,transcriber's ,notes3 ,underscores 80 before and after a word or phrase indicate italics in the original text4 ,a single underscore after a symbol indicates a subscript4 ,carat symbol 80 designates a superscript4 ,small capitals have been converted to ,,solid capitals4 ,illustrations have been moved so they do not break up paragraphs4 ,typographical errors have been silently corrected4 ,the numerical references to the ,,notes1 e4 g4 #a have been changed to 87see ,,note x70 in order to avoid confusion with the true footnotes4 ,,the ,,evolution ,,of ,,worlds ,illustration ,,the ,,macmillan ,,company ,,new ,,york ,,boston ,,chicago ,,atlanta ,,san ,,francisco ,,macmillan ,,co41 ,,limited ,,london ,,bombay ,,calcutta ,,melbourne ,,the ,,macmillan ,,co4 ,,of ,,canada1 ,,ltd4 ,,toronto ,illustration3 ,,saturn--,,photographed ,,at ,,the ,,lowell ,,observatory ,,by ,,mr4 ,e4 ,c4 ,,slipher4 ,,september1 #aiji4 ,,the ,,evolution ,,of ,,worlds ,,by ,,percival ,,lowell1 ,a4,b41 ,,ll4,d4 ,,author ,,of 8,,mars ,,and ,,its ,,canals10 8,,mars ,,as ,,the ,,abode ,,of ,,life10 ,,etc4 ,,director ,,of ,,the ,,observatory ,,at ,,flagstaff1 ,,arizona2 ,,non-,,resident ,,professor ,,of ,,astronomy ,,at ,,the ,,massachusetts ,,institute ,,of ,,technology2 ,,fellow ,,of ,,the ,,american ,,academy ,,of ,,arts ,,and ,,sciences2 ,,membre ,,de ,,la ,,soci,t ,,astronomique ,,de ,,france2 ,,member ,,of ,,the ,,astronomical ,,and ,,astrophysical ,,society ,,of ,,america2 ,,mitglied ,,der ,,astronomische ,,gesellschaft2 ,,membre ,,de ,,la ,,soci,t ,,belge ,d',,astronomie2 ,,honorary ,,member ,,of ,,the ,,sociedad ,,astronomica ,,de ,,mexico2 ,,janssen ,,medallist ,,of ,,the ,,soci,t ,,astronomique ,,de ,,france1 #aijd1 ,,for ,,researches ,,on ,,mars2 ,,medallist ,,of ,,the ,,sociedad ,,astronomica ,,de ,,mexico ,,for ,,studies ,,on ,,mars1 #aijh ,,illustrated ,new ,york ,,the ,,macmillan ,,company #aiji ,all rights reserved ,,copyright1 #aiji1 ,,by ,,the ,,macmillan ,,company4 ,set up and electrotyped4 ,published ,december1 #aiji4 ,norwood ,press ,j4 ,s4 ,cushing ,co4--,berwick ,smith ,co4 ,norwood1 ,mass41 ,u4,s4,a4 ,,to ,,the ,,president ,,of ,,the ,,massachusetts ,,institute ,,of ,,technology ,,to ,,my ,,colleagues ,,there ,,and ,,to ,,its ,,student ,,body ,,to ,,whose ,,interest ,,and ,,attention ,,these ,,lectures ,,are ,,indebted ,,they ,,are ,,appreciatively ,,inscribed 8,si je n'tais pas devenu gnral en chef et l'instrument du sort d'un grand people1 j'aurais couru les bureaux et les salons pour me mettre dans la dpendance de qui que ce ft1 en qualit de ministre ou d'ambassadeur8 ,non1 non6 je me serais jet dans l'tude des sciences exactes4 ,j'aurais fait mon chemin dans la route des ,galile1 des ,newton4 ,et puisque j'ai russi constamment dans mes grandes entreprises1 eh bien1 je me serais hautement distingu aussi par des travaux scientifiques4 ,j'aurais laiss le souvenir de belles dcouvertes4 ,aucune autre gloire n'aurait pu tenter mon ambition40 --,,napoleon ,i1 ,,quoted ,,by ,,arago4 ,the substance of the following pages was written and presented in a university course of lectures before the ,massachusetts ,institute of ,technology--in ,february and ,march of this year4 ,the kind interest with which the lectures were received1 not only by the students and professional bodies1 but by the public1 was followed by an immediate request from ,the ,macmillan ,company to issue them in book form1 and as such they now appear4 ,,percival ,,lowell4 ,,boston1 ,,mass41 ,may #bi1 #aiji4 ,,contents ,,chapter ,,page ,i4 ,,birth ,,of ,a ,,solar ,,system #a ,,ii4 ,,evidence ,,of ,,the ,,initial ,,catastrophe ,,in ,,our ,,own ,,case #ca ,,iii4 ,,the ,,inner ,,planets #eh ,,iv4 ,,the ,,outer ,,planets #id ,v4 ,,formation ,,of ,,planets #abg ,,vi4 ,a ,,planet',s ,,history--,,self-,,sustained ,,stage #aee ,,vii4 ,a ,,planet',s ,,history--,,sun-,,sustained ,,stage #ahb ,,viii4 ,,death ,,of ,a ,,world #bac ,,notes #a4 ,,meteor ,,orbits #bda #b4 ,,densities ,,of ,,the ,,planets #bdc #c4 ,,variation ,,in ,,spectroscopic ,,shift #bdc #d4 ,,on ,,the ,,planets' ,,orbital ,,tilts #bdd #e4 ,,planets ,,and ,,their ,,satellite ,,systems #bde #f4 ,,on ,,the ,,induced ,,circularity ,,of ,,orbits ,,through ,,collision #bej #g4 ,,capture ,,of ,,satellites #bea ,,index #bec ,,list ,,of ,,illustrations ,,plates ,i4 ,saturn ,frontispiece ,,opposite ,,page ,,ii4 ,the ,moving ,nebula surrounding ,nova ,persei1 #aija-aijb #ad ,,iii4 ,representative ,stellar ,spectra #bd ,,iv4 ,spectra of the ,major ,planets #eb ,v4 ,venus1 #ahif-ahig #hb ,,vi4 ,asteroids3 ,major ,axes of ,orbits #ih ,,vii4 ,saturn--,a ,drawing showing ,agglomerations #ajh ,,viii4 ,spectrogram of ,jupiter1 ,moon ,comparison #aeb ,,ix4 ,spectrogram showing ,water-vapor in ,atmosphere of ,mars #afj ,x4 ,tree ,fern #agf ,,xi4 ,ten ,views of ,mercury1 showing ,effect of ,libration #bbb ,,xii4 ,spectrogram of ,saturn #bcb ,,cuts ,,appearing ,,in ,,text ,,page ,algol and its ,dark ,companion #d ,nova ,persei #aa ,spectrum of ,nova ,persei #ab ,the ,moving ,nebula surrounding ,nova ,persei1 #aija #ac ,great ,nebula in ,orion #ag ,great ,nebula in ,andromeda #ah ,nebula ,m4 #ajj ,com #ai ,nebula ,i4 #bbf ,urs ,majoris #bj ,nebula ,v4 #bd ,com4 ,showing ,globular ,structure #ba ,nebula ,m4 #aja ,urs ,majoris #bc ,the ,radiant of a ,meteoric ,shower #cg ,diagram explaining ,proportionate ,visibility of ,meteors #ch ,the ,mart ,iron #da ,section of ,meteorite showing ,widmannstttian ,lines #db ,meteorite1 ,toluca #dc ,nebula ,v4 #ad ,cygni #de ,nebula ,n4,g4,c4 #adii ,persei #df ,nebula ,n4,g4,c4 #fifj in ,cygnus #dg ,nebula ,m4 #ea ,canum ,venaticorum #dh ,orbits of the ,inner ,planets #ei ,sulla ,rotazione di ,mercurio4--,di ,g4 ,v4 ,schiaparelli #fd ,map of ,mercury4 ,lowell #fi ,venus4 ,october1 #ahif-,march1 #ahig #gh ,venus4 ,april #ab1 #aiji4 #gi ,diagram3 ,convection ,currents in ,atmosphere of ,venus #ha ,diagram3 ,shift in ,central ,barometric ,depression #ha ,spectrogram of ,venus1 showing its ,long ,day #hg ,spectrogram of ,jupiter1 giving the ,length of its ,day by the ,tilt of its ,spectral ,lines #hi ,orbits of the ,outer ,planets #ie ,drawing of ,jupiter showing its ,ellipticity #ajc ,two ,drawings of ,jupiter and its ,wisps #aje ,photograph of ,jupiter1 #aiji #ajg ,diagram of ,saturn's ,rings #aac ,the ,tores of ,saturn #aad ,chart showing increasing ,tilts of the ,major ,planets #aca ,orbital ,tilts and ,eccentricities of ,satellites #acc ,masses of ,planets and ,satellites #acf ,two ,drawings of ,jupiter and its 8,great ,red ,spot0 #afd ,sun ,spots #afe ,photograph of a ,sun ,spot #aff ,the ,volcano ,colima1 ,mexico1 ,march #bd1 #aijc #afi ,jukes ,butte1 a ,denuded ,laccolith1 as seen from the ,northwest #agj ,ideal ,section of a ,laccolith #agj ,earth as seen from above4--,photographed at an ,altitude of #eejj ,feet #ahc ,tracks of ,sauropus ,primvus #ahh ,adventures of a ,heat ,ray #aic ,polar ,caps of ,mars at their ,maxima and ,minima #aih ,glacial ,map of ,eurasia #bjj ,map showing the ,glaciated ,area of ,north ,america #bja ,photograph of the ,moon #bje ,petrified ,bridge1 ,third ,petrified ,forest1 near ,adamana1 ,arizona #baj ,three ,views of ,venus1 showing ,agreement at ,different ,distances #bbj ,diagram of ,libration in ,longitude due to ,rotation #bbb ,moon1--,full and ,half #bbe ,diagram illustrating ,molecular ,motion in a ,gas #bbg ,distribution of ,molecular ,velocities in a ,gas #bbi ,,the ,,evolution ,,of ,,worlds ,,chapter ,i ,,birth ,,of ,a ,,solar ,,system ,astronomy is usually thought of as the study of the bodies visible in the sky4 ,and such it largely is when the present state of the universe alone is considered4 ,but when we attempt to peer into its past and to foresee its future1 we find ourselves facing a new side of the heavens--the contemplation of the invisible there4 ,for in the evolution of worlds not simply must the processes be followed by the mind's eye1 so short the span of human life1 but they begin and end in what we cannot see4 ,what the solar system sprang from1 and what it will eventually become1 is alike matter devoid of light4 ,out of darkness into darkness again3 such are the bourns of cosmic action4 ,the stars are suns2 past1 present1 or potential4 ,each of those diamond points we mark studding the heavens on a winter's night are globes comparable with1 and in many cases greatly excelling1 our own ruler of the day4 ,the telescope discloses myriads more4 ,yet these self-confessed denizens of space form but a fraction of its occupants4 ,quite as near1 and perhaps much nearer1 are orbs of which most of us have no suspicion4 ,unimpressing our senses and therefore ignored by our minds1 bodies people it which1 except for rare occurrences1 remain forever invisible4 ,for dark stars in countless numbers course hither and thither throughout the universe at speeds as stupendous as the lucent ones themselves4 ,had we no other knowledge of them1 reasoning would suffice to demonstrate their existence4 ,it is the logic of unlimited subtraction4 ,every self-shining star is continually giving out light and heat4 ,now such an expenditure cannot go on forever1 as the source of its replenishing by contraction1 accretion1 or disintegration is finite4 ,long to our measures of time as the process may last1 it must eventually have an end and the star finally become a cold dark body1 pursuing as before its course1 but in itself inert and dead2 an orb grown orbd1 in the old ,french sense4 ,so it must remain unless some cosmic catastrophe rekindle it to life4 ,the chance of such occurrence in a given time compared with the duration of the star's light-emitting career will determine the number of dark stars relative to the lucent ones4 ,the chance is undoubtedly small1 and the number of dark bodies in space proportionally large4 ,reasoning1 then1 informs us first that such bodies must exist all about us1 and second that their multitude must be great4 ,valid as this reasoning is1 however1 we are not left to inference for our knowledge of them4 ,there is a certain star amid the polar constellations known as ,algol1--el ,ghoul1 the ,arabs called it1 or ,the ,dmon4 ,the name shows they noticed how it winked its eye and recognized something sarcastically sinister in its intent4 ,for once in two days and twenty hours its light fades to one-third of its usual amount1 remains thus for about twenty minutes1 and then slowly regains its brightness4 ,seemingly unmoved itself1 its steady blinking from the time man first observed it took on an uncanniness he felt4 ,to untelescoped man it certainly seemed demoniacal1 this punctual recurrent wink4 ,spectroscoped man has learnt its cause4 ,goodricke in #agie divined it1 and research since has confirmed his keen intuition4 ,its loss of light is occasioned by the passing in front of it of a dark companion almost of its own size revolving about it in a close elliptic orbit4 ,that this is the explanation of its strange behavior1 the shift of its spectral lines makes certain1 by showing that the bright star is receding from us at twenty-seven miles a second seventeen hours before the eclipse and coming towards us at about the same rate seventeen hours after it2 its dark companion1 therefore1 doing the reverse4 ,algol is no solitary specimen of a mind-seen invisible star4 ,many eclipsing binaries of the same class are now known2 and considering that the phenomenon could not be disclosed unless the orbital plane of the pair traversed the observer's eye1 an unlikely chance in a fortuitous distribution1 we perceive how many such in truth there must be which escape recognition for their tilt4 ,illustration3 ,,algol ,,and ,,its ,,dark ,,companion1 ,,as ,,seen ,,from ,,the ,,earth1 ,illustration3 ,,as ,,seen ,,from ,,above ,,orbit4 ,but if dark stars exist in connection with lucent ones1 there must be many more that travel alone4 ,our own ,sun is an instance in embryo4 ,if he live long enough1 he will become such a solitary shrouded tramp in his old age4 ,for he has no companion to betray him4 ,the only way in which we could become cognizant of these wanderers would be by their chance collision with some other star1 dark or lucent as the case might be4 ,the impact of the catastrophe would generate so much light and heat that the previously dark body would be converted into a blazing sun and a new star make its advent in the sky4 ,star births of the sort have actually been noted4 ,every now and then a new star suddenly appears in the firmament--a nova as it is technically called4 ,these apparitions date from the dawn of astronomic history4 ,the earliest chronicled is found in the ,chinese ,annals of #acd ,b4,c4 ,it shone out in ,scorpio and was probably the new star which ,pliny tells us incited ,hipparchus1 8,the ,father of ,astronomy10 to make his celebrated catalogue of stars4 ,from this time down we have recorded instances of like character4 ,one of the most famous was the 8,pilgrim ,star0 of ,tycho ,brahe4 ,that astronomer has left us a full account of it4 8,while ,i was living10 he tells us1 8with my uncle in the monastery of ,hearitzwadt1 on quitting my chemical laboratory one evening1 ,i raised my eyes to the well-known vault of heaven and observed1 with indescribable astonishment1 near the zenith1 in ,cassiopeia1 a radiant fixed star of a magnitude never before seen4 ,in my amazement ,i doubted the evidence of my senses4 ,however1 to convince myself that it was no illusion1 and to have the testimony of others1 ,i summoned my assistants from the laboratory and inquired of them1 and of all the country people that passed by1 if they also observed the star that had thus suddenly burst forth4 ,i subsequently heard that in ,germany wagoners and other common people first called the attention of astronomers to this great phenomenon in the heavens1--a circumstance which1 as in the case of non-predicted comets1 furnished fresh occasion for the usual raillery at the expense of the learned40 ,the new star1 he informs us1 was just like all other fixed stars1 but as bright as ,venus at her brightest4 ,those gifted with keen sight could discern it in the daytime and even at noon4 ,it soon began to wane4 ,in ,december1 #aegb1 it resembled ,jupiter1 and a year and three months later had sunk beyond recognition to the naked eye4 ,it changed color as it did so1 passing from white through yellow to red4 ,in ,may1 #aegc1 it returned to yellow 78the hue of ,saturn10 he expressly states71 and so remained till it disappeared from sight1 scintillating strongly in proportion to its faintness4 ,thirty-two years later another stranger appeared and was seen by ,kepler1 who wrote a paper about it entitled 8,the ,new ,star in the ,foot of the ,serpent40 ,it shone out in the same sudden manner and faded in the same leisurely way4 ,since #ahfj there have been several such apparitions1 and since #ahgf it has been possible to study them with the spectroscope1 which has immensely increased our knowledge of their constitution4 ,indeed1 this instrument of research has really opened our eyes to what they are4 ,nova ,cygni1 in #ahgf1 ,nova ,aurig1 in #ahib1 and ,nova ,persei1 in #aija1 besides several others found by ,mrs4 ,fleming on the ,arequipa plates1 were excellent examples1 and all agreed in their main features1 showing that nov constitute a type of stars by themselves1 whose appearing in the first place and whose behavior afterwards prove them to have started from like cause and to have pursued parallel lines of development4 ,as a typical case we may review the history of ,nova ,aurig4 ,on ,february #a1 #ahib1 an anonymous post-card was received by ,dr4 ,copeland of the ,royal ,observatory1 ,edinburgh1 that read as follows3 8,nova in ,aurig4 ,in ,milky ,way1 about #b south of ,aurig1 preceding #bf ,aurig4 ,fifth magnitude slightly brighter than 40 ,the observatory staff at once looked for the nova and easily found it with an opera glass4 ,they then examined it through a prism placed before their #bd-;inch reflector and found its spectrum4 ,it proved to be that of a 8blaze star40 ,dr4 ,thomas ,d4 ,anderson turned out to be the writer of the anonymous post-card--his name modestly self-obliterated by the nova's light4 ,he had detected the star on ,january #bd1 but had only verified it as a new one on the #cast4 ,harvard ,college ,observatory then looked up its archived plates4 ,the plates showed that it had appeared sometime between ,december #a and #aj4 ,its maximum had been attained on ,december #bj1 after which it declined1 to record apparently another maximum on ,february #c of the #c4e magnitude4 ,from this time its light steadily waned till on ,april #a it was only of the #afth magnitude or _/ of what it had been4 ,in ,august it brightened again and then waned once more4 ,meanwhile its spectrum underwent equally strange fluctuations4 ,at first it exhibited the bright lines characteristic of the flaming red solar prominences1 the calcium1 hydrogen1 and helium lines flanked by their dark correlatives upon a continuous background1 showing that both glowing and cooler gases were here concerned4 ,the sodium lines1 too1 appeared1 like those that come out in comets as they approach the furnace of the ,sun4 ,an outburst such as occurs in miniature in the solar chromosphere or outermost gaseous layer of the ,sun was here going on upon a gigantic scale4 ,a veritable spectral chaos next supervened1 staying until the star had practically faded away4 ,then1 on its reappearance1 in ,august1 ,holden1 ,schaeberle1 and ,campbell discovered to their surprise not what had been at all1 but something utterly new3 the soberly bright lines only of a nebula4 ,finally1 ten years later1 ,january1 #aijb1 ,campbell found its spectrum had become continuous1 the body having reverted to the condition of a star4 ,now how are we to interpret these grandiose vicissitudes1 visually and spectrally revealed8 ,that we witnessed some great catastrophe is clear4 ,the sudden increase of light of many thousand fold from invisibility to prominence shows that a tremendous cataclysm occurred4 ,the bright lines in the spectrum confirm it and imply that vast upheavals like those that shake the ,sun were there in progress1 but on so stupendous a scale that1 if for no other reason1 we must dismiss the idea that explosions alone can possibly be concerned4 ,the dark correlatives of the bright lines have been interpreted as indicating that two bodies were concerned1 each travelling at velocities of hundreds of miles a second4 ,but in ,nova ,aurig shiftings of the spectral lines implying six bodies at least were recorded1 if such be attributed to motion in the line of sight1 and ,vogel was minded to throw in a few planets as well--as ,miss ,clerke pithily puts it4 ,there is not room for so many on the stage of the cosmic drama4 ,other causes1 as we now know1 may also displace the spectral lines4 ,great pressure has been shown to do it1 thanks to the labors of ,humphreys and ,mohler at ,baltimore4 8,anomalous refraction0 may do it1 as ,professor ,julius of ,utrecht has found out4 ,finally1 changes of density may produce it1 as ,michelson has discovered4 ,to these causes we may confidently ascribe most of the shiftings in the stellar spectrum1 for just such forces must be there at work4 ,mr4 ,monck suggested the idea that new stars are the result of old dark stars rushing through gaseous fields in space and rendered luminous by the encounter4 ,seeliger revived and developed this idea1 which in certain cases is undoubtedly the truth4 ,probably this occurred to the new star of #ahhe which suddenly blazed out almost in the centre of the great nebula in ,andromeda4 ,it behaved like a typical nova and in due course faded to indistinguishability4 ,something like it happened1 too1 in the nova of #ahfj1 which suddenly flared up in the star cluster #hj ,messier1 outdoing in lustre the cluster itself1 and then1 too1 faded away4 ,but just