfall or even make a short excursion in a damp meadow4 ,in the quiet-flowing stretches of the river or in the ponds they feed and grow for years and years4 ,they account for a good many young fishes4 ,eventually1 after five or six years in the case of the males1 six to eight years in the case of the females1 the well-grown fishes1 perhaps a foot and a half to two feet long1 are seized by a novel restlessness4 ,they are beginning to be mature4 ,they put on a silvery jacket and become large of eye1 and they return to the sea4 ,in getting away from the pond it may be necessary to wriggle through the damp meadow-grass before reaching the river4 ,they travel by night and rather excitedly4 ,the ,arctic ,ocean is too cold for them and the ,north ,sea too shallow4 ,they must go far out to sea1 to where the old margin of the once larger continent of ,europe slopes down to the great abysses1 from the ,hebrides southwards4 ,eels seem to spawn in the deep dark water2 but the just liberated eggs have not yet been found4 ,the young fry rises to near the surface and becomes a knife-blade-like larva1 transparent all but its eye4 ,it lives for many months in this state1 growing to be about three inches long1 rising and sinking in the water1 and swimming gently4 ,these open-sea young eels are known as ,leptocephali1 a name given to them before their real nature was proved4 ,they gradually become shorter1 and the shape changes from knife-blade-like to cylindrical4 ,during this change they fast1 and the weight of their delicate body decreases4 ,they turn into glass-eels1 about #b-a_/b inches long1 like a knitting-needle in girth4 ,they begin to move towards the distant shores and rivers1 and they may be a year and a half old before they reach their destination and go up-stream as elvers4 ,those that ascend the rivers of the ,eastern ,baltic must have journeyed three thousand miles4 ,it is certain that no eel ever matures or spawns in fresh water4 ,it is practically certain that all the young eels ascending the rivers of ,north ,europe have come in from the ,atlantic1 some of them perhaps from the ,azores or further out still4 ,it is interesting to inquire how the young eels circumvent the ,falls of the ,rhine and get into ,lake ,constance1 or how their kindred on the other side of the ,atlantic overcome the obstacle of ,niagara2 but it is more important to lay emphasis on the variety of habitats which this fish is trying--the deep waters1 the open sea1 the shore1 the river1 the pond1 and even1 it may be1 a little taste of solid earth4 ,it seems highly probable that the common eel is a deep-water marine fish which has learned to colonise the freshwaters4 ,it has been adventurous and it has succeeded4 ,the only shadow on the story of achievement is that there seems to be no return from the spawning4 ,there is little doubt that death is the nemesis of their reproduction4 ,in any case1 no adult eel ever comes back from the deep sea4 ,we are minded of ,goethe's hard saying3 ,death is ,nature's expert advice to get plenty of life4 #d ,forming ,new ,habits ,there is a well-known mudfish of ,australia1 ,neoceratodus by name1 which has turned its swim-bladder into a lung and comes to the surface to spout4 ,it expels vitiated air with considerable force and takes fresh gulps4 ,at the same time1 like an ordinary fish1 it has gills which allow the usual interchange of gases between the blood and the water4 ,now this ,australian mudfish or double-breather 7,dipnoan71 which may be a long way over a yard in length1 is a direct and little-changed descendant of an ancient extinct fish1 ,ceratodus1 which lived in ,mesozoic times1 as far back as the ,jurassic1 which probably means over five millions of years ago4 ,the ,queensland mudfish is an antiquity1 and there has not been much change in its lineage for millions of years4 ,we might take it as an illustration of the inertia of evolution4 ,and yet1 though its structure has changed but little1 the fish probably illustrates evolution in process1 for it is a fish that is learning to breathe dry air4 ,it cannot leave the water2 but it can live comfortably in pools which are foul with decomposing animal and vegetable matter4 ,in partially dried-up and foul waterholes1 full of dead fishes of various kinds1 ,neoceratodus has been found vigorous and lively4 ,unless we take the view1 which is possible1 that the swim-bladder of fishes was originally a lung1 the mud-fishes are learning to breathe dry air4 ,they illustrate evolution agoing4 ,illustration3 ,,diagram ,,of ,,the ,,life ,,history ,,of ,,the ,,common ,,eel 7,anguilla ,vulgalis7 #a4 ,the transparent open-sea knife-blade-like larva called a ,leptocephalus4 #b and #c4 ,the gradual change of shape from knife-blade-like to cylindrical4 ,the body becomes shorter and loses weight4 #d4 ,the young elver1 at least a year old1 which makes its way from the open sea to the estuaries and rivers4 ,it is #b_/c inches long and almost cylindrical4 #e4 ,the fully-formed eel4 ,illustration3 ,photo3 ,gambier ,bolton4 ,,cassowary ,its bare head is capped with a helmet4 ,unlike the plumage of most birds its feathers are loose and hair-like1 whilst its wings are merely represented by a few black quills4 ,it is flightless and entirely dependent on its short powerful legs to carry it out of danger4 ,illustration3 ,photo3 ,gambier ,bolton4 ,,the ,,kiwi1 ,,another ,,flightless ,,bird1 ,,of ,,remarkable ,,appearance1 ,,habits1 ,,and ,,structure ,the herring-gull is by nature a fish-eater2 but of recent years1 in some parts of ,britain1 it has been becoming in the summer months more and more of a vegetarian1 scooping out the turnips1 devouring potatoes1 settling on the sheaves in the harvest field and gorging itself with grain4 ,similar experiments1 usually less striking1 are known in many birds2 but the most signal illustration is that of the kea or ,nestor parrot of ,new ,zealand1 which has taken to lighting on the loins of the sheep1 tearing away the fleece1 cutting at the skin1 and gouging out fat4 ,now the parrot belongs to a vegetarian or frugivorous stock1 and this change of diet in the relatively short time since sheep-ranches were established in ,new ,zealand is very striking4 ,here1 since we know the dates1 we may speak of evolution going on under our eyes4 ,it must be remembered that variations in habit may give an animal a new opportunity to test variations in structure which arise mysteriously from within1 as expressions of germinal changefulness rather than as imprints from without4 ,for of the transmissibility of the latter there is little secure evidence4 ,experiments in ,locomotion ,it is very interesting to think of the numerous types of locomotion which animals have discovered--pulling and punting1 sculling and rowing1 and of the changes that are rung on these four main methods4 ,how striking is the case of the frilled lizard 7,chlamydosaurus7 of ,australia1 which at the present time is1 as it were1 experimenting in bipedal progression--always a rather eventful thing to do4 ,it gets up on its hind-legs and runs totteringly for a few feet1 just like a baby learning to walk4 ,how beautiful is the adventure which has led our dipper or water-ouzel--a bird allied to the wrens--to try walking and flying under water6 ,how admirable is the volplaning of numerous parachutists--flying fish1 flying frog1 flying dragon1 flying phalanger1 flying squirrel1 and more besides1 which take great leaps through the air4 ,for are these not the splendid failures that might have succeeded in starting new modes of flight8 ,most daring of all1 perhaps1 are the aerial journeys undertaken by many small spiders4 ,on a breezy morning1 especially in the autumn1 they mount on gate-posts and palings and herbage1 and1 standing with their head to the wind1 pay out three or four long threads of silk4 ,when the wind tugs at these threads1 the spinners let go1 and are borne1 usually back downwards1 on the wings of the wind from one parish to another4 ,it is said that if the wind falls they can unfurl more sail1 or furl if it rises4 ,in any case1 these wingless creatures make aerial journeys4 ,when tens of thousands of the used threads sink to earth1 there is a shower of gossamer4 ,on his ,beagle voyage ,darwin observed that vast numbers of small gossamer spiders were borne on to the ship when it was sixty miles distant from the land4 ,illustration3 ,,the ,,australian ,,frilled ,,lizard1 ,,which ,,is ,,at ,,present ,,trying ,,to ,,become ,a ,,biped ,when it gets up on its hind-legs and runs for a short distance it folds its big collar round its neck4 ,illustration3 ,a ,,carpet ,,of ,,gossamer ,the silken threads used by thousands of gossamer spiders in their migrations are here seen entangled in the grass1 forming what is called a shower of gossamer4 ,at the edge of the grass the gossamer forms a curtain1 floating out and looking extraordinarily like waves breaking on a seashore4 ,illustration3 ,,the ,,water-,,spider ,the spider is seen just leaving its diving-bell to ascend to the surface to capture air4 ,the spider jerks its body and legs out at the surface and then dives-- --carrying with it what looks like a silvery air-bubble--air entangled in the hair4 ,the spider reaches its air-dome4 ,note how the touch of its legs indents the inflated balloon4 ,running down the side of the nest1 the spider --brushes off the air at the entrance1 and the bubble ascends into the silken balloon4 ,photos3 ,j4 ,j4 ,ward1 ,f4,e4,s4 ,new ,devices ,it is impossible1 we must admit1 to fix dates1 except in a few cases1 relatively recent2 but there is a smack of modernity in some striking devices which we can observe in operation to-day4 ,thus no one will dispute the statement that spiders are thoroughly terrestrial animals breathing dry air1 but we have the fact of the water-spider conquering the under-water world4 ,there are a few spiders about the seashore1 and a few that can survive douching with freshwater1 but the particular case of the true water-spider1 ,argyroneta natans1 stands by itself because the creature1 as regards the female at least1 has conquered the sub-aquatic environment4 ,a flattish web is woven1 somehow1 underneath the water1 and pegged down by threads of silk4 ,along a special vertical line the mother spider ascends to the surface and descends again1 having entangled air in the hairs of her body4 ,she brushes off this air underneath her web1 which is thereby buoyed up into a sort of dome4 ,she does this over and over again1 never getting wet all the time1 until the domed web has become like a diving-bell1 full of dry air4 ,in this eloquent anticipation of man's rational device1 this creature--far from being endowed with reason--lays her eggs and looks after her young4 ,the general significance of the facts is that when competition is keen1 a new area of exploitation is a promised land4 ,thus spiders have spread over all the earth except the polar areas4 ,but here is a spider with some spirit of adventure1 which has endeavoured1 instead of trekking1 to find a new corner near at home4 ,it has tackled a problem surely difficult for a terrestrial animal1 the problem of living in great part under water1 and it has solved it in a manner at once effective and beautiful4 ,in ,conclusion ,we have given but a few representative illustrations of a great theme4 ,when we consider the changefulness of living creatures1 the transformations of cultivated plants and domesticated animals1 the gradual alterations in the fauna of a country1 the search after new haunts1 the forming of new habits1 and the discovery of many inventions1 are we not convinced that ,evolution is going on8 ,and why should it stop8 ,,vii ,,the ,,dawn ,,of ,,mind ,,the ,,dawn ,,of ,,mind ,in the story of evolution there is no chapter more interesting than the emergence of mind in the animal kingdom4 ,but it is a difficult chapter to read1 partly because mind cannot be seen or measured1 only inferred from the outward behaviour of the creature1 and partly because it is almost impossible to avoid reading ourselves into the much simpler animals4 #a ,two ,extremes to be ,avoided ,the one extreme is that of uncritical generosity which credits every animal1 like ,brer ,rabbit--who1 by the way1 was the hare--with human qualities4 ,the other extreme is that of thinking of the animal as if it were an automatic machine1 in the working of which there is no place or use for mind4 ,both these extremes are to be avoided4 ,when ,professor ,whitman took the eggs of the ,passenger ,pigeon 7which became extinct not long ago with startling rapidity7 and placed them a few inches to one side of the nest1 the bird looked a little uneasy and put her beak under her body as if to feel for something that was not there4 ,but she did not try to retrieve her eggs1 close at hand as they were4 ,in a short time she flew away altogether4 ,this shows that the mind of the pigeon is in some respects very different from the mind of man4 ,on the other hand1 when a certain clever dog1 carrying a basket of eggs1 with the handle in his mouth1 came to a stile which had to be negotiated1 he laid the basket on the ground1 pushed it gently through a low gap to the other side1 and then took a running leap over4 ,we dare not talk of this dog as an automatic machine4 ,a ,caution in ,regard to ,instinct ,in studying the behaviour of animals1 which is the only way of getting at their mind1 for it is only of our own mind that we have direct knowledge1 it is essential to give prominence to the fact that there has been throughout the evolution of living creatures a strong tendency to enregister or engrain capacities of doing things effectively4 ,thus certain abilities come to be inborn2 they are parts of the inheritance1 which will express themselves whenever the appropriate trigger is pulled4 ,the newly born child does not require to learn its breathing movements1 as it afterwards requires to learn its walking movements4 ,the ability to go through the breathing movements is inborn1 engrained1 enregistered4 ,in other words1 there are hereditary pre-arrangements of nerve-cells and muscle-cells which come into activity almost as easily as the beating of the heart4 ,in a minute or two the newborn pigling creeps close to its mother and sucks milk4 ,it has not to learn how to do this any more than we have to learn to cough or sneeze4 ,thus animals have many useful ready-made1 or almost ready-made1 capacities of doing apparently clever things4 ,in simple cases of these inborn pre-arrangements we speak of reflex actions2 in more complicated cases1 of instinctive behaviour4 ,now the caution is this1 that while these inborn capacities usually work well in natural conditions1 they sometimes work badly when the ordinary routine is disturbed4 ,we see this when a pigeon continues sitting for many days on an empty nest1 or when it fails to retrieve its eggs only two inches away4 ,but it would be a mistake to call the pigeon1 because of this1 an unutterably stupid bird4 ,we have only to think of the achievements of homing pigeons to know that this cannot be true4 ,we must not judge animals in regard to those kinds of behaviour which have been handed over to instinct1 and go badly agee when the normal routine is disturbed4 ,in ninety-nine cases out of a hundred the enregistered instinctive capacities work well1 and the advantage of their becoming stereotyped was to leave the animal more free for adventures at a higher level4 ,being a slave of instinct may give the animal a security that enables it to discover some new home or new food or new joy4 ,somewhat in the same way1 a man of methodical habits1 which he has himself established1 may gain leisure to make some new departure of racial profit4 ,illustration3 ,photo3 ,o4 ,j4 ,wilkinson4 ,,jackdaw ,,balancing ,,on ,a ,,gatepost ,the jackdaw is a big-brained1 extremely alert1 very educable1 loquacious bird4 ,illustration3 ,from ,ingersoll's ,the ,wit of the ,wild4 ,,two ,,opossums ,,feigning ,,death ,the ,opossums are mainly arboreal marsupials1 insectivorous and carnivorous1 confined to the ,american ,continent from the ,united ,states to ,patagonia4 ,many have no pouch and carry their numerous young ones on their back1 the tail of the young twined round that of the mother4 ,the opossums are agile1 clever creatures1 and famous for playing 'possum1 lying inert just as if they were dead4 ,illustration3 ,,male ,,of ,,three-,,spined ,,stickleback1 ,,making ,a ,,nest ,,of ,,water-,,weed1 ,,glued ,,together ,,by ,,viscid ,,threads ,,secreted ,,from ,,the ,,kidneys ,,at ,,the ,,breeding ,,season ,illustration3 ,a ,,female ,,stickleback ,,enters ,,the ,,nest ,,which ,,the ,,male ,,has ,,made1 ,,lays ,,the ,,eggs ,,inside1 ,,and ,,then ,,departs ,in many cases two or three females use the same nest1 the stickleback being polygamous4 ,above the nest the male1 who mounts guard1 is seen driving away an intruder4 ,when we draw back our finger from something very hot1 or shut our eye to avoid a blow from a rebounding branch1 we do not will the action2 and this is more or less the case1 probably1 when a young mammal sucks its mother for the first time4 ,some ,mound-birds of ,celebes lay their eggs in warm volcanic ash by the shore of the sea1 others in a great mass of fermenting vegetation2 it is inborn in the newly hatched bird to struggle out as quickly as it can from such a strange nest1 else it will suffocate4 ,if it stops struggling too soon1 it perishes1 for it seems that the trigger of the instinct cannot be pulled twice4 ,similarly1 when the eggs of the turtle1 that have been laid in the sand of the shore1 hatch out1 the young ones make instinctively for the sea4 ,some of the crocodiles bury their eggs two feet or so below the surface among sand and decaying vegetation--an awkward situation for a birthplace4 ,when the young crocodile is ready to break out of the egg-shell1 just as a chick does at the end of the three weeks of brooding1 it utters instinctively a piping cry4 ,on hearing this1 the watchful mother digs away the heavy blankets1 otherwise the young crocodile would be buried alive at birth4 ,now there is no warrant for believing that the young ,mound-birds1 young crocodiles1 and young turtles have an intelligent appreciation of what they do when they are hatched4 ,they act instinctively1 as to the manner born4 ,but this is not to say that their activity is not backed by endeavour or even suffused with a certain amount of awareness4 ,of course1 it is necessarily difficult for man1 who is so much a creature of intelligence1 to get even an inkling of the mental side of instinctive behaviour4 ,in many of the higher reaches of animal instinct1 as in courtship or nest-building1 in hunting or preparing the food1 it looks as if the starting of the routine activity also rang up the higher centres of the brain and put the intelligence on the qui vive1 ready to interpose when needed4 ,so the twofold caution is this3 7#a7 ,we must not depreciate the creature too much if1 in unusual circumstances1 it acts in an ineffective way along lines of behaviour which are normally handed over to instinct2 and 7#b7 we must leave open the possibility that even routine instinctive behaviour may be suffused with awareness and backed by endeavour4 #b ,a ,useful ,law ,but how are we to know when to credit the animal with intelligence and when with something less spontaneous8 ,above all1 how are we to know when the effective action1 like opening the mouth the very instant it is touched by food in the mother's beak1 is just a physiological action like coughing or sneezing1 and when there is behind it--a mind at work8 ,the answer to this question is no doubt that given by ,prof4 ,lloyd ,morgan1 who may be called the founder of comparative psychology1 that we must describe the piece of behaviour very carefully1 just as it occurred1 without reading anything into it1 and that we must not ascribe it to a higher faculty if it can be satisfactorily accounted for in terms of a lower one4 ,in following this principle we may be sometimes niggardly1 for the behaviour may have a mental subtlety that we have missed2 but in nine cases out of ten our conclusions are likely to be sound4 ,it is the critical1 scientific way4 ,bearing this law in mind1 let us take a survey of the emergence of mind among backboned animals4 ,senses of ,fishes ,fishes cannot shut their eyes1 having no true lids2 but the eyes themselves are very well developed and the vision is acute1 especially for moving objects4 ,except in gristly fishes1 the external opening to the ear has been lost1 so that sound-waves and coarser vibrations must influence the inner ear1 which is well developed1 through the surrounding flesh and bones4 ,it seems that the main use of the ear in fishes is in connection with balancing1 not with hearing4 ,in many cases1 however1 the sense of hearing has been demonstrated2 thus fishes will come to the side of a pond to be fed when a bell is rung or when a whistle is blown by someone not visible from the water4 ,the fact that many fishes pay no attention at all to loud noises does not prove that they are deaf1 for an animal may hear a sound and yet remain quite indifferent or irresponsive4 ,this merely means that the sound has no vital interest for the animal4 ,some fishes1 such as bullhead and dogfish1 have a true sense of smell1 detecting by their nostrils very dilute substances permeating the water from a distance4 ,others1 such as members of the cod family1 perceive their food in part at least by the sense of taste1 which is susceptible to substances near at hand and present in considerable quantity4 ,this sense of taste may be located on the fins as well as about the mouth4 ,at this low level the senses of smell and taste do not seem to be very readily separated4 ,the chief use of the sensitive line or lateral line seen on each side of a bony fish is to make the animal aware of slow vibrations and changes of pressure in the water4 ,the skin responds to pressures1 the ear to vibrations of high frequency2 the lateral line is between the two in its function4 ,interesting ,ways of ,fishes ,the brain of the ordinary bony fish is at a very low level4 ,thus the cerebral hemispheres1 destined to become more and more the seat of intelligence1 are poorly developed4 ,in gristly fishes1 like skates and sharks1 the brain is much more promising4 ,but although the state of the brain does not lead one to expect very much from a bony fish like trout or eel1 haddock or herring1 illustrations are not wanting of what might be called pretty pieces of behaviour4 ,let us select a few cases4 ,the ,stickleback's ,nest ,the three-spined and two-spined sticklebacks live equally well in fresh or salt water2 the larger fifteen-spined stickleback is entirely marine4 ,in all three species the male fish makes a nest1 in fresh or brackish water in the first two cases1 in shore-pools in the third case4 ,the little species use the leaves and stems of water-plants2 the larger species use seaweed and zoophyte4 ,the leaves or fronds are entangled together and fastened by glue-like threads1 secreted1 strange to say1 by the kidneys4 ,it is just as if a temporary diseased condition had been regularised and turned to good purpose4 ,going through the nest several times1 the male makes a little room in the middle4 ,partly by coercion and partly by coaxing he induces a female--first one and then another--to pass through the nest with two doors1 depositing eggs during her short sojourn4 ,the females go their way1 and the male mounts guard over the nest4 ,he drives off intruding fishes much bigger than himself4 ,when the young are hatched1 the male has for a time much to do1 keeping his charges within bounds until they are able to move about with agility4 ,it seems that sticklebacks are short-lived fishes1 probably breeding only once2 and it is reasonable to suppose that their success as a race depends to some extent on the paternal care4 ,now if we could believe that the nesting behaviour had appeared suddenly in its present form1 we should be inclined to credit the fish with considerable mental ability4 ,but we are less likely to be so generous if we reflect that the routine has been in all likelihood the outcome of a long racial process of slight improvements and critical testings4 ,the secretion of the glue probably came about as a pathological variation2 its utilisation was perhaps discovered by accident2 the types that had wit enough to take advantage of this were most successful2 the routine became enregistered hereditarily4 ,the stickleback is not so clever as it looks4 ,illustration3 ,photo3 ,imperial ,war ,museum4 ,,homing ,,pigeon ,a blue chequer hen1 which during the ,war 7in ,september of #aiah7 flew #bb miles in as many minutes1 saving the crew of an aeroplane in difficulties4 ,illustration3 ,photo3 ,imperial ,war ,museum4 ,,carrier ,,pigeon ,carrier pigeons were much used in the ,war to carry messages4 ,the photograph shows how the message is fixed to the carrier pigeon's leg1 in the form of light rings4 ,illustration3 ,photo3 ,james's ,press ,agency4 ,,yellow-,,crowned ,,penguin ,notice the flightless wings turned into flippers1 which are often flapped very vigorously4 ,the very strong feet are also noteworthy4 ,penguins are mostly confined to the ,far ,south4 ,illustration3 ,photo3 ,cagcombe ,co4 ,,penguins ,,are ,a ,,peculiar ,,people ,their wings have been turned into flippers for swimming in the sea and tobogganing on snow4 ,the penguins come back over hundreds of miles of trackless waste to their birthplace1 where they breed4 ,when they reach the ,antarctic shore they walk with determination to a suitable site1 often at the top of a steep cliff4 ,some species waddle #acj steps per minute1 #f inches per step1 two-thirds of a mile per hour4 ,the ,mind of a ,minnow ,to find solid ground on which to base an appreciation of the behaviour of fishes1 it is necessary to experiment1 and we may refer to ,miss ,gertrude ,white's interesting work on ,american minnows and sticklebacks4 ,after the fishes had