as psychology teaches us that not only do we cry because we are sorrowful1 but that we are sorrowful because we cry1 so while a nova may be made by a nebula1 no less may a nebula be made by a star4 ,let us see how this might be brought about and what sign manuals it would present4 ,suppose that the two bodies actually grazed4 ,then the disruption would affect the star's cuticle1 first raising the outer parts1 consisting rather of carbon than of the metals1 since that substance is the lighter1 to intense heat and the gases about it at the same time4 ,the glowing carbon would be intensely bright1 and at first its light would overpower that from the gases1 and not till its great glow had partially subsided would theirs be seen4 ,then the gases1 hydrogen1 helium1 and so forth1 would make themselves evident4 ,finally only the most tenuous ones1 those peculiar to a nebula1 would remain visible4 ,after which the more solid particles due to the disruption would fall together and light up again by their individual collisions4 ,much the same would result if without striking the stars passed close4 ,illustration3 #aija ,february #bjth #aija ,february #bhth ,before appearance of ,nova ,the ,nova ,,nova ,,persei4 ,photographs by ,a4 ,,stanley ,,williams1 ,hove1 ,sussex4 ,illustration3 ,,spectrum ,,of ,,nova ,,persei4 7,f4 ,ellerman1 #dj in4 ,yerkes47 ,now to put this theory to the proof4 ,in the early morning of the #bb;d of ,february1 #aija1 ,dr4 ,anderson1 the discoverer of ,nova ,aurig1 perceived that ,algol had a neighbor1 a star as bright as itself1 which had never been there before4 ,within twenty-four hours of its detection the newcomer rivalled ,capella1 and shortly after took rank as the premier star of the northern hemisphere4 ,its spectrum on the #bb;d was found at ,harvard ,college ,observatory to be like that of ,rigel1 a continuous one crossed by some thirty faint dark lines4 ,on the #bdth1 however1 so soon as it began to wane1 the bright lines of hydrogen were conspicuous with their dark correlatives1 just as they had been with ,nova ,aurig and other nov4 ,at the same time each particular spectral line proved a law unto itself1 some shifted more than others1 thus negativing motion as their only cause and indicating change of pressure or density as concerned concomitants of the affair4 ,blue emissions like those of ,wolf-,rayet stars next made their appearance2 then a band1 found by ,wright at the ,lick to characterize nebul1 shone out1 and finally in ,july the change to a nebular spectrum stood complete4 ,illustration3 ,,the ,,moving ,,nebula ,,surrounding ,,nova ,,persei4 #aija1 ,september #bjth4 #aija1 ,november #acth4 ,drawn by ,g4 ,w4 ,,ritchey1 from ,photographs taken with the #bd-;in4 ,reflector1 ,,yerkes ,,observatory4 ,then came what is the most suggestive feature in the whole event4 ,on ,august #bb and #bc ,dr4 ,wolf at ,knigstahl took with his then new ,bruce objective some long exposure plates of the nova1 and on them found1 to his surprise1 wisps of nebulous matter to the southeast of the star4 ,on ,september #bj ,ritchey1 with a two-foot mirror of his own constructing exposed for four hours1 brought the whole formation to light4 ,it turned out to be a spiral nebula encircling and apparently emanating from the star4 ,its connection with the nova was patent4 ,but there was more to come4 ,later plates taken at the ,lick on ,november #g disclosed the startling fact that the nebula was visibly expanding1 uncoiling outward from the star4 ,a plate by ,ritchey on ,november #ac confirmed this1 and still later plates by him in ,december1 ,january1 and ,february showed the motion to be progressive4 ,at the same time the star showed no parallax1 and the speed of the motion seemed thus to be indicated as enormous4 ,kapteyn suggested to account for it that appearance1 not reality1 was here concerned2 that the nebula had always existed1 and was only shown up by the light from the conflagration travelling outward from the nova at the rate of one hundred and eighty-six thousand miles a second4 ,this would make the catastrophe to have occurred as far back as the time of ,james ,i1 of which the news more truthful but less timely than that of the morning papers had only just reached us4 ,illustration3 ,december #ad1 #aija4 ,illustration3 ,january #g and #i1 #aijb4 ,illustration3 #aijb4 ,february #h1 #aijb4 ,,the ,,moving ,,nebula ,,surrounding ,,nova ,,persei--,,after ,,ritchey4 ,but a little of that simple reasoning by which ,zadig recovered the lost horses of the ,sultan1 and which from its unaccustomedness in the affairs of men got him suspected of having stolen them and very nearly caused his death1 will show the untenableness of this idea and help us to a solution4 ,in the first place we note that the star holds the very centre of the nebular stage1 a remarkable prominence if the star has no creative right to the position4 ,then the same knots and patches of the nebulous configuration are visible in all the photographs1 in the same relative positions1 turned through corresponding angles as one will see for himself1 all having moved symmetrically from one date to another4 ,at the truly marvellous mimicry implied if different objects were concerned common sense instinctively shies1 and very properly1 as the chances against it are millions to one4 ,clearly it was not a mere matter of ethereal motion1 but a very material motion of matter1 which was here concerned4 ,something corpuscular emanating from the nova spread outward into space4 ,clinching this conclusion is the result of a search by ,perrine for traces of the nebula on earlier plates4 ,for on one taken by him on ,march #bi 7#aija7 he found the process already started in two close coils1 its conception thus clearly dating from the time of the star's outburst4 ,in ,nova ,persei1 then1 we actually witnessed a spiral nebula evolved from a disrupted star4 ,what was this ejectum and what drove it forth8 ,professor ,very regarded it as composed of corpuscles such as give rise to cathode rays discharged from the star under the stress of light pressure or electric repulsion4 ,but ,i think we may see in it something simpler still2 to wit1 gaseous molecules driven off by light pressure alone--the smoke1 as one may say1 of the catastrophe--akin exactly to the constituents of comet's tails4 ,the mere light of the conflagration pushed the hydrogen molecules away4 ,this would explain their presence and their exceeding hurry at the same time4 ,they were started on their travels by domestic jars and kept going by the vivid after-effects of that infelicity4 ,the fairly steady rate of regression from the nova observed may be explained by the observed decrease in the light of the repellent source4 ,such combined with the retarding effect of gravity might make the regression equable4 ,this is the more explanatory as the speed was certainly much less than that of light1 though greatly exceeding any possible from the direct disruption4 ,at the same time both the bright and the dark lines of hydrogen seen in the spectrum stand accounted for2 the colliding molecules1 at their starting on their travels from the star1 shining through their sparser fellows farther out4 ,an interesting biograph of the levity of light6 ,nova ,persei thus introduces us at its birth to one of a class of most interesting objects comparatively recently discovered and of most pregnant import1--the spiral nebul4 ,illustration3 ,,great ,,nebula ,,in ,,orion--,,after ,,ritchey4 ,illustration3 ,,great ,,nebula ,,in ,,andromeda--,,after ,,ritchey4 ,illustration3 ,,nebula ,m4 #ajj ,,com--,,after ,,roberts4 ,in #ahdc when ,lord ,rosse's giant speculum1 six feet across1 was turned upon the sky1 a nebula was brought to light which was unlike any ever before seen4 ,it was neither irregular like the great nebula in ,orion nor round like the so called planetary nebul1--the two great classes at that time known1--but exhibited a striking spiral structure4 ,it proved the forerunner of a remarkable revelation4 ,for the specimen thus disclosed has turned out to typify not only the most interesting form of those heavenly wreaths of light1 but by far the commonest as well4 ,as telescopic and especially photographic means improved1 the number of such objects detected steadily increased until about thirteen years ago ,keeler by his systematic discoveries of them came to the conclusion that a spiral structure pervaded the great majority of all the nebul visible4 ,their relative universality was outdone only by the invariability of their form4 ,for they all represent spirals of one type3 two coiled arms radiating diametrically from a central nucleus and dilating outward4 ,even nebul not originally supposed spiral have disclosed on better revelation the dominant form4 ,thus the great nebula in ,andromeda formerly thought lens-shaped proves to be a huge spiral coiled in a plane not many degrees inclined to the plane of sight4 ,illustration3 ,,nebula ,i4 #bbf ,,urs ,,majoris--,,after ,,roberts4 ,as should happen if the spirals are unrelated1 left-handed and right-handed ones are about equally common4 ,in ,dr4 ,roberts' great collection of those in which the structure is distinctly discernible1 nine are right-handed1 ten left-handed1 showing that they partake of the ambidextrous impartiality of space4 ,illustration3 ,,nebula ,v4 #bd ,,com--,,after ,,roberts4 ,showing globular structure4 ,lastly the spirals are evidently thicker near the centre1 thinning out at the edge1 and when the central nucleus is pronounced1 it seems to have a certain globularity not shared by the arms1 and more or less detached from them4 ,this appears in those cases where they are shown us edgewise1 and it has been thought perceptible in the great nebula of ,andromeda4 ,the difficulty in establishing the phenomenon comes from the impossibility of both features showing at their best together4 ,for the globularity to come out well1 the spiral must be presented to us nearly in the plane of sight2 for the spirality1 in a plane at right angles to it4 ,much may be learnt by pondering on these peculiarities4 ,the widespread character of the phenomenon points to some universal law4 ,we are here clearly confronted by the embodiment of a great cosmic principle1 causing the helices it is for us to uncoil4 ,it is a problem in mechanics4 ,in the first place1 a spiral structure denotes action on the face of it4 ,it implies a rotation combined with motion out or in4 ,we are familiar with the fact in the sparks of pin-wheel pyrotechnics4 ,any rotating fluid urged by an outward or an inward impulse must take the spiral form4 ,a common example occurs in the water let out of a basin through a hole in the centre when we draw out the plug4 ,here the force is inward1 and because the bowl and orifice are not perfectly symmetric1 a rotation is set up in the water trying to escape1 and the two combine to give us a beautiful conchoidal swirl4 ,in this case the particles seek the centre1 but the same general shape is assumed when they seek to leave it4 ,another point to be noticed is that a spiral nebula could not develop of itself and subsist4 ,to continue it must have outside help4 ,for if it were due to internal explosive action in the pristine body1 each ejectum must return to the point it started from1 or else depart forever into space1 for the orbit it would describe must either be closed or unclosed4 ,if the former1 it would revisit its starting-point2 if the latter1 it would never return4 ,explosion1 therefore1 of itself could not have produced the forms we see1 unless they be ephemeral apparitions1 a supposition their presence throughout the heavens seems effectually to exclude4 ,illustration3 ,,nebula ,m4 #aja ,,urs ,,majoris--,,after ,,ritchey4 ,the form of the spiral nebul proclaims their motion1 but one of its particular features discloses more4 ,for it implies the past cause which set this motion going4 ,a distinctive detail of these spirals1 which so far as we know is shared by all of them1 are the two arms which leave the centre from diametrically opposite sides4 ,this indicates that the outward driving force acted only in two places1 the one the antipodes of the other4 ,now what kind of force is capable of this peculiar effect8 ,if we think of the matter1 we shall realize that tidal action would produce just this result4 ,we see it daily in the case of the ,moon2 when it is high tide in the open ocean hereabouts1 it is high tide also at the opposite end of the ,earth4 ,the reason is that the tideraising body pulls the fluid nearest it more strongly than it pulls the ,earth as a whole1 and pulls the ,earth as a whole more than it pulls the fluid at the opposite extremity4 ,suppose1 now1 a stranger to approach a body in space near enough2 it will inevitably raise tides in the other's mass1 and if the approach be very close1 the tides will be so great as to tear the body in pieces along the line due to their action2 that is1 parts of the body will be separated from the main mass in two antipodal directions4 ,this is precisely what we see in the spiral nebula4 ,nor is there any other action that we know of which would thus handle the body4 ,if it were to disintegrate under increased speed of rotation due to contraction upon itself1 parts of its periphery should be shed continually and a pin-wheel of matter1 not a two-armed spiral1 be thrown off4 ,if explosion were the disintegrating cause1 disruption would occur unsymmetrically in one or more directions1 not symmetrically as here4 ,illustration3 ,,representative ,,stellar ,,spectra ,photographed1 in #aijg and #aijh1 by ,v4 ,m4 ,,slipher1 at ,,lowell ,,observatory ,flagstaff1 ,arizona1 with prism spectrograph4 ,as the stranger passed on1 his effect would diminish until his attraction no longer overbalanced that of the body for its disrupted portions4 ,these might then be controlled and forced to move in elliptic orbits about the mass of which they had originally made part4 ,thence would come into being a solar system1 the knots in the nebula going to form the planets that were to be4 ,before proceeding to what proof we have that it actually did occur in this way we may pause to consider some consequences of what we have already learned4 ,thus what brought about the beginning of the system may also compass its end4 ,if one random encounter took place in the past1 a second is as likely to occur in the future4 ,another celestial body may any day run into the ,sun1 and it is to a dark body that we must look for such destruction1 because they are so much more numerous in space4 ,that any of the lucent stars1 the stars commonly so called1 could collide with the ,sun1 or come near enough to amount to the same thing1 is demonstrably impossible for ons of years4 ,but this is far from the case for a dark star4 ,such a body might well be within a hundredth of the distance of the nearest of our known neighbors1 ,alpha ,centauri1 at the present moment without our being aware of it at all4 ,our senses could only be cognizant of its proximity by the borrowed light it reflected from our own ,sun4 ,dark in itself1 our own head-lights alone would show it up when close upon us4 ,it would loom out of the void thus suddenly before the crash4 ,we can calculate how much warning we should have of the coming catastrophe4 ,the ,sun with its retinue is speeding through space at the rate of eleven miles a second toward a point near the bright star ,vega4 ,since the tramp would probably also be in motion with a speed comparable with our own1 it might hit us coming from any point in space1 the likelihood depending upon the direction and amount of its own speed4 ,so that at the present moment such a body may be in any part of the sky4 ,but the chances are greatest if it be coming from the direction toward which the sun is travelling1 since it would then be approaching us head on4 ,if it were travelling itself as fast as the ,sun1 its relative speed of approach would be twenty-two miles a second4 ,the previousness of the warning would depend upon the stranger's size4 ,the warning would be long according as the stranger was large4 ,let us assume it the mass of the ,sun1 a most probable supposition4 ,being dark1 it must have cooled to a solid1 and its density therefore be much greater than the ,sun's1 probably something like eight times as great1 giving it a diameter about half his or four hundred and thirty thousand miles4 ,its apparent brightness would depend both upon its distance and upon its intrinsic brightness or albedo1 and this last would itself vary according to its distance from the ,sun4 ,while it was still in the depths of space and its atmosphere lay inert1 owing to the cold there1 its intrinsic brightness might be that of the ,moon or ,mercury4 ,as its own rotation would greatly affect the speed with which its sunward side was warmed1 we can form no exact idea of the law of its increase in light4 ,that the augmentation would be great we see from the behavior of comets as they approach the great hearth of our solar system4 ,but we are not called upon to evaluate the question to that nicety4 ,we shall assume1 therefore1 that its brilliancy would be only that of the ,moon1 remembering that the last stages of its fateful journey would be much more resplendently set off4 ,with these data we can find how long it would be visible before the collision occurred4 ,as a very small telescopic star it would undoubtedly escape detection4 ,it is not likely that the stranger would be noticed simply from its appearance until it had attained the eleventh magnitude4 ,it would then be one hundred and forty-nine astronomical units from the ,sun or at five times the distance of ,neptune4 ,but its detection would come about not through the eye of the body1 but through the eye of the mind4 ,long before it could have attracted man's attention to itself directly its effects would have betrayed it4 ,previous1 indeed1 to its possible showing in any telescope the behavior of the outer planets of the system would have revealed its presence4 ,the far plummet of man's analysis would have sounded the cause of their disturbance and pointed out the point from which that disturbance came4 ,celestial mechanics would have foretold1 as once the discovery of another planet1 so now the end of the world4 ,unexplained perturbations in the motions of the planets1 the far tremors of its coming1 would have spoken to astronomers as the first heralding of the stranger and of the destruction it was about to bring4 ,neptune and ,uranus would begin to deviate from their prescribed paths in a manner not to be accounted for except by the action of some new force4 ,their perturbations would resemble those caused by an unknown exterior planet1 but with this difference that the period of the disturbance would be exactly that of the disturbed planet's own period of revolution round the ,sun4 ,our exterior sentinels might fail thus to give us warning of the foreign body because of being at the time in the opposite parts of their orbits4 ,we should then be first apprised of its coming by ,saturn1 which would give us less prefatory notice4 ,it would be some twenty-seven years from the time it entered the range of vision of our present telescopes before it rose to that of the unarmed eye4 ,it would then have reached forty-nine astronomical units' distance1 or two-thirds as far again as ,neptune4 ,from here1 however1 its approach would be more rapid4 ,humanity by this time would have been made acquainted with its sinister intent from astronomic calculation1 and would watch its slow gaining in conspicuousness with ever growing alarm4 ,during the next three years it would have ominously increased to a first magnitude star1 and two years and three months more have reached the distance of ,jupiter and surpassed by far in lustre ,venus at her brightest4 ,meanwhile the disturbance occasioned not simply in the outer planets but in our own ,earth would have become very alarming indeed4 ,the seasons would have been already greatly changed1 and the year itself lengthened1 and all these changes fraught with danger to everything upon the ,earth's face would momentarily grow worse4 ,in one hundred and forty-five days from the time it passed the distance of ,jupiter it would reach the distance of the ,earth4 ,coming from ,vega1 it would not hit the ,earth or any of the outer planets1 as the ,sun's way is inclined to the planetary planes by some sixty degrees1 but the effects would be none the less marked for that4 ,day and night alone of our astronomic relations would remain4 ,it would be like going mad and yet remaining conscious of the fact4 ,instead of following the ,sun we should now in whole or part1 according to the direction of its approach1 obey the stranger4 ,for nineteen more days this frightful chaos would continue2 as like some comet glorified a thousand fold the tramp dropped silently upon the ,sun4 ,toward the close of the nineteenth day the catastrophe would occur1 and almost in merciful deliverance from the already chaotic cataclysm and the yet greater horror of its contemplation1 we should know no more4 ,unless the universe is otherwise articulated than we have reason to suppose1 such a catastrophe sometime seems certain4 ,but we may bear ourselves with equanimity in its prospect for two mitigating details4 ,one is that there is no sign whatever at the moment that any such stranger is near4 ,the unaccounted-for errors in the planetary theories are not such as point to the advent of any tramp4 ,another is1 that judged by any scale of time we know1 the chance of such occurrence is immeasurably remote4 ,not only may each of us rest content in the thought that he will die from causes of his own choosing or neglect1 but the ,earth herself will cease to be a possible abode of life1 and even the ,sun will have become cold and dark and dead so long before that day arrives that when the final shock shall come1 it will be quite ready for another resurrection4 ,,chapter ,,ii ,,evidence ,,of ,,the ,,initial ,,catastrophe ,,in ,,our ,,own ,,case ,by quite another class of dark bodies than those we contemplated in the last chapter is the immediate space about us tenanted4 ,for that1 too1 is anything but the void our senses give us to understand4 ,could we rise a hundred miles above the ,earth's surface we should be highly sorry we came1 for we should incontinently be killed by flying brickbats4 ,instead of masses of a sunlike size we should have to do with bits of matter on the average smaller than ourselves but hardly on that account innocuous1 as they would strike us with fifteen hundred times the speed of an express train4 ,only in one respect are the two classes of erratics alike1 both remain invisible till they are upon us4 ,even so1 the cause of their visibility is different4 ,the one is announced by the light it reflects1 the other by the glow it gives out on its destruction4 ,these last are the meteorites or shooting-stars4 ,they are as well known to every one for their commonness as1 fortunately1 the first are rare4 ,on any starlight night one need not tarry long before one of these visitants darts across the sky1 a brilliant thread of fire gone almost ere it be descried4 ,usually this is all of which one is made aware4 ,silent1 ghostlike1 the apparition comes and goes1 and nothing more of it is either seen or heard4 ,but sometimes there is a good deal more4 ,occasionally a large ball of flame shoots through the air1 a detonation like distant thunder startles the ear1 and a luminous train1 persisting for several seconds1 floats slowly away4 ,finally if one be fortunate to be near1--but not too near1--one or more masses of stone are seen to fall swiftly and bury themselves in the ground4 ,these are meteorites3 far wanderers come at last to rest in graves they have dug themselves4 ,a great revolution has taken place lately in our ideas concerning meteorites4 ,indeed1 it was not so very long ago1 since modern man admitted their astronomic character at all4 ,he looked as askance at them as he did at fossils4 ,it was the fall at ,aigle1 in ,switzerland1 ,april #bf1 #ahjc1 that first opened men's eyes to the fact that such falls actually occurred4 ,it is more than a nine days' wonder at times how long men1 as well as puppies1 can remain blind4 ,to admit that stones fell from heaven1 however1 was not to see whence they came4 ,their paternity was imputed to nearly every body in the sky4 ,they were at first supposed to have been ejected from earthly volcanic vents1 then from volcanoes in the ,moon4 ,that they are of domestic manufacture is1 however1 negatived by the paths they severally pursue4 ,nor can they for like reason have been ejected from the ,sun4 ,the ,earth was not their birthplace4 ,it is alien ground in which they lie at last and from which we transfer them to glass cases in our museums4 ,this fact about their parentage they tell by the speed with which they enter our air4 ,they become visible #ajj miles up and explode at from #bj to #aj1 and their speed has been found to be from #aj to #dj miles a second1 which is that of cosmic bodies moving in large elliptic orbits about the ,sun1--a speed greater than the ,earth could ever have imparted4 ,four classes of such small celestial bodies tenant space where the planets move3 sporadic shooting-stars1 meteorites1 meteor-streams1 and comets4 ,the discovery of the relation of each of these to the solar system and then to each other forms one of the latest chapters of astronomic history4 ,for they turn out to be generically one4 ,it was long1 however1 before this was perceived4 ,the first step was taken simultaneously by ,professor ,olmstead of ,yale and ,twining in #ahcc from reasoning on the superb ,november meteor-shower of that year4 ,all the shooting-stars1 8thick as snowflakes in a storm10 had a common radiant from which they seemed to come4 ,thus they argued that the meteors must all be travelling in parallel lines along an orbit which the previous shower1 of #agii1 showed to be periodic4 ,this was the first recognition of a meteor-swarm4 ,the next advance was when ,schiaparelli1 in #ahfb1 pointed out the remarkable connection between meteor-swarms and comets4 ,on calculation the ,august meteor-stream and the comet of #ahfb proved to be pursuing exactly the same path4 ,soon other instances of like association were discovered1 and we now know mathematically that meteor-streams can be1 deductively that they must be1 and observationally that they are1 disintegrated comets4 ,more than one comet has even been seen to split4 ,then came the recognition that comets are not visitors from space1 as ,sir ,isaac ,newton and ,laplace supposed1 but part and parcel of our own solar system4 ,without going into the history of the subject1 which includes ,gauss1 ,schiaparelli1 and finally ,fabry's great ,memoir1 much too little known1 the proof can1 ,i think1 be made comprehensible without too much technique1 thanks to the fact that the ,sun is speeding through space at the rate of eleven miles a second4 ,orbits described by bodies under the action of a central force are always conic sections1 as ,sir ,isaac ,newton proved4 ,there are two classes of such curves3 those which return into themselves1 such as the circle and ellipse1 and those which do not1 the hyperbol4 ,if a body travel in the first or closed class about the ,sun1 it is clearly a member of his family2 if in the second1 it is a visitor who bows to him only in passing and never returns4 ,which orbit it shall pursue depends at a given distance solely upon the speed of the body2 if that speed be one the ,sun can control1 the body will move in an ellipse2 if greater1 in an hyperbola4 ,obviously the ,sun can control just the speed he can impart4 ,now a comet entering the system from without would already possess a motion of its own which1 when compounded with the solar-acquired speed1 would make one greater than the ,sun could master4 ,comets1 therefore1 if visitors from space1 should all move in hyperbol4 ,none for certain do2 and only six out of four hundred even hint at it4 ,comets1 then1 are all members of the solar family1 excentric ones1 but not to be denied recognition of kinship for such behavior4 ,still1 admittance to the solar family circle was denied to meteorites and shooting-stars4 ,thus ,professor ,kirkwood1 in #ahfa1 had considered 8that the motions of some luminous meteors 7or cometoids1 as perhaps they might be called7 have been decidedly indicative of an origin beyond the limits of the solar system40 ,here cometoid was an apt coinage1 but when comets were later shown not to be of extra-solar origin1 the reasoning carried luminous meteors in its train4#a ,finally ,schiaparelli1 in #ahga1 concluded an able ,memoir on the subject with the decision that 8a stellar origin for meteorites was the most likely and that meteorites were identifiable with shooting-stars40#b ,a pregnant remark this1 though not exactly as the author thought1 for instead of proving both interstellar1 as he intended1 both have proved to be solar bound4 #a 8,mem4 del ,reale ,inst4 ,lombardo10 ,vol4 ,,xii4 ,,iii della serie ,,iii4 #b ,quoted in 8,luminous ,meteors10 ,committee's ,report for #ahgj-ahga1 p4 #dh4 ,it was ,professor ,newton1 in #ahhi1 who first showed that meteorites were pursuing1 as a rule1 small elliptic orbits about the ,sun1 and that their motion was direct4 ,he1 too1 was the first to surmise that meteorites are but bigger shooting-stars4 ,now1 as to their connection4 ,of direct evidence we have little4 ,a few meteors have been observed to come from the known radiants of shooting-stars4 ,two instances we have of the fall of meteorites during star showers4 ,one in #ajie1 when the ,saxon ,chronicle tells us stars fell 8so thickly that no man could count them1 one of which struck the ground and when a bystander cast water upon it steam was raised with a great noise of boiling40 ,the second case was the fall of a siderite1 eight pounds' worth of nickel-iron1 at ,mazapil during the ,andromede shower of #ahhe1 which was by many supposed to be a part of the lost ,biela comet4 ,it contained graphite enough to pencil its own history1 but unfortunately could not write4 ,the direction from which it came was not recorded1 and so the connection between it and the comet not made out4 ,illustration3 ,,the ,,radiant ,,of ,a ,,meteoric ,,shower1 ,,showing ,,also ,,the ,,paths ,,of ,,three ,,meteors ,,which ,,do ,,not ,,belong ,,to ,,this ,,shower--,,after ,,denning4 ,if our direct knowledge is thus scanty1 reasoning affords surer ground for belief4 ,for at this point there steps in a bit of news about the family relations of shooting-stars from a source hardly to have been anticipated4 ,indeed1 it arose from the thought to examine a qualitative statement in ,young's 8,astronomy0 quantitatively4 ,mathematics is simply precise reasoning1 applied usually to the discovery that a pet theory will not work4 ,but sometimes it presents one with an unexpected find4 ,this is what it did here4 ,it is an interesting fact of observation that more meteors are visible at six o'clock in the morning than at six o'clock at night in the proportion of #c to #a4 ,this seeming preference for early rising is due to no matutinality on the part of the meteors1 but to the matin aspect then presented by the ,earth combined with its orbital motion round the ,sun4 ,for at six in the morning the observer stands on the advancing side of the ,earth1 at the bow of the airship2 at six at night he is at the stern4 ,he1 therefore1 runs into the meteors at sunrise and slips away from them at sunset4 ,he is pelted in the morning in consequence4 ,just as a pedestrian facing a storm gets wetter in front than behind4 ,illustration3 ,,meteors ,diagram explaining their proportionate visibility4 ------------ denotes true paths4 ---- - ---- 0 apparent paths4 ------------ - - - 0 ,earth's path4 ,so far the books4 ,now let us examine this quantitatively according to the direction in which the meteors themselves may be moving before the encounter4 ,suppose1 in the first place1 that they were travelling in every possible direction1 with the average velocity of the most erratic members of the family1 the great comets4 ,on this supposition calculation shows that we ought to meet #e4h times as many at six in the morning as at six at night4 ,if their orbits were smaller than this1 say1 something like those of the asteroids1 we should find #g4f to #a for the ratio4 ,suppose1 however1 that they were all travelling in the same sense as the ,earth1 direct as it is called in contradistinction to retrograde1 and let us calculate what proportion in that case we should meet at the two hours respectively4 ,it turns out to be #b4d to #a for the parabolic ones1 #c4c to #a for the smaller orbited1 or almost precisely what observation shows to be the case see ,,note #a4 ,here1 then1 a bit of abstract reasoning has apprized us of a most interesting family fact2 to wit1 that the great majority of shooting-stars are travelling in the same orderly sense as ourselves4 ,furthermore1 as some must be moving in smaller orbits than the mean1 others must be journeying in greater2 or1 in other words1 shooting-stars are scattered throughout the system4 ,in short1 these little bodies are tiny planets themselves1 as truly planets as the asteroids1--asteroids of a general instead of a localized habit4 ,thus meteorites and shooting-stars are kin1 and from the fact that they are pursuing orbits not very unlike our own we get our initial hint of a community of origin4 ,indeed1 they are the little bricks out of which the whole structure of our solar system was built up4 ,what we encounter to-day are the left-over fragments of what once was1 the fraction that has not as yet been swept up by the larger bodies4 ,and this is why these latter-day survivors move1 as a rule1 direct4 ,to run counter to the consensus of trend is to be subjected to greater chance of extermination4 ,those that did so have already been weeded out4 ,illustration3 ,,the ,,mart ,,iron4 7,proc4 ,wash4 ,acad4 of ,sci4 vol4 ,,ii4 ,plate ,,vi47 ,from the behavior of meteorites we proceed to scan their appearance4 ,and here we notice some further telltale facts about them4 ,their conduct informed us of their relationship1 their character bespeaks their parentage4 ,most meteorites are stones1 but one or two per cent are nearly pure iron mixed with nickel4 ,when picked up1 they are usually covered with a glossy thin black crust4 ,this overcoat they have put on in coming through our air4 ,air-begotten1 too1 are the holes with which many of them are pitted4 ,for entering our atmosphere with their speed in space is equivalent to immersing them suddenly in a blowpipe flame of several thousand degrees ,fahrenheit4 ,thus their surface is burnt and fused to a cinder4 ,yet in spite of being warm to the touch their hearts are still cosmically cold4 ,the ,dhurmsala meteorite falling into moist earth was found an hour afterwards coated with frost4 ,agassiz likened it to the ,chinese culinary chef d'uvre 8fried ice40 ,it is the cold of space1 #bjj or more ,centigrade below zero1 that they bear within1 proof of their cosmic habitat4 ,that they are bits of a once larger mass is evident on their face4 ,their shape shows that they are not wholes but parts1 while their constitution bespeaks them anything but elementary4 ,diagnosis of it yields perhaps their most interesting bit of news4 ,for it shows their origin4 ,their autopsy proves them to contain thirty known elements1 and not one that is new4 ,the list includes all the substances most common on the ,earth's surface1 which is suggestive2 but1 what is still more instructive1 these are combined into minerals which largely differ from those with which we are superficially familiar4 ,professor ,newton1 whose specialty they were1 has said3 8,in general they show no resemblance in their mechanical or mineralogical structure to the granitic and surface rocks of the ,earth4 ,one condition was certainly necessary in their formation1 viz4 the absence of free oxygen and of enough water to oxidize the iron40 ,thus they are not of the ,earth earthy2 nor yet1 poor little waifs1 of the upper crust of any other body4 ,illustration3 ,,section ,,of ,,meteorite ,,showing ,,widmannst,,ttian ,,lines4 7,field ,columbian ,museum1 ,chicago47 ,illustration3 ,,meteorite1 ,,toluca4 7,field ,columbian ,museum1 ,chicago47 ,in them prove to be occluded gases1 which can be got out by heating in the laboratory1 and which must have got in when the meteorites were still subjected to great heat and pressure4 ,for only thus could these gases have been absorbed4 ,both such heat and such pressure accuse some great solid body as origin of this flotsam of the sky4 ,fragments now1 they owe to its disruption their present separate state4 ,this parent mass must have been much larger and more massive than the ,earth1 as the grate amount of occluded hydrogen1 sometimes one-third the volume at #ejj ,c41 of the meteorite seems to testify4 ,the two classes of meteorites1 the stone and the iron1 show this further by the very differences they exhibit between themselves4 ,for both the amount and the proportions of the occluded gases in the two prove to be quite distinct4 ,in the stones the quantity of gas is greater and the composition is diverse4 ,in the stones carbonic acid gas is common1 carbon monoxide rare2 in the irons the ratio is just the other way4 ,thus ,wright found in nine specimens of the iron meteorites3-- ,,co ,,co ,h ,,ch #aa4e #cb4d #ed4a #jj of the total2 in ten of stone3-- ,,co ,,co ,h ,,ch #fj4a #c4d #cb4j #b4a ,the stones are much lighter than the iron1 their specific gravities being as #c to #g or #h for the metallic4 ,the stones1 therefore1 came from a more superficial layer of the body torn apart than the iron1 and the composition of their occluded gases bears this out4 ,those in the stones are such as we may conceive absorbed nearer the surface1 those in the iron from regions deeper down4 ,here1 then1 the meteorites tell us of another1 an earlier1 stage of our solar system's history1 one that mounts back to before even the nebula arose to which we owe our birth4 ,for the large body to whose dismemberment the meteorites were due can have been no other than the one whose cataclysmic shattering produced that very nebula which was for us the origin of things4 ,the meteorites1 by continuing unchanged1 link the present to that far-off past4 ,and they tell us1 too1 that this body must have been dark4 ,for solid1 they inform us1 it was1 and solidity in a heavenly body means deficiency of light4 ,that such corroborative testimony to a cataclysmic origin is forthcoming in the sky we shall see by turning again to the spiral nebul4 ,of the two classes of nebul which we contemplated in the last chapter1 the amorphous and the structural1 there is more to be said than we touched on then4 ,illustration3 ,,nebula ,v4 #ad ,,cygni--,,after ,,roberts4 ,not only in look are the two quite unlike1 but the spectroscope shows that the difference in appearance is associated with dissimilarity of character4 ,for the spectrum of the amorphous proves to consist of a few bright lines1 due to hydrogen and nebulium chiefly1 in the green1 whence the name green nebul4 ,that of the spirals1 on the other hand1 is continuous1 and therefore white4 ,the great nebula in ,andromeda was one of the first in which this was recognized2 and the perception was pregnant1 for no nebula defies resolution more determinedly than it4 ,we may1 therefore1 infer that it is not made up of stars1 certainly big enough for us to see4 ,on the other hand1 from the fact that its spectrum is continuous it must be solid or liquid4 ,young pointed out that this did not follow1 because a gas under great