become quite at home in their artificial surroundings1 their lessons began4 ,cloth packets1 one of which contained meat and the other cotton1 were suspended at opposite ends of the aquarium4 ,the mud-minnows did not show that they perceived either packet1 though they swam close by them2 the sticklebacks were intrigued at once4 ,those that went towards the packet containing meat darted furiously upon it and pulled at it with great excitement4 ,those that went towards the cotton packet turned sharply away when they were within about two inches off4 ,they then perceived what those at the other end were after and joined them--a common habit amongst fishes4 ,although the minnows were not interested in the tiny bags of mystery1 they were even more alert than the sticklebacks in perceiving moving objects in or on the water1 and there is no doubt that both these shallow-water species discover their food largely by sense of sight4 ,the next set of lessons had to do with colour-associations4 ,the fishes were fed on minced snail1 chopped earthworm1 fragments of liver1 and the like1 and the food was given to them from the end of forceps held above the surface of the water1 so that the fishes could not be influenced by smell4 ,they had to leap out of the water to take the food from the forceps4 ,discs of coloured cardboard were slipped over the end of the forceps1 so that what the fishes saw was a morsel of food in the centre of a coloured disc4 ,after a week or so of preliminary training1 they were so well accustomed to the coloured discs that the presentation of one served as a signal for the fishes to dart to the surface and spring out of the water4 ,when baits of paper were substituted for the food1 the fishes continued to jump at the discs4 ,when1 however1 a blue disc was persistently used for the paper bait and a red disc for the real food1 or vice versa1 some of the minnows learned to discriminate infallibly between shadow and substance1 both when these were presented alternately and when they were presented simultaneously4 ,this is not far from the dawn of mind4 ,in the course of a few lessons1 both minnows and sticklebacks learned to associate particular colours with food1 and other associations were also formed4 ,a kind of larva that a minnow could make nothing of after repeated trials was subsequently ignored4 ,the approach of the experimenter or anyone else soon began to serve as a food-signal4 ,there can be no doubt that in the ordinary life of fishes there is a process of forming useful associations and suppressing useless responses4 ,given an inborn repertory of profitable movements that require no training1 given the power of forming associations such as those we have illustrated1 and given a considerable degree of sensory alertness along certain lines1 fishes do not require much more4 ,and in truth they have not got it4 ,moving with great freedom in three dimensions in a medium that supports them and is very uniform and constant1 able in most cases to get plenty of food without fatiguing exertions and to dispense with it for considerable periods if it is scarce1 multiplying usually in great abundance so that the huge infantile mortality hardly counts1 rarely dying a natural death but usually coming with their strength unabated to a violent end1 fishes hold their own in the struggle for existence without much in the way of mental endowment4 ,their brain has more to do with motion than with mentality1 and they have remained at a low psychical level4 ,yet just as we should greatly misjudge our own race if we confined our attention to everyday routine1 so in our total1 as distinguished from our average1 estimate of fishes1 we must remember the salmon surmounting the falls1 the wary trout eluding the angler's skill1 the common mud-skipper 7,periophthalmus7 of many tropical shores which climbs on the rocks and the roots of the mangrove-trees1 or actively hunts small shore-animals4 ,we must remember the adventurous life-history of the eel and the quaint ways in which some fishes1 males especially1 look after their family4 ,the male sea-horse puts the eggs in his breast-pocket2 the male ,kurtus carries them on the top of his head2 the cock-paidle or lumpsucker guards them and aerates them in a corner of a shore-pool4 #c ,the ,mind of ,amphibians ,towards the end of the age of the ,old ,red ,sandstone or ,devonian1 a great step in evolution was taken--the emergence of ,amphibians4 ,the earliest representatives had fish-like characters even more marked than those which may be discerned in the tadpoles of our frogs and toads1 and there is no doubt that amphibians sprang from a fish stock4 ,but they made great strides1 associated in part with their attempts to get out of the water on to dry land4 ,from fossil forms we cannot say much in regard to soft parts2 but if we consider the living representatives of the class1 we may credit amphibians with such important acquisitions as fingers and toes1 a three-chambered heart1 true ventral lungs1 a drum to the ear1 a mobile tongue1 and vocal cords4 ,when animals began to be able to grasp an object and when they began to be able to utter sufficient sounds1 two new doors were opened4 ,apart from insects1 whose instrumental music had probably begun before the end of the ,devonian age1 amphibians were the first animals to have a voice4 ,the primary meaning of this voice was doubtless1 as it is to-day in our frogs1 a sex-call2 but it was the beginning of what was destined to play a very important part in the evolution of the mind4 ,in the course of ages the significance of the voice broadened out2 it became a parental call2 it became an infant's cry4 ,broadening still1 it became a very useful means of recognition among kindred1 especially in the dark and in the intricacies of the forest4 ,ages passed1 and the voice rose on another turn of the evolutionary spiral to be expressive of particular emotions beyond the immediate circle of sex--emotions of joy and of fear1 of jealousy and of contentment4 ,finally1 we judge1 the animal--perhaps the bird was first--began to give utterance to particular words1 indicative not merely of emotions1 but of particular things with an emotional halo1 such as food1 enemy1 home4 ,long afterwards1 words became in man the medium of reasoned discourse4 ,sentences were made and judgments expressed4 ,but was not the beginning in the croaking of ,amphibia8 ,senses of ,amphibians ,frogs have good eyes1 and the toad's eyes are jewels4 ,there is evidence of precise vision in the neat way in which a frog catches a fly1 flicking out its tongue1 which is fixed in front and loose behind4 ,there is also experimental proof that a frog discriminates between red and blue1 or between red and white1 and an interesting point is that while our skin is sensitive to heat rays but not to light1 the skin of the frog answers back to light rays as well4 ,professor ,yerkes experimented with a frog which had to go through a simple labyrinth if it wished to reach a tank of water4 ,at the first alternative between two paths1 a red card was placed on the wrong side and a white one on the other4 ,when the frog had learned to take the correct path1 marked by the white card1 ,prof4 ,yerkes changed the cards4 ,the confusion of the frog showed how thoroughly it had learned its lesson4 ,we know very little in regard to sense of smell or taste in amphibians2 but the sense of hearing is well developed1 more developed than might be inferred from the indifference that frogs show to almost all sounds except the croaking of their kindred and splashes in the water4 ,the toad looks almost sagacious when it is climbing up a bank1 and some of the tree-frogs are very alert2 but there is very little that we dare say about the amphibian mind4 ,we have mentioned that frogs may learn the secret of a simple maze1 and toads sometimes make for a particular spawning-pond from a considerable distance4 ,but an examination of their brains1 occupying a relatively small part of the broad1 flat skull1 warns us not to expect much intelligence4 ,on the other hand1 when we take frogs along a line that is very vital to them1 namely1 the discrimination of palatable and unpalatable insects1 we find1 by experiment1 that they are quick to learn and that they remember their lessons for many days4 ,frogs sometimes deposit their eggs in very unsuitable pools of water2 but perhaps that is not quite so stupid as it looks4 ,the egg-laying is a matter that has been1 as it were1 handed over to instinctive registration4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge4 ,,harpy-,,eagle ,clean and dainty and proud as a ,spanish ,don4 ,it is an arboreal and cliff-loving bird1 feeding chiefly on mammals1 very fierce and strong4 ,the under parts are mostly white1 with a greyish zone on the chest4 ,the upper parts are blackish-grey4 ,the harpy occurs from ,mexico to ,paraguay and ,bolivia4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge1 ,f4,z4,s4 ,,the ,,dingo ,,or ,,wild ,,dog ,,of ,,australia1 ,,perhaps ,,an ,,indigenous ,,wild ,,species1 ,,perhaps ,a ,,domesticated ,,dog ,,that ,,has ,,gone ,,wild ,,or ,,feral ,it does much harm in destroying sheep4 ,it is famous for its persistent death-feigning1 for an individual has been known to allow part of its skin to be removed1 in the belief that it was dead1 before betraying its vitality4 ,illustration3 ,,woodpecker1 ,,hammering ,,at ,a ,,cotton-,,reel1 ,,attached ,,to ,a ,,tree ,notice how the stiff tail-feathers braced against the stem help the bird to cling on with its toes4 ,the original hole1 in which this woodpecker inserted nuts for the purposes of cracking the shell and extracting the kernel1 is seen towards the top of the tree4 ,but the taker of the photograph tied on a hollowed-out cotton-reel as a receptacle for a nut1 and it was promptly discovered and used by the bird4 ,experiments in ,parental ,care ,it must be put to the credit of amphibians that they have made many experiments in methods of parental care1 as if they were feeling their way to new devices4 ,a common frog lays her clumps of eggs in the cradle of the water1 sometimes far over a thousand together2 the toad winds two long strings round and between water-weeds2 and in both cases that is all4 ,there is no parental care1 and the prolific multiplication covers the enormous infantile mortality4 ,this is the spawning solution of the problem of securing the continuance of the race4 ,but there is another solution1 that of parental care associated with an economical reduction of the number of eggs4 ,thus the male of the ,nurse-,frog 7,alytes71 not uncommon on the ,continent1 fixes a string of twenty to fifty eggs to the upper part of his hind-legs1 and retires to his hole1 only coming out at night to get some food and to keep up the moisture about the eggs4 ,in three weeks1 when the tadpoles are ready to come out1 he plunges into the pond and is freed from his living burden and his family cares4 ,in the case of the thoroughly aquatic ,surinam ,toad 7,pipa71 the male helps to press the eggs1 perhaps a hundred in number1 on to the back of the female1 where each sinks into a pocket of skin with a little lid4 ,by and by fully formed young toads jump out of the pockets4 ,in the ,south ,american tree-frogs called ,nototrema there is a pouch on the back of the female in which the eggs develop1 and it is interesting to find that in some species what come out are ordinary tadpoles1 while in other species the young emerge as miniatures of their parents4 ,strangest of all1 perhaps1 is the case of ,darwin's ,frog 7,rhinoderma of ,chili71 where the young1 about ten to fifteen in number1 develop in the male's croaking-sacs1 which become in consequence enormously distended4 ,eventually the strange spectacle is seen of miniature frogs jumping out of their father's mouth4 ,needless to say we are not citing these methods of parental care as examples of intelligence2 but perhaps they correct the impression of amphibians as a rather humdrum race4 ,whatever be the mental aspect of the facts1 there has certainly been some kind of experimenting1 and the increase of parental care1 so marked in many amphibians1 with associated reduction of the number of offspring is a finger-post on the path of progress4 #d ,the ,reptilian ,mind ,we speak of the wisdom of the serpent2 but it is not very easy to justify the phrase4 ,among all the multitude of reptiles--snakes1 lizards1 turtles1 and crocodiles1 a motley crowd--we cannot see much more than occasional traces of intelligence4 ,the inner life remains a tiny rill4 ,no doubt many reptiles are very effective2 but it is an instinctive rather than an intelligent efficiency4 ,the well-known soft-shell tortoise of the ,united ,states swims with powerful strokes and runs so quickly that it can hardly be overtaken4 ,it hunts vigorously for crayfish and insect larv in the rivers4 ,it buries itself in the mud when cold weather comes4 ,it may lie on a floating log ready to slip into the water at a moment's notice2 it may bask on a sunny bank or in the warm shallows4 ,great wariness is shown in choosing times and places for egg-laying4 ,the mother tramps the earth down upon the buried eggs4 ,all is effective4 ,similar statements might be made in regard to scores of other reptiles2 but what we see is almost wholly of the nature of instinctive routine1 and we get little glimpse of more than efficiency and endeavour4 ,in a few cases there is proof of reptiles finding their way back to their homes from a considerable distance1 and recognition of persons is indubitable4 ,gilbert ,white remarks of his tortoise3 ,whenever the good old lady came in sight who had waited on it for more than thirty years1 it always hobbled with awkward alacrity towards its benefactress1 while to strangers it was altogether inattentive4 ,of definite learning there are a few records4 ,thus ,professor ,yerkes studied a sluggish turtle of retiring disposition1 taking advantage of its strong desire to efface itself4 ,on the path of the darkened nest of damp grass he interposed a simple maze in the form of a partitioned box4 ,after wandering about constantly for thirty-five minutes the turtle found its way through the maze by chance4 ,two hours afterwards it reached the nest in fifteen minutes2 and after another interval of two hours it only required five minutes4 ,after the third trial1 the routes became more direct1 there was less aimless wandering4 ,the time of the twentieth trial was forty-five seconds2 that of the thirtieth1 forty seconds4 ,in the thirtieth case1 the path followed was quite direct1 and so it was on the fiftieth trip1 which only required thirty-five seconds4 ,of course1 the whole thing did not amount to very much2 but there was a definite learning1 a learning from experience1 which has played an important part in the evolution of animal behaviour4 ,comparing reptiles with amphibians1 we may recognise an increased masterliness of behaviour and a hint of greater plasticity4 ,the records of observers who have made pets of reptiles suggest that the life of feeling or emotion is growing stronger1 and so do stories1 if they can be accepted1 which suggest the beginning of conjugal affection4 ,the error must be guarded against of interpreting in terms of intelligence what is merely the outcome of long-continued structure adaptation4 ,when the limbless lizard called the ,slow-worm is suddenly seized by the tail1 it escapes by surrendering the appendage1 which breaks across a preformed weak plane4 ,but this is a reflex action1 not a reflective one4 ,it is comparable to our sudden withdrawal of our finger from a very hot cinder4 ,the ,egg-eating ,african snake ,dasypeltis gets the egg of a bird into its gullet unbroken1 and cuts the shell against downward-projecting sharp points of the vertebr4 ,none of the precious contents is lost and the broken empties are returned4 ,it is admirable1 indeed unsurpassable2 but it is not intelligent4 #e ,mind in ,birds ,sight and hearing are highly developed in birds1 and the senses1 besides pulling the triggers of inborn efficiencies1 supply the raw materials for intelligence4 ,there is some truth1 though not the whole truth1 in the old philosophical dictum1 that there is nothing in the intellect which was not previously in the senses4 ,many people have admired the certainty and alacrity with which gulls pick up a fragment of biscuit from the white wake of a steamer1 and the incident is characteristic4 ,in their power of rapidly altering the focus of the eye1 birds are unsurpassed4 ,to the sense of sight in birds1 the sense of hearing comes a good second4 ,a twig breaks under our feet1 and out sounds the danger-call of the bird we were trying to watch4 ,many young birds1 like partridges1 respond when two or three hours old to the anxious warning note of the parents1 and squat motionless on the ground1 though other sounds1 such as the excited clucking of a foster-mother hen1 leave them indifferent4 ,they do not know what they are doing when they squat2 they are obeying the living hand of the past which is within them4 ,their behaviour is instinctive4 ,but the present point is the discriminating quality of the sense of hearing2 and that is corroborated by the singing of birds4 ,it is emotional art1 expressing feelings in the medium of sound4 ,on the part of the females1 who are supposed to listen1 it betokens a cultivated ear4 ,illustration3 ,,the ,,beaver ,the beaver will gnaw through trees a foot in diameter2 to save itself more trouble than is necessary1 it will stop when it has gnawed the trunk till there is only a narrow core left1 having the wit to know that the autumn gales will do the rest4 ,illustration3 ,photo3 ,f4 ,r4 ,hinkins ,son4 ,,the ,,thrush ,,at ,,its ,,anvil ,the song-thrush takes the snail's shell in its bill1 and knocks it against a stone until it breaks1 making the palatable flesh available4 ,many broken shells are often found around the anvil4 ,as to the other senses1 touch is not highly developed except about the bill1 where it reaches a climax in birds like the wood-cock1 which probe for unseen earthworms in the soft soil4 ,taste seems to be poorly developed1 for most birds bolt their food1 but there is sometimes an emphatic rejection of unpalatable things1 like toads and caterpillars4 ,of smell in birds little is known1 but it has been proved to be present in certain cases1 e4g4 in some nocturnal birds of prey4 ,it seems certain that it is by sight1 not by smell1 that the eagles gather to the carcass2 but perhaps there is more smell in birds than they are usually credited with4 ,one would like to experiment with the oil from the preen gland of birds to see whether the scent of this does not help in the recognition of kin by kin at night or amid the darkness of the forest4 ,there may be other senses in birds1 such as a sense of temperature and a sense of balance2 but no success has attended the attempts made to demonstrate a magnetic sense1 which has been impatiently postulated by students of bird migration in order to explain how the birds find their way4 ,the big fact is that in birds there are two widely open gateways of knowledge1 the sense of sight and the sense of hearing4 ,instinctive ,aptitudes ,many a young water-bird1 such as a coot1 swims right away when it is tumbled into water for the first time4 ,so chicks peck without any learning or teaching1 very young ducklings catch small moths that flit by1 and young plovers lie low when the danger-signal sounds4 ,but birds seem strangely limited as regards many of these instinctive capacities--limited when compared with the little-brained ants and bees1 which have from the first such a rich repertory of ready-made cleverness4 ,the limitation in birds is of great interest1 for it means that intelligence is coming to its own and is going to take up the reins at many corners of the daily round4 ,professor ,lloyd ,morgan observed that his chickens incubated in the laboratory had no instinctive awareness of the significance of their mother's cluck when she was brought outside the door4 ,although thirsty and willing to drink from a moistened finger-tip1 they did not instinctively recognize water1 even when they walked through a saucerful4 ,only when they happened to peck their toes as they stood in the water did they appreciate water as the stuff they wanted1 and raise their bills up to the sky4 ,once or twice they actually stuffed their crops with worms of red worsted6 ,instinctive aptitudes1 then1 the young birds have1 but these are more limited than in ants1 bees1 and wasps2 and the reason is to be found in the fact that the brain is now evolving on the tack of what ,sir ,ray ,lankester has called educability4 ,young birds learn with prodigious rapidity2 the emancipation of the mind from the tyranny of hereditary obligations has begun4 ,young birds make mistakes1 like the red worsted mistake1 but they do not make the same mistakes often4 ,they are able to profit by experience in a very rapid way4 ,we do not mean that creatures of the little-brain type1 like ants1 bees1 and wasps1 are unable to profit by experience or are without intelligence4 ,there are no such hard-and-fast lines4 ,we mean that in the ordinary life of insects the enregistered instinctive capacities are on the whole sufficient for the occasion1 and that intelligent educability is very slightly developed4 ,nor do we mean that birds are quite emancipated from the tyranny of engrained instinctive obligations1 and can always ring up intelligence in a way that is impossible for the stereotyped bee4 ,the sight of a pigeon brooding on an empty nest1 while her two eggs lie disregarded only a couple of inches away1 is enough to show that along certain lines birds may find it impossible to get free from the trammels of instinct4 ,the peculiar interest of birds is that they have many instincts and yet a notable power of learning intelligently4 ,intelligence co-operating with ,instinct ,professor ,lloyd ,morgan was foster-parent to two moorhens which grew up in isolation from their kindred4 ,they swam instinctively1 but they would not dive1 neither in a large bath nor in a current4 ,but it happened one day when one of these moorhens was swimming in a pool on a ,yorkshire stream1 that a puppy came barking down the bank and made an awkward feint towards the young bird4 ,in a moment the moorhen dived1 disappeared from view1 and soon partially reappeared1 his head just peeping above the water beneath the overhanging bank4 ,this was the first time the bird had dived1 and the performance was absolutely true to type4 ,there can be little doubt as to the meaning of this observation4 ,the moorhen has an hereditary or instinctive capacity for swimming and diving1 but the latter is not so easily called into activity as the former4 ,the particular moorhen in question had enjoyed about two months of swimming experience1 which probably counted for something1 but in the course of that experience nothing had pulled the trigger of the diving capacity4 ,on an eventful day the young moorhen saw and heard the dog2 it was emotionally excited2 it probably did to some extent intelligently appreciate a novel and meaningful situation4 ,intelligence cooperated with instinct1 and the bird dived appropriately4 ,birds have inborn predispositions to certain effective ways of pecking1 scratching1 swimming1 diving1 flying1 crouching1 lying low1 nest-building1 and so on2 but they are marked off from the much more purely instinctive ants and bees by the extent to which individual nurture seems to mingle with the inherited nature4 ,the two together result in the fine product which we call the bird's behaviour4 ,after ,lloyd ,morgan's chicks had tried a few conspicuous and unpalatable caterpillars1 they had no use for any more4 ,they learned in their early days with prodigious rapidity1 illustrating the deep difference between the big-brain type1 relatively poor in its endowment of instinctive capacities1 but eminently educable1 and the little-brain type1 say1 of ants and bees1 richly endowed with instinctive capacities1 but very far from being quick or glad to learn4 ,we owe it to ,sir ,ray ,lankester to have made it clear that these two types of brain are1 as it were1 on different tacks of evolution1 and should not be directly pitted against one another4 ,the little-brain type makes for a climax in the ant1 where instinctive behaviour reaches a high degree of perfection2 the big-brain type reaches its climax in horse and dog1 in elephant and monkey4 ,the particular interest that attaches to the behaviour of birds is in the combination of a good deal of instinct with a great deal of intelligent learning4 ,this is well illustrated when birds make a nest out of new materials or in some quite novel situation4 ,it is clearly seen when birds turn to some new kind of food1 like the ,kea parrot1 which attacks the sheep in ,new ,zealand4 ,some young woodpeckers are quite clever in opening fir cones to get at the seeds1 and this might be hastily referred to a well-defined hereditary capacity4 ,but the facts are that the parents bring their young ones first the seeds themselves1 then partly opened cones1 and then intact ones4 ,there is an educative process1 and so it is in scores of cases4 ,using their ,wits ,when the ,greek eagle lifts the ,greek tortoise in its talons1 and lets it fall from a height so that the strong carapace is broken and the flesh exposed1 it is making intelligent use of an expedient4 ,whether it discovered the expedient by experimenting1 as is possible1 or by chance1 as is more likely1 it uses it intelligently4 ,in the same way herring-gulls lift sea-urchins and clams in their bills1 and let them fall on the rocks so that the shells are broken4 ,in the same way rooks deal with freshwater mussels4 ,the ,thrush's ,anvil ,a very instructive case is the behaviour of the song-thrush when it takes a wood-snail in its beak and hammers it against a stone1 its so-called anvil4 ,to a young thrush1 which she had brought up by hand1 ,miss ,frances ,pitt offered some wood-snails1 but it took no interest in them until one put out its head and began to move about4 ,the bird then pecked at the snail's horns1 but was evidently puzzled when the creature retreated within the shelter of the shell4 ,this happened over and over again1 the thrush's inquisitive interest increasing day by day4 ,it pecked at the shell and even picked it up by the lip1 but no real progress was made till the sixth day1 when the thrush seized the snail and beat it on the ground as it would a big worm4 ,on the same day it picked up a shell and knocked it repeatedly against a stone1 trying first one snail and then another4 ,after fifteen minutes' hard work1 the thrush managed to break one1 and after that it was all easy4 ,a certain predisposition to beat things on the ground was doubtless present1 but the experiment showed that the use of an anvil could be arrived at by an untutored bird4 ,after prolonged trying it found out how to deal with a difficult situation4 ,it may be said that in more natural conditions this might be picked up by imitation1 but while this is quite possible1 it is useful to notice that experiments with animals lead us to doubt whether imitation counts for nearly so much as used to be believed4 #f ,the ,mind of the ,mammal ,when we watch a collie at a sheep-driving competition1 or an elephant helping the forester1 or a horse shunting waggons at a railway siding1 we are apt to be too generous to the mammal mind4 ,for in the cases we have just mentioned1 part of man's mind has1 so to speak1 got into the animal's4 ,on the other hand1 when we study rabbits and guinea-pigs1 we are apt to be too stingy1 for these rodents are under the average of mammals1 and those that live in domestication illustrate the stupefying effect of a too sheltered life4 ,the same applies to domesticated sheep contrasted with wild sheep1 or even with their own lambs4 ,if we are to form a sound judgment on the intelligence of mammals we must not attend too much to those that have profited by man's training1 nor to those whose mental life has been dulled by domestication4 ,instinctive ,aptitudes ,what is to be said of the behaviour of beavers who gnaw the base of a tree with their chisel-edged teeth till only a narrow core is left--to snap in the first gale1 bringing the useful branches down to the ground8 ,what is to be said of the harvest-mouse constructing its nest1 or of the squirrel making cache after cache of nuts8 ,these and many similar pieces of behaviour are fundamentally instinctive1 due to inborn predispositions of nerve-cells and muscle-cells4 ,but in mammals they seem to be often attended by a certain amount of intelligent attention1 saving the creature from the tyranny of routine so marked in the ways of ants and bees4 ,sheer ,dexterity ,besides instinctive aptitudes1 which are exhibited in almost equal perfection by all the members of the same species1 there are acquired dexterities which depend on individual opportunities4 ,they are also marked by being outside and beyond ordinary routine--not that any rigorous boundary line can be drawn4 ,we read that at ,mathura on the ,jumna doles of food are provided by the piety of pilgrims for the sacred river-tortoises1 which are so crowded when there is food going that their smooth carapaces form a more or less continuous raft across the river4 ,on that unsteady slippery bridge the ,langur monkeys 7,semnopithecus entellus7 venture out and in spite of vicious snaps secure a share of the booty4 ,this picture of the monkeys securing a footing on the moving mass of turtle-backs is almost a diagram of sheer dexterity4 ,it illustrates the spirit of adventure1 the will to experiment1 which is1 we believe1 the main motive-force in new departures in behaviour4 ,illustration3 ,photo3 ,lafayette ,,alsatian ,,wolf-,,dog ,an animal of acute senses and great intelligence4 ,it was of great service in the war4 7,the dog shown1 ,arno von ,indetal1 is a trained police dog and did service abroad during the war47 ,illustration3 ,photo3 ,w4 ,s4 ,berridge4 ,,the ,,polar ,,bear ,,of ,,the ,,far ,,north ,an animal of extraordinary strength1 able with a stroke of its paw to lift a big seal right out of the water and send it crashing along the ice4 ,the food consists chiefly of seals4 ,the sexes wander separately4 ,a hole is often dug as a winter retreat1 but there is no hibernation4 ,a polar bear in captivity has been seen making a current with its paw in the water of its pool in order to secure floating buns without trouble--an instance of sheer intelligence4 ,illustration3 ,from the ,smithsonian ,report1 #aiad ,,an ,,alligator ,,yawning ,,in ,,expectation ,,of ,,food ,note the large number of sharp conical teeth fixed in sockets along the jaws4 ,power of ,association ,a bull-terrier called ,jasper1 studied by ,prof4 ,j4 ,b4 ,watson1 showed great power of associating certain words with certain actions4 ,from a position invisible to the dog the owner would give certain commands1 such as ,go into the next room and bring me a paper lying on the floor4 ,jasper did this at once1 and a score of similar things4 ,lord ,avebury's dog ,van was accustomed to go to a box containing a small number of printed cards and select the card ,,tea or ,,out1 as the occasion suggested4 ,it had established an association between certain black marks on a white background and the gratification of certain desires4 ,it is probable that some of the extraordinary things horses and dogs have been known to do in the way of stamping a certain number of times in supposed indication of an answer to an arithmetical question 7in the case of horses71 or of the name of an object drawn 7in the case of dogs71 are dependent on clever associations established by the teacher between minute signs and a number of stampings4 ,what is certain is that mammals have in varying degrees a strong power of establishing associations4 ,there is often some delicacy in the association established4 ,everyone knows of cases where a dog1 a cat1 or a horse will remain quite uninterested1 to all appearance1 in its owner's movements until some little detail1 such as taking a key from its peg1 pulls the trigger4 ,now the importance of this in the wild life of the fox or the hare1 the otter or the squirrel1 is obviously that the young animals learn to associate certain sounds in their environment with definite possibilities4 ,they have to learn an alphabet of woodcraft1 the letters of which are chiefly sounds and scents4 ,the ,dancing ,mouse as a ,pupil ,the dancing or waltzing mouse is a ,japanese variety with many peculiarities1 such as having only one of the three semicircular canals of the ear well developed4 ,it has a strong tendency to waltz round and round in circles without sufficient cause and to trip sideways towards its dormitory instead of proceeding in the orthodox head-on fashion4 ,but this freak is a very educable creature1 as ,professor ,yerkes has shown4 ,in a careful way he confronted his mouse-pupil with alternative pathways marked by different degrees of illumination1 or by different colours4 ,if the mouse chose compartment ,a1 it found a clear passage direct to its nest2 if it chose compartment ,b1 it was punished by a mild electric shock and it had to take a roundabout road home4 ,needless to say1 the ,a compartment was sometimes to the right hand1 sometimes to the left1 else mere position would have been a guide4 ,the experiments showed that the dancing mice learn to discriminate the right path from the wrong1 and similar results have been got from other mammals1 such as rats and squirrels4 ,there is no proof of learning by ideas1 but there is proof of learning by experience4 ,and the same must be true in wild life4 ,many mammals1 such as cats and rats1 learn how to manipulate puzzle-boxes and how to get at the treasure at the heart of a ,hampton ,court maze4 ,some of the puzzle-boxes1 with a reward of food inside1 are quite difficult1 for the various bolts and bars have to be dealt with in a particular order1 and yet many mammals master the problem4 ,what is plain is that they gradually eliminate useless movements1 that they make fewer and fewer mistakes1 that they eventually succeed1 and that they register the solution within themselves so that it remains with them for a time4 ,it looks a little like the behaviour of a man who learns a game of skill without thinking4 ,it is a learning by experience1 not by ideas or reflection4 ,thus it is very difficult to suppose that a rat or a cat could form any idea or even picture of the ,hampton ,court maze--which they nevertheless master4 ,learning ,tricks ,given sufficient inducement many of the cleverer mammals will learn to do very sensible things1 and no one is wise enough to say that they never understand what they are doing4 ,yet it is certain that trained animals often exhibit pieces of behaviour which are not nearly so clever as they look4 ,the elephant at the ,belle ,vue ,gardens in ,manchester used to collect pennies from benevolent visitors4 ,when it got a penny in its trunk it put it in the slot of an automatic machine which delivered up a biscuit4 ,when a visitor gave the elephant a halfpenny it used to throw it back with disgust4 ,at first sight this seemed almost wise1 and there was no doubt some intelligent appreciation of the situation4 ,but it was largely a matter of habituation1 the outcome of careful and prolonged training4 ,the elephant was laboriously taught to put the penny in the slot and to discriminate between the useful pennies and the useless halfpennies4 ,it was not nearly so clever as it looked4 ,using their ,wits ,in the beautiful ,zoological ,park in ,edinburgh the ,polar ,bear was wont to sit on a rocky peninsula of a water-filled quarry4 ,the visitors threw in buns1 some of which floated on the surface4 ,it was often easy for the ,polar ,bear to collect half a dozen by plunging into the pool4 ,but it had discovered a more interesting way4 ,at the edge of the peninsula it scooped the water gently with its huge paw and made a current which brought the buns ashore4 ,this was a simple piece of behaviour1 but it has the smack of intelligence--of putting two and two together in a novel way4 ,it suggests the power of making what is called a perceptual inference4 ,on the occasion of a great flood in a meadow it was observed that a number of mares brought their foals to the top of a knoll1 and stood round about them protecting them against the rising water4 ,a dog has been known to show what was at any rate a plastic appreciation of a varying situation in swimming across a tidal river4 ,it changed its starting-point1 they say1 according to the flow or ebb of the tide4 ,arctic foxes and some other wild mammals show great cleverness in dealing with traps1 and the manipulative intelligence of elephants is worthy of all our admiration4 #g ,why is there not more ,intelligence8 ,when we allow for dexterity and power of association1 when we recognise a certain amount of instinctive capacity and a capacity for profiting by experience in an intelligent way1 we must admit a certain degree of disappointment when we take a survey of the behaviour of mammals1 especially of those with very fine brains1 from which we should naturally expect great things4 ,why is there not more frequent exhibition of intelligence in the stricter sense8 ,the answer is that most mammals have become in the course of time very well adapted to the ordinary conditions of their life1 and tend to leave well alone4 ,they have got their repertory of efficient answers to the ordinary questions of everyday life1 and why should they experiment8 ,in the course of the struggle for existence what has been established is efficiency in normal circumstances1 and therefore even the higher animals tend to be no cleverer than is necessary4 ,so while many mammals are extraordinarily efficient1 they tend to be a little dull4 ,their mental equipment is adequate for the everyday conditions of their life1 but it is not on sufficiently generous lines to admit of1 let us say1 an interest in ,nature or adventurous experiment4 ,mammals always tend to play for safety4 ,we hasten1 however1 to insert here some very interesting saving clauses4 ,experimentation in ,play ,a glimpse of what mammals are capable of1 were it necessary1 may be obtained by watching those that are playful1 such as lambs and kids1 foals and calves1 young foxes and others4 ,for these young creatures let themselves go irresponsibly1 they are still unstereotyped1 they test what they and their fellows can do4 ,the experimental character of much of animal play is very marked4 ,it is now recognised by biologists that play among animals is the young form of work1 and that the playing period1 often so conspicuous1 is vitally important as an apprenticeship to the serious business of life and as an opportunity for learning the alphabet of ,nature4 ,but the playing period is much more2 it is one of the few opportunities animals have of making experiments without too serious responsibilities4 ,play is ,nature's device for allowing elbow-room for new departures 7behaviour-variations7 which may form part of the raw materials of progress4 ,play1 we repeat1 gives us a glimpse of the possibilities of the mammal mind4 ,other ,glimpses of ,intelligence ,a squirrel is just as clever as it needs to be and no more2 and of some vanishing mammals1 like the beaver1 not even this can be said4 ,humdrum non-plastic efficiency is apt to mean stagnation4 ,now we have just seen that in the play of young mammals there is an indication of unexhausted possibilities1 and we get the same impression when we think of three other facts4 7a7 ,in those mammals1 like dog and horse1 which have entered into active cooperative relations with man1 we see that the mind of the mammal is capable of much more than the average would lead us to think4 ,when man's sheltering is too complete and the domesticated creature is passive in his grip1 the intelligence deteriorates4 7b7 ,when we study mammals1 like the otter1 which live a versatile life in a very complex and difficult environment1 we get an inspiriting picture of the play of wits4 7c7 ,thirdly1 when we pass to monkeys1 where the fore-limb has become a free hand1 where the brain shows a relatively great improvement1 where words are much used1 we cannot fail to recognise the emergence of something new--a restless inquisitiveness1 a desire to investigate the world1 an unsatisfied tendency to experiment4 ,we are approaching the ,dawn of ,reason4 ,,the ,,mind ,,of ,,monkeys #h ,there is a long gamut between the bushy-tailed1 almost squirrel-like marmosets and the big-brained chimpanzee4 ,there is great variety of attainment at different levels in the ,simian tribe4 ,keen ,senses ,to begin at the beginning1 it is certain that monkeys have a first-class sensory equipment1 especially as regards sight1 hearing1 and touch4 ,the axes of the two eyes are directed forwards as in man1 and a large section of the field of vision is common to both eyes4 ,in other words1 monkeys have a more complete stereoscopic vision than the rest of the mammals enjoy4 ,they look more and smell less4 ,they can distinguish different colours1 apart from different degrees of brightness in the coloured objects4 ,they are quick to discriminate differences in the shapes of things1 e4g4 boxes similar in size but different in shape1 for if the prize is always put in a box of the same shape they soon learn 7by association7 to select the profitable one4 ,they learn to discriminate cards with short words or with signs printed on them1 coming down when the ,yes card is shown1 remaining on their perch when the card says ,no4 ,bred to a forest life where alertness is a life-or-death quality1 they are quick to respond to a sudden movement or to pick out some new feature in their surroundings4 ,and what is true of vision holds also for hearing4 ,power of ,manipulation ,another quality which separates monkeys very markedly from ordinary mammals is their manipulative expertness1 the co-ordination of hand and eye4 ,this great gift follows from the fact that among monkeys the fore-leg has been emancipated4 ,it has ceased to be indispensable as an organ of support2 it has become a climbing1 grasping1 lifting1 handling organ4 ,the fore-limb has become a free hand1 and everyone who knows monkeys at all is aware of the zest with which they use their tool4 ,they enjoy pulling things to pieces--a kind of dissection--or screwing the handle off a brush and screwing it on again4 ,illustration3 ,photo3 ,w4 ,p4 ,dando ,,baby ,,orang ,notice the small ears and the suggestion of good temper4 ,the mother orang will throw prickly fruits and pieces of branches at those who intrude on her maternal care4 ,illustration3 ,photo3 ,gambier ,bolton4 ,,orang-,,utan ,a large and heavy ape1 frequenting forests in ,sumatra and ,borneo1 living mainly in trees1 where a temporary nest is made4 ,the expression is melancholy1 the belly very protuberant1 the colour yellow-brown1 the movements are cautious and slow4 ,illustration3 #a4 ,,chimpanzee #b4 ,,baby ,,orang-,,utan #c4 ,,orang-,,utan #d4 ,,baby ,,chimpanzees ,photos3 ,james's ,press ,agency4 ,in his famous book on ,the ,expression of the ,emotions in ,man and ,animals 7#ahgb7 ,charles ,darwin showed that many forms of facial expression familiar in man have their counterparts in apes and other mammals4 ,he also showed how important the movements of expression are as means of communication between mother and offspring1 mate and mate1 kith and kin4 ,the anthropoid apes show notable differences of temperament as the photographs show4 ,the chimpanzee is lively1 cheerful1 and educable4 ,the orang is also mild of temper1 but often and naturally appears melancholy in captivity4 ,this is not suggested1 however1 by our photograph of the adult4 ,both chimpanzee and orang are markedly contrasted with the fierce and gloomy gorilla4 ,activity for ,activity's ,sake ,professor ,thorndike hits the nail on the head when he lays stress on the intensity of activity in monkeys--activity both of body and mind4 ,they are pent-up reservoirs of energy1 which almost any influence will tap4 ,watch a cat or a dog1 ,professor ,thorndike says2 it does comparatively few things and is content for long periods to do nothing4 ,it will be splendidly active in response to some stimulus such as food or a friend or a fight1 but if nothing appeals to its special make-up1 which is very utilitarian in its interests1 it will do nothing4 ,watch a monkey and you cannot enumerate the things he does1 cannot discover the stimuli to which he reacts1 cannot conceive the raison d'etre of his pursuits4 ,everything appeals to him4 ,he likes to be active for the sake of activity4 ,this applies to mental activity as well1 and the quality is one of extraordinary interest1 for it shows the experimenting mood at a higher turn of the spiral than in any other creature1 save man4 ,it points forward to the scientific spirit4 ,we cannot1 indeed1 believe in the sudden beginning of any quality1 and we recall the experimenting of playing mammals1 such as kids and kittens1 or of inquisitive adults like ,kipling's mongoose1 ,riki-,tiki-,tavi1 which made it his business in life to find out about things4 ,but in monkeys the habit of restless experimenting rises to a higher pitch4 ,they appear to be curious about the world4 ,the psychologist whom we have quoted tells of a monkey which happened to hit a projecting wire so as to make it vibrate4 ,he went on repeating the performance hundreds of times during the next few days4 ,of course1 he got nothing out of it1 save fun1 but it was grist to his mental mill4 ,the fact of mental life is to monkeys it own reward4 ,the monkey's brain is tender all over1 functioning throughout1 set off in action by anything and everything4 ,sheer ,quickness ,correlated with the quality of restless inquisitiveness and delight in activity for its own sake there is the quality of quickness4 ,we mean not merely the locomotor agility that marks most monkeys1 but quickness of perception and plan4 ,it is the sort of quality that life among the branches will engender1 where it is so often a case of neck or nothing4 ,it is the quality which we describe as being on the spot1 though the phrase has slipped from its original moorings4 ,speaking of his ,bonnet ,monkey1 an ,indian macaque1 second cousin to the kind that lives on the ,rock of ,gibraltar1 ,professor ,s4 ,j4 ,holmes writes3 ,for keenness of perception1 rapidity of action1 facility in forming good practical judgments about ways and means of escaping pursuit and of attaining various other ends1 ,lizzie had few rivals in the animal world4444 ,her perceptions and decisions were so much more rapid than my own that she would frequently transfer her attention1 decide upon a line of action1 and carry it into effect before ,i was aware of what she was about4 ,until ,i came to guard against her nimble and unexpected manoeuvres1 she succeeded in getting possession of many apples and peanuts which ,i had not intended to give her except upon the successful performance of some task4 ,quick to ,learn ,quite fundamental to any understanding of animal behaviour is the distinction so clearly drawn by ,sir ,ray ,lankester between the little-brain type1 rich in inborn or instinctive capacities1 but relatively slow to learn1 and the big-brain type1 with a relatively poor endowment of specialised instincts1 but with great educability4 ,the little-brain type finds its climax in ants and bees2 the big-brain type in horses and dogs1 elephants and monkeys4 ,and of all animals monkeys are the quickest to learn1 if we use the word learn to mean the formation of useful associations between this and that1 between a given sense-presentation and a particular piece of behaviour4 ,the ,case of ,sally ,some of us remember ,sally1 the chimpanzee at the ,zoo with which ,dr4 ,romanes used to experiment4 ,she was taught to give her teacher the number of straws he asked for1 and she soon learned to do so up to five4 ,if she handed a number not asked for1 her offer was refused2 if she gave the proper number1 she got a piece of fruit4 ,if she was asked for five straws1 she picked them up individually and placed them in her mouth1 and when she had gathered five she presented them together in her hand4 ,attempts to teach her to give six to ten straws were not very successful4 ,for ,sally above six meant many1 and besides1 her limits of patience were probably less than her range of computation4 ,this was hinted at by the highly interesting circumstance that when dealing with numbers above five she very frequently doubled over a straw so as to make it present two ends and thus appear as two straws4 ,the doubling of the straw looked like an intelligent device to save time1 and it was persistently resorted to in spite of the fact that her teacher always refused to accept a doubled straw as equivalent to two straws4 ,here we get a glimpse of something beyond the mere association of a sound--,five--and that number of straws4 ,the ,case of ,lizzie ,the front of the cage in which ,professor ,holmes kept ,lizzie was made of vertical bars which allowed her to reach out with her arm4 ,on a board with an upright nail as handle1 there was placed an apple--out of ,lizzie's reach4 ,she reached immediately for the nail1 pulled the board in and got the apple4 ,there was no employment of the method of trial and error2 there was direct appropriate action following the perception of her relation to board1 nail1 and apple4 ,of course her ancestors may have been adepts at drawing a fruit-laden branch within their reach1 but the simple experiment was very instructive4 ,all the more instructive because in many other cases the experiments indicate a gradual sifting out of useless movements and an eventful retention of the one that pays4 ,when ,lizzie was given a vaseline bottle containing a peanut and closed with a cork1 she at once pulled the cork out with her teeth1 obeying the instinct to bite at new objects1 but she never learned to turn the bottle upside down and let the nut drop out4 ,she often got the nut1 and after some education she got it more quickly than she did at first1 but there was no indication that she ever perceived the fit and proper way of getting what she wanted4 ,in the course of her intent efforts her mind seemed so absorbed with the object of desire that it was never focussed on the means of attaining that object4 ,there was no deliberation1 and no discrimination between the important and the unimportant elements in her behaviour4 ,the gradually increasing facility of her performances depended on the apparently unconscious elimination of useless movements4 ,this may be called learning1 but it is learning at a very low level2 it is far from learning by ideas2 it is hardly even learning by experiment2 it is not more than learning by experience1 it is not more than fumbling at learning6 ,trial and ,error ,a higher note is struck in the behaviour of some more highly endowed monkeys4 ,in many experiments1 chiefly in the way of getting into boxes difficult to open1 there is evidence 7#a7 of attentive persistent experiment 7#b7 of the rapid elimination of ineffective movements1 and 7#c7 of remembering the solution when it was discovered4 ,kinnaman taught two macaques the ,hampton ,court ,maze1 a feat which probably means a memory of movements1 and we get an interesting glimpse in his observation that they began to smack their lips audibly when they reached the latter part of their course1 and began to feel1 dare one say1 ,we are right this time4 ,in getting into puzzle-boxes and into combination-boxes 7where the barriers must be overcome in a definite order71 monkeys learn by the trial and error method much more quickly than cats and dogs do1 and a very suggestive fact emphasized by ,professor ,thorndike is a process of sudden acquisition by a rapid1 often apparently instantaneous abandonment of the unsuccessful movements and selection of the appropriate one1 which rivals in suddenness the selections made by human beings in similar performances4 ,a higher note still was sounded by one of ,thorndike's monkeys which opened a puzzle-box at once1 eight months after his previous experience with it4 ,for here was some sort of registration of a solution4 ,imitation ,two chimpanzees in the ,dublin ,zoo were often to be seen washing the two shelves of their cupboard and wringing the wet cloth in the approved fashion4 ,it was like a caricature of a washerwoman1 and someone said1 ,what mimics they are6 ,now we do not know whether that was or was not the case with the chimpanzees1 but the majority of the experiments that have been made do not lead us to attach to imitation so much importance as is usually given to it by the popular interpreter4 ,there are instances where a monkey that had given up a puzzle in despair returned to it when it had seen its neighbour succeed1 but most of the experiments suggested that the creature has to find out for itself4 ,even with such a simple problem as drawing food near with a stick1 it often seems of little use to show the monkey how it is done4 ,placing a bit of food outside his monkey's cage1 ,professor ,holmes poked it about with the stick so as to give her a suggestion of how the stick might be employed to move the food within reach1 but although the act was repeated many times ,lizzie never showed the least inclination to use the stick to her advantage4 ,perhaps the idea of a tool is beyond the ,bonnet ,monkey1 yet here again we must be cautious1 for ,professor ,l4 ,t4 ,hobhouse had a monkey of the same macaque genus which learned in the course of time to use a crooked stick with great effect4 ,the ,case of ,peter ,perhaps the cleverest monkey as yet studied was a performing chimpanzee called ,peter1 which has been generally described by ,dr4 ,lightner ,witmer4 ,peter could skate and cycle1 thread needles and untie knots1 smoke a cigarette and string beads1 screw in nails and unlock locks4 ,but what ,peter was thinking about all the time it was hard to guess1 and there is very little evidence to suggest that his rapid power of putting two and two together ever rose above a sort of concrete mental experimenting1 which ,dr4 ,romanes used to call perceptual inference4 ,without supposing that there are hard-and-fast boundary lines1 we cannot avoid the general conclusion that1 while monkeys are often intelligent1 they seldom1 if ever1 show even hints of reason1 i4e4 of working or playing with general ideas4 ,that remains ,man's prerogative4 ,the ,bustle of the ,mind ,in mammals like otters1 foxes1 stoats1 hares1 and elephants1 what a complex of tides and currents there must be in the brain-mind6 ,we may think of a stream with currents at different levels4 ,lowest there are the basal appetites of hunger and sex1 often with eddies rising to the surface4 ,then there are the primary emotions1 such as fear of hereditary enemies and maternal affection for offspring4 ,above these are instinctive aptitudes1 inborn powers of doing clever things without having to learn how4 ,but in mammals these are often expressed along with1 or as it were through1 the controlled life of intelligent activity1 where there is more clear-cut perceptual influence4 ,illustration3 ,photo3 ,w4 ,p4 ,dando4 ,,chimpanzee ,an ,african ape1 at home in the equatorial forests1 a lively and playful creature1 eminently educable4 ,illustration3 ,photo3 ,w4 ,s4 ,berridge4 ,,young ,,cheetahs1 ,,or ,,hunting ,,leopards ,trained to hunt from time immemorial and quite easily tamed4 ,cheetahs occur in ,india1 ,persia1 ,turkestan1 and ,africa4 ,illustration3 ,photo3 ,c4 ,reid4 ,,common ,,otter ,one of the most resourceful of animals and the most playsomest crittur on ,god's earth4 ,it neither stores nor hibernates1 but survives in virtue of its wits and because of the careful education of the young4 ,the otter is a roving animal1 often with more than one resting-place2 it has been known to travel fifteen miles in a night4 ,higher still are the records or memories of individual experience and the registration of individual habits1 while on the surface is the instreaming multitude of messages from the outside world1 like raindrops and hailstones on the stream1 some of them penetrating deeply1 being1 as we say1 full of meaning4 ,the mind of the higher animal is in some respects like a child's mind1 in having little in the way of clear-cut ideas1 in showing no reason in the strict sense1 and in its extraordinary educability1 but it differs from the child's mind entirely in the sure effectiveness of a certain repertory of responses4 ,it is efficient to a degree4 ,until at last arose the ,man4 ,man's brain is more complicated than that of the higher apes--gorilla1 orang1 and chimpanzee--and it is relatively larger4 ,but the improvements in structure do not seem in themselves sufficient to account for man's great advance in intelligence4 ,the rill of inner life has become a swift stream1 sometimes a rushing torrent4 ,besides perceptual inference or ,intelligence--a sort of picture-logic1 which some animals likewise have--there is conceptual inference--or ,reason--an internal experimenting with general ideas4 ,even the cleverest animals1 it would seem1 do not get much beyond playing with particulars2 man plays an internal game of chess with universals4 ,intelligent behaviour may go a long way with mental images2 rational conduct demands general ideas4 ,it may be1 however1 that percepts and concepts differ rather in degree than in kind1 and that the passage from one to the other meant a higher power of forming associations4 ,a clever dog has probably a generalised percept of man1 as distinguished from a memory-image of the particular men it has known1 but man alone has the concept ,man1 or ,mankind1 or ,humanity4 ,experimenting with concepts or general ideas is what we call ,reason4 ,here1 of course1 we get into deep waters1 and perhaps it is wisest not to attempt too much4 ,so we shall content ourselves here with pointing out that ,man's advance in intelligence and from intelligence to reason is closely wrapped up with his power of speech4 ,what animals began--a small vocabulary--he has carried to high perfection4 ,but what is distinctive is not the vocabulary so much as the habit of making sentences1 of expressing judgments in a way which admitted of communication between mind and mind4 ,the multiplication of words meant much1 the use of words as symbols of general ideas meant even more1 for it meant the possibility of playing the internal game of thinking2 but perhaps the most important advance of all was the means of comparing notes with neighbours1 of corroborating individual experience by social intercourse4 ,with words1 also1 it became easier to enregister outside himself the gains of the past4 ,it is not without significance that the ,greek ,logos1 which may be translated the word1 may also be translated ,mind4 #i ,looking ,backwards ,when we take a survey of animal behaviour we see a long inclined plane4 ,the outer world provokes simple creatures to answer back2 simple creatures act experimentally on their surroundings4 ,from the beginning this twofold process has been going on1 receiving stimuli from the environment and acting upon the environment1 and according to the efficiency of the reactions and actions living creatures have been sifted for millions of years4 ,one main line of advance has been opening new gateways of knowledge--the senses1 which are far more than five in number4 ,the other main line of advance has been in most general terms1 experimenting or testing1 probing and proving1 trying one key after another till a door is unlocked4 ,there is progress in multiplying the gateways of knowledge and making them more discriminating1 and there is progress in making the modes of experimenting more wide-awake1 more controlled1 and more resolute4 ,but behind both of these is the characteristically vital power of enregistering within the organism the lessons of the past4 ,in the life of the individual these enregistrations are illustrated by memories and habituations and habits2 in the life of the race they are illustrated by reflex actions and instinctive capacities4 ,body and ,mind ,we must not shirk the very difficult question of the relation between the bodily and the mental side of behaviour4 7a7 ,some great thinkers have taught that the mind is a reality by itself which plays upon the instrument of the brain and body4 ,as the instrument gets worn and dusty the playing is not so good as it once was1 but the player is still himself4 ,this theory of the essential independence of the mind is a very beautiful one1 but those who like it when applied to themselves are not always so fond of it when it is applied to other intelligent creatures like rooks and elephants4 ,it may be1 however1 that there is a gradual emancipation of the mind which has gone furthest in ,man and is still progressing4 7b7 ,some other thinkers have taught that the inner life of thought and feeling is only1 as it were1 an echo of the really important activity--that of the body and brain4 ,ideas are just foam-bells on the hurrying streams and circling eddies of matter and energy that make up our physiological life4 ,to most of us this theory is impossible1 because we are quite sure that ideas and feelings and purposes1 which cannot be translated into matter and motion1 are the clearest realities in our experience1 and that they count for good and ill all through our life4 ,they are more than the tickings of the clock2 they make the wheels go round4 7c7 ,there are others who think that the most scientific position is simply to recognise both the bodily and the mental activities as equally important1 and so closely interwoven that they cannot be separated4 ,perhaps they are just the outer and the inner aspects of one reality--the life of the creature4 ,perhaps they are like the concave and convex curves of a dome1 like the two sides of a shield4 ,perhaps the life of the organism is always a unity1 at one time appearing more conspicuously as ,mind-body1 at another time as ,body-mind4 ,the most important fact is that neither aspect can be left out4 ,by no jugglery with words can we get ,mind out of ,matter and ,motion4 ,and since we are in ourselves quite sure of our ,mind1 we are probably safe in saying that in the beginning was ,mind4 ,this is in accordance with ,aristotle's saying that there is nothing in the end which was not also in kind present in the beginning--whatever we mean by beginning4 ,in conclusion ,what has led to the truly wonderful result which we admire in a creature like a dog or an otter1 a horse or a hare8 ,in general1 we may say1 just two main processes--7#a7 testing all things1 and 7#b7 holding fast that which is good4 ,new departures occur and these are tested for what they are worth4 ,idiosyncrasies crop up and they are sifted4 ,new cards come mysteriously from within into the creature's hand1 and they are played--for better or for worse4 ,so by new variations and their sifting1 by experimenting and enregistering the results1 the mind has gradually evolved and will continue to evolve4 ,,viii ,,foundations ,,of ,,the ,,universe ,,the ,,world ,,of ,,atoms ,most people have heard of the oriental race which puzzled over the foundations of the universe1 and decided that it must be supported on the back of a giant elephant4 ,but the elephant8 ,they put it on the back of a monstrous tortoise1 and there they let the matter end4 ,if every animal in nature had been called upon1 they would have been no nearer a foundation4 ,most ancient peoples1 indeed1 made no effort to find a foundation4 ,the universe was a very compact little structure1 mainly composed of the earth and the great canopy over the earth which they called the sky4 ,they left it1 as a whole1 floating in nothing4 ,and in this the ancients were wiser than they knew4 ,things do not fall down unless they are pulled down by that mysterious force which we call gravitation4 ,the earth1 it is true1 is pulled by the sun1 and would fall into it2 but the earth escapes this fiery fate by circulating at great speed round the sun4 ,the stars pull each other2 but it has already been explained that they meet this by travelling rapidly in gigantic orbits4 ,yet we do1 in a new sense of the word1 need foundations of the universe4 ,our mind craves for some explanation of the matter out of which the universe is made4 ,for this explanation we turn to modern ,physics and ,chemistry4 ,both these sciences study1 under different aspects1 matter and energy2 and between them they have put together a conception of the fundamental nature of things which marks an epoch in the history of human thought4 #a ,the ,bricks of the ,cosmos ,more than two thousand years ago the first men of science1 the ,greeks of the cities of ,asia ,minor1 speculated on the nature of matter4 ,you can grind a piece of stone into dust4 ,you can divide a spoonful of water into as many drops as you like4 ,apparently you can go on dividing as long as you have got apparatus fine enough for the work4 ,but there must be a limit1 these ,greeks said1 and so they supposed that all matter was ultimately composed of minute particles which were indivisible4 ,that is the meaning of the ,greek word atom4 ,like so many other ideas of these brilliant early ,greek thinkers1 the atom was a sound conception4 ,we know to-day that matter is composed of atoms4 ,but science was then so young that the way in which the ,greeks applied the idea was not very profound4 ,a liquid or a gas1 they said1 consisted of round1 smooth atoms1 which would not cling together4 ,then there were atoms with rough surfaces1 hooky surfaces1 and these stuck together and formed solids4 ,the atoms of iron or marble1 for instance1 were so very hooky that1 once they got together1 a strong man could not tear them apart4 ,the ,greeks thought that the explanation of the universe was that an infinite number of these atoms had been moving and mixing in an infinite space during an infinite time1 and had at last hit by chance on the particular combination which is our universe4 ,this was too simple and superficial4 ,the idea of atoms was cast aside1 only to be advanced again in various ways4 ,it was the famous ,manchester chemist1 ,john ,dalton1 who restored it in the early years of the nineteenth century4 ,he first definitely formulated the atomic theory as a scientific hypothesis4 ,the whole physical and chemical science of that century was now based upon the atom1 and it is quite a mistake to suppose that recent discoveries have discredited atomism4 ,an atom is the smallest particle of a chemical element4 ,no one has ever seen an atom4 ,even the wonderful new microscope which has just been invented cannot possibly show us particles of matter which are a million times smaller than the breadth of a hair2 for that is the size of atoms4 ,we can weigh them and measure them1 though they are invisible1 and we know that all matter is composed of them4 ,it is a new discovery that atoms are not indivisible4 ,they consist themselves of still smaller particles1 as we shall see4 ,but the atoms exist all the same1 and we may still say that they are the bricks of which the material universe is built4 ,illustration3 ,photo3 ,elliott ,fry4 ,,sir ,,ernest ,,rutherford ,one of our most eminent physicists who has succeeded ,sir ,j4 ,j4 ,thomson as ,cavendish ,professor of ,physics at the ,university of ,cambridge4 ,the modern theory of the structure of the atom is largely due to him4 ,illustration3 ,photo3 ,rischgitz ,collection4 ,j4 ,,clerk-,,maxwell ,one of the greatest scientific men who have ever lived4 ,he revolutionised physics with his electro-magnetic theory of light1 and practically all modern researches have had their origin1 direct or indirect1 in his work4 ,together with ,faraday he constitutes one of the main scientific glories of the nineteenth century4 ,illustration3 ,photo3 ,ernest ,h4 ,mills4 ,,sir ,,william ,,crookes ,sir ,william ,crookes experimented on the electric discharge in vacuum tubes and described the phenomena as a fourth state of matter4 ,he was actually observing the flight of electrons1 but he did not fully appreciate the nature of his experiments4 ,illustration3 ,photo3 ,photo ,press ,,professor ,,sir ,w4 ,h4 ,,bragg ,one of the most distinguished physicists of the present day4 ,but if we had some magical glass by means of which we could see into the structure of material things1 we should not see the atoms put evenly together as bricks are in a wall4 ,as a rule1 two or more atoms first come together to form a larger particle1 which we call a molecule4 ,single atoms do not1 as a rule1 exist apart from other atoms2 if a molecule is broken up1 the individual atoms seek to unite with other atoms of another kind or amongst themselves4 ,for example1 three atoms of oxygen form what we call ozone2 two atoms of hydrogen uniting with one atom of oxygen form water4 ,it is molecules that form the mass of matter2 a molecule1 as it has been expressed1 is a little building of which atoms are the bricks4 ,in this way we get a useful first view of the material things we handle4 ,in a liquid the molecules of the liquid cling together loosely4 ,they remain together as a body1 but they roll over and away from each other4 ,there is cohesion between them1 but it is less powerful than in a solid4 ,put some water in a kettle over the lighted gas1 and presently the tiny molecules of water will rush through the spout in a cloud of steam and scatter over the kitchen4 ,the heat has broken their bond of association and turned the water into something like a gas2 though we know that the particles will come together again1 as they cool1 and form once more drops of water4 ,in a gas the molecules have full individual liberty4 ,they are in a state of violent movement1 and they form no union with each other4 ,if we want to force them to enter into the loose sort of association which molecules have in a liquid1 we have to slow down their individual movements by applying severe cold4 ,that is how a modern man of science liquefies gases4 ,no power that we have will liquefy air at its ordinary temperature4 ,in very severe cold1 on the other hand1 the air will spontaneously become liquid4 ,some day1 when the fires of the sun have sunk very low1 the temperature of the earth will be less than -#bjj ,c43 that is to say1 more than two hundred degrees ,centigrade below freezing-point4 ,it will sink to the temperature of the moon4 ,our atmosphere will then be an ocean of liquid air1 #ce feet deep1 lying upon the solidly frozen masses of our water-oceans4 ,in a solid the molecules cling firmly to each other4 ,we need a force equal to twenty-five tons to tear asunder the molecules in a bar of iron an inch thick4 ,yet the structure is not solid in the popular sense of the word4 ,if you put a piece of solid gold in a little pool of mercury1 the gold will take in the mercury between its molecules1 as if it were porous like a sponge4 ,the hardest solid is more like a lattice-work than what we usually mean by solid2 though the molecules are not fixed1 like the bars of a lattice-work1 but are in violent motion2 they vibrate about equilibrium positions4 ,if we could see right into the heart of a bit of the hardest steel1 we should see billions of separate molecules1 at some distance from each other1 all moving rapidly to and fro4 ,this molecular movement can1 in a measure1 be made visible4 ,it was noticed by a microscopist named ,brown that1 in a solution containing very fine suspended particles1 the particles were in constant movement4 ,under a powerful microscope these particles are seen to be violently agitated2 they are each independently darting hither and thither somewhat like a lot of billiard balls on a billiard table1 colliding and bounding about in all directions4 ,thousands of times a second these encounters occur1 and this lively commotion is always going on1 this incessant colliding of one molecule with another is the normal condition of affairs2 not one of them is at rest4 ,the reason for this has been worked out1 and it is now known that these particles move about because they are being incessantly bombarded by the molecules of the liquid4 ,the molecules cannot1 of course1 be seen1 but the fact of their incessant movement is revealed to the eye by the behaviour of the visible suspended particles4 ,this incessant movement in the world of molecules is called the ,brownian movement1 and is a striking proof of the reality of molecular motions4 #b ,the ,wonder-,world of ,atoms ,the exploration of this wonder-world of atoms and molecules by the physicists and chemists of to-day is one of the most impressive triumphs of modern science4 ,quite apart from radium and electrons and other sensational discoveries of recent years1 the study of ordinary matter is hardly inferior1 either in interest or audacity1 to the work of the astronomer4 ,and there is the same foundation in both cases--marvellous apparatus1 and trains of mathematical reasoning that would have astonished ,euclid or ,archimedes4 ,extraordinary1 therefore1 as are some of the facts and figures we are now going to give in connection with the minuteness of atoms and molecules1 let us bear in mind that we owe them to the most solid and severe processes of human thought4 ,yet the principle can in most cases be made so clear that the reader will not be asked to take much on trust4 ,it is1 for instance1 a matter of common knowledge that gold is soft enough to be beaten into gold leaf4 ,it is a matter of common sense1 one hopes1 that if you beat a measured cube of gold into a leaf six inches square1 the mathematician can tell the thickness of that leaf without measuring it4 ,as a matter of fact1 a single grain of gold has been beaten into a leaf seventy-five inches square4 ,now the mathematician can easily find that when a single grain of gold is beaten out to that size1 the leaf must be #a_/cfg1jjj of an inch thick1 or about a thousand times thinner than the paper on which these words are printed2 yet the leaf must be several molecules thick4 ,the finest gold leaf is1 in fact1 too thick for our purpose1 and we turn with a new interest to that toy of our boyhood the soap-bubble4 ,if you carefully examine one of these delicate films of soapy water1 you notice certain dark spots or patches on them4 ,these are their thinnest parts1 and by two quite independent methods--one using electricity and the other light--we have found that at these spots the bubble is less than the three-millionth of an inch thick6 ,but the molecules in the film cling together so firmly that they must be at least twenty or thirty deep in the thinnest part4 ,a molecule1 therefore1 must be far less than the three-millionth of an inch thick4 ,we found next that a film of oil on the surface of water may be even thinner than a soap-bubble4 ,professor ,perrin1 the great ,french authority on atoms1 got films of oil down to the fifty-millionth of an inch in thickness6 ,he poured a measured drop of oil upon water4 ,then he found the exact limits of the area of the oil-sheet by blowing upon the water a fine powder which spread to the edge of the film and clearly outlined it4 ,the rest is safe and simple calculation1 as in the case of the beaten grain of gold4 ,now this film of oil must have been at least two molecules deep1 so a single molecule of oil is considerably less than a hundred-millionth of an inch in diameter4 ,innumerable methods have been tried1 and the result is always the same4 ,a single grain of indigo1 for instance1 will colour a ton of water4 ,this obviously means that the grain contains billions of molecules which spread through the water4 ,a grain of musk will scent a room--pour molecules into every part of it--for several years1 yet not lose one-millionth of its mass in a year4 ,there are a hundred ways of showing the minuteness of the ultimate particles of matter1 and some of these enable us to give definite figures4 ,on a careful comparison of the best methods we can say that the average molecule of matter is less than the #a_/abe1jjj1jjj of an inch in diameter4 ,in a single cubic centimetre of air--a globule about the size of a small marble--there are thirty million trillion molecules4 ,and since the molecule is1 as we saw1 a group or cluster of atoms1 the atom itself is smaller4 ,atoms1 for reasons which we shall see later1 differ very greatly from each other in size and weight4 ,it is enough to say that some of them are so small that it would take #djj1jjj1jjj of them1 in a line1 to cover an inch of space2 and that it takes at least a quintillion atoms of gold to weigh a single gramme4 ,five million atoms of helium could be placed in a line across the diameter of a full stop4 ,illustration3 ,an atom is the smallest particle of a chemical element4 ,two or more atoms come together to form a molecule3 thus molecules form the mass of matter4 ,a molecule of water is made up of two atoms of hydrogen and one atom of oxygen4 ,molecules of different substances1 therefore1 are of different sizes according to the number and kind of the particular atoms of which they are composed4 ,a starch molecule contains no less than #be1jjj atoms4 ,molecules1 of course1 are invisible4 ,the above diagram illustrates the comparative sizes of molecules4 ,illustration3 ,,inconceivable ,,numbers ,,and ,,inconceivably ,,small ,,particles ,the molecules1 which are inconceivably small1 are1 on the other hand1 so numerous that if one was able to place1 end to end1 all those contained in1 for example1 a cubic centimetre of gas 7less than a fifteenth of a cubic inch71 one would obtain a line capable of passing two hundred times round the earth4 ,illustration3 ,,what ,,is ,a ,,million8 ,in dealing with the infinitely small1 it is difficult to apprehend the vast figures with which scientists confront us4 ,a million is one thousand thousand4 ,we may realise what this implies if we consider that a clock1 beating seconds1 takes approximately #bgh hours 7i4e4 one week four days fourteen hours7 to tick one million times4 ,a billion is one million million4 ,to tick a billion the clock would tick for over #ca1gce years4 7,in ,france and ,america a thousand millions is called a billion47 ,illustration3 ,,the ,,brownian ,,movement ,a diagram1 constructed from actual observations1 showing the erratic paths pursued by very fine particles suspended in a liquid1 when bombarded by the molecules of the liquid4 ,this movement is called the ,brownian movement1 and it furnishes a striking illustration of the truth of the theory that the molecules of a body are in a state of continual motion4 ,the ,energy of ,atoms ,and this is only the beginning of the wonders that were done with ordinary matter1 quite apart from radium and its revelations1 to which we will come presently4 ,most people have heard of atomic energy1 and the extraordinary things that might be accomplished if we could harness this energy and turn it to human use4 ,a deeper and more wonderful source of this energy has been discovered in the last twenty years1 but it is well to realise that the atoms themselves have stupendous energy4 ,the atoms of matter are vibrating or gyrating with extraordinary vigour4 ,the piece of cold iron you hold in your hand1 the bit of brick you pick up1 or the penny you take from your pocket is a colossal reservoir of energy1 since it consists of trillions of moving atoms4 ,to realise the total energy1 of course1 we should have to witness a transformation such as we do in atoms of radio-active elements1 about which we shall have something to say presently4 ,if we put a grain of indigo in a glass of water1 or a grain of musk in a perfectly still room1 we soon realise that molecules travel4 ,similarly1 the fact that gases spread until they fill every empty available space shows definitely that they consist of small particles travelling at great speed4 ,the physicist brings his refined methods to bear on these things1 and he measures the energy and velocity of these infinitely minute molecules4 ,he tells us that molecules of oxygen1 at the temperature of melting ice1 travel at the rate of about #ejj yards a second--more than a quarter of a mile a second4 ,molecules of hydrogen travel at four times that speed1 or three times the speed with which a bullet leaves a rifle4 ,each molecule of the air1 which seems so still in the house on a summer's day1 is really travelling faster than a rifle bullet does at the beginning of its journey4 ,it collides with another molecule every twenty-thousandth of an inch of its journey4 ,it is turned from its course #e1jjj1jjj1jjj times in every second by collisions4 ,if we could stop the molecules of hydrogen gas1 and utilise their energy1 as we utilise the energy of steam or the energy of the water at ,niagara1 we should find enough in every gramme of gas 7about two-thousandths of a pound7 to raise a third of a ton to a height of forty inches4 ,i have used for comparison the speed of a rifle bullet1 and in an earlier generation people would have thought it impossible even to estimate this4 ,it is1 of course1 easy4 ,we put two screens in the path of the bullet1 one near the rifle and the other some distance away4 ,we connect them electrically and use a fine time-recording machine1 and the bullet itself registers the time it takes to travel from the first to the second screen4 ,now this is very simple and superficial work in comparison with the system of exact and minute measurements which the physicist and chemist use4 ,in one of his interesting works ,mr4 ,charles ,r4 ,gibson gives a photograph of two exactly equal pieces of paper in the opposite pans of a fine balance4 ,a single word has been written in pencil on one of these papers1 and that little scraping of lead has been enough to bring down the scale6 ,the spectroscope will detect a quantity of matter four million times smaller even than this2 and the electroscope is a million times still more sensitive than the spectroscope4 ,we have a heat-measuring instrument1 the bolometer1 which makes the best thermometer seem ,early ,victorian4 ,it records the millionth of a degree of temperature4 ,it is such instruments1 multiplied by the score1 which enable us to do the fine work recorded in these pages4 ,illustration3 ,reproduced from ,the ,forces of ,nature 7,messrs4 ,macmillan74 ,a ,,soap ,,bubble ,the iridescent colours sometimes seen on a soap bubble1 as in the illustration1 may also be seen in very fine sections of crystals1 in glass blown into extremely fine bulbs1 on the wings of dragon-flies and the surface of oily water4 ,the different colours correspond to different thicknesses of the surface4 ,part of the light which strikes these thin coatings is reflected from the upper surface1 but another part of the light penetrates the transparent coating and is reflected from the lower surface4 ,it is the mixture of these two reflected rays1 their interference as it is called1 which produces the colours observed4 ,the black spots on a soap bubble are the places where the soapy film is thinnest4 ,at the black spots the thickness of the bubble is about the three-millionth part of an inch4 ,if the whole bubble were as thin as this it would be completely invisible4 #c ,,the ,,discovery ,,of ,x-,,rays ,,and ,,radium ,the ,discovery of ,sir ,wm4 ,crookes ,but these wonders of the atom are only a prelude to the more romantic and far-reaching discoveries of the new physics--the wonders of the electron4 ,another and the most important phase of our exploration of the material universe opened with the discovery of radium in #ahih4 ,in the discovery of radio-active elements1 a new property of matter was discovered4 ,what followed on the discovery of radium and of the ,x-rays we shall see4 ,as ,sir ,ernest ,rutherford1 one of our greatest authorities1 recently said1 the new physics has dissipated the last doubt about the reality of atoms and molecules4 ,the closer examination of matter which we have been able to make shows positively that it is composed of atoms4 ,but we must not take the word now in its original ,greek meaning 7an indivisible thing74 ,the atoms are not indivisible4 ,they can be broken up4 ,they are composed of still smaller particles4 ,the discovery that the atom was composed of smaller particles was the welcome realisation of a dream that had haunted the imagination of the nineteenth century4 ,chemists said that there were about eighty different kinds of atoms--different kinds of matter--but no one was satisfied with the multiplicity4 ,science is always aiming at simplicity and unity4 ,it may be that science has now taken a long step in the direction of explaining the fundamental unity of all the matter4 ,the chemist was unable to break up these elements into something simpler1 so he called their atoms indivisible in that sense4 ,but one man of science after another expressed the hope that we would yet discover some fundamental matter of which the various atoms were composed--one primordial substance from which all the varying forms of matter have been evolved or built up4 ,prout suggested this at the very beginning of the century1 when atoms were rediscovered by ,dalton4 ,father ,secchi1 the famous ,jesuit astronomer said that all the atoms were probably evolved from ether2 and this was a very favoured speculation4 ,sir ,william ,crookes talked of prothyl as the fundamental substance4 ,others thought hydrogen was the stuff out of which all the other atoms were composed4 ,the work which finally resulted in the discovery of radium began with some beautiful experiments of ,professor 7later ,sir ,william7 ,crookes in the eighties4 ,it had been noticed in #ahfi that a strange colouring was caused when an electric charge was sent through a vacuum tube--the walls of the glass tube began to glow with a greenish phosphorescence4 ,a vacuum tube is one from which nearly all the air has been pumped1 although we can never completely empty the tube4 ,crookes used such ingenious methods that he reduced the gas in his tubes until it was twenty million times thinner than the atmosphere4 ,he then sent an electric discharge through1 and got very remarkable results4 ,the negative pole of the electric current 7the cathode7 gave off rays which faintly lit the molecules of the thin gas in the tube1 and caused a pretty fluorescence on the glass walls of the tube4 ,what were these ,rays8 ,crookes at first thought they corresponded to a new or fourth state of matter4 ,hitherto we had only been familiar with matter in the three conditions of solid1 liquid1 and gaseous4 ,now ,crookes really had the great secret under his eyes4 ,but about twenty years elapsed before the true nature of these rays was finally and independently established by various experiments4 ,the experiments proved that the rays consisted of a stream of negatively charged particles travelling with enormous velocities from #aj1jjj to #ajj1jjj miles a second4 ,in addition1 it was found that the mass of each particle was exceedingly small1 about #a_/ahjj of the mass of a hydrogen atom1 the lightest atom known to science4 ,these particles or electrons1 as they are now called1 were being liberated from the atom4 ,the atoms of matter were breaking down in ,crookes tubes4 ,at that time1 however1 it was premature to think of such a thing1 and ,crookes preferred to say that the particles of the gas were electrified and hurled against the walls of the tube4 ,he said that it was ordinary matter in a new state--radiant matter4 ,another distinguished man of science1 ,lenard1 found that1 when he fitted a little plate of aluminum in the glass wall of the tube1 the mysterious rays passed through this as if it were a window4 ,they must be waves in the ether1 he said4 ,illustration3 ,from ,scientific ,ideas of ,to-day4 ,,detecting ,a ,,small ,,quantity ,,of ,,matter ,in the left-hand photograph the two pieces of paper exactly balance4 ,the balance used is very sensitive1 and when the single word atoms has been written with a lead pencil upon one of the papers the additional weight is sufficient to depress one of the pans as shown in the second photograph4 ,the spectroscope will detect less than one-millionth of the matter contained in the word pencilled above4 ,illustration3 ,reproduced by permission of ,x-,rays ,ltd4 ,,this ,x-,,ray ,,photograph ,,is ,,that ,,of ,a ,,hand ,,of ,a ,,soldier ,,wounded ,,in ,,the ,,great ,,war ,note the pieces of shrapnel which are revealed4 ,illustration3 ,photo3 ,national ,physical ,laboratory4 ,,an ,x-,,ray ,,photograph ,,of ,a ,,golf ,,ball1 ,,revealing ,,an ,,imperfect ,,core ,illustration3 ,reproduced by permission of ,x-,rays ,ltd4 ,a ,,wonderful ,x-,,ray ,,photograph ,note the fine details revealed1 down to the metal tags of the bootlace and the nails in the heel of the boot4 #d ,the ,discovery of ,x-rays ,so the story went on from year to year4 ,we shall see in a moment to what it led4 ,meanwhile the next great step was when1 in #ahie1 ,rntgen discovered the ,x-rays1 which are now known to everybody4 ,he was following up the work of ,lenard1 and he one day covered a ,crookes tube with some black stuff4 ,to his astonishment a prepared chemical screen which was near the tube began to glow4 ,the rays had gone through the black stuff2 and on further experiment he found that they would go through stone1 living flesh1 and all sorts of opaque substances4 ,in a short time the world was astonished to learn that we could photograph the skeleton in a living man's body1 locate a penny in the interior of a child that had swallowed one1 or take an impression of a coin through a slab of stone4 ,and what are these ,x-rays8 ,they are not a form of matter2 they are not material particles4 ,x-rays were found to be a new variety of light with a remarkable power of penetration4 ,we have seen what the spectroscope reveals about the varying nature of light wave-lengths4 ,light-waves are set up by vibrations in ether1#b and1 as we shall see1 these ether disturbances are all of the same kind2 they only differ as regards wave-lengths4 ,the ,x-rays which ,rntgen discovered1 then1 are light1 but a variety of light previously unknown to us2 they are ether waves of very short length4 ,x-rays have proved of great value in many directions1 as all the world knows1 but that we need not discuss at this point4 ,let us see what followed ,rntgen's discovery4 #b ,we refer throughout to the ether because1 although modern theories dispense largely with this conception1 the theories of physics are so inextricably interwoven with it that it is necessary1 in an elementary exposition1 to assume its existence4 ,the modern view will be explained later in the article on ,einstein's ,theory4 ,while the world wondered at these marvels1 the men of science were eagerly following up the new clue to the mystery of matter which was exercising the mind of ,crookes and other investigators4 ,in #ahif ,becquerel brought us to the threshold of the great discovery4 ,certain substances are phosphorescent--they become luminous after they have been exposed to sunlight for some time1 and ,becquerel was trying to find if any of these substances give rise to ,x-rays4 ,one day he chose a salt of the metal uranium4 ,he was going to see if1 after exposing it to sunlight1 he could photograph a cross with it through an opaque substance4 ,he wrapped it up and laid it aside1 to wait for the sun1 but he found the uranium salt did not wait for the sun4 ,some strong radiation from it went through the opaque covering and made an impression of the cross upon the plate underneath4 ,light or darkness was immaterial4 ,the mysterious rays streamed night and day from the salt4 ,this was something new4 ,here was a substance which appeared to be producing ,x-rays2 the rays emitted by uranium would penetrate the same opaque substances as the ,x-rays discovered by ,rntgen4 ,discovery of ,radium ,now1 at the same time as many other investigators1 ,professor ,curie and his ,polish wife took up the search4 ,they decided to find out whether the emission came from the uranium itself or from something associated with it1 and for this purpose they made a chemical analysis of great quantities of minerals4 ,they found a certain kind of pitchblende which was very active1 and they analysed tons of it1 concentrating always on the radiant element in it4 ,after a time1 as they successively worked out the non-radiant matter1 the stuff began to glow4 ,in the end they extracted from eight tons of pitchblende about half a teaspoonful of something that was a million times more radiant than uranium4 ,there was only one name for it--,radium4 ,that was the starting-point of the new development of physics and chemistry4 ,from every laboratory in the world came a cry for radium salts 7as pure radium was too precious71 and hundreds of brilliant workers fastened on the new element4 ,the inquiry was broadened1 and1 as year followed year1 one substance after another was found to possess the power of emitting rays1 that is1 to be radio-active4 ,we know to-day that nearly every form of matter can be stimulated to radio-activity2 which1 as we shall see1 means that its atoms break up into smaller and wonderfully energetic particles which we call electrons4 ,this discovery of electrons has brought about a complete change in our ideas in many directions4 ,so1 instead of atoms being indivisible1 they are actually dividing themselves1 spontaneously1 and giving off throughout the universe tiny fragments of their substance4 ,we shall explain presently what was later discovered about the electron2 meanwhile we can say that every glowing metal is pouring out a stream of these electrons4 ,every arc-lamp is discharging them4 ,every clap of thunder means a shower of them4 ,every star is flooding space with them4 ,we are witnessing the spontaneous breaking up of atoms1 atoms which had been thought to be indivisible4 ,the sun not only pours out streams of electrons from its own atoms1 but the ultra-violet light which it sends to the earth is one of the most powerful agencies for releasing electrons from the surface-atoms of matter on the earth4 ,it is fortunate for us that our atmosphere absorbs most of this ultra-violet or invisible light of the sun--a kind of light which will be explained presently4 ,it has been suggested that1 if we received the full flood of it from the sun1 our metals would disintegrate under its influence and this steel civilisation of ours would be impossible6 ,but we are here anticipating1 we are going beyond radium to the wonderful discoveries which were made by the chemists and physicists of the world who concentrated upon it4 ,the work of ,professor and ,mme4 ,curie was merely the final clue to guide the great search4 ,how it was followed up1 how we penetrated into the very heart of the minute atom and discovered new and portentous mines of energy1 and how we were able to understand1 not only matter1 but electricity and light1 will be told in the next chapter4 ,,the ,,discovery ,,of ,,the ,,electron ,,and ,,how ,,it ,,effected ,a ,,revolution ,,in ,,ideas ,what the discovery of radium implied was only gradually realised4 ,radium captivated the imagination of the world2 it was a boon to medicine1 but to the man of science it was at first a most puzzling and most attractive phenomenon4 ,it was felt that some great secret of nature was dimly unveiled in its wonderful manifestations1 and there now concentrated upon it as gifted a body of men--conspicuous amongst them ,sir ,j4 ,j4 ,thomson1 ,sir ,ernest ,rutherford1 ,sir ,w4 ,ramsay1 and ,professor ,soddy--as any age could boast1 with an apparatus of research as far beyond that of any other age as the ,aquitania is beyond a ,roman galley4 ,within five years the secret was fairly mastered4 ,not only were all kinds of matter reduced to a common basis1 but the forces of the universe were brought into a unity and understood as they had never been understood before4 ,illustration3 ,,electric ,,discharge ,,in ,a ,,vacuum ,,tube ,the two ends1 marked and -1 of a tube from which nearly all air has been exhausted are connected to electric terminals1 thus producing an electric discharge in the vacuum tube4 ,this discharge travels straight along the tube1 as in the upper diagram4 ,when a magnetic field is applied1 however1 the rays are deflected1 as shown in the lower diagram4 ,the similarity of the behaviour of the electric discharge with the radium rays 7see diagram of deflection of radium rays1 post7 shows that the two phenomena may be identified4 ,it was by this means that the characteristics of electrons were first discovered4 ,illustration3 ,,the ,,relative ,,sizes ,,of ,,atoms ,,and ,,electrons ,an atom is far too small to be seen4 ,in a bubble of hydrogen gas no larger than the letter ,o there are billions of atoms1 whilst an electron is more than a thousand times smaller than the smallest atom4 ,how their size is ascertained is described in the text4 ,in this diagram a bubble of gas is magnified to the size of the world4 ,adopting this scale1 each atom in the bubble would then be as large as a tennis ball4 ,illustration3 ,,if ,,an ,,atom ,,were ,,magnified ,,to ,,the ,,size ,,of ,,st4 ,,paul',s ,,cathedral1 ,,each ,,electron ,,in ,,the ,,atom 7,,as ,,represented ,,by ,,the ,,cathedral7 ,,would ,,then ,,be ,,about ,,the ,,size ,,of ,a ,,small ,,bullet ,illustration3 ,,electrons ,,streaming ,,from ,,the ,,sun ,,to ,,the ,,earth ,there are strong reasons for supposing that sun-spots are huge electronic cyclones4 ,the sun is constantly pouring out vast streams of electrons into space4 ,many of these streams encounter the earth1 giving rise to various electrical phenomena4 #e ,the ,discovery of the ,electron ,physicists did not take long to discover that the radiation from radium was very like the radiation in a ,crookes tube4 ,it was quickly recognised1 moreover1 that both in the tube and in radium 7and other metals7 the atoms of matter were somehow breaking down4 ,however1 the first step was to recognise that there were three distinct and different rays that were given off by such metals as radium and uranium4 ,sir ,ernest ,rutherford christened them1 after the first three letters of the ,greek alphabet1 the ,alpha1 the ,beta1 and ,gamma rays4 ,we are concerned chiefly with the second group and purpose here to deal with that group only4#c #c ,the ,alpha rays were presently recognised as atoms of helium gas1 shot out at the rate of #ab1jjj miles a second4 ,the ,gamma rays are waves1 like the ,x-rays1 not material particles4 ,they appear to be a type of ,x-rays4 ,they possess the remarkable power of penetrating opaque substances2 they will pass through a foot of solid iron1 for example4 ,the ,beta rays1 as they were at first called1 have proved to be one of the most interesting discoveries that science ever made4 ,they proved what ,crookes had surmised about the radiations he discovered in his vacuum tube4 ,but it was not a fourth state of matter that had been found1 but a new property of matter1 a property common to all atoms of matter4 ,the ,beta rays were later christened ,electrons4 ,they are particles of disembodied electricity1 here spontaneously liberated from the atoms of matter3 only when the electron was isolated from the atom was it recognised for the first time as a separate entity4 ,electrons1 therefore1 are a constituent of the atoms of matter1 and we have discovered that they can be released from the atom by a variety of agencies4 ,electrons are to be found everywhere1 forming part of every atom4 ,an electron1 ,sir ,william ,bragg says1 can only maintain a separate existence if it is travelling at an immense rate1 from one three-hundredth of the velocity of light upwards1 that is to say1 at least #fjj miles a second1 or thereabouts4 ,otherwise the electron sticks to the first atom it meets4 ,these amazing particles may travel with the enormous velocity of from #aj1jjj to more than #ajj1jjj miles a second4 ,it was first learned that they are of an electrical nature1 because they are bent out of their normal path if a magnet is brought near them4 ,and this fact led to a further discovery3 to one of those sensational estimates which the general public is apt to believe to be founded on the most abstruse speculations4 ,the physicist set up a little chemical screen for the ,beta rays to hit1 and he so arranged his tube that only a narrow sheaf of the rays poured on to the screen4 ,he then drew this sheaf of rays out of its course with a magnet1 and he accurately measured the shift of the luminous spot on the screen where the rays impinged on it4 ,but when he knows the exact intensity of his magnetic field--which he can control as he likes--and the amount of deviation it causes1 and the mass of the moving particles1 he can tell the speed of the moving particles which he thus diverts4 ,these particles were being hurled out of the atoms of radium1 or from the negative pole in a vacuum tube1 at a speed which1 in good conditions1 reached nearly the velocity of light1 i4e4 nearly #ahf1jjj miles a second4 ,their speed has1 of course1 been confirmed by numbers of experiments2 and another series of experiments enabled physicists to determine the size of the particles4 ,only one of these need be described1 to give the reader an idea how men of science arrived at their more startling results4 ,fog1 as most people know1 is thick in our great cities because the water-vapour gathers on the particles of dust and smoke that are in the atmosphere4 ,this fact was used as the basis of some beautiful experiments4 ,artificial fogs were created in little glass tubes1 by introducing dust1 in various proportions1 for supersaturated vapour to gather on4 ,in the end it was possible to cause tiny drops of rain1 each with a particle of dust at its core1 to fall upon a silver mirror and be counted4 ,it was a method of counting the quite invisible particles of dust in the tube2 and the method was now successfully applied to the new rays4 ,yet another method was to direct a slender stream of the particles upon a chemical screen4 ,the screen glowed under the cannonade of particles1 and a powerful lens resolved the glow into distinct sparks1 which could be counted4 ,in short1 a series of the most remarkable and beautiful experiments1 checked in all the great laboratories of the world1 settled the nature of these so-called rays4 ,they were streams of particles more than a thousand times smaller than the smallest known atom4 ,the mass of each particle is1 according to the latest and finest measurements #a_/ahde of that of an atom of hydrogen4 ,the physicist has not been able to find any character except electricity in them1 and the name electrons has been generally adopted4 ,the ,key to many ,mysteries ,the ,electron is an atom1 of disembodied electricity2 it occupies an exceedingly small volume1 and its mass is entirely electrical4 ,these electrons are the key to half the mysteries of matter4 ,electrons in rapid motion1 as we shall see1 explain what we mean by an electric current1 not so long ago regarded as one of the most mysterious manifestations in nature4 ,what a wonder1 then1 have we here6 says ,professor ,r4 ,k4 ,duncan4 ,an innocent-looking little pinch of salt and yet possessed of special properties utterly beyond even the fanciful imaginings of men of past time2 for nowhere do we find in the records of thought even the hint of the possibility of things which we now regard as established fact4 ,this pinch of salt projects from its surface bodies i4e4 electrons possessing the inconceivable velocity of over #ajj1jjj miles a second1 a velocity sufficient to carry them1 if unimpeded1 five times around the earth in a second1 and possessing with this velocity1 masses a thousand times smaller than the smallest atom known to science4 ,furthermore1 they are charged with negative electricity2 they pass straight through bodies considered opaque with a sublime indifference to the properties of the body1 with the exception of its mere density2 they cause bodies which they strike to shine out in the dark2 they affect a photographic plate2 they render the air a conductor of electricity2 they cause clouds in moist air2 they cause chemical action and have a peculiar physiological action4 ,who1 to-day1 shall predict the ultimate service to humanity of the beta-rays from radium6 #f ,,the ,,electron ,,theory1 ,,or ,,the ,,new ,,view ,,of ,,matter ,the ,structure of the ,atom ,there is general agreement amongst all chemists1 physicists1 and mathematicians upon the conclusions which we have so far given4 ,we know that the atoms of matter are constantly--either spontaneously or under stimulation--giving off electrons1 or breaking up into electrons2 and they therefore contain electrons4 ,thus we have now complete proof of the independent existence of atoms and also of electrons4 ,when1 however1 the man of science tries to tell us how electrons compose atoms1 he passes from facts to speculation1 and very difficult speculation4 ,take the letter o as it is printed on this page4 ,in a little bubble of hydrogen gas no larger than that letter there are trillions of atoms2 and they are not packed together1 but are circulating as freely as dancers in a ball-room4 ,we are asking the physicist to take one of these minute atoms and tell us how the still smaller electrons are arranged in it4 ,naturally he can only make mental pictures1 guesses or hypotheses1 which he tries to fit to the facts1 and discards when they will not fit4 ,at present1 after nearly twenty years of critical discussion1 there are two chief theories of the structure of the atom4 ,at first ,sir ,j4 ,j4 ,thomson imagined the electrons circulating in shells 7like the layers of an onion7 round the nucleus of the atom4 ,this did not suit1 and ,sir ,e4 ,rutherford and others worked out a theory that the electrons circulated round a nucleus rather like the planets of our solar system revolving round the central sun4 ,is there a nucleus1 then1 round which the electrons revolve8 ,the electron1 as we saw1 is a disembodied atom of electricity2 we should say1 of negative electricity4 ,let us picture these electrons all moving round in orbits with great velocity4 ,now it is suggested that there is a nucleus of positive electricity attracting or pulling the revolving electrons to it1 and so forming an equilibrium1 otherwise the electrons would fly off in all directions4 ,this nucleus has been recently named the proton4 ,we have thus two electricities in the atom3 the positive the nucleus2 the negative the electron4 ,of recent years ,dr4 ,langmuir has put out a theory that the electrons do not revolve round the nucleus1 but remain in a state of violent agitation of some sort at fixed distances from the nucleus4 ,illustration3 ,,professor ,,sir ,j4 ,j4 ,,thomson ,experimental discoverer of the electronic constitution of matter1 in the ,cavendish ,physical ,laboratory1 ,cambridge4 ,a great investigator1 noted for the imaginative range of his hypotheses and his fertility in experimental devices4 ,illustration3 ,from the ,smithsonian ,report1 #aiae4 ,,electrons ,,produced ,,by ,,passage ,,of ,x-,,rays ,,through ,,air ,a photograph clearly showing that electrons are definite entities4 ,as electrons leave atoms they may traverse matter or pass through the air in a straight path ,the illustration shows the tortuous path of electrons resulting from collision with atoms4 ,illustration3 ,,magnetic ,,deflection ,,of ,,radium ,,rays ,the radium rays are made to strike a screen1 producing visible spots of light4 ,when a magnetic field is applied the rays are seen to be deflected1 as in the diagram4 ,this can only happen if the rays carry an electric charge1 and it was by experiments of this kind that we obtained our knowledge respecting the electric charges carried by radium rays4 ,illustration3 ,reproduced by permission of ,scientific ,american4 ,,professor ,r4 ,a4 ,,millikan',s ,,apparatus ,,for ,,counting ,,electrons ,but we will confine ourselves here to the facts1 and leave the contending theories to scientific men4 ,it is now pretty generally accepted that an atom of matter consists of a number of electrons1 or charges of negative electricity1 held together by a charge of positive electricity4 ,it is not disputed that these electrons are in a state of violent motion or strain1 and that therefore a vast energy is locked up in the atoms of matter4 ,to that we will return later4 ,here1 rather1 we will notice another remarkable discovery which helps us to understand the nature of matter4 ,a brilliant young man of science who was killed in the war1 ,mr4 ,moseley1 some years ago showed that1 when the atoms of different substances are arranged in order of their weight1 they are also arranged in the order of increasing complexity of structure4 ,that is to say1 the heavier the atom1 the more electrons it contains4 ,there is a gradual building up of atoms containing more and more electrons from the lightest atom to the heaviest4 ,here it is enough to say that as he took element after element1 from the lightest 7hydrogen7 to the heaviest 7uranium7 he found a strangely regular relation between them4 ,if hydrogen were represented by the figure one1 helium by two1 lithium three1 and so on up to uranium1 then uranium should have the figure ninety-two4 ,this makes it probable that there are in nature ninety-two elements--we have found eighty-seven--and that the number ,mr4 ,moseley found is the number of electrons in the atom of each element2 that is to say1 the number is arranged in order of the atomic numbers of the various elements4 #g ,the ,new ,view of ,matter ,up to the point we have reached1 then1 we see what the new view of ,matter is4 ,every atom of matter1 of whatever kind throughout the whole universe1 is built up of electrons in conjunction with a nucleus4 ,from the smallest atom of all--the atom of hydrogen--which consists of one electron1 rotating round a positively charged nucleus1 to a heavy complicated atom1 such as the atom of gold1 constituted of many electrons and a complex nucleus1 we have only to do with positive and negative units of electricity4 ,the electron and its nucleus are particles of electricity4 ,all ,matter1 therefore1 is nothing but a manifestation of electricity4 ,the atoms of matter1 as we saw1 combine and form molecules4 ,atoms and molecules are the bricks out of which nature has built up everything2 ourselves1 the earth1 the stars1 the whole universe4 ,but more than bricks are required to build a house4 ,there are other fundamental existences1 such as the various forms of energy1 which give rise to several complex problems4 ,and we have also to remember1 that there are more than eighty distinct elements1 each with its own definite type of atom4 ,we shall deal with energy later4 ,meanwhile it remains to be said that1 although we have discovered a great deal about the electron and the constitution of matter1 and that while the physicists of our own day seem to see a possibility of explaining positive and negative electricity1 the nature of them both is unknown4 ,there exists the theory that the particles of positive and negative electricity1 which make up the atoms of matter1 are points or centres of disturbances of some kind in a universal ether1 and that all the various forms of energy are1 in some fundamental way1 aspects of the same primary entity which constitutes matter itself4 ,but the discovery of the property of radio-activity has raised many other interesting questions1 besides that which we have just dealt with4 ,in radio-active elements1 such as uranium for example1 the element is breaking down2 in what we call radio-activity we have a manifestation of the spontaneous change of elements4 ,what is really taking place is a transmutation of one element into another1 from a heavier to a lighter4 ,the element uranium spontaneously becomes radium1 and radium passes through a number of other stages until it1 in turn1 becomes lead4 ,each descending element is of lighter atomic weight than its predecessor4 ,the changing process1 of course1 is a very slow one4 ,it may be that all matter is radio-active1 or can be made so4 ,this raises the question whether all the matter in the universe may not undergo disintegration4 ,there is1 however1 another side of the question1 which the discovery of radio-activity has brought to light1 and which has effected a revolution in our views4 ,we have seen that in radio-active substances the elements are breaking down4 ,is there a process of building up at work8 ,if the more complicated atoms are breaking down into simpler forms1 may there not be a converse process--a building up from simpler elements to more complicated elements8 ,it is probably the case that both processes are at work4 ,there are some eighty-odd chemical elements on the earth to-day3 are they all the outcome of an inorganic evolution1 element giving rise to element1 going back and back to some primeval stuff from which they were all originally derived infinitely long ago8 ,is there an evolution in the inorganic world which may be going on1 parallel to that of the evolution of living things2 or is organic evolution a continuation of inorganic evolution8 ,we have seen what evidence there is of this inorganic evolution in the case of the stars4 ,we cannot go deeply into the matter here1 nor has the time come for any direct statement that can be based on the findings of modern investigation4 ,taking it altogether the evidence is steadily accumulating1 and there are authorities who maintain that already the evidence of inorganic evolution is convincing enough4 ,the heavier atoms would appear to behave as though they were evolved from the lighter4 ,the more complex forms1 it is supposed1 have evolved from the simpler forms4 ,moseley's discovery1 to which reference has been made1 points to the conclusion that the elements are built up one from another4 #h ,other ,new ,views ,we may here refer to another new conception to which the discovery of radio-activity has given rise4 ,lord ,kelvin1 who estimated the age of the earth at twenty million years1 reached this estimate by considering the earth as a body which is gradually cooling down1 losing its primitive heat1 like a loaf taken from the oven1 at a rate which could be calculated1 and that the heat radiated by the sun was due to contraction4 ,uranium and radio-activity were not known to ,kelvin1 and their discovery has upset both his arguments4 ,radio-active substances1 which are perpetually giving out heat1 introduce an entirely new factor4 ,we cannot now assume that the earth is necessarily cooling down2 it may even1 for all we know1 be getting hotter4 ,at the #aiba meeting of the ,british ,association1 ,professor ,rayleigh stated that further knowledge had extended the probable period during which there had been life on this globe to about one thousand million years1 and the total age of the earth to some small multiple of that4 ,the earth1 he considers1 is not cooling1 but contains an internal source of heat from the disintegration of uranium in the outer crust4 ,on the whole the estimate obtained would seem to be in agreement with the geological estimates4 ,the question1 of course1 cannot1 in the present state of our knowledge1 be settled within fixed limits that meet with general agreement4 ,illustration3 ,,making ,,the ,,invisible ,,visible ,radium1 as explained in the text1 emits rays--the ,alpha1 the ,beta 7electrons71 and ,gamma rays4 ,the above illustration indicates the method by which these invisible rays are made visible1 and enables the nature of the rays to be investigated4 ,to the right of the diagram is the instrument used1 the ,spinthariscope1 making the impact of radium rays visible on a screen4 ,the radium rays shoot out in all directions2 those that fall on the screen make it glow with points of light4 ,these points of light are observed by the magnifying lens4 ,a4 ,magnifying lens4 ,b4 ,a zinc sulphite screen4 ,c4 ,a needle on whose point is placed a speck of radium4 ,the lower picture shows the screen and needle magnified4 ,illustration3 ,,the ,,theory ,,of ,,electrons ,an atom of matter is composed of electrons4 ,we picture an atom as a sort of miniature solar system1 the electrons 7particles of negative electricity7 rotating round a central nucleus of positive electricity1 as described in the text4 ,in the above pictorial representation of an atom the whirling electrons are indicated in the outer ring4 ,electrons move with incredible speed as they pass from one atom to another4 ,illustration3 ,,arrangements ,,of ,,atoms ,,in ,a ,,diamond ,the above is a model 7seen from two points of view7 of the arrangement of the atoms in a diamond4 ,the arrangement is found by studying the ,x-ray spectra of the diamond4 ,as we have said1 there are other fundamental existences which give rise to more complex problems4 ,the three great fundamental entities in the physical universe are matter1 ether1 and energy2 so far as we know1 outside these there is nothing4 ,we have dealt with matter1 there remain ether and energy4 ,we shall see that just as no particle of matter1 however small1 may be created or destroyed1 and just as there is no such thing as empty space--ether pervades everything--so there is no such thing as rest4 ,every particle that goes to make up our solid earth is in a state of perpetual unremitting vibration2 energy is the universal commodity on which all life depends4 ,separate and distinct as these three fundamental entities--matter1 ether1 and energy--may appear1 it may be that1 after all1 they are only different and mysterious phases of an essential oneness of the universe4 #i ,the ,future ,let us1 in concluding this chapter1 give just one illustration of the way in which all this new knowledge may prove to be as valuable practically as it is wonderful intellectually4 ,we saw that electrons are shot out of atoms at a speed that may approach #afj1jjj miles a second4 ,sir ,oliver ,lodge has written recently that a seventieth of a grain of radium discharges1 at a speed a thousand times that of a rifle bullet1 thirty million electrons a second4 ,professor ,le ,bon has calculated that it would take #a1cdj1jjj barrels of powder to give a bullet the speed of one of these electrons4 ,he shows that the smallest ,french copper coin--smaller than a farthing--contains an energy equal to eighty million horsepower4 ,a few pounds of matter contain more energy than we could extract from millions of tons of coal4 ,even in the atoms of hydrogen at a temperature which we could produce in an electric furnace the electrons spin round at a rate of nearly a hundred trillion revolutions a second6 ,every man asks at once3 ,will science ever tap this energy8 ,if it does1 no more smoke1 no mining1 no transit1 no bulky fuel4 ,the energy of an atom is of course only liberated when an atom passes from one state to another4 ,the stored up energy is fortunately fast bound by the electrons being held together as has been described4 ,if it were not so the earth would explode and become a gaseous nebula6 ,it is believed that some day we shall be able to release1 harness1 and utilise atomic energy4 ,i am of opinion1 says ,sir ,william ,bragg1 that atom energy will supply our future need4 ,a thousand years may pass before we can harness the atom1 or to-morrow might see us with the reins in our hands4 ,that is the peculiarity of ,physics--research and 'accidental' discovery go hand in hand4 ,half a brick contains as much energy as a small coal-field4 ,the difficulties are tremendous1 but1 as ,sir ,oliver ,lodge reminds us1 there was just as much scepticism at one time about the utilisation of steam or electricity4 ,is it to be supposed1 he asks1 that there can be no fresh invention1 that all the discoveries have been made8 ,more than one man of science encourages us to hope4 ,here are some remarkable words written by ,professor ,soddy1 one of the highest authorities on radio-active matter1 in our chief scientific weekly 7,nature1 ,november #f1 #aiai73 ,the prospects of the successful accomplishment of artificial transmutation brighten almost daily4 ,the ancients seem to have had something more than an inkling that the accomplishment of transmutation would confer upon men powers hitherto the prerogative of the gods4 ,but now we know definitely that the material aspect of transmutation would be of small importance in comparison with the control over the inexhaustible stores of internal atomic energy to which its successful accomplishment would inevitably lead4 ,it has become a problem1 no longer redolent of the evil associations of the age of alchemy1 but one big with the promise of a veritable physical renaissance of the whole world4 ,if that promise is ever realised1 the economic and social face of the world will be transformed4 ,before passing on to the consideration of ether1 light1 and energy1 let us see what new light the discovery of the electron has thrown on the nature and manipulation of electricity4 ,,what ,,is ,,electricity8 ,the ,nature of ,electricity ,there is at least one manifestation in nature1 and so late as twenty years ago it seemed to be one of the most mysterious manifestations of all1 which has been in great measure explained by the new discoveries4 ,already1 at the beginning of this century1 we spoke of our age of electricity1 yet there were few things in nature about which we knew less4 ,the electric current rang our bells1 drove our trains1 lit our rooms1 but none knew what the current was4 ,there was a vague idea that it was a sort of fluid that flowed along copper wires as water flows in a pipe4 ,we now suppose that it is a rapid movement of electrons from atom to atom in the wire or wherever the current is4 ,let us try to grasp the principle of the new view of electricity and see how it applies to all the varied electrical phenomena in the world about us4 ,as we saw1 the nucleus of an atom of matter consists of positive electricity which holds together a number of electrons1 or charges of negative electricity4#d ,this certainly tells us to some extent what electricity is1 and how it is related to matter1 but it leaves us with the usual difficulty about fundamental realities4 ,but we now know that electricity1 like matter1 is atomic in structure2 a charge of electricity is made up of a number of small units or charges of a definite1 constant amount4 ,it has been suggested that the two kinds of electricity1 i4e4 positive and negative1 are right-handed and left-handed vortices or whirlpools in ether1 or rings in ether1 but there are very serious difficulties1 and we leave this to the future4 #d ,the words positive and negative electricity belong to the days when it was regarded as a fluid4 ,a body overcharged with the fluid was called positive2 an undercharged body was called negative4 ,a positively-electrified body is now one whose atoms have lost some of their outlying electrons1 so that the positive charge of electricity predominates4 ,the negatively-electrified body is one with more than the normal number of electrons4 #aj ,what an ,electric ,current is ,the discovery of these two kinds of electricity has1 however1 enabled us to understand very fairly what goes on in electrical phenomena4 ,the outlying electrons1 as we saw1 may pass from atom to atom1 and this1 on a large scale1 is the meaning of the electric current4 ,in other words1 we believe an electric current to be a flow of electrons4 ,let us take1 to begin with1 a simple electrical cell1 in which a feeble current is generated3 such a cell as there is in every house to serve its electric bells4 ,in the original form this simple sort of battery consisted of a plate of zinc and a plate of copper immersed in a chemical4 ,long before anything was known about electrons it was known that1 if you put zinc and copper together1 you produce a mild current of electricity4 ,we know now what this means4 ,zinc is a metal the atoms of which are particularly disposed to part with some of their outlying electrons4 ,why1 we do not know2 but the fact is the basis of these small batteries4 ,electrons from the atoms of zinc pass to the atoms of copper1 and their passage is a current4 ,each atom gives up an electron to its neighbour4 ,it was further found long ago that if the zinc and copper were immersed in certain chemicals1 which slowly dissolve the zinc1 and the two metals were connected by a copper wire1 the current was stronger4 ,in modern language1 there is a brisker flow of electrons4 ,the reason is that the atoms of zinc which are stolen by the chemical leave their detachable electrons behind them1 and the zinc has therefore more electrons to pass on to the copper4 ,illustration3 ,,disintegration ,,of ,,atoms ,an atom of ,uranium1 by ejecting an ,alpha particle1 becomes ,uranium ,x4 ,this substance1 by ejecting ,beta and ,gamma rays1 becomes ,radium4 ,radium passes through a number of further changes1 as shown in the diagram1 and finally becomes lead4 ,some radio-active substances disintegrate much faster than others4 ,thus ,uranium changes very slowly1 taking #e1jjj1jjj1jjj years to reach the same stage of disintegration that ,radium ,a reaches in #c minutes4 ,as the disintegration proceeds1 the substances become of lighter and lighter atomic weights4 ,thus ,uranium has an atomic weight of #bch1 whereas lead has an atomic weight of only #bjf4 ,the breaking down of atoms is fully explained in the text4 ,illustration3 ,reproduced by permission from ,the ,interpretation of ,radium 7,john ,murray74 ,,silk ,,tassel ,,electrified ,the separate threads of the tassel1 being each electrified with the same kind of electricity1 repel one another1 and thus the tassel branches out as in the photograph4 ,illustration3 ,,silk ,,tassel ,,discharged ,,by ,,the ,,rays ,,from ,,radium ,when the radium rays1 carrying an opposite electric charge to that on the tassel1 strikes the threads1 the threads are neutralised1 and hence fall together again4 ,illustration3 ,a ,,huge ,,electric ,,spark ,this is an actual photograph of an electric spark4 ,it is leaping a distance of about #aj feet1 and is the discharge of a million volts4 ,it is a graphic illustration of the tremendous energy of electrons4 ,illustration3 ,from ,scientific ,ideas of ,to-day4 ,,electrical ,,attraction ,,between ,,common ,,objects ,take an ordinary flower-vase well dried and energetically rub it with a silk handkerchief4 ,the vase which thus becomes electrified will attract any light body1 such as a feather1 as shown in the above illustration4 ,such cells are now made of zinc and carbon1 immersed in sal-ammoniac1 but the principle is the same4 ,the flow of electricity is a flow of electrons2 though we ought to repeat that they do not flow in a body1 as molecules of water do4 ,you may have seen boys place a row of bricks1 each standing on one end1 in such order that the first1 if it is pushed1 will knock over the second1 the second the third1 and so on to the last4 ,there is a flow of movement all along the line1 but each brick moves only a short distance4 ,so an electron merely passes to the next atom1 which sends on an electron to a third atom1 and so on4 ,in this case1 however1 the movement from atom to atom is so rapid that the ripple of movement1 if we may call it so1 may pass along at an enormous speed4 ,we have seen how swiftly electrons travel4 ,but how is this turned into power enough even to ring a bell8 ,the actual mechanical apparatus by which the energy of the electron current is turned into sound1 or heat1 or light will be described in a technical section later in this work4 ,we are concerned here only with the principle1 which is clear4 ,while zinc is very apt to part with electrons1 copper is just as obliging in facilitating their passage onward4 ,electrons will travel in this way in most metals1 but copper is one of the best conductors4 ,so we lengthen the copper wire between the zinc and the carbon until it goes as far as the front door and the bell1 which are included in the circuit4 ,when you press the button at the door1 two wires are brought together1 and the current of electrons rushes round the circuit2 and at the bell its energy is diverted into the mechanical apparatus which rings the bell4 ,copper is a good conductor--six times as good as iron--and is therefore so common in electrical industries4 ,some other substances are just as stubborn as copper is yielding1 and we call them insulators1 because they resist the current instead of letting it flow4 ,their atoms do not easily part with electrons4 ,glass1 vulcanite1 and porcelain are very good insulators for this reason4 ,what the ,dynamo does ,but even several cells together do not produce the currents needed in modern industry1 and the flow is produced in a different manner4 ,as the invisible electrons pass along a wire they produce what we call a magnetic field around the wire1 they produce a disturbance in the surrounding ether4 ,to be exact1 it is through the ether surrounding the wire that the energy originated by the electrons is transmitted4 ,to set electrons moving on a large scale we use a dynamo4 ,by means of the dynamo it is possible to transform mechanical energy into electrical energy4 ,the modern dynamo1 as ,professor ,soddy puts it1 may be looked upon as an electron pump4 ,we cannot go into the subject deeply here1 we would only say that a large coil of copper wire is caused to turn round rapidly between the poles of a powerful magnet4 ,that is the essential construction of the dynamo1 which is used for generating strong currents4 ,we shall see in a moment how magnetism differs from electricity1 and will say here only that round the poles of a large magnet there is a field of intense disturbance which will start a flow of electrons in any copper that is introduced into it4 ,on account of the speed given to the coil of wire its atoms enter suddenly this magnetic field1 and they give off crowds of electrons in a flash4 ,it is found that a similar disturbance is caused1 though the flow is in the opposite direction1 when the coil of wire leaves the magnetic field4 ,and as the coil is revolving very rapidly we get a powerful current of electricity that runs in alternate directions--an alternating current4 ,electricians have apparatus for converting it into a continuous current where this is necessary4 ,a current1 therefore1 means a steady flow of the electrons from atom to atom4 ,sometimes1 however1 a number of electrons rush violently and explosively from one body to another1 as in the electric spark or the occasional flash from an electric tram or train4 ,the grandest and most spectacular display of this phenomenon is the thunderstorm4 ,as we saw earlier1 a portentous furnace like the sun is constantly pouring floods of electrons from its atoms into space4 ,the earth intercepts great numbers of these electrons4 ,in the upper regions of the air the stream of solar electrons has the effect of separating positively-electrified atoms from negatively-electrified ones1 and the water-vapour1 which is constantly rising from the surface of the sea1 gathers more freely round the positively-electrified atoms1 and brings them down1 as rain1 to the earth4 ,thus the upper air loses a proportion of positive electricity1 or becomes negatively electrified4 ,in the thunderstorm we get both kinds of clouds--some with large excesses of electrons1 and some deficient in electrons--and the tension grows until at last it is relieved by a sudden and violent discharge of electrons from one cloud to another or to the earth--an electric spark on a prodigious scale4 #aa ,magnetism ,we have seen that an electric current is really a flow of electrons4 ,now an electric current exhibits a magnetic effect4 ,the surrounding space is endowed with energy which we call electro-magnetic energy4 ,a piece of magnetised iron attracting other pieces of iron to it is the popular idea of a magnet4 ,if we arrange a wire to pass vertically through a piece of cardboard and then sprinkle iron filings on the cardboard we shall find that1 on passing an electric current through the wire1 the iron filings arrange themselves in circles round it4 ,the magnetic force1 due to the electric current1 seems to exist in circles round the wire1 an ether disturbance being set up4 ,even a single electron1 when in movement1 creates a magnetic field1 as it is called1 round its path4 ,there is no movement of electrons without this attendant field of energy1 and their motion is not stopped until that field of energy disappears from the ether4 ,the modern theory of magnetism supposes that all magnetism is produced in this way4 ,all magnetism is supposed to arise from the small whirling motions of the electrons contained in the ultimate atoms of matter4 ,we cannot here go into the details of the theory nor explain why1 for instance1 iron behaves so differently from other substances1 but it is sufficient to say that here1 also1 the electron theory provides the key4 ,this theory is not yet definitely proved1 but it furnishes a sufficient theoretical basis for future research4 ,the earth itself is a gigantic magnet1 a fact which makes the compass possible1 and it is well known that the earth's magnetism is affected by those great outbreaks on the sun called sun-spots4 ,now it has been recently shown that a sun-spot is a vast whirlpool of electrons and that it exerts a strong magnetic action4 ,there is doubtless a connection between these outbreaks of electronic activity and the consequent changes in the earth's magnetism4 ,the precise mechanism of the connection1 however1 is still a matter that is being investigated4 ,,ether ,,and ,,waves ,ether and ,waves ,the whole material universe is supposed to be embedded in a vast medium called the ether4 ,it is true that the notion of the ether has been abandoned by some modern physicists1 but1 whether or not it is ultimately dispensed with1 the conception of the ether has entered so deeply into the scientific mind that the science of physics cannot be understood unless we know something about the properties attributed to the ether4 ,the ether was invented to explain the phenomena of light1 and to account for the flow of energy across empty space4 ,light takes time to travel4 ,we see the sun at any moment by the light that left it #h minutes before4 ,it has taken that #h minutes for the light from the sun to travel that #ic1jjj1jjj miles odd which separates it from our earth4 ,besides the fact that light takes time to travel1 it can be shown that light travels in the form of waves4 ,we know that sound travels in waves2 sound consists of waves in the air1 or water or wood or whatever medium we hear it through4 ,if an electric bell be put in a glass jar and the air be pumped out of the jar1 the sound of the bell becomes feebler and feebler until1 when enough air has been taken out1 we do not hear the bell at all4 ,sound cannot travel in a vacuum4 ,we continue to see the bell1 however1 so that evidently light can travel in a vacuum4 ,the invisible medium through which the waves of light travel is the ether1 and this ether permeates all space and all matter4 ,between us and the stars stretch vast regions empty of all matter4 ,but we see the stars2 their light reaches us1 even though it may take centuries to do so4 ,we conceive1 then1 that it is the universal ether which conveys that light4 ,all the energy which has reached the earth from the sun and which1 stored for ages in our coal-fields1 is now used to propel our trains and steamships1 to heat and light our cities1 to perform all the multifarious tasks of modern life1 was conveyed by the ether4 ,without that universal carrier of energy we should have nothing but a stagnant1 lifeless world4 ,illustration3 ,photo3 ,leadbeater4 ,,an ,,electric ,,spark ,an electric spark consists of a rush of electrons across the space between the two terminals4 ,a state of tension is established in the ether by the electric charges1 and when this tension passes a certain limit the discharge takes place4 ,illustration3 ,from ,scientific ,ideas of ,to-day4 ,,an ,,ether ,,disturbance ,,around ,,an ,,electron ,,current ,in the left-hand photograph an electric current is passing through the coil1 thus producing a magnetic field and transforming the poker into a magnet4 ,the poker is then able to support a pair of scissors4 ,as soon as the electric current is broken off1 as in the second photograph1 the ether disturbance ceases4 ,the poker loses its magnetism1 and the scissors fall4 ,we have said that light consists of waves4 ,the ether may be considered as resembling1 in some respects1 a jelly4 ,it can transmit vibrations4 ,the waves of light are really excessively small ripples1 measuring from crest to crest4 ,the distance from crest to crest of the ripples in a pond is sometimes no more than an inch or two4 ,this distance is enormously great compared to the longest of the wave-lengths that constitute light4 ,we say the longest1 for the waves of light differ in length2 the colour depends upon the length of the light4 ,red light has the longest waves and violet the shortest4 ,the longest waves1 the waves of deep-red light1 are seven two hundred and fifty thousandths of an inch in length 7#g_/bej1jjj inch74 ,this is nearly twice the length of deep-violet light-waves1 which are #a_/fg1jjj inch4 ,but light-waves1 the waves that affect the eye1 are not the only waves carried by the ether4 ,waves too short to affect the eye can affect the photographic plate1 and we can discover in this way the existence of waves only half the length of the deep-violet waves4 ,still shorter waves can be discovered1 until we come to those excessively minute rays1 the ,x-rays4 ,below the ,limits of ,visibility ,but we can extend our investigations in the other direction2 we find that the ether carries many waves longer than light-waves4 ,special photographic emulsions can reveal the existence of waves five times longer than violet-light waves4 ,extending below the limits of visibility are waves we detect as heat-waves4 ,radiant heat1 like the heat from a fire1 is also a form of wave-motion in the ether1 but the waves our senses recognise as heat are longer than light-waves4 ,there are longer waves still1 but our senses do not recognise them4 ,but we can detect them by our instruments4 ,these are the waves used in wireless telegraphy1 and their length may be1 in some cases1 measured in miles4 ,these waves are the so-called electro-magnetic waves4 ,light1 radiant heat1 and electro-magnetic waves are all of the same nature2 they differ only as regards their wave-lengths4 ,,light--,,visible ,,and ,,invisible ,if ,light1 then1 consists of waves transmitted through the ether1 what gives rise to the waves8 ,whatever sets up such wonderfully rapid series of waves must be something with an enormous vibration4 ,we come back to the electron3 all atoms of matter1 as we have seen1 are made up of electrons revolving in a regular orbit round a nucleus4 ,these electrons may be affected by out-side influences1 they may be agitated and their speed or vibration increased4 ,electrons and ,light ,the particles even of a piece of cold iron are in a state of vibration4 ,no nerves of ours are able to feel and register the waves they emit1 but your cold poker is really radiating1 or sending out a series of wave-movements1 on every side4 ,after what we saw about the nature of matter1 this will surprise none4 ,put your poker in the fire for a time4 ,the particles of the glowing coal1 which are violently agitated1 communicate some of their energy to the particles of iron in the poker4 ,they move to and fro more rapidly1 and the waves which they create are now able to affect your nerves and cause a sensation of heat4 ,put the poker again in the fire1 until its temperature rises to #ejj ,c4 ,it begins to glow with a dull red4 ,its particles are now moving very violently1 and the waves they send out are so short and rapid that they can be picked up by the eye--we have visible light4 ,they would still not affect a photographic plate4 ,heat the iron further1 and the crowds of electrons now send out waves of various lengths which blend into white light4 ,what is happening is the agitated electrons flying round in their orbits at a speed of trillions of times a second4 ,make the iron blue hot1 and it pours out1 in addition to light1 the invisible waves which alter the film on the photographic plate4 ,and beyond these there is a long range of still shorter waves1 culminating in the ,x-rays1 which will pass between the atoms of flesh or stone4 ,nearly two hundred and fifty years ago it was proved that light travelled at least #fjj1jjj times faster than sound4 ,jupiter1 as we saw1 has moons1 which circle round it4 ,they pass behind the body of the planet1 and reappear at the other side4 ,but it was noticed that1 when ,jupiter is at its greatest distance from us1 the reappearance of the moon from behind it is #af minutes and #cf seconds later than when the planet is nearest to us4 ,plainly this was because light took so long to cover the additional distance4 ,the distance was then imperfectly known1 and the speed of light was underrated4 ,we now know the distance1 and we easily get the velocity of light4 ,no doubt it seems far more wonderful to discover this within the walls of a laboratory1 but it was done as long ago as #ahej4 ,a cogged wheel is so mounted that a ray of light passes between two of the teeth and is reflected back from a mirror4 ,now1 slight as is the fraction of a second which light takes to travel that distance1 it is possible to give such speed to the wheel that the next tooth catches the ray of light on its return and cuts it off4 ,the speed is increased still further until the ray of light returns to the eye of the observer through the notch next to the one by which it had passed to the mirror6 ,the speed of the wheel was known1 and it was thus possible again to gather the velocity of light4 ,if the shortest waves are #a_/fg1jjj of an inch in length1 and light travels at #ahf1jjj miles a second1 any person can work out that about #hjj trillion waves enter the eye in a second when we see violet4 ,sorting out ,light-waves ,the waves sent out on every side by the energetic electrons become faintly visible to us when they reach about #a_/ce1jjj of an inch4 ,as they become shorter and more rapid1 as the electrons increase their speed1 we get1 in succession1 the colours red1 orange1 yellow1 green1 blue1 indigo1 and violet4 ,each distinct sensation of colour means a wave of different length4 ,when they are all mingled together1 as in the light of the sun1 we get white light4 ,when this white light passes through glass1 the speed of the waves is lessened2 and1 if the ray of light falls obliquely on a triangular piece of glass1 the waves of different lengths part company as they travel through it1 and the light is spread out in a band of rainbow-colour4 ,the waves are sorted out according to their lengths in the obstacle race through the glass4 ,anyone may see this for himself by holding up a wedge-shaped piece of crystal between the sunlight and the eye2 the prism separates the sunlight into its constituent colours1 and these various colours will be seen quite readily4 ,or the thing may be realised in another way4 ,if the seven colours are painted on a wheel as shown opposite page #bhj 7in the proportion shown71 and the wheel rapidly revolved on a pivot1 the wheel will appear a dull white1 the several colours will not be seen4 ,but omit one of the colours1 then the wheel1 when revolved1 will not appear white1 but will give the impression of one colour1 corresponding to what the union of six colours gives4 ,another experiment will show that some bodies held up between the eye and a white light will not permit all the rays to pass through1 but will intercept some2 a body that intercepts all the seven rays except red will give the impression of red1 or if all the rays except violet1 then violet will be the colour seen4 ,illustration3 ,photo3 ,h4 ,j4 ,shepstone4 ,,lightning ,in a thunderstorm we have the most spectacular display in lightning of a violent and explosive rush of electrons 7electricity7 from one body to another1 from cloud to cloud1 or to the earth4 ,in this wonderful photograph of an electrical storm note the long branched and undulating flashes of lightning4 ,each flash lasts no longer than the one hundred-thousandth part of a second of time4 ,illustration3 ,,light ,,waves ,light consists of waves transmitted through the ether4 ,waves of light differ in length4 ,the colour of the light depends on the wave-length4 ,deep-red waves 7the longest7 are #g_/bejjjj inch and deep-violet waves #a_/fgjjj inch4 ,the diagram shows two wave-motions of different wave-lengths4 ,from crest to crest1 or from trough to trough1 is the length of the wave4 ,illustration3 ,,the ,,magnetic ,,circuit ,,of ,,an ,,electric ,,current ,the electric current passing in the direction of the arrow round the electric circuit generates in the surrounding space circular magnetic circuits as shown in the diagram4 ,it is this property which lies at the base of the electro-magnet and of the electric dynamo4 ,illustration3 ,,the ,,magnet ,the illustration shows the lines of force between two magnets4 ,the lines of force proceed from the north pole of one magnet to the south pole of the other4 ,they also proceed from the north to the south poles of the same magnet4 ,these facts are shown clearly in the diagram4 ,the north pole of a magnet is that end of it which turns to the north when the magnet is freely suspended4 ,the ,fate of the ,world ,professor ,soddy has given an interesting picture of what might happen when the sun's light and heat is no longer what it is4 ,the human eye has adapted itself through the ages to the peculiarities of the sun's light1 so as to make the most of that wave-length of which there is most4444 ,let us indulge for a moment in these gloomy prognostications1 as to the consequences to this earth of the cooling of the sun with the lapse of ages1 which used to be in vogue1 but which radio-activity has so rudely shaken4 ,picture the fate of the world when the sun has become a dull red-hot ball1 or even when it has cooled so far that it would no longer emit light to us4 ,that does not all mean that the world would be in inky darkness1 and that the sun would not emit light to the people then inhabiting this world1 if any had survived and could keep themselves from freezing4 ,to such1 if the eye continued to adapt itself to the changing conditions1 our blues and violets would be ultra-violet and invisible1 but our dark heat would be light and hot bodies would be luminous to them which would be dark to us4 #ab ,what the ,blue ,sky means ,we saw in a previous chapter how the spectroscope splits up light-waves into their colours4 ,but nature is constantly splitting the light into its different-lengthed waves1 its colours4 ,the rainbow1 where dense moisture in the air acts as a spectroscope1 is the most familiar example4 ,a piece of mother-of-pearl1 or even a film of oil on the street or on water1 has the same effect1 owing to the fine inequalities in its surface4 ,the atmosphere all day long is sorting out the waves4 ,the blue sky overhead means that the fine particles in the upper atmosphere catch the shorter waves1 the blue waves1 and scatter them4 ,we can make a tubeful of blue sky in the laboratory at any time4 ,the beautiful pink-flush on the ,alps at sunrise1 the red glory that lingers in the west at sunset1 mean that1 as the sun's rays must struggle through denser masses of air when it is low on the horizon1 the long red waves are sifted out from the other shafts4 ,then there is the varied face of nature which1 by absorbing some waves and reflecting others1 weaves its own beautiful robe of colour4 ,here and there is a black patch1 which absorbs all the light4 ,white surfaces reflect the whole of it4 ,what is reflected depends on the period of vibration of the electrons in the particular kind of matter4 ,generally1 as the electrons receive the flood of trillions of waves1 they absorb either the long or the medium or the short1 and they give us the wonderful colour-scheme of nature4 ,in some cases the electrons continue to radiate long after the sunlight has ceased to fall upon them4 ,we get from them black or invisible light1 and we can take photographs by it4 ,other bodies1 like glass1 vibrate in unison with the period of the light-waves and let them stream through4 ,light without ,heat ,there are substances--phosphorescent things we call them--which give out a mysterious cold light of their own4 ,it is one of the problems of science1 and one of profound practical interest4 ,if we could produce light without heat our gas bill would shrink amazingly4 ,so much energy is wasted in the production of heat-waves and ultra-violet waves which we do not want1 that #ij per cent4 or more of the power used in illumination is wasted4 ,would that the glow-worm1 or even the dead herring1 would yield us its secret6 ,phosphorus is the one thing we know as yet that suits the purpose1 and--it smells6 ,indeed1 our artificial light is not only extravagant in cost1 but often poor in colour4 ,the unwary person often buys a garment by artificial light1 and is disgusted next morning to find in it a colour which is not wanted4 ,the colour disclosed by the sun was not in the waves of the artificial light4 ,illustration3 ,,rotating ,,disc ,,of ,,sir ,,isaac ,,newton ,,for ,,mixing ,,colours ,the ,spectroscope sorts out the above seven colours from sunlight 7which is compounded of these seven colours74 ,if painted in proper proportions on a wheel1 as shown in the coloured illustration1 and the wheel be turned rapidly on a pivot through its centre1 only a dull white will be perceived4 ,if one colour be omitted1 the result will be one colour--the result of the union of the remaining six4 ,beyond the waves of violet light are the still shorter and more rapid waves--the ultra-violet waves--which are precious to the photographer4 ,as every amateur knows1 his plate may safely be exposed to light that comes through a red or an orange screen4 ,such a screen means no thoroughfare for the blue and beyond-blue waves1 and it is these which arrange the little grains of silver on the plate4 ,it is the same waves which supply the energy to the little green grains of matter 7chlorophyll7 in the plant1 preparing our food and timber for us1 as will be seen later4 ,the tree struggles upward and spreads out its leaves fanwise to the blue sky to receive them4 ,in our coal-measures1 the mighty dead forests of long ago1 are vast stores of sunlight which we are prodigally using up4 ,the ,x-rays are the extreme end1 the highest octave1 of the series of waves4 ,their power of penetration implies that they are excessively minute1 but even these have not held their secret from the modern physicist4 ,from a series of beautiful experiments1 in which they were made to pass amongst the atoms of a crystal1 we learned their length4 ,it is about the ten-millionth of a millimetre1 and a millimetre is about the #a_/be of an inch6 ,one of the most recent discoveries1 made during a recent eclipse of the sun1 is that light is subject to gravitation4 ,a ray of light from a star is bent out of its straight path when it passes near the mass of the sun4 ,professor ,eddington tells us that we have as much right to speak of a pound of light as of a pound of sugar4 ,professor ,eddington even calculates that the earth receives #afj tons of light from the sun every year6 ,,energy3 ,,how ,,all ,,life ,,depends ,,on ,,it ,as we have seen in an earlier chapter1 one of the fundamental entities of the universe is matter4 ,a second1 not less important1 is called energy4 ,energy is indispensable if the world is to continue to exist1 since all phenomena1 including life1 depend on it4 ,just as it is humanly impossible to create or to destroy a particle of matter1 so is it impossible to create or to destroy energy4 ,this statement will be more readily understood when we have considered what energy is4 ,energy1 like matter1 is indestructible1 and just as matter exists in various forms so does energy4 ,and we may add1 just as we are ignorant of what the negative and positive particles of electricity which constitute matter really are1 so we are ignorant of the true nature of energy4 ,at the same time1 energy is not so completely mysterious as it once was4 ,it is another of nature's mysteries which the advance of modern science has in some measure unveiled4 ,it was only during the nineteenth century that energy came to be known as something as distinct and permanent as matter itself4 ,forms of ,energy ,the existence of various forms of energy had been known1 of course1 for ages2 there was the energy of a falling stone1 the energy produced by burning wood or coal or any other substance1 but the essential identity of all these forms of energy had not been suspected4 ,the conception of energy as something which1 like matter1 was constant in amount1 which could not be created nor destroyed1 was one of the great scientific acquisitions of the past century4 ,illustration3 ,,wave ,,shapes ,wave-motions are often complex4 ,the above illustration shows some fairly complicated wave shapes4 ,all such wave-motions can be produced by superposing a number of simple wave forms4 ,illustration3 ,,the ,,power ,,of ,a ,,magnet ,the illustration is that of a ,phoenix electric magnet lifting scrap from railway trucks4 ,the magnet is #eb inches in diameter and lifts a weight of #bf tons4 ,the same type of magnet1 #fb inches in diameter1 lifts a weight of #dj tons4 ,illustration3 ,photo3 ,the ,locomotive ,publishing ,co41 ,ltd4 ,,the ,,speed ,,of ,,light ,a train travelling at the rate of sixty miles per hour would take rather more than seventeen and a quarter days to go round the earth at the equator1 i4e4 a distance of #be1jjj miles4 ,light1 which travels at the rate of #ahf1jjj miles per second1 would take between one-seventh and one-eighth of a second to go the same distance4 ,illustration3 ,,rotating ,,disc ,,of ,,sir ,,isaac ,,newton ,,for ,,mixing ,,colours ,the ,spectroscope sorts out the above seven colours from sunlight 7which is compounded of these seven colours74 ,if painted in proper proportions on a wheel1 as shown in the coloured illustration1 and the wheel turned rapidly on a pivot through its centre1 only a dull white will be perceived4 ,if one colour be omitted1 the result will be one colour--the result of the union of the remaining six4 ,it is not possible to enter deeply into this subject here4 ,it is sufficient if we briefly outline its salient aspects4 ,energy is recognised in two forms1 kinetic and potential4 ,the form of energy which is most apparent to us is the energy of motion2 for example1 a rolling stone1 running water1 a falling body1 and so on4 ,we call the energy of motion kinetic energy4 ,potential energy is the energy a body has in virtue of its position--it is its capacity1 in other words1 to acquire kinetic energy1 as in the case of a stone resting on the edge of a cliff4 ,energy may assume different forms2 one kind of energy may be converted directly or indirectly into some other form4 ,the energy of burning coal1 for example1 is converted into heat1 and from heat energy we have mechanical energy1 such as that manifested by the steam-engine4 ,in this way we can transfer energy from one body to another4 ,there is the energy of the great waterfalls of ,niagara1 for instance1 which are used to supply the energy of huge electric power stations4 ,what ,heat is ,an important fact about energy is1 that all energy tends to take the form of heat energy4 ,the impact of a falling stone generates heat2 a waterfall is hotter at the bottom than at the top--the falling particles of water1 on striking the ground1 generate heat2 and most chemical changes are attended by heat changes4 ,energy may remain latent indefinitely in a lump of wood1 but in combustion it is liberated1 and we have heat as a result4 ,the atom of radium or of any other radio-active substance1 as it disintegrates1 generates heat4 ,every hour radium generates sufficient heat to raise the temperature of its own weight of water1 from the freezing point to the boiling point4 ,and what is heat8 ,heat is molecular motion4 ,the molecules of every substance1 as we have seen on a previous page1 are in a state of continual motion1 and the more vigorous the motion the hotter the body4 ,as wood or coal burns1 the invisible molecules of these substances are violently agitated1 and give rise to ether waves which our senses interpret as light and heat4 ,in this constant movement of the molecules1 then1 we have a manifestation of the energy of motion and of heat4 ,that energy which disappears in one form reappears in another has been found to be universally true4 ,it was ,joule who1 by churning water1 first showed that a measurable quantity of mechanical energy could be transformed into a measurable quantity of heat energy4 ,by causing an apparatus to stir water vigorously1 that apparatus being driven by falling weights or a rotating flywheel or by any other mechanical means1 the water became heated4 ,a certain amount of mechanical energy had been used up and a certain amount of heat had appeared4 ,the relation between these two things was found to be invariable4 ,every physical change in nature involves a transformation of energy1 but the total quantity of energy in the universe remains unaltered4 ,this is the great doctrine of the ,conservation of ,energy4 #ac ,substitutes for ,coal ,consider the source of nearly all the energy which is used in modern civilisation--coal4 ,the great forests of the ,carboniferous epoch now exists as beds of coal4 ,by the burning of coal--a chemical transformation--the heat energy is produced on which at present our whole civilisation depends4 ,whence is the energy locked up in the coal derived8 ,from the sun4 ,for millions of years the energy of the sun's rays had gone to form the vast vegetation of the ,carboniferous era and had been transformed1 by various subtle processes1 into the potential energy that slumbers in those immense fossilized forests4 ,the exhaustion of our coal deposits would mean1 so far as our knowledge extends at present1 the end of the world's civilisation4 ,there are other known sources of energy1 it is true4 ,there is the energy of falling water2 the great falls of ,niagara are used to supply the energy of huge electric power stations4 ,perhaps1 also1 something could be done to utilise the energy of the tides--another instance of the energy of moving water4 ,and attempts have been made to utilise directly the energy of the sun's rays4 ,but all these sources of energy are small compared with the energy of coal4 ,a suggestion was made at a recent ,british ,association meeting that deep borings might be sunk in order to utilise the internal heat of the earth1 but this is not1 perhaps1 a very practical proposal4 ,by far the most effective substitutes for coal would be found in the interior energy of the atom1 a source of energy which1 as we have seen1 is practically illimitable4 ,if the immense electrical energy in the interior of the atom can ever be liberated and controlled1 then our steadily decreasing coal supply will no longer be the bugbear it now is to all thoughtful men4 ,the stored-up energy of the great coal-fields can be used up1 but we cannot replace it or create fresh supplies4 ,as we have seen1 energy cannot be destroyed1 but it can become unavailable4 ,let us consider what this important fact means4 #ad ,dissipation of ,energy ,energy may become dissipated4 ,where does it go8 since if it is indestructible it must still exist4 ,it is easier to ask the question than to give a final answer1 and it is not possible in this ,,outline1 where an advanced knowledge of physics is not assumed on the part of the reader1 to go fully into the somewhat difficult theories put forward by physicists and chemists4 ,we may raise the temperature1 say1 of iron1 until it is white-hot4 ,if we stop the process the temperature of the iron will gradually settle down to the temperature of surrounding bodies4 ,as it does so1 where does its previous energy go8 ,in some measure it may pass to other bodies in contact with the piece of iron1 but ultimately the heat becomes radiated away in space where we cannot follow it4 ,it has been added to the vast reservoir of unavailable heat energy of uniform temperature4 ,it is sufficient here to say that if all bodies had a uniform temperature we should experience no such thing as heat1 because heat only travels from one body to another1 having the effect of cooling the one and warming the other4 ,in time the two bodies acquire the same temperature4 ,the sum-total of the heat in any body is measured in terms of the kinetic energy of its moving molecules4 ,there must come a time1 so far as we can see at present1 when1 even if all the heat energy of the universe is not radiated away into empty infinite space1 yet a uniform temperature will prevail4 ,if one body is hotter than another it radiates heat to that body until both are at the same temperature4 ,each body may still possess a considerable quantity of heat energy1 which it has absorbed1 but that energy1 so far as reactions between those two bodies are concerned1 is now unavailable4 ,the same principle applies whatever number of bodies we consider4 ,before heat energy can be utilised we must have bodies with different temperature4 ,if the whole universe were at some uniform temperature1 then1 although it might possess an enormous amount of heat energy1 this energy would be unavailable4 ,what a ,uniform ,temperature would mean ,and what does this imply8 ,it implies a great deal3 for if all the energy in the world became unavailable1 the universe1 as it now is1 would cease to be4 ,it is possible that1 by the constant interchange of heat radiations1 the whole universe is tending to some uniform temperature1 in which case1 although all molecular motion would not have ceased1 it would have become unavailable4 ,in this sense it may be said that the universe is running down4 ,illustration3 ,,niagara ,,falls ,the energy of this falling water is prodigious4 ,it is used to generate thousands of horse-power in great electrical installations4 ,the power is used to drive electric trams in cities #aej to #bej miles away4 ,illustration3 ,photo3 ,stephen ,cribb4 ,,transformation ,,of ,,energy ,an illustration of ,energy4 ,the chemical energy brought into existence by firing the explosive manifesting itself as mechanical energy1 sufficient to impart violent motion to tons of water4 ,illustration3 ,photo3 ,underwood ,underwood4 ,,boiling ,a ,,kettle ,,on ,,ice ,when a kettle containing liquid air is placed on ice it boils because the ice is intensely hot when compared with the very low temperature of the liquid air4 ,if all the molecules of a substance were brought to a standstill1 that substance would be at the absolute zero of temperature4 ,there could be nothing colder4 ,the temperature at which all molecular motions would cease is known3 it is -#bgc ,c4 ,no body could possibly attain a lower temperature than this3 a lower temperature could not exist4 ,unless there exists in nature some process1 of which we know nothing at present1 whereby energy is renewed1 our solar system must one day sink to this absolute zero of temperature4 ,the sun1 the earth1 and every other body in the universe is steadily radiating heat1 and this radiation cannot go on for ever1 because heat continually tends to diffuse and to equalise temperatures4 ,but we can see1 theoretically1 that there is a way of evading this law4 ,if the chaotic molecular motions which constitute heat could be regulated1 then the heat energy of a body could be utilised directly4 ,some authorities think that some of the processes which go on in the living body do not involve any waste energy1 that the chemical energy of food is transformed directly into work without any of it being dissipated as useless heat energy4 ,it may be1 therefore1 that man will finally discover some way of escape from the natural law that1 while energy cannot be destroyed1 it has a tendency to become unavailable4 ,the primary reservoir of energy is the atom2 it is the energy of the atom1 the atom of elements in the sun1 the stars1 the earth1 from which nature draws for all her supply of energy4 ,shall we ever discover how we can replenish the dwindling resources of energy1 or find out how we can call into being the at present unavailable energy which is stored up in uniform temperature8 ,it looks as if our successors would witness an interesting race1 between the progress of science on the one hand and the depletion of natural resources upon the other4 ,the natural rate of flow of energy from its primary atomic reservoirs to the sea of waste heat energy of uniform temperature1 allows life to proceed at a complete pace sternly regulated by the inexorable laws of supply and demand1 which the biologists have recognised in their field as the struggle for existence4#e #e ,matter and ,energy1 by ,professor ,soddy4 ,it is certain that energy is an actual entity just as much as matter1 and that it cannot be created or destroyed4 ,matter and ether are receptacles or vehicles of energy4 ,as we have said1 what these entities really are in themselves we do not know4 ,it may be that all forms of energy are in some fundamental way aspects of the same primary entity which constitutes matter3 how all matter is constituted of particles of electricity we have already seen4 ,the question to which we await an answer is3 ,what is electricity8 #ae ,,matter1 ,,ether1 ,,and ,,einstein ,the supreme synthesis1 the crown of all this progressive conquest of nature1 would be to discover that the particles of positive and negative electricity1 which make up the atoms of matter1 are points or centres of disturbances of some kind in a universal ether1 and that all our energies 7light1 magnetism1 gravitation1 etc47 are waves or strains of some kind set up in the ether by these clusters of electrons4 ,it is a fascinating1 tantalising dream4 ,larmor suggested in #aijj that the electron is a tiny whirlpool1 or vortex1 in ether2 and1 as such a vortex may turn in either of two opposite ways1 we seem to see a possibility of explaining positive and negative electricity4 ,but the difficulties have proved very serious1 and the nature of the electron is unknown4 ,a recent view is that it is a ring of negative electricity rotating about its axis at a high speed1 though that does not carry us very far4 ,the unit of positive electricity is even less known4 ,we must be content to know the general lines on which thought is moving toward the final unification4 ,we say unification1 but it would be a grave error to think that ether is the only possible basis for such unity1 or to make it an essential part of one's philosophy of the universe4 ,ether was never more than an imagined entity to which we ascribed the most extraordinary properties1 and which seemed then to promise considerable aid4 ,it was conceived as an elastic solid of very great density1 stretching from end to end of the universe1 transmitting waves from star to star at the rate of #ahf1jjj miles a second2 yet it was believed that the most solid matter passed through it as if it did not exist4 ,some years ago a delicate experiment was tried for the purpose of detecting the ether4 ,since the earth1 in travelling round the sun1 must move through the ether if the ether exists1 there ought to be a stream of ether flowing through every laboratory2 just as the motion of a ship through a still atmosphere will make a wind4 ,in #ahhg ,michelson and ,morley tried to detect this4 ,theoretically1 a ray of light in the direction of the stream ought to travel at a different rate from a ray of light against the stream or across it4 ,they found no difference1 and scores of other experiments have failed4 ,this does not prove that there is no ether1 as there is reason to suppose that our instruments would appear to shrink in precisely the same proportion as the alteration of the light2 but the fact remains that we have no proof of the existence of ether4 ,j4 ,h4 ,jeans says that nature acts as if no such thing existed4 ,even the phenomena of light and magnetism1 he says1 do not imply ether2 and he thinks that the hypothesis may be abandoned4 ,the primary reason1 of course1 for giving up the notion of the ether is that1 as ,einstein has shown1 there is no way of detecting its existence4 ,if there is an ether1 then1 since the earth is moving through it1 there should be some way of detecting this motion4 ,the experiment has been tried1 as we have said1 but1 although the method used was very sensitive1 no motion was discovered4 ,it is ,einstein who1 by revolutionising our conceptions of space and time1 showed that no such motion ever could be discovered1 whatever means were employed1 and that the usual notion of the ether must be abandoned4 ,we shall explain this theory more fully in a later section4 ,,influence ,,of ,,the ,,tides3 ,,origin ,,of ,,the ,,moon3 ,,the ,,earth ,,slowing ,,down #af ,until comparatively recent times1 until1 in fact1 the full dawn of modern science1 the tides ranked amongst the greatest of nature's mysteries4 ,and1 indeed1 what agency could be invoked to explain this mysteriously regular flux and reflux of the waters of the ocean8 ,it is not surprising that that steady1 rhythmical rise and fall suggested to some imaginative minds the breathing of a mighty animal4 ,and even when man first became aware of the fact that this regular movement was somehow associated with the moon1 was he much nearer an explanation8 ,what bond could exist between the movements of that distant world and the diurnal variation of the waters of the earth8 ,it is reported that an ancient astronomer1 despairing of ever resolving the mystery1 drowned himself in the sea4 ,the ,earth ,pulled by the ,moon ,but it was part of the merit of ,newton's mighty theory of gravitation that it furnished an explanation even of this age-old mystery4 ,we can see1 in broad outlines at any rate1 that the theory of universal attraction can be applied to this case4 ,for the moon1 ,newton taught us1 pulls every particle of matter throughout the earth4 ,if we imagine that part of the earth's surface which comprises the ,pacific ,ocean1 for instance1 to be turned towards the moon1 we see that the moon's pull1 acting on the loose and mobile water1 would tend to heap it up into a sort of mound4 ,the whole earth is pulled by the moon1 but the water is more free to obey this pull than is the solid earth1 although small tides are also caused in the earth's solid crust4 ,it can be shown also that a corresponding hump would tend to be produced on the other side of the earth1 owing1 in this case1 to the tendency of the water1 being more loosely connected1 to lag behind the solid earth4 ,if the earth's surface were entirely fluid the rotation of the earth would give the impression that these two humps were continually travelling round the world1 once every day4 ,at any given part of the earth's surface1 therefore1 there would be two humps daily1 i4e4 two periods of high water4 ,such is the simplest possible outline of the gravitational theory of the tides4 ,illustration3 ,,the ,,cause ,,of ,,tides ,the tides of the sea are due to the pull of the moon1 and1 in lesser degree1 of the sun4 ,the whole earth is pulled by the moon1 but the loose and mobile water is more free to obey this pull than is the solid earth1 although small tides are also caused in the earth's solid crust4 ,the effect which the tides have on slowing down the rotation of the earth is explained in the text4 ,illustration3 ,photo3 ,g4 ,brocklehurst4 ,,the ,,aegir ,,on ,,the ,,trent ,an exceptionally smooth formation due to perfect weather conditions4 ,the wall-like formation of these tidal waves 7see next page also7 will be noticed4 ,the reason for this is that the downward current in the river heads the sea-water back1 and thus helps to exaggerate the advancing slope of the wave4 ,the exceptional spring tides are caused by the combined operation of the moon and the sun1 as is explained in the text4 ,illustration3 ,photo3 ,g4 ,brocklehurst4 ,a ,,big ,,spring ,,tide1 ,,the ,,aegir ,,on ,,the ,,trent ,the actually observed phenomena are vastly more complicated1 and the complete theory bears very little resemblance to the simple form we have just outlined4 ,everyone who lives in the neighbourhood of a port knows1 for instance1 that high water seldom coincides with the time when the moon crosses the meridian4 ,it may be several hours early or late4 ,high water at ,london ,bridge1 for instance1 occurs about one and a half hours after the moon has passed the meridian1 while at ,dublin high water occurs about one and a half hours before the moon crosses the meridian4 ,the actually observed phenomena1 then1 are far from simple2 they have1 nevertheless1 been very completely worked out1 and the times of high water for every port in the world can now be prophesied for a considerable time ahead4 ,the ,action of ,sun and ,moon ,it would be beyond our scope to attempt to explain the complete theory1 but we may mention one obvious factor which must be taken into account4 ,since the moon1 by its gravitational attraction1 produces tides1 we should expect that the sun1 whose gravitational attraction is so much stronger1 should also produce tides and1 we would suppose at first sight1 more powerful tides than the moon4 ,but while it is true that the sun produces tides1 it is not true that they are more powerful than those produced by the moon4 ,the sun's tide-producing power is1 as a matter of fact1 less than half that of the moon4 ,the reason of this is that distance plays an enormous rle in the production of tides4 ,the mass of the sun is #bf1jjj1jjj times that of the moon2 on the other hand it is #chf times as far off as the moon4 ,this greater distance more than counterbalances its greater mass1 and the result1 as we have said1 is that the moon is more than twice as powerful4 ,sometimes the sun and moon act together1 and we have what are called spring tides2 sometimes they act against one another1 and we have neap tides4 ,these effects are further complicated by a number of other factors1 and the tides1 at various places1 vary enormously4 ,thus at ,st4 ,helena the sea rises and falls about three feet1 whereas in the ,bay of ,fundy it rises and falls more than fifty feet4 ,but here1 again1 the reasons are complicated4 #ag ,origin of the ,moon ,but there is another aspect of the tides which is of vastly greater interest and importance than the theory we have just been discussing4 ,in the hands of ,sir ,george ,h4 ,darwin1 the son of ,charles ,darwin1 the tides had been made to throw light on the evolution of our solar system4 ,in particular1 they have illustrated the origin and development of the system formed by our earth and moon4 ,it is quite certain that1 long ages ago1 the earth was rotating immensely faster than it is now1 and that the moon was so near as to be actually in contact with the earth4 ,in that remote age the moon was just on the point of separating from the earth1 of being thrown off by the earth4 ,earth and moon were once one body1 but the high rate of rotation caused this body to split up into two pieces2 one piece became the earth we now know1 and the other became the moon4 ,such is the conclusion to which we are led by an examination of the tides4 ,in the first place let us consider the energy produced by the tides4 ,we see evidences of this energy all round the word's coastlines4 ,estuaries are scooped out1 great rocks are gradually reduced to rubble1 innumerable tons of matter are continually being set in movement4 ,whence is this energy derived8 ,energy1 like matter1 cannot be created from nothing2 what1 then1 is the source which makes this colossal expenditure possible4 ,the ,earth ,slowing down ,the answer is simple1 but startling4 ,the source of tidal energy is the rotation of the earth4 ,the massive bulk of the earth1 turning every twenty-four hours on its axis1 is like a gigantic flywheel4 ,in virtue of its rotation it possesses an enormous store of energy4 ,but even the heaviest and swiftest flywheel1 if it is doing work1 or even if it is only working against the friction of its bearings1 cannot dispense energy for ever4 ,it must1 gradually1 slow down4 ,there is no escape from this reasoning4 ,it is the rotation of the earth which supplies the energy of the tides1 and1 as a consequence1 the tides must be slowing down the earth4 ,the tides act as a kind of brake on the earth's rotation4 ,these masses of water1 held back by the moon1 exert a kind of dragging effect on the rotating earth4 ,doubtless this effect1 measured by our ordinary standards1 is very small2 it is1 however1 continuous1 and in the course of the millions of years dealt with in astronomy1 this small but constant effect may produce very considerable results4 ,but there is another effect which can be shown to be a necessary mathematical consequence of tidal action4 ,it is the moon's action on the earth which produces the tides1 but they also react on the moon4 ,the tides are slowing down the earth1 and they are also driving the moon farther and farther away4 ,this result1 strange as it may seem1 does not permit of doubt1 for it is the result of an indubitable dynamical principle1 which cannot be made clear without a mathematical discussion4 ,some interesting consequences follow4 ,since the earth is slowing down1 it follows that it was once rotating faster4 ,there was a period1 a long time ago1 when the day comprised only twenty hours4 ,going farther back still we come to a day of ten hours1 until1 inconceivable ages ago1 the earth must have been rotating on its axis in a period of from three to four hours4 ,at this point let us stop and inquire what was happening to the moon4 ,we have seen that at present the moon is getting farther and farther away4 ,it follows1 therefore1 that when the day was shorter the moon was nearer4 ,as we go farther back in time we find the moon nearer and nearer to an earth rotating faster and faster4 ,when we reach the period we have already mentioned1 the period when the earth completed a revolution in three or four hours1 we find that the moon was so near as to be almost grazing the earth4 ,this fact is very remarkable4 ,everybody knows that there is a critical velocity for a rotating flywheel1 a velocity beyond which the flywheel would fly into pieces because the centrifugal force developed is so great as to overcome the cohesion of the molecules of the flywheel4 ,we have already likened our earth to a flywheel1 and we have traced its history back to the point where it was rotating with immense velocity4 ,we have also seen that1 at that moment1 the moon was barely separated from the earth4 ,the conclusion is irresistible4 ,in an age more remote the earth did fly in pieces1 and one of those pieces is the moon4 ,such1 in brief outline1 is the tidal theory of the origin of the earth-moon system4 ,the ,day ,becoming ,longer ,at the beginning1 when the moon split off from the earth1 it obviously must have shared the earth's rotation4 ,it flew round the earth in the same time that the earth rotated1 that is to say1 the month and the day were of equal length4 ,as the moon began to get farther from the earth1 the month1 because the moon took longer to rotate round the earth1 began to get correspondingly longer4 ,the day also became longer1 because the earth was slowing down1 taking longer to rotate on its axis1 but the month increased at a greater rate than the day4 ,presently the month became equal to two days1 then to three1 and so on4 ,it has been calculated that this process went on until there were twenty-nine days in the month4 ,after that the number of days in the month began to decrease until it reached its present value or magnitude1 and will continue to decrease until once more the month and the day are equal4 ,in that age the earth will be rotating very slowly4 ,the braking action of the tides will cause the earth always to keep the same face to the moon2 it will rotate on its axis in the same time that the moon turns round the earth4 ,if nothing but the earth and moon were involved this state of affairs would be final4 ,but there is also the effect of the solar tides to be considered4 ,the moon makes the day equal to the month1 but the sun has a tendency1 by still further slowing down the earth's rotation on its axis1 to make the day equal to the year4 ,it would do this1 of course1 by making the earth take as long to turn on its axis as to go round the sun4 ,it cannot succeed in this1 owing to the action of the moon1 but it can succeed in making the day rather longer than the month4 ,surprising as it may seem1 we already have an illustration of this possibility in the satellites of ,mars4 ,the ,martian day is about one half-hour longer than ours1 but when the two minute satellites of ,mars were discovered it was noticed that the inner one of the two revolved round ,mars in about seven hours forty minutes4 ,in one ,martian day1 therefore1 one of the moons of ,mars makes more than three complete revolutions round that planet1 so that1 to an inhabitant of ,mars1 there would be more than three months in a day4 ,,bibliography ,,arrhenius1 ,,svante1 ,worlds in the ,making4 ,,clerk-,,maxwell1 ,,james1 ,matter and ,motion4 ,,daniell1 ,,alfred1 ,a ,text-,book of the ,principles of ,physics4 ,,darwin1 ,,sir ,g4 ,h41 ,the ,tides4 ,,holman1 ,matter1 ,energy1 ,force and ,work4 ,,kapp1 ,,gisbert1 ,electricity4 ,,kelvin1 ,,lord1 ,popular ,lectures and ,addresses4 ,vol4 i4 ,constitution of ,matter4 ,,lockyer1 ,,sir ,,norman1 ,inorganic ,evolution4 ,,lodge1 ,,sir ,,oliver1 ,electrons and ,the ,ether of ,space4 ,,perrin1 ,,jean1 ,brownian ,movement and ,molecular ,reality4 ,,soddy1 ,,frederick1 ,matter and ,energy and ,the ,interpretation of ,radium4 ,,thompson1 ,,silvanus ,p41 ,light1 ,visible and ,invisible4 ,,thomson1 ,,sir ,j4 ,j41 ,the ,corpuscular ,theory of ,matter4