pressure also gives a continuous spectrum4 ,but he forgot that here no such pressure could exist4 ,a nebula of compressed gas could not have an irregular form and would have1 in the case of the ,andromeda nebula1 a mass so enormous as to preclude supposition4 ,continuity of spectrum here means discontinuity of mass4 ,the spectral solidity of the nebula speaks of a status quo ante1 not of a condition of condensation now going on4 ,illustration3 ,,nebula ,n4 ,g4 ,c4 #adii ,,persei--,,after ,,roberts4 ,illustration3 ,,nebula ,n4 ,g4 ,c4 #fifj ,,in ,,cygnus--,,after ,,ritchey4 ,advanced spectroscopic means reveals that the spectra of these 8white0 nebul are not simply continuous4 ,thus that of the ,andromeda nebula shows very faint dark lines crossing it1 apparently accordant with those of the solar spectrum and faint bright ones falling near and probably coincident with those of the ,wolf-,rayet stars1 due to hydrogen1 helium1 and so forth4 ,these later observations make practically certain what earlier ones permitted us just now only to infer3 that it is not composed of stars1 but of something subtler still2 to wit1 of meteorites4 ,the reasoning is interesting1 as showing that if one have hold of a true idea1 the stars in their courses fight for him4 ,illustration3 ,,nebula ,m4 #ea ,,canum ,,venaticorum--,,after ,,ritchey4 ,although ,lockyer has long been of opinion that the nebul are composed of meteorites1 the present argument differs from his4 ,the way in which their spectra establish their constitution may be outlined as follows3 the white nebul are from their structure evidently in process of evolution1 and if they are in stable motion1 as we suppose them to be1 their parts are moving round their common centre of gravity4 ,as the white nebul resist resolution as obstinately as the green1 these parts must be not only solid but comminuted 7composed of small particles74 ,now this would be the case were they flocks of meteorites such as we have seen composed our own system once upon a time4 ,though all are travelling round the centre of gravity of the flock1 each is pursuing its own orbit slightly different from1 and intersecting those of1 its neighbors4 ,collisions between the meteors must therefore constantly occur1 and the question is1 are these shocks sufficient to cause light4 ,let us take our own system and consider two meteorites at our distance from the ,sun1 travelling in the same sense1 the one in an ellipse1 the other in a circle1 with a major axis five per cent greater and meeting the other at aphelion4 ,this would be no improper jostle for such heavenly bodies4 ,if we calculate the speeds of both and deduct the elliptic from the circular1 we shall have the relative speed of collision4 ,it proves to be a half a mile a second or #cj times the speed of an express train4 ,as such a train brought up suddenly against a stone wall would certainly elicit sparks1 we see that a speed #cj times as great1 whose energy is #ijj times greater1 is quite competent to a shock sufficient to make us see stars en masse4 ,but1 indeed1 there must be collisions much more violent than this2 both because the central mass is often much greater and because the orbits differ much more1 and the effect would increase as the square of the speed4 ,the heat thus generated would cause the meteorites to glow1 and at the same time raise the temperature of the gases in and about them4 ,furthermore1 the light would come to us through other non-affected portions of gas between us and the scene of the collision4 ,thus all three peculiarities of the spectra stand explained3 we have a continuous background of light due to heated solid meteorites1 the bright lines of glowing gases1 and dark lines due to other gases not ignited1 lying in our line of sight4 ,in addition we should perceive another result4 ,collisions would be both more numerous and more pronounced toward the centre of the nebula1 for it must speedily grow denser toward its core owing to the falling in of meteorites1 in consequence of shock4 ,being denser in the centre1 the particles would there be thicker and be travelling at greater speed4 ,the nebul1 therefore1 should be brightest at their centres1 which is accordant with observation4 ,thus from having offered themselves exemplars of the way in which our own system came into being1 the white nebul assert their present constitution to be that from which we know our system sprang4 ,another suggestive fact about the present members of our solar system which has something to say about a past collision is the densities of the different planets4 ,the average density of the four inner planets1 ,mars1 the ,earth1 ,venus1 and ,mercury is nearly four times that of the four outer ones ,neptune1 ,uranus1 ,saturn1 and ,jupiter see ,,note #b4 ,the discrepancy is striking and cannot be explained by size1 as the smallest are the most massive1 and if all were primally of like constitution1 should be the least compressed4 ,nor can it be explained simply by greater heat tending to expand them1 for ,neptune and ,uranus show no signs of being very hot4 ,the minor differences between members of each group are probably explicable in part by these two factors1 mass and heat1 but the great gulf between the two groups cannot so be spanned4 ,we are then driven to the supposition that the materials composing the outer ones were originally lighter4 ,now this is precisely what should happen had all eight been formed by disruption of a previous body4 ,for its cuticle would be its least dense portion1 and on disruption would travel farthest away1 not because of being lighter1 but because of being on the outside4 ,parts coming from deeper down would remain near1 and be denser intrinsically4 ,what the present densities of the planets enable us to infer of the cataclysm from which they came1 a remarkable set of spectrograms taken not long ago by ,dr4 ,v4 ,m4 ,slipher1 at ,flagstaff1 seems to confirm4 ,the spectrograms in question were made possible by his production of a new kind of plate4 ,his object was to obtain one which should combine sufficient speed with great photographic extension of the spectrum into the red4 ,for it is in the red end that the absorption lines due to the planets' atmospheres chiefly lie4 ,with the plates heretofore used it was impossible to go much beyond the yellow1 the ,c line marking the ,ultima ,thule of attent4 ,not only was it advisable to get more particularity in the parts previously explored1 but it was imperative to go beyond into parts as yet unknown4 ,after several attempts he succeeded1 the plates when exposed showing the spectra beyond even the ,a band4 ,of their wealth of depiction it is only necessary to say that in the spectrum of ,neptune #acj lines and bands can easily be counted between the wave-lengths #dfjj 1 #gfjj 4 ,of these1 #ca belong to the planet1 which compares with #f found by ,huggins1 #aj by ,vogel1 and #i by ,keeler in the part of its spectrum they were able to obtain4 ,illustration3 ,,the ,,spectra ,,of ,,the ,,major ,,planets4 ,photographed1 in #aijg1 by ,v4 ,m4 ,slipher1 at ,,the ,,lowell ,,observatory ,flagstaff1 ,arizona4 ,the result was a revelation4 ,the plates exposed a host of lines never previously seen2 lines that do not appear in the spectrum of the ,sun1 nor yet in the added spectrum of the atmosphere of the ,earth1 but are due to the planets' own envelopes4 ,but this was only the starting-point of their disclosures4 ,when in this manner he had taken the color signatures of ,jupiter1 ,saturn1 ,uranus1 and ,neptune1 an orderly sequence in their respective absorption bands stood strikingly confessed4 ,in other words1 their atmospheres proved not only peculiar to themselves and unlike what we have on ,earth1 but progressively so according to a definite law4 ,that law was distance from the ,sun4 ,when the spectra were arranged vertically in ordered orbital relation outward from the ,sun1 with that of the lunar for comparison on top1 a surprising progression showed down the column in the strange bands1 an increase in number and a progressive deepening in tint4 ,the lunar1 of course1 gives us the ,sun and our own air4 ,all else must therefore be of the individual planet's own4 ,beginning1 then1 with ,jupiter1 we note1 besides the renforcement of what we know to be the great water-vapor bands #8a1' several new ones1 which show still darker in the spectrum of ,saturn4 ,the strongest of these is apparently not identifiable with a band in the spectra of ,mira ,ceti in spite of falling near it4 ,passing on to ,uranus1 we perceive these bands still more accentuated1 and with them others1 some strangers1 some solar lines enhanced4 ,thus the hydrogen lines stand out as in the ,sirian stars4 ,all deepen in ,neptune1 while further newcomers appear4 ,thus we are sure that free hydrogen exists in large quantities in the atmospheres of the two outermost planets and most so in the one farthest off4 ,helium1 too1 apparently is there1 and other gases which in part may be those of long-period stars1 decadent suns1 in part substances we do not know4 ,from the fact that these bands are not present in the ,sun and apparently in no type of stars1 we may perhaps infer that the substances occasioning them are not elements but compounds to us unknown4 ,and from the fact that free hydrogen exists there alongside of them1 and apparently helium1 too1 we may further conclude that they are of a lighter order than can be retained by the ,earth4 ,but now1 we may ask1 why should these lighter gases be found where they are8 ,it cannot be in consequence simply of the kinetic theory of gases from which a corollary shows that the heaviest bodies would retain their gases longest1 because the strange gases are not apportioned according to the sizes of their hosts4 ,jupiter1 by all odds the biggest in mass1 has the least1 and ,saturn1 the next weightiest1 the next in amount4 ,nor can title to such gaseous ownership be lodged in the planet's present state4 ,for though ,jupiter is the hottest and ,saturn the next so1 the increased mass more than makes up in restraint what increased temperature adds in molecular volatility--as we perceive in the cases of the ,sun and ,earth4 ,no2 their envelopes are increasingly strange because their internal constituents are different1 and as hydrogen is most abundant in ,neptune1 the lightest of all the gases1 it is inferable that this planet's material is lighter4 ,as distance from the ,sun determines their atmospheric clothing1 so distance decides upon their bodies1 too4 ,it was all a case of primogeniture4 ,the light strange matter that constitutes them was so because it came from the outer part of the dismembered parent orb4 ,neptune the outermost1 ,uranus the next1 then ,saturn and ,jupiter came in that order from the several successive layers of the pristine body1 while the inner planets came from parts of it deeper down4 ,the major planets were of the skin of the dismembered body1 we of its lower flesh4 ,very interesting the study of these curious spectral lines from the outer planets for themselves alone2 even more so for what one would hardly have imagined3 that they should actually tell us something of the genesis of our whole solar system4 ,they corroborate in so far what the meteorites have to say4 ,that the meteorites are solid and1 except for their experiences in coming through our air1 bear no marks of external heat1 is a fact which is itself significant4 ,it seems to hint not at a crash as their occasioning but at disruptive tidal strains4 ,the parent body appears to have been torn apart without much development of heat4 ,perhaps1 then1 we had no gloriously pyrotechnic birth1 but a more modest coming into existence4 ,but about this we must ourselves modestly be content to remain for the present in the dark4 ,not the least important feature of the theory ,i have thus outlined is that it finishes out the round of evolution4 ,it becomes a conception sapiens in se ipso totus1 teres atque rotundus4 ,to frame a theory that carries one back into the past1 to leave one there hung up in heaven1 is for inconclusiveness as bad as the ancient fabulous support of the world1 which ,atlas carried standing on an elephant upheld by a tortoise4 ,what supported the tortoise we were not told4 ,so here1 if meteorites were our occasioning1 we must account for the meteorites1 starting from our present state4 ,this the present presentation does4 ,thus do the stones that fall from the sky inform us of two historic events in our solar system's career4 ,they tell us first and directly of a nebula made up of them1 out of which the several planets were by agglomeration formed and of which material they are the last ungathered remains4 ,and then they speak to us more remotely but with no less certainty of a time antedating that nebula itself1 a time when the nebula's constituents still lay enfolded in the womb of a former ,sun4 ,man's interest in them hitherto has been1 as with other things1 chiefly proprietary4 ,greed of them has grown so keen that legal questions have been raised of the ownership of their finding1 and our courts have solemnly declared them not 8wild game0 but 8real estate10 and as such belonging to the owner of the land on which they fall4 ,but to the scientific eye their estate is something more than 8real10 for theirs is the oldest real estate in the solar system4 ,they were what they are now when the ,earth we pride ourselves in owning was but a molten mass4 ,so that when in future you see these strange stones in rows upon a museum's shelves1 regard them not as rarities1 in which each museum strives to outdo its neighbors by the quantity it can possess1 but as rosetta stones telling us of an epoch in cosmic history long since passed away--of which they alone hold the key4 ,look at them as the literary do their books1 for that which they contain1 not as the bibliophile to whom a misprint copy outvalues a corrected one and by whom 8uncuts0 are the most prized of all4 ,,chapter ,,iii ,,the ,,inner ,,planets ,when we recall that the ,ptolemaic system of the universe was once taught side by side with the ,copernican at ,harvard and at ,yale1 we are impressed1 not so much with the age of our universities1 as with the youth of modern astronomy and with the extraordinary vitality of old ideas4 ,that the ,ptolemaic system in its fundamental principle was antiquated at the start1 the older ,greeks having had juster conceptions1 does not lessen our wonder at its tenacity4 ,but the fact helps us to understand why so much fossil error holds its ground in many astronomic text-books to-day4 ,that stale intellectual bread is deemed better for the digestion of the young1 is one reason why it often seems to them so dry4 ,illustration3 ,,orbits ,,of ,,the ,,inner ,,planets4 ,before entering upon the problem of the genesis and career of a world1 it is essential to have acquaintance with the data upon which our deductions are to rest4 ,to set forth1 therefore1 what is known of the several planets of our solar system1 is a necessary preliminary to any understanding of how they came to be or whither they are tending2 and as our knowledge has been vitally affected by modern discoveries about them1 it is imperative that this exposition of the facts should be as near as possible abreast of the research itself4 ,i shall1 therefore1 give the reader in this chapter a bird's-eye view of the present state of planetary astronomy1 which he will find almost a different part of speech from what it was thirty years ago4 ,it is not so much in our knowledge of their paths as of their persons that our acquaintance with the planets has been improved4 ,and this knowledge it is which has made possible our study of their evolution as worlds4 ,could we get a cosmic view of the solar system by leaving the world we live on for some suitable vantage-point in space1 two attributes of it would impose themselves upon us--the general symmetry of the whole1 and the impressively graded proportions of its particular parts4 ,round a great central globular mass1 the ,sun1 far exceeding in size any of his attendants1 circle a series of bodies at distances from him quite vast1 compared with their dimensions4 ,these1 his principal planets1 are in their turn centres to satellite systems of like character1 but on a correspondingly reduced scale4 ,all of them travel substantially in one plane1 a fact giving the system thus seen in its entirety a remarkably level appearance1 as of an ideal surface passing through the centre of the ,sun4 ,departing somewhat from this general uniformity in their directions of motion1 and also deviating more from circularity in their paths1 some much smaller bodies1 a certain distance out1 dart now up now down across it at different angles and from all the points of the compass1 agreeing with the others only in having the centre of the ,sun their seemingly never attained goal of endeavor4 ,these bodies are the asteroids4 ,surrounding the whole1 and even penetrating within its orderly precincts1 a third class would be visible which might be described for size as cosmic dust1 and for display as heavenly pyrotechnics4 ,coming from all parts of space indifferently they would seem to seek the ,sun in almost straight lines1 bow to him in circuit1 and then depart whence they came4 ,for in such long ellipses do they journey that these seem to be parabolas4 ,these visitants are the comets and their associates the meteor-streams4 ,although for purposes of discrimination we have labelled the several classes apart1 an essential fact about the whole company is to be noted3 that no hard and fast line can be drawn separating the several constituents from one another4 ,in size the members of the one class merge insensibly into the other4 ,some of the planets are hardly larger than some of the satellites2 some of the satellites than some of the asteroids2 some of the asteroids than comets and shooting-stars4 ,in path1 too1 we find every gradation from almost perfect circularity like the orbits of ,io and ,europa to the very threshold of where one step more would cease to leave the body a member of the ,sun's family by turning its ellipse into an hyperbola4 ,finally1 in inclination we have every angle of departure from orthodox platitude to unconforming uprightness4 ,this point1 that heavenly bodies1 like terrestrial ones1 show all possible grades of indistinction1 is kin to that specific generalization by which ,darwin revolutionized zology a generation ago4 ,it is as fundamental to planets as to plants4 ,for it shows that the whole solar system is evolutionarily one4 ,a second point to be noticed in passing is that undue inclination and excessive eccentricity go together4 ,the bodies that have their paths least circular have them1 as a rule1 the most atilt4 ,and with these two qualities goes lack of size4 ,it is the smallest bodies that deviate most from the general consensus of the system4 ,with so much by way of generic preface1 the pregnancy of which will become apparent as we proceed1 we come now to particular consideration of its members in turn4 ,nearest to the ,sun of all the planets comes ,mercury4 ,so close is he to that luminary1 and so far within the orbit of the earth1 that he is not a very common object to the unaided eye4 ,copernicus is said never to have seen him1 owing1 doubtless1 to the mists of the ,vistula4 ,by knowing when to look1 however1 he may be seen for a few days early in the spring in the west after sunset1 or before sunrise in the east in autumn4 ,he is then conspicuous1 being about as bright as ,capella1 for which star or ,arcturus he is easily mistaken by one not familiar with the constellations4 ,his mean distance from the ,sun is thirty-six million miles1 but so eccentric is his orbit1 the most so of any of the principal planets1 that he is at times half as far off again as at others4 ,even his orbital behavior is the least understood of any in the solar system4 ,his orbit swings round at a rate which so far has defied analysis4 ,it may be a case of reflected perturbation1 one1 that is1 of which the indirect effect from another body becomes more perceptible than would be the direct effect on the body itself4 ,as yet it baffles geometers4 ,as to his person1 our ignorance until lately was profound4 ,it is only recently that such fundamental facts about him as his size1 his mass1 and his density have been reached with any approach to precision4 ,this was because he so closely hugs the ,sun that observations upon his full1 or nearly full1 disk had never been attempted4 ,when ,i say that his volume was not known to within a third of its amount1 his mass not closer than one-half1 while his received density was nearly double what we now have reason to suppose the fact1 some idea of the depth of our nescience may be imagined4 ,this1 of course1 did not prevent text-books from confidently misinstructing youth1 or ,nautical ,almanacs from misguiding computers with figures that thus almost achieved immortality1 so long had they passed current in spite of lacking that perfection which is usually assigned as its warrant4 ,illustration3 ,,sulla ,,rotazione ,,di ,,mercurio--,,di ,g4 ,v4 ,,schiaparelli4 ,schiaparelli first put astronomy on the right track4 ,by attempting daylight observations of the planet1 not toward night1 but actually at midday1 he made some remarkable discoveries1 and though he did not detect the hitherto erroneous values of the volume1 the mass1 or the density1 his method of observation paved the way for their ascertainment4 ,what he sought1 and found1 was evidence of markings upon the disk by which the planet's time of rotation might be determined4 ,up to then1 ,schroeter's value of about twenty-four hours had been accepted1 on very slender evidence indeed1 and passed into all the books4 ,but when the planet came to be observed by noon1 very definite markings stood out on its face1 which showed its rotation to take place1 not in twenty-four hours1 but in eighty-eight days4 ,by a persistence equal to his able choice of observing time1 he established this beyond dispute4 ,he proved the revolutionizing fact that ,mercury's periods of rotation and of revolution were the same4 ,he detected1 too1 the evidence in the position of the markings of the planet's great libratory swing due to the eccentricity of its orbit1 a result as remarkable as a feat of observation as it was conclusive as a proof4 ,if ,schiaparelli had never done any other astronomical work1 this study of ,mercury would have placed him as the first observer of his day4 ,for the observations are so difficult that the planet not only baffled all his predecessors1 but has foiled many since who are credited with being observers of eminence4 ,in #ahif the study of ,mercury was taken up at the ,lowell ,observatory in ,arizona along the same lines that had proved so successful with ,schiaparelli1 but without using his observations as guide4 ,indeed1 his papers had not then been read there4 ,the two conclusions were1 therefore1 independent of one another4 ,the outcome was a complete corroboration and an extension of ,schiaparelli's work4 ,we shall begin with the consideration of the most fundamental point4 ,in the clear and steady air of ,flagstaff1 permitting of measurement of his disk up to within a few degrees of the ,sun1 ,mercury was found to be much larger than previously thought4 ,instead of a diameter of three thousand miles he proved to have one of thirty-four hundred1 making his volume nearly half as large again as had been credited him4 ,these measures bore intrinsic evidence of their trustworthiness in an interesting manner1 and at the same time produced internal testimony that accounted for the smallness of previous determinations4 ,measures heretofore had been made1 usually if not invariably1 either when the planet transited the ,sun or when it exhibited a pronounced phase4 ,now in both these cases the planet looks smaller than it is4 ,in the first case this is due to irradiation1 the surrounding disk of the ,sun encroaching both to the eye and to the camera upon the silhouette of ,mercury4 ,and this inevitable effect had not been allowed for in the measures4 ,in the second case the horns of the planet never seem to extend quite to their true position4 ,this was rendered evident by the ,flagstaff series of measures1 which began when the planet was a half-moon and continued till it was almost full4 ,as it did so1 the values for the diameter steadily increased1 even after irradiation was allowed for1 although this against the brilliant background of the noonday sky must have been exceeding small1 and tended in part to be diminished as the planet attained the full1 because of its consequent nearing of the ,sun4 ,the measures thus explained themselves and vouched for their own accuracy4#c ,then came a curious bit of unexpected proof to corroborate them4 ,in his 8,astronomical ,constants10#d published but a short time before1 ,newcomb had detected a systematic error in the right ascensions of ,mercury which he was not able to explain4 ,by diligent mousing that eminent computer had discovered that ,mercury was registered by observers too far from the ,sun on whichever side of him it happened to be1 and in proportion roughly not to its distance off but to the phase the planet exhibited4 ,when the disk was a crescent the discrepancy between observation and theory was large1 and thence decreased as the planet passed to the full4 ,he suspected the cause1 and would have found it had he not considered the diametral measures of the planet too well assured to permit of doubt4 ,as it was1 he neglected a factor which has vitiated almost all the observations made on the planets up to within a few years1 the correction for irradiation4 ,this was the case here4 ,the received measures1 beginning with ,bradley and ending with ,todd1 had almost without exception been made in transit1 and1 as no regard had been paid to the contracting effect of irradiation1 had been invalidated in consequence4 ,the new method supplied almost exactly the amount needed to explain the right ascensions1 a second of arc1 and in precise accordance with the place which the discrepancy demanded4 #c ,new ,observations of the ,planet ,mercury1 ,memoirs ,amer4 ,acad4 #ahig4 ,vol4 ,,xii1 ,no4 #d4 #d 8,astronomical ,constants10 #ahie1 pp4 #fg1 #fh4 ,about the mass there has been1 and still is1 great uncertainty4 ,this is because it can only be found from the perturbing effect it has on ,venus1 the ,earth1 or ,encke's comet4 ,modern determinations1 however1 are smaller than the older ones2 thus ,backlund in #ahid got from the effect on ,encke's comet only one-half the mass that ,encke had1 fifty-three years before4 ,probably the most reliable information comes from ,venus1 which ,tisserand found to give for ,mercury _/ of the mass of the ,sun1 or _/ of the mass of the ,earth4 ,if we take _/ as the nearest round number1 we find the planet's density to be #j4ff that of the ,earth4 ,illustration3 ,,map ,,of ,,mercury ,,lowell ,,observatory #ahif-ig ,the same observations that disclosed at ,flagstaff the planet's size revealed a set of markings on his face so definite as to make the rotation period unmistakable4 ,it takes place1 as ,schiaparelli found1 in eighty-eight days1 or the time of the planet's revolution round the ,sun4 ,the markings disclosed the fact1 as ,schiaparelli had also discovered1 in a most interesting manner1 for the ellipticity of the planet's orbit stood reflected in the swing of the markings across the face of the disk1 a definiteness in the proof of a really surprising kind4 ,what this means we shall see in a subsequent chapter when we take up the mechanical problem of the tides4 ,another result that issued from the positions of the markings was the determination of the planet's pole4 ,except for the libration above noticed1 the markings kept an invariable longitudinal position upon the illuminated disk1 showing that the planet turned always the same face to the ,sun2 but latitudinally a difference was noticeable between their place in ,october-,november1 #ahif1 and in ,february-,march1 #ahig1 the latter being #d farther north4 ,now this is just what the orbital position should have caused1 if the pole stood vertically to it4 ,thus a difference of #d from perpendicularity should have been discernible1 had it existed1--a very small amount in such a determination4 ,we may1 therefore1 conclude that the axis stands plumb to the orbit1 and this is what theory demands4 ,the state of things this introduces to us upon that other world is to our ideas exceeding strange4 ,it is not so much the slowness of the diurnal spin1 eighty-eight times as long as our own1 which is surprising1 as the fact that this makes its day infinite in length4 ,two antipodal hemispheres divide the planet1 the one of which frizzles under eternal sun1 the other freezes amid everlasting night4 ,the ,sun does not1 indeed1 stand stock-still in the sky1 but nods like some huge pendulum to and fro along a parallel of latitude4 ,in consequence of libration the two great domains of day and night are sundered by a strip of debatable ground #bc in breadth on either side1 upon which the ,sun alternately rises and sets4 ,here there is a true day1 eighty-eight of our days in length from one sunrise to the next4 ,but its day and night are not apportioned alike4 ,the eastern strip has its daylight briefer than its starlight hours2 the western has them longer4 ,nor are different portions of the strips similarly circumstanced in their sunward regard4 ,only the edge next perpetual day has anything approaching an equal distribution of sunlight and shade4 ,the farther one just peeps at the ,sun for a moment every eighty-eight days1 and then sinks back again into obscurity4 ,the transition from day to night is equally instantaneous and profound4 ,for little or no twilight here prolongs the light2 since the air1 if there be any at all1 is too thin to bend it to service round the edge to illuminate the night4 ,when the libratory ,sun sets1 darkness like a mantle falls swiftly over the face of the ground4 ,no evidence of atmosphere has ever been perceived1 and theory informs that it should be nearly1 if not wholly1 absent4 ,in consequence of the rigid uprightness of the planet's axis1 seasons do not exist4 ,their nearest simulacrum comes from the seeming dilatation of the ,sun during half the year1 and its apparent contraction during the other half4 ,it expands so much between its ,january and its ,july as to receive more heat in the ratio of nine to four4 ,a seasonless1 dayless1 and almost yearless planet1 it is better to look at than to look from2 but its study opens our eyes to the great diversity which even one of our nearest neighbors exhibits from what we take as matters of course on ,earth4 ,that what we take offhand to be purely astronomic phenomena should turn out to be so essentially of the particular world1 worldly1 clarifies vision of what these really are1 and how dependent on and interwoven with everyday life astronomy is4 ,or1 we may consider it turned about and realize how purely astronomic relations1 such abstract mechanical matters as rotations and revolutions1 result in completely changing the very face and character of the globe concerned4 ,mercury to-day stares forever at the ,sun4 ,the markings we see have stereotyped this stare to its inevitable result4 ,for they seem to mark a globe sun-cracked4 ,at such a condition the curious crisscross of dark1 irregular lines certainly hints1 accentuated and perfected as it is by a bounding curve where the mean sunward side terminates to the enclosing them as by the carapace of a tortoise4 ,though they cannot probably be actual cracks1 however much they may resemble such1 yet they may well owe their existence to that fundamental cause4 ,in color the planet is ghastly white2 of that wan hue that suggests a body from which all life has fled4 ,far whiter than ,venus in point of fact1 the rosy tint with which it sparkles in the sunset glow is all borrowed of the dying day and vanishes when the planet is looked at in the uncompromising light of noon4 ,seen close together once at ,flagstaff it was possible directly to compare the two2 when ,mercury1 although lit by the ,sun two and a half times as brilliantly as ,venus1 was1 surface for surface1 more than twice as faint4 ,mller has found its intrinsic brightness about that of our ,moon1 which in some respects it resembles1 though it apparently departs widely from any similarity in others4 ,the bleached bones of a world2 that is what ,mercury seems to be4 ,venus comes next in order outward from the ,sun4 ,to us her incomparable beauty is partly the result of propinquity3 nearness to ourselves and nearness to the ,sun4 ,relatively so close is she to both that she does not need the ,sun's withdrawal to appear1 but may nearly always be seen in the daytime in clear air if one knows where to look for her4 ,situate about seven-tenths of our own distance from our common giver of light and heat1 she gets about double the amount that falls to our lot1 so that her surface is proportionately brilliantly illuminated4 ,being also relatively near us1 she displays a correspondingly large surface4 ,but though part of her lustre is due to her position1 a part is her own4 ,direct visual observation1 as we remarked above1 shows her intrinsic brightness to be more than five times that of ,mercury1 square mile to square mile of surface for the two4 ,now this has been determined very carefully photometrically by ,mller at ,potsdam4 ,the result of his inquiry was to indicate that ,mercury shines with #j4ag of absolute reflection1 ,venus with #j4ib4 ,so high a value has seemed to many astronomers impossible1 because so far surpassing that which has tacitly been taken as the ne plus ultra of planetary brightness1 that of cloud1 #j4gb4 ,now1 one of the direct outcomes of the study of ,venus at the ,lowell ,observatory was an explanation of this seemingly incredible phenomenon4 ,when the planet came to be critically examined there under conditions of seeing which permitted discovery1 markings very faint1 but nevertheless assurable1 stood presented on the planet's face4 ,these markings1 of which we shall have more to say in a moment1 had this of pertinency to our present point1 that they kept an invariable position to one another4 ,they thus betrayed themselves to be surface features4 ,furthermore1 their dimness was as invariable an attribute of them as their place4 ,they were not obscured on some occasions and revealed at others1 but stayed1 so far as one might judge1 permanently the same4 ,they were thus neither clouds themselves nor subject to the caprice of cloud4 ,the old idea that ,venus was a cloud-wrapped planet and owed her splendor to this envelope1 vanished literally into thin air4 ,it is precisely because she is not cloud-covered that her lustre is so great4 ,she 8clothes herself with light as with a garment0 by a physical process of some interest4 ,as becomes the ,mother of the ,loves1 this is gauze of the most attenuated character1 and yet a wonderful heightener of effect4 ,for it consists solely of the atmosphere that compasses her about4 ,it is well known that a substance when comminuted reflects much more light than when condensed into a solid state4 ,now an atmosphere is itself such a comminuted affair1 and1 furthermore1 holds in suspension a variety of dust4 ,this would particularly be the case with the atmosphere of ,venus1 as we shall have reason to see when we consider the conditions upon that planet made evident by study of its surface markings4 ,to her atmosphere1 then1 she owes four-fifths or more of her brilliancy4 ,and this stands corroborated by the low albedo of both ,mercury and the ,moon1 which have no atmosphere1 and by the intermediate lustre of ,mars1 which has some1 but little4#e #e ,astr4 ,nach4 ,no4 #cdjf4 ,monthly ,notices ,r4 ,a4 ,s41 ,march1 #ahig4 ,the rotation time of ,venus1 the determination1 that is1 of the planet's day1 is one of the fundamental astronomical acquisitions of recent years4 ,for upon it turns our whole knowledge of the planet's physical condition4 ,more than this1 it adds something which must be reckoned with in the framing of any cosmogony4 ,it is not a question of academic accuracy merely1 of a little more or a little less in actual duration1 but one which carries in its train a completely new outlook on ,venus and sheds a valuable side-light upon the history of our whole planetary system4 ,unconsciously influenced1 one is inclined to think1 by terrestrial analogies1 astronomers for more than a couple of centuries1 ever since the time of the first ,cassini in #afff1 deemed the day of ,venus to be just under twenty-four hours in length4 ,so well attested was its determination1 and so precisely figured to the minute1 that it imposed itself upon text-books which stated it as an acquired fact down to the last second4 ,nevertheless1 ,schiaparelli was not so sure1 and proceeded to look into the matter4 ,he first looked for himself1 and then looked up all the old observations4 ,his chief observational departure was observing by day as near to noon as possible2 because then the planet was highest1 to say nothing of the taking off from its glare by the more brilliant sky4 ,from certain dark markings around two bright spots near the southern cusp1 of one of which spots the detection dates from the time of ,schroeter1 and from a long1 dark streak stretching thence well down the disk1 he convinced himself that no such period as twenty-four hours could possibly be correct1 inasmuch as whenever he looked1 the markings were always there4 ,his notes read1 8,same appearance as yesterday10 day after day1 until he would really have saved ink and penmanship had he had the phrase cut into a die and stamped4 ,he concluded that the rotation was at least six months long1 and was probably synchronous with the planet's time of revolution4 ,this was in #ahhi4 ,in #ahie he became still more sure1 and showed how the older observations were really compatible with what he had found4 ,in #ahif the subject was taken up at ,flagstaff4 ,very soon it became evident there that markings existed on the disk1 most noticeable as fingerlike streaks pointing in from the terminator1 faint but unmistakable from the identity of their successive presentation4 ,schroeter's projection near the south cusp was also clearly discernible as well as two others1 one in mid-terminator1 one near the northern cusp4 ,schiaparelli's dark markings also came out1 developing into a sort of collar round the southern pole4 ,other spots and streaks also were discernible1 and all proved permanent in place4 ,by watching them assiduously it was possible to note that no change in position occurred in them1 first through an interval of five hours1 then through one of days1 then of weeks4 ,care was taken to guard against illusion4 ,it thus became evident that they bore always the same relation to the illuminated portion of the disk4 ,this illuminated part1 then1 never changed4 ,in other words1 the planet turned always the same face to the ,sun4 ,the fact lay beyond a doubt1 though of course not beyond a doubter4#f #f ,monthly notices ,r4 ,a4 ,s41 ,march1 #ahig4 ,illustration3 ,,venus4 ,,october1 #ahif--,,march1 #ahig--;,,drawings ,,by ,,dr4 ,,lowell4 ,illustration3 ,,venus4 ,,april #ab1 #aiji1 #c;,h #bf,m--#d;,h #bb,m--,,by ,,dr4 ,,lowell4 ,the years that have passed since these observations were made have brought corroboration of them4 ,several observers at ,flagstaff have seen and drawn them and added discoveries of their own1 among whom are especially to be mentioned1 of the observatory staff3 ,miss ,leonard1 ,dr4 ,slipher1 and ,mr4 ,e4 ,c4 ,slipher4#g #g ,lowell ,observatory ,bulletin #f4 ,in character these markings were peculiar and distinctive4 ,in addition to some of more ordinary character were a set of spokelike streaks which started from the planet's periphery and ran inwards to a point not very distant from the centre4 ,the spokes started well-defined and broad at the edge1 dwindling and growing fainter as they proceeded1 requiring the best of definition for their following to their central hub4 ,the peculiar symmetry thus displayed1 a symmetry associated with the planet's sunrise and sunset line1 or1 strictly speaking1 what would be such did the ,sun for ,venus ever rise or set1 would seem inexplicable1 except for that very association4 ,when we reflect1 however1 upon what this means1 a very potent cause for them becomes apparent1 so potent that surprise is turned into appreciation that nothing else could well exist4 ,that ,venus turns on her axis in the same time that she revolves about the ,sun1 in consequence of which she turns always the same face to him1 must cause a state of things of which we can form but faint conception1 from any earthly analogy4 ,one face baked for countless ons1 and still baking1 backed by one chilled by everlasting night1 while both are still surrounded by air1 must produce indraughts from the cold to the hot side of tremendous power4 ,a funnel-like rise must take place in the centre of the illuminated hemisphere1 and the partial vacuum thus formed would be filled by air drawn from its periphery1 which1 in its turn1 would draw from the regions of the night side4 ,such winds would sweep the surface as they entered1 becoming less superficial as they advanced1 and the marks of their inrush might well be discernible even at the distance we are off4 ,deltas of such inroad would thus seam the bounding circle of light and shade4 ,illustration3 ,i ,showing convection currents in the planet's atmosphere4 ,illustration3 ,,ii ,showing shift in central barometric depression due to rotation of the planet affecting the winds4 ,,venus4 ,another result of the arial circulation would be the removal of all moisture from the sunward face1 and its depositing in the form of ice upon the night one4 ,for the heated air would be able to carry much water in suspension1 which1 on cooling1 after it had reached the dark hemisphere would unload it there4 ,in the low temperature there prevailing1 this moisture would all be frozen1 and so largely estopped from return4 ,this process continuing for ages would finally deplete one side of all its water to heap it up in the form of ice upon the other4 ,now it is not a little odd that a phenomenon has been observed upon ,venus which seems to display just this state of things4 ,many observers have noted an ashen light on the dark side of her disk4 ,some have tried to account for it as ,earth shine1 the same earth-reflected light that makes dimly visible the old moon in the new moon's arms4 ,but the ,earth is too far away from ,venus to permit of any such effect2 nor is there any other body that could thus relieve its night4 ,but if the night hemisphere of ,venus be one vast polar sheet1 we have there a substance able to mirror the stars to a ghostlike gleam which might be discernible even from our distant post4 ,illustration3 ,venus ,rotation #bbe days4 ,thus when we reason upon them we see that the peculiar markings of the planet lose their oddity1 becoming the very pattern and prototype of what we should expect to view4 ,interpreted1 they present us the picture of a plight more pitiable even than that of ,mercury4 ,for the nearly perfect circularity of ,venus' orbit prevents even that slight change from everlasting sameness which the libration of ,mercury's affords4 ,to ,venus the ,sun stands substantially stock-still in the sky1--a fact which must prove highly reassuring to ,ptolemaic astronomers there1 if there be any still surviving from her past4 ,no day1 no seasons1 practically no year1 diversifies existence or records the flight of time4 ,monotony eternalized1--such is ,venus' lot4 ,what visual observations have thus discovered of the rotation time of ,venus1 with all that follows from it1 the spectroscope at ,flagstaff has confirmed4 ,at ,dr4 ,slipher's hands1 spectrograms of the planet have told the same tale as the markings4 ,it was with special reference to this point that the spectrograph there was constructed1 and the first object to which it was directed was ,venus4#h #h ,lowell ,observatory ,bulletin ,no4 #c4 ,the planet's rotation time was to be investigated by means of the motion it brought about in the line of sight4 ,visual observation1 telescopically1 reveals motion thwart-wise by the displacement it produces in the field of view2 spectroscopic observation discloses motion to or from the observer by the shift it causes in the spectral lines due to a stretching or shortening of their wave-lengths4 ,the spectroscope is an instrument for analyzing light4 ,ordinary light consists of light of various wave-lengths4 ,by means of a prism or grating these are dispersed into a colored ribbon or band1 the longer waves lying at the red end of the spectrum1 as the ribbon is called1 the shorter at the violet4 ,now the spectroscope is primarily such a prism or grating placed between the image and the observer1 by means of which a series of colored images of the object are produced4 ,in order that these may not overlap and so confuse one another1 the light is allowed to enter the prism only through a narrow slit placed across the telescopic image of the object to be examined4 ,thus successive images of what is contained by the slit are presented arranged according to their wave-lengths4 ,in practice the rays of light from the slit enter a small telescope called the collimator1 and are there rendered parallel1 in which condition they fall upon the prism4 ,this spreads them out into the spectrum and another small telescope focusses them1 each according to its kind1 into a spectral image band which may then be viewed by the eye or caught upon a photographic plate4 ,now1 if an object be coming toward the observer1 emitting or reflecting light as it does so1 each wave-length of its spectrum will be shortened in proportion to the relative speed of its approach as compared with the speed of light1 because each new wave is given out by so much nearer the observer and in reflection the body may also meet it4 ,reversely it will be lengthened if the object be receding from the observer or he from it4 ,this would change the color of the object were it not that while each hue moves into the place of the next1 like the guests at ,alice's tea-party in ,wonderland1 some red rays pass off the visible spectrum1 but new violet rays come up from the infraviolet and the spectrum is as complete as before4 ,fortunately1 however1 in all spectra are gaps where individual wave-lengths are absorbed or omitted1 and these1 the lines in the spectrum1 tell the tale of shift4 ,now if a body be rotating1 one side of it will be approaching the observer1 while the opposite side is receding from him1 and if the slit be placed perpendicular to the axis about which the spin takes place1 each spectral line will appear not straight across the spectrum of the object1 but skewed1 the approaching side being tilted to the violet end1 the receding side to the red4 ,this was to be the procedure adopted for the rotation of ,venus4 ,by placing the slit parallel to the ecliptic1 or1 more properly1 to the orbit of ,venus1 which is practically the same thing1 it found itself along what we have reason to suppose the equator of the planet4 ,even a considerable error on this point would make little difference in the rotational result4 ,in order that there might be no question of illusion or personal bias1 photographs instead of eye observations of the spectrum were made4 ,for reference and check side by side with that of ,venus were taken on either hand the spectra of iron1 made by sparking a tube containing the vapor of that metal4 ,the vapor1 of course1 had no motion with regard to the observer1 and therefore its spectral lines could have no tilt1 but must represent motional verticality4 ,dr4 ,slipher chose his time astutely4 ,he selected the occasion when ,venus was passing through superior conjunction1 or the point in her orbit as regards us directly beyond the sun4 ,at first sight this might seem to be the worst as well as the most impracticable of epochs1 inasmuch as the planet is then not only at her farthest from the ,earth1 but in a line with the ,sun1 and so drowned in his glare4 ,but in point of fact any tilt of the spectral lines is then1 owing to phase1 twice what it is at elongation1 and exceeds still more what it is when ,venus has her greatest lustre see ,,note #c4 ,in his purpose he was abetted by the ,flagstaff air1 which enabled the planet to be spectrographed much nearer the sun than would otherwise have been the case4 ,he thus selected the best possible opportunity4 ,to guard against any subsequent bias on the part of the examiner of the plates1 after the spectroscope had taken a plate it was then reversed1 and the process repeated on another one1 the iron being sparked as before4 ,what had been the right side of ,venus with regard to the red end of the spectrum thus became the left one1 and vice versa4 ,in this manner1 when the plates came to be measured for tilt1 the measurer would have no indication from the spectrum itself which way the lines might be expected to tilt2 he could1 therefore1 not be influenced either consciously or unconsciously in his decision4 ,illustration3 ,,spectrogram ,,of ,,venus1 ,,showing ,,its ,,long ,,day--,v4 ,m4 ,,slipher1 ,,lowell ,,observatory1 #aijc4 ,eight plates with their comparison ferric spectra were thus secured2 four with the spectroscope direct1 four with it reversed4 ,they were then shuffled1 their numbers hidden1 and given to ,dr4 ,slipher to measure4 ,the spectral lines told their own story1 and without prompting4 ,all the plates agreed within the margin of error accordant with their possible precision1 a precision some thirty times that of ,belopolski's experiment on the same lines1--a result not derogatory of that investigator1 but merely illustrative of superior equipment4 ,they showed conclusively that a rotation of anything like twenty-four hours was out of the question4 ,they yielded1 indeed1 testimony to a negative rotation of three months1 which1 interpreted1 means that so slow a spin as this was beyond their power to precise4 ,for ,dr4 ,slipher was at no less care to determine just what precision was possible in the case1 although a speed corresponding to a spin of twenty-four hours on a globe the size of ,venus is well known to be spectroscopically measurable4 ,it would mean a motion toward us of one thousand miles an hour1 or about a third of a mile a second4 ,the tilt occasioned by this speed is well within the spectroscope's ability to disclose4 ,not content with this1 however1 by two special investigations1 he proved the spectroscope's actual limits of performance to be far within the quantity concerned4 ,one of them was the determination by the same means and in like manner of the rotation time of ,mars1 the length of that planet's day1 which in other ways we know to the hundredth of a second1 and which is #bd #cg #bc4ff ,now ,mars offers a test nearly twice as difficult as ,venus1 even supposing the apparent disks of the two the same1 because his diameter being less in the proportion roughly of one-half1 the actual speed of a particle at his edge is less for the same time of rotation in the like proportion1 and it is only with the speed in miles1 not in angular amount1 that the spectroscope is concerned4 ,nevertheless1 when a like number of plates were tried on him1 they indicated on measurement a rotation time within an hour of the true4 ,this corresponds to half an hour on ,venus4 ,we see1 therefore1 that had ,venus' day been anywhere in the neighborhood of twenty-four hours1 ,dr4 ,slipher's investigation would have disclosed it to within thirty-one minutes4 ,illustration3 ,,spectrogram ,,of ,,jupiter1 ,,giving ,,the ,,length ,,of ,,its ,,day ,,by ,,the ,,tilt ,,of ,,its ,,spectral ,,lines--,v4 ,m4 ,,slipher1 ,,lowell ,,observatory4 ,this result was further borne out by a similar test made by him of ,jupiter4 ,inasmuch as the diameter of ,jupiter is twelve times that of ,venus1 while the rotation time is #i #ej4d at the equator1 the precision attained on ,venus should here have been about a minute4 ,and this is what resulted4 ,slipher found the rotation time spectrographically #i #ej1 or in accordance with the known facts1 while previous determinations with the spectroscope had somehow fallen short of it4 ,the care at ,flagstaff with which the possibility of error was sought to be excluded in this investigation of the length of ,venus' day and the concordant precision in the results are worthy of notice4 ,for it is by thus being particular and systematic that the accuracy of the determinations made there1 in other lines besides this1 has been secured4 ,in size1 ,venus of all the planets most nearly approaches the ,earth4 ,she is #gfcj miles in diameter to the ,earth's #giah4 ,her density1 too1 is but just inferior to ours4 ,and she stands next us in place1 closest in condition and constitution in the primal nebula4 ,yet in her present state she could hardly be more diverse4 ,this shows us how dangerous it is to dogmatize upon what can or cannot be1 and how enlightening beyond expectation often is prolonged and systematic study of the facts4 ,the next planet outward is our own abode4 ,it is one of which most of us think we know considerable from experience and yet about which we often reason cosmically so ill4 ,if we knew more1 we should not deem ourselves nearly so unique4 ,for we really differ from other members of our system not more than they do from one another4 ,much that appears to us fundamental is not so in fact4 ,thus many things which seem matters of course are merely accidents of size and position4 ,our very day and night upon which turn the habits of all animals and1 even in a measure1 those of plants1 are1 as we have seen1 not the possession of our nearest of cosmic kin4 ,our seasons which both vegetally and vitally mean so much are absent next door4 ,and so the list of our globe's peculiar attributes might be run through to the finding of diversity to our familiar ways at every turn4 ,but1 as we shall see later1 these differences from one planet to the next are not only not incompatible with a certain oneness of the whole1 but actually help to make the family relationship discoverable4 ,analogy alone is a dangerous guide1 but analogy crossed with diversity is of all clews the most pregnant of understanding4 ,the very fact that we can tell them apart when we see them together1 as the ,irishman remarked of two brothers he was in the habit of confusing1 points to their brotherly relation4 ,proceeding still further1 we come to ,mars at a mean distance of one hundred and forty-one million miles4 ,smaller than ourselves1 his diameter is but a little over half the ,earth's1 or forty-two hundred miles1 his mass one-ninth of ours1 and his density about seven-tenths as much4 ,here1 again1 but in a different way1 we find a planet unlike ourselves1 and we know more about him than of any body outside the ,earth and ,moon4 ,so much about him has been set forth elsewhere that it is enough to mention here that no oceans diversify his surface1 no mountains relieve it1 and but a thin air wraps it about1--an air containing water-vapor1 but so clear that the surface itself is almost never veiled from view4 ,about the satellites ,mars possesses1 ,deimos and ,phobos1 we may perhaps say a word1 as recent knowledge concerning them exemplifies the care now taken to such ascertainment and the importance of considering factors often overlooked4 ,soon after they were discovered in #ahgg1 they were measured photometrically1 with the result of giving a diameter of six miles to ,deimos and one of seven miles to ,phobos1 and these values unchallenged entered the text-books4 ,when the satellites came to be critically considered at ,flagstaff1 it was found that these determinations were markedly in error1 ,phobos being very much the larger of the two1 the actual values reaching nearer ten miles for ,deimos and thirty-six for ,phobos4 ,in getting the ,flagstaff values1 the size to the eye of the satellite was corrected for the background upon which it shone2 for the background is all-important to the brilliancy of a star4 ,in the case of a small star near a planet1 the swamping glare of the planet is something like the inverse cube of its distance away4 ,furthermore1 the ,flagstaff observations indicated how the previous error had crept in4 ,for before correction for the differing brilliancies of the field of view1 the apparent size of the satellites judged by conspicuousness was about six to seven4 ,the photometric values must have been taken just as they came out1 no correction apparently having been made for the background4 ,now the background is a fundamental factor in all photometric determinations1 a factor somewhat too important in this case to neglect1 since it affected the result #bejj per cent4 ,,chapter ,,iv ,,the ,,outer ,,planets ,beyond ,mars lies the domain of the asteroids1 a domain vast in extent1 that1 untenanted by any large planet1 stretches out to ,jupiter4 ,occupied solely by a host of little bodies agreeing only in lack of size1 even this space seems too small to contain them1 for recent research has shown some transgressing its bounds4 ,one1 ,eros1 discovered by ,de ,witt1 more than trenches on ,mars' territory1 having an orbit smaller than that of the god of war1 and may be considered perhaps the forerunner of more yet to be found between ,mars and the ,earth4 ,on the other side1 three recently detected by ,max ,wolf at ,heidelberg have periods equal to that of ,jupiter1 and in their motions appear to exemplify an interesting case of celestial mechanics pointed out theoretically by ,lagrange long before its corroboration in fact was so much as dreamt4 ,achilles1 ,patroclus1 and ,hector1 as the triad are called1 so move as always to keep their angular distance from ,jupiter unaltered in their similar circuits of the ,sun4 ,illustration3 ,,orbits ,,of ,,the ,,outer ,,planets4 ,before considering these bodies individually1 we may well look upon them en bloc1 inasmuch as one attribute of the asteroids concerns them generically rather than specifically1 and is of great interest both from a mechanical and an historical point of view4 ,for1 in fact1 it is what led to their discovery4 ,titius of ,wittenburg1 about the middle of the eighteenth century1 noticed a curious relation between the distances from the ,sun of the then known planets4 ,it consisted in a sort of regular progression1 but with one significant gap4 ,bode was so struck by the gap that he peopled it with a supposed planet1 and so brought the relation into general regard in #aggb4 ,in consequence1 it usually bears his name4 ,it is this3 if we take the geometrical series1 #c1 #f1 #ab1 #bd1 #dh1 #if and add #d to each term1 we shall represent to a fair degree of precision the distances of the several planets1 beginning with ,mercury at #d and ending with ,saturn at #ajj1 which was the outermost planet then known4 ,all the terms were represented except #bd #d1 or #bh--;a gap lying between ,mars and ,jupiter4 ,when ,uranus was discovered by ,sir ,william ,herschel in #agha and was found to be travelling at what corresponded to the next outer term #aib #d1 or #aif1 the opinion became quite general that the series represented a real law and that #bh must be occupied by a planet4 ,von ,zach actually calculated what he called its analogical elements1 and finally got up in #ahjj a company to look for it which he jocularly described as his celestial police4 ,considering that ,bode's law is not a law at all1 but a curious coincidence1 as ,gauss early showed in its lack of precision and in its failure to mark the place of ,mercury with any approach to accuracy1 and as the discovery of ,neptune amply bore out1 it was perhaps just in fate that the honor of filling the gap did not fall to any of the 8celestial police10 but to an ,italian astronomer1 ,piazzi1 at the time engaged on a new star chart4 ,an illness of ,piazzi caused it to be lost almost as soon as found4 ,in this plight an appeal was made to the remarkable ,gauss1 just starting on his career4 ,gauss undertook the problem and devised formul by which its place was predicted and the planet itself recovered4 ,it proved to fit admirably the gap4 ,but it had hardly been recovered before another planet turned up equally filling the conditions4 ,ceres1 the first1 lay at #bf4fg astronomical units from the ,sun2 ,pallas1 the second1 at #bg4gb4 ,two claimants were one too many4 ,but the inventive genius of ,olbers came to the rescue4 ,by a bold hypothesis he suggested that since two had appeared where only one was wanted1 both must originally have formed parts of a single exploded planet4 ,he predicted that others would be detected by watching the place where the explosion had occurred1 to wit3 where the orbits of ,ceres and ,pallas nearly intersected in the signs of the ,virgin and the ,whale4 ,for in the case of an explosion the various parts1 unless perturbed1 must all return in time to the scene of the catastrophe4 ,by following his precept1 two more were in fact detected in the next two years1 ,juno and ,vesta4 ,his hypothesis seemed to be confirmed4 ,no new planets were discovered1 and the old fulfilled fairly what was required of them4 ,lagrange on calculation gave it his mathematical assent4 ,nevertheless1 it was incorrect1 as events eventually showed1 though for forty years it slept in peace1 no new asteroids being found4 ,we now know that this was because the rest were all much smaller1 and for such nobody looked4 ,it was not till #ahde that ,hencke1 an ex-postmaster of ,driessen in ,prussia1 after fifteen years of search detected another1 ,astra1 of the #aath magnitude4 ,after this discoveries of them came on apace1 until now more than six hundred are known1 and their real number seems to be legion4 ,but those discovered are smaller each year on the average1 showing that the larger have already been found4 ,their orbits are such that they cannot possibly ever have all formed part of a pristine whole4 ,the idea1 not the body1 was exploded4 ,for they are now recognized as having always been much as they are to-day4 ,illustration3 ,,asteroids4 ,,major ,,axes ,,of ,,orbits4 ,they prove to be thickest at nearly the point where ,bode's law required1 the spot where ,ceres and ,pallas were found4 ,the mean of their distances is less1 being #b4fe instead of #b4h astronomical units1 probably simply because the nearer ones are easier discovered4 ,the fact that they are clustered most thickly just inside #b4h astronomical units implies that there of all points within the space between ,mars and ,jupiter a planet would have formed if it could4 ,a definite reason exists for its failure to do so--,jupiter's disturbing presence4 ,throughout this whole region ,jupiter's influence is great2 so great that his scattering effect upon the particles exceeds their own tendency to come together4 ,we see this in the arrangement of the orbits4 ,if we plot the orbits of the asteroids1 we shall be struck by the emergence of certain blanks in the ribbon representing sections of their path4 ,it is the woof of a plaid of ,jupiter's weaving4 ,the gaps are where asteroids revolving about the ,sun would have periods commensurate with his1 _/1 _/1 _/1 _/1 and the like4 ,such bodies would return after a few revolutions1 five of theirs1 for instance1 to ,jupiter's two1 into the same configurations with him at the same points of their orbits4 ,thus the same perturbation would be repeated over and over again until the asteroid's path was so changed that commensurability ceased to exist4 ,and it would be long before perturbation brought it back again4 ,thus the orbits are constantly swinging out and in1 all of them within certain limits1 but those are most disturbed which synchronize with his4 ,in this manner he has fashioned their arrangement and even prevented any large planet from forming in the gap4 ,such restrictive action is not only at work to-day in the distribution of the asteroids and in the partitions of ,saturn's ring1 but it must have operated still more in the past while the system was forming4 ,to ,professor ,milham of ,williamstown is due the brilliant suggestion that this was the force that fashioned the planetary orbits4 ,for a planet once given off from a central mass would exercise a prohibitive action upon any planet trying to form within4 ,in certain places it would not allow it to collect at all4 ,the evolution of the solar family would resemble that of some human ones in which each child brings up the next in turn4 ,so that the planetary system made itself1 as regards position1 a steadily accumulative set of prohibitions combining to leave only certain places tenantable4 ,in this manner we may perhaps be brought back to ,bode's law as representing within a certain degree of approximation a true mechanical result1 although no such exact relation as the law demands exists4 ,that a relation seemingly close to it is necessitated by the several successive inhibitions of each planet upon the next to form1 is quite possible4 ,one other general trait about their orbits is worth animadversion4 ,in spite of being eccentric and inclined1 they are all traversed in the same sense4 ,every one of the asteroids travels direct like the larger planets4 ,in this they differ from cometary paths1 which are as often retrograde as direct4 ,thus in more ways than one they hold a mid-course in regularity between the steady1 even character of the planets proper and what was for long deemed the erratic behavior of the cometary class of cosmic bodies4 ,very telling this fact will be found with regard to the genesis of the solar family1 as we shall see later4 ,with regard now to their more individual characteristics1 the asteroids may be said to agree in one point--their diversity1 not only to all the larger members of the solar family1 but to one another4 ,for they travel in orbits ranging in ellipticity all the way from such as nearly approach circles to ellipses of cometary eccentricity4 ,they voyage1 too1 without regard to the dynamical plane of the system1 or1 what is close to it1 the ecliptic2 departing from the general level often #cj and1 in one instance1 that of the little planet dubbed ,w4 ,d41 by as much as #dh4 ,this eccentricity and inclination put them in a class by themselves4 ,it is associated and unquestionably connected mechanically with another trait which likewise distinguishes them from the planets more particularly called--their diminutive size4 ,only four--,vesta1 ,ceres1 ,pallas1 and ,juno--out of the six hundred odd now known exceed a hundred miles in diameter1 and the greater number are hardly over ten or twenty miles across4 ,very tiny worlds indeed they would seem1 could we get near enough to them to discern their forms and features4 ,curiously enough1 reasoning on certain light changes they exhibit has enabled us to divine something of their shapes1 and even character4 ,thus it was soon perceived that ,eros fluctuated in the light he sent us1 being at times much brighter than at others4 ,in ,february and ,march1 #aija1 the changes were such that their maximum exceeded three times their minimum two hours and a half later4 ,then in ,may the variation vanished4 ,more than one explanation has been put forward1 but the best so far1 because the most simple1 is that the body is not a sphere but a jagged mass1 a mountain alone in space1 and that as it turns upon its axis first one corner and then another is presented to our view or throws a shade upon its neighbor4 ,when the pole directly faces us1 no great change occurs1 especially if it also nearly faces the ,sun4 ,yet even this fails to explain all its vagaries4 ,eros is not alone in thus exhibiting variation4 ,sirona1 ,hertha1 and ,tercidina have also shown periodic variability1 and it is suspected in others4 ,indeed1 it would be surprising did they not show change4 ,for they are too small to have drawn their contents into symmetry1 and so remain as they were when launched in space4 ,mammoth meteorites they undoubtedly are4 ,with the asteroids we leave the inner half of the ,sun's retinue and pass to the outer4 ,indeed1 the asteroids not only mark in place the transition bound between the two1 but stamp it such mechanically4 ,in their own persons they witness that no large body was here allowed to form4 ,the culmination of coalition was reached in ,jupiter1 and that very acme of accretion prevented through a long distance any other4 ,illustration3 ,,drawing ,,of ,,jupiter ,,by ,,dr4 ,,lowell4 ,,april #ab1 #aijg4 ,in bulk1 the major planets compared with the inner or terrestrial ones form a class apart2 and among the major ,jupiter is by all odds first4 ,his mass is #cah times the ,earth's and his volume nearly #adjj times hers4 ,from this it appears that his density is very much less4 ,indeed1 his substance is only fractionally denser than water4 ,this and its tremendous spin1 carrying a point at its equator two hundred and eighty thousand miles round in less than ten hours1 flatten it to a very marked oval with an ellipticity of #a_/ae4e4 ,not the least beautiful of the revelations of astronomy are the geometrical shapes of the heavenly bodies1 proceeding from nearly perfect spheres like the ,sun or ,moon to marked spheroids like ,jupiter or ,saturn4 ,so enormous are the masses and the forces concerned that the forms assumed under them are mechanically regular4 ,they are the visible expression of gravitation1 and so delight the brain while they satisfy the eye4 ,it is to appreciation of the detail visible on ,jupiter's disk that modern advance in the study of the planet is indebted4 ,examination has shown its features to be of great interest4 ,to ,mr4 ,stanley ,williams of ,brighton1 ,england1 much of our knowledge is due1 and ,mr4 ,scriven ,bolton has also made some interesting contributions4 ,the big print of the subject1 read long ago1 is that the planet's disk is noticeably banded by dark belts4 ,two characteristics of these belts are important4 ,one is that they exhibit a regular secular progression with the lapse of years1 the south tropical belt being broader and more salient for many years in succession1 and then gradually fading out while the northern one increases in prominence4 ,it has been suspected that the rhythm of their change is connected with that of sun spots4 ,the second is that the belts do not preserve in their several features the same relation in longitude toward one another4 ,they all rotate1 but at different speeds4 ,there could be no better proof that ,jupiter is no solid1 but a seething mass of heavy vapors boiling like a caldron4 ,tempered by distance we can form but a faint idea of the turmoil there going on4 ,further indication of it is furnished by its glow4 ,for all the dark belts are a beautiful cherry red1 a tint extending even to the darkish hoods over the planet's caps4 ,this hue comes out well in good seeing1 and best1 as with all planetary markings1 in twilight1 not at night1 because the excessive brightness of the disk is then taken off1 preventing the colors from being swamped4 ,this brings us to the planet's albedo1 which ,mller at ,potsdam has found to be #ge per cent4 ,now the interest attaching to this determination is twofold1 that it bespeaks cloud and that it seems to imply something else4 ,the albedo of cloud is #gb per cent of absolute whiteness4 ,what looks like cloud1 then1 is such1 on that distant disk4 ,but ,jupiter surpasses cloud in lustre1 since his albedo exceeds #gb per cent4 ,yet a large part of his surface is strikingly darker than that4 ,the inference from this is that he shines by intrinsic light1 in part at least4 ,the fact may not be stated dogmatically1 as there is no astronomic determination so uncertain as this one of determining albedoes1 and therefore ,herr ,mller's results must be accepted with every reserve1 but they suggest that ,jupiter is still a semi-sun1 to be recognized as such by light as well as heat1 though his self-luminosity1 if it exist at all1 can hardly exceed a dull red glow4 ,illustration3 ,i4 ,,jupiter ,,and ,,its ,,wisps4--,a ,,drawing ,,by ,,dr4 ,,lowell1 ,,april #aa1 #aijg4 ,illustration3 ,,ii4 ,,jupiter ,,and ,,its ,,wisps4--,a ,,drawing ,,by ,,dr4 ,,lowell1 ,,april #aa1 #aijg4 ,illustration3 ,s4 ,n4 ,,photograph ,,of ,,jupiter1 #aiji4 ,p4 ,l4 ,a modern detection on ,jupiter's disk has been that of wisps or lacings across the bright equatorial belt1 a detail of importance due to ,mr4 ,scriven ,bolton4 ,requested to look for them1 the observatory at ,flagstaff was not long in corroborating this interesting phenomenon4 ,the peculiarity about them pointed out by ,mr4 ,bolton is that they traverse the belt at an angle of about #de to the vertical1 proceeding from caret-shaped dark spots projecting into the bright belt from the dark ones on either side4 ,they exist all round the equator and are found indifferently dextrous or sinister--sometimes vertical4 ,for there are others that go straight across4 ,nor are they confined to the bright equatorial belt1 but are to be seen traversing all of the bright belts both north or south up to the polar hoods4 ,from its sombreness it seems that we are here regarding a phenomenon in the negative2 remarking it by what it has left behind1 not by what it has accomplished4 ,for the wisps are not wisps of cloud1 since they are dark1 not light1 but gaps strung out in the clouds themselves4 ,recently photographs of ,jupiter have been secured at ,flagstaff1 by the new methods there of planetary photography1 showing a surprising amount of detail4 ,the wisps come out with certainty1 and the white spots1 which are such a curious feature of the disk1 have also left their impress on the plate4 ,not the least of the services thus rendered by the camera is the accurate positioning of the belts made possible by it4 ,micrometric measures are all very well when nothing better is attainable1 but any one who has made such upon a planet's disk swinging like a lantern in the field of view under a variety of causes instrumental and optical1 knows how encumbered they inevitably are with error4 ,to have the disk caught and fixed on a plate where it may be measured at leisure and as often as one likes1 is a distinct advance toward fundamental accuracy4 ,measures thus effected upon the ,jupiter images of #aiji proved the bright equatorial belt to lie exactly upon the planet's equator when allowance was made for the tilt of the planet's axis toward the ,earth4 ,this showed that the aspect of the planet toward the ,sun had no effect upon the position of the belt4 ,jupiter's cloud formation1 therefore1 is not dependent1 as all ours are1 upon the solar heat4 ,a like indifference to solar action is exhibited in the utter obliviousness of the belts to day or night4 ,to them darkness and light are nugatory alike4 ,they reappear round the sunrise edge of the disk just as they left it when they sank from sight round the sunset one1 and they march across its sunlit face without so much as a flicker on their features4 ,yet this seeming immobility from moment to moment takes place in what is really a seething furnace1 the fiery glow of which we catch below the vast ebullition of cloud in the cherry hue of its darker portions4 ,distance has merged the turmoil into the semblance of quiescence and left only its larger secular changes to show4 ,even so the ,colorado ,river from the brink of the ,grand ,caon is seen apparently at rest1 the billows of its rapids so stereotyped to stability one takes the rippled sand bank for the river and the billows of the river for the ripple marks of its banks4 ,at twice the distance of ,jupiter we cross the orbit of ,saturn4 ,here the ringed planet1 with an annual sweep of twenty-nine and a half of our years1 pursues his majestic circuit of the ,sun4 ,diademed with three or more circlets of light and diamonded by ten satellites1 he rivals in his cortge that of his own lord4 ,in some ways his surpasses the ,sun's4 ,for certainly his retinue is the more spectacular of the two2 the more so that it is much of it fairly comprised within a single glance4 ,very impressive ,saturn is as1 attended thus1 he sails into the field of view4 ,illustration3 ,,saturn--,a ,,drawing ,,by ,,dr4 ,,lowell1 ,,showing ,,agglomerations4 ,in our survey we may best begin with his globe4 ,if ,jupiter's compression is striking1 ,saturn's is positively startling when well displayed4 ,this happens but at rare intervals4 ,as the plane of his equator is almost exactly that of the rings1 the flattening is conspicuous only on those occasions when the rings disappear because their plane passes through the line of sight4 ,seen at such times the effect of the discrowned orb is so strange as to suggest delusion4 ,this occurred two years ago in #aijg1 and when the planet was picked up by its position and entered the field unheralded by its distinctive appendage1 it was almost impossible to believe there had not been some mistake and a caricatured ,jupiter had taken its place4 ,for the flattening outdoes that of ,jupiter as #c to #b1 being of the equatorial diameter4 ,such a bulging almost suggests disruption and is due to the extreme lightness of the planet's substance1 which is actually only #j4gb of that of water4 ,like ,jupiter1 the disk exhibits belts1 though very much fainter1 and1 like his1 these are of a cherry red4 ,as the planet's albedo is even greater1 #j4gh of absolute whiteness1 as deduced from ,h4 ,struve's measures of the diameter1 the same suspicion of shining1 at least in part1 from inherent light1 applies equally to him4 ,but it is practically certain that in neither case does this light equal that of the planet's clouds1 or add anything to them4 ,both planets are red-hot1 not white-hot4 ,the determination of the albedo depends upon that of the diameter1 and an increase in the latter would lower the albedo to that of cloud4 ,his most unique possession are his rings4 ,broad1 yet tenuous1 they weigh next to nothing1 being1 as ,struve has dubbed them1 8,immaterial light40 ,nevertheless1 it is not their lightness but their make-up that prevents from lying uneasy the head that wears this crown4 ,the mechanical marvel was not appreciated by early astronomers1 who took it for granted that they were what they seemed1 solid1 flat rings1 all of a piece4 ,even ,laplace considered it sufficient to divide them up concentrically to insure stability4 ,to ,edouard ,roche of ,montpellier1 as retiringly modest as he was penetratingly profound1 is due the mathematical detection that to subsist they must be composed of discrete particles1--brickbats1 ,clerk ,maxwell called them1 when1 later1 unaware of ,roche's work1 he proved independently the same thing in his essay on ,saturn's rings4 ,peirce1 too1 in ignorance of ,roche1 had half taken the same step a little before1 showing that they must at least be fluid4 ,then in #ahie ,keeler ingeniously photographed the spectrum of both ball and rings to the revealing of velocities in the line of sight of the different portions of the spectrum exactly agreeing with the values mechanics demanded4 ,the rings have usually been considered to be flat4 ,at the time of their disappearance1 however1 knots have been seen upon them4 ,it is as if their filament had suddenly been strung with beads4 ,at the last occurrence of the sort in #aijg1 these beads were particularly well seen at several observatories1 and were critically studied at ,flagstaff4 ,in connection with a new phenomenon detected there1 that of a dark core in the shadow the rings threw across the planet's face1 an explanation suggested itself to account for both them and it3 to wit1 that the rings were not really flat1 but tores2 rings1 that is1 like an anchor ring1 any cross-section of which would be of the nature of an oval flattened on its inner side4 ,the cogency of the explanation consisted in its solution not only of the appearances but of the cause competent to bring those appearances about4 ,for measurement showed that the knots were permanent in position1 which1 since the ring revolved1 indicated that they extended all round it in spite of their not seeming to do so1 and that their distances from ,saturn were just what this cause should produce4 ,the action observed was a corollary from the important principle of commensurability of orbital period4 ,as we saw in the case of the asteroids1 if two bodies be travelling round a third and their respective periods of revolution be commensurate1 they will constantly meet one another in such a manner that great perturbation will ensue and the bodies be thrown out of commensurability of period4 ,what has happened to the asteroids has likewise occurred in ,saturn's rings4 ,the disturber in this case has been1 not ,jupiter1 as with them1 but one or other of ,saturn's own satellites4 ,for when we calculate the problem1 we find that ,mimas1 ,enceladus1 and ,tethys have periods exactly commensurate with the divisions of the rings2 in other words1 these three inner satellites1 whose action because of proximity is the greatest1 have fashioned the rings into the three parts we know1 called ,a1 the outermost2 ,b1 the middle one2 and ,c1 the crpe ring1 nearest to the body of the planet4 ,mimas has been the chief actor1 though helped by the two others1 while ,enceladus has further subdivided ring ,a by what is known as ,encke's division4 ,such has been the chief action of the satellites on the rings3 it has made them into the system we see4 ,but if we consider the matter1 we shall realize that a secondary result must have ensued--when we remember that the particles composing the rings must be very crowded for the rings to show as bright as they do1 and also that1 though relatively thin1 the rings are nevertheless some eighty miles through4 ,now it is evident that any disturbance in so closely packed a system of small bodies as that constituting ,saturn's rings must result in collisions between the bodies concerned4 ,particles pulled out or in must come in contact with others pursuing their own paths1 and as at each collision some energy is lost by the blow1 a general falling in toward the planet results4 ,at the same time1 as the blow will not usually be exactly in the plane in which either particle was previously moving1 both will be thrown more or less out of the general plane of their fellows1 and the ring at that point1 even if originally flat1 will not remain so4 ,for the ring1 though very narrow relatively1 has a real thickness1 quite sufficient for slantwise collision1 if the bodies impinge4 ,illustration3 ,saturn's ,rings4 ,november #aijg4 ,now the knots or beads on the rings appeared exactly inside the points where the satellites' disturbing action is greatest1 or1 in other words1 in precisely their theoretic place4 ,we can hardly doubt that such1 then1 was their origin4#i #i ,paper by the writer in the ,phil4 ,mag41 ,april1 #aijh4 ,the result must be gradually to force the particles as a rule nearer the planet1 until they fall upon its surface1 while a few are forced out to where they may coalesce into a satellite1--a result foreseen long ago by ,maxwell4 ,it is this process which in the knots we are actually witnessing take place1 and which1 like the corona about the eclipsed ,sun1 only comes out to view when the obliterating brightness of the main body of the rings is withdrawn by their edgewise presentation4 ,the reason the out-of-plane particles are most numerous just inside the point of disturbance is not only that there the action throwing them out is most violent1 but that all the time a levelling action quite apart from disturbance is all the time tending to reduce them again to one plane1 as we shall see further on when we come to the mechanical forces at work4 ,thus the tore is most pronounced on its outer edge1 and falls to a uniform level at its inner boundary4 ,the effect is somewhat as represented in the adjoining cut1 in which the vertical scale is greatly magnified3-- ,illustration3 ,,the ,,tores ,,of ,,saturn4 ,not drawn to scale4 ,with ,saturn ended the bounds of the solar system as known to the civilized world until #agha4 ,on ,march #ac of that year ,sir ,william ,herschel in one of his telescopic voyages through space came upon a strange object which he at once saw was not a star1 because of its very perceptible round disk1 and which he therefore took for a peculiar kind of comet4 ,nearly a year rolled by before ,lexell showed by calculation of its motion that it was no comet1 but undoubtedly a new planet beyond ,saturn travelling at almost twice that body's mean distance from the ,sun4 ,by reckoning backward1 it was found to have been seen and mapped several times as a star1--no less than twelve times by ,lemonnier alone1--and yet its planetary character had slipped through his fingers4 ,it can even be seen with the naked eye as a star of the #fth magnitude1 and its course is said to have been watched by savage tribes in ,polynesia long before ,sir ,william ,herschel discovered it4 ,its greenish blue disk indicates that it is about thirty-two thousand miles in diameter1 and its mass that its density is about #j4bb of the ,earth's or1 like ,jupiter's1 somewhat greater than water4 ,of its surface we probably see nothing4 ,indeed1 it is very doubtful if it have any surface properly so called1 being but a ball of vapors4 ,its flattening1 _/ according to ,schiaparelli1 which is probably the best determination1 agrees with the density given above1 indicating its substance to be very light4 ,belts have faintly been descried traversing its disk after the analogy of ,jupiter and ,saturn4 ,these would be much better known than they are but for the great tilt of the planet's axis to the ecliptic1 so that during a part of its immense annual sweep its poles are pointed nearly at the ,earth1 and its tropical features1 the places where the belts lie1 are wholly hidden or greatly foreshortened from our point of view4 ,as the planet's year is eighty-four of our years long1 it is only at intervals of forty odd years that the disk is well enough displayed to bring the belts into observable position4 ,the planet is attended by four satellites1--,ariel1 ,umbriel1 ,titania1 and ,oberon1--a midsummer night's dream to a watcher of the skies4 ,they travel in a plane inclined #ih to the ecliptic1 so that their motion is nearly up and down to that plane and even a little backward4 ,whether their plane is also the equatorial plane of the planet1 we do not know for certain4 ,the observations as yet are not conclusive one way or the other4 ,if the two planes should turn out not to coincide1 it will open up some new fields in celestial mechanics4 ,the belts have been thought to indicate divergence1 but the most recent observations by ,perrotin on them minimize this4 ,they suggest1 too1 a rotation period of about ten hours1 which is what we should expect4 ,its albedo1 or intrinsic brightness1 is1 according to ,mller1 #j4gc1 or almost exactly that of cloud4 ,this tallies with the lack of pronouncement of the belts and is another argument against the reality of the recent diametral measurements1 as all ,mller's values are got by dividing the amount of light received by the amount of surface sending it4 ,if the diameter were much less than thirty-two thousand miles1 the resulting albedo would become impossibly high4 ,if we know but little about the actual surface of ,uranus1 we know now a good deal about its atmosphere4 ,and this partly because atmosphere is almost all that it is4 ,the satellites are the only solid thing in the system4 ,if we needed a telltale that the solar system had evolved1 the gaseous constitution of its primaries and the condensed state of their attendants would sufficiently inform us4 ,probably all the major planets are nothing but gas4 ,it has been debated whether ,jupiter be almost all vapor with a solid kernel beneath1 or vapor entirely4 ,that he grows denser toward the core is doubtless the case1 but that he is anywhere other than a gaseous fluid is very unlikely4 ,for if he had really begun to condense1 he must have contracted to far within his present dimensions4 ,the same is true of ,uranus4 ,the surprising thing about ,uranus is the enormous extent of his atmosphere4 ,the earliest spectroscopists perceived this1 but the more spectroscopy advances1 the greater and more interesting it proves to be4 ,by pushing inquiry into the red end of the spectrum1 hitherto a terra incognita1 ,dr4 ,slipher has uncovered a mass of as yet unexplained revelation4 ,of these remarkable spectrograms we shall speak later4 ,here it is sufficient to say that so great is the absorption in the red that only the blue and green in anything like their entirety get through2 which accounts for the well-known sea-green look of the planet4 ,furthermore1 the spectroscope shows that this atmosphere1 or the great bulk of it1 must lie above what we see as the contour of the disk4 ,for the spectroscope is as incapable of seeing through opacity as the eye1 though it distances the eye in seeing the invisible4 ,it is not what is condensed into cloud1 but what is not1 of which it reveals the presence4 ,we are thus made aware of a great shell of air enveloping the planet4 ,in ,uranus1 then1 we see a body in an early amorphous state1 before the solid1 the liquid1 and the gaseous conditions of matter have become differentiate and settled each into distinctive place4 ,without even an embryo core its substance passes from viscosity to cloud4 ,neptune has proved a planet of surprises4 ,though its orbital revolution is performed direct1 its rotation apparently takes place backward1 in a plane tilted about #ce to its orbital course4 ,its satellite certainly travels in this retrograde manner4 ,then its appearance is unexpectedly bright1 while its spectrum shows bands which as yet1 for the most part1 defy explanation1 though they state positively the vast amount of its atmosphere and its very peculiar constitution4 ,but first and not least of its surprises was its discovery1--a set of surprises1 in fact4 ,for after owing recognition to one of the most brilliant mathematical triumphs1 it turned out not to be the planet expected4 8,neptune is much nearer the ,sun than it ought to be10 is the authoritative way in which a popular historian puts the intruding planet in its place4 ,for the planet failed to justify theory by not fulfilling ,bode's law1 which ,leverrier and ,adams1 in pointing out the disturber of ,uranus1 assumed 8as they could do no otherwise40 ,though not strictly correct1 as not only did both geometers do otherwise1 but neither did otherwise enough1 the quotation may serve to bring ,bode's law into court1 as it was at the bottom of one of the strangest and most generally misunderstood chapters in celestial mechanics4 ,very soon after ,uranus was recognized as a planet1 approximate ephemerides of its motion resulted in showing that it had several times previously been recorded as a fixed star4 ,bode himself discovered the first of these records1 one by ,mayer in #agef1 and ,bode and others found another made by ,flamstead in #afij4 ,these observations enabled an elliptic orbit to be calculated which satisfied them all4 ,subsequently others were detected4 ,lemonnier discovered that he had himself not discovered it several times1 cataloguing it as a fixed star4 ,flamstead was spared a like mortification by being dead4 ,for both these observers had recorded it two or more nights running1 from which it would seem almost incredible not to have suspected its character from its change of place4 ,sixteen of these pre-discovery observations were found 7there are now nineteen known71 which with those made upon it since gave a series running back a hundred and thirty years1 when ,alexis ,bouvard prepared his tables of the planet1 the best up to that time1 published in #ahba4 ,in doing so1 however1 he stated that he had been unable to find any orbit which would satisfy both the new and the old observations4 ,he therefore rejected the old as untrustworthy1 forgetting that they had been satisfied thirty years before1 and based his tables solely on the new1 leaving it to posterity1 he said1 to decide whether the old observations were faulty or whether some unknown influence had acted on the planet4 ,he had hardly made this invidious distinction against the accuracy of the ancient observers when his own tables began to be out and grew seriously more so1 so that within eleven years they quite failed to represent the planet4 ,the discrepancies between theory and observation attracted the attention of the astronomic world1 and the idea of another planet began to be in the air4 ,the great ,bessel was the first to state definitely his conviction in a popular lecture at ,knigsberg in #ahdj1 and thereupon encouraged his talented assistant ,flemming to begin reductions looking to its locating4 ,unfortunately1 in the midst of his labors ,flemming died1 and shortly after ,bessel himself1 who had taken up the matter after ,flemming's death4 ,somewhat later ,arago1 then head of the ,paris observatory1 who had also been impressed with the existence of such a planet1 requested one of his assistants1 a remarkable young mathematician named ,leverrier1 to undertake its investigation4 ,leverrier1 who had already evidenced his marked ability in celestial mechanics1 proceeded to grapple with the problem in the most thorough manner4 ,he began by looking into the perturbations of ,uranus by ,jupiter and ,saturn4 ,he started with ,bouvard's work1 with the result of finding it very much the reverse of good4 ,the farther he went1 the more errors he found1 until he was obliged to cast it aside entirely and recompute these perturbations himself4 ,the catalogue of ,bouvard's errors he gave must have been an eye-opener generally1 and it speaks for the ability and precision with which ,leverrier conducted his investigation that neither ,airy1 ,bessel1 nor ,adams had detected these errors1 with the exception of one term noticed by ,bessel and subsequently by ,adams4#aj ,the result of this recalculation of his was to show the more clearly that the irregularities in the motion of ,uranus could not be explained except by the existence of another planet exterior to him4 ,he next set himself to locate this body4 ,influenced by ,bode's law1 he began by assuming it to lie at twice ,uranus' distance from the ,sun1 and1 expressing the observed discrepancies in longitude in equations1 comprising the perturbations and possible errors in the elements of ,uranus1 proceeded to solve them4 ,he could get no rational solution4 ,he then gave the distance and the extreme observations a certain elasticity1 and by this means was able to find a position for the disturber which sufficiently satisfied the conditions of the problem4 ,leverrier's first memoir on the subject was presented to the ,french ,academy on ,november #aj1 #ahde1 that giving the place of the disturbing planet on ,june #a1 #ahdf4 ,there is no evidence that the slightest search in consequence was made by anybody1 with the possible exception of the ,naval ,observatory at ,washington4 ,on ,august #ca he presented his third paper1 giving an orbit1 mass1 and more precise place for the unknown4 ,still no search followed4 ,taking advantage of the acknowledging of a memoir1 ,leverrier1 in ,september1 wrote to ,dr4 ,galle in ,berlin asking him to look for the planet4 ,the letter reached ,galle on the #bc;d1 and that very night he found a planet showing a disk just as ,leverrier had foretold1 and within #ee of its predicted place4 #aj ,adams1 8,explanation of the ,motion of ,uranus10 #ahdf4 ,the planet had scarcely been found when1 on ,october #a1 a letter from ,sir ,john ,herschel appeared in the ,london ,athenum announcing that a young ,cambridge graduate1 ,mr4 ,j4 ,c4 ,adams1 had been engaged on the same investigation as ,leverrier1 and with similar results4 ,this was the first public announcement of ,mr4 ,adams' labors4 ,it then appeared that he had started as early as #ahdc1 and had communicated his results to ,airy in ,october1 #ahde1 a year before4 ,into the sad set of circumstances which prevented the brilliant young mathematician from reaping the fruit of what might have been his discovery1 we need not go4 ,it reflected no credit on any one concerned except ,adams1 who throughout his life maintained a dignified silence4 ,suffice it to say that ,adams had found a place for the unknown within a few degrees of ,leverrier's2 that he had communicated these results to ,airy2 that ,airy had not considered them significant until ,leverrier had published an almost identical place2 that then ,challis1 the head of the ,cambridge ,observatory1 had set to work to search for the planet but so routinely that he had actually mapped it several times without finding that he had done so1 when word arrived of its discovery by ,galle4 ,but now came an even more interesting chapter in this whole strange story4 ,mr4 ,walker at ,washington and ,dr4 ,petersen of ,altona independently came to the conclusion from a provisional circular orbit for the newcomer that ,lalande had catalogued in the vicinity of its path4 ,they therefore set to work to find out if any ,lalande stars were missing4 ,dr4 ,petersen compared a chart directly with the heavens to the finding a star absent1 which his calculations showed was about where ,neptune should have been at the time4 ,walker found that ,lalande could only have swept in the neighborhood of ,neptune on the #hth and #ajth of ,may1 #agie4 ,by assuming different eccentricities for ,neptune's orbit under two hypotheses for the place of its perihelion1 he found a star catalogued on the latter date which sufficiently satisfied his computations4 ,he predicted that on searching the sky this star would be found missing4 ,on the next fine evening ,professor ,hubbard looked for it1 and the star was gone4 ,it had been ,neptune4#aa #aa ,proc4 ,amer4 ,acad41 ,vol4 ,i1 p4 #fd4 ,this discovery enabled elliptic elements to be computed for it1 when the surprising fact appeared that it was not moving in anything approaching the orbit either ,leverrier or ,adams had assigned4 ,instead of a mean distance of #cf astronomical units or more1 the stranger was only at #cj4 ,the result so disconcerted ,leverrier that he declared that 8the small eccentricity which appeared to result from ,mr4 ,walker's computations would be incompatible with the nature of the perturbations of the planet ,herschel10 as he called ,uranus4 ,in other words1 he expressly denied that ,neptune was his planet4 ,for the newcomer proceeded to follow the path ,walker had computed4 ,this was strikingly confirmed by ,mauvais' discovering that ,lalande had observed the star on the #hth of ,may as well as on the #ajth1 but because the two places did not agree1 he had rejected the first observation1 and marked the second as doubtful1 thus carefully avoiding a discovery that actually knocked at his door4 ,meanwhile ,peirce had made a remarkable contribution to the whole subject4 ,in a series of profound papers presented to the ,american ,academy1 he went into the matter more generally than either of the discoverers1 to the startling conclusion 8that the planet ,neptune is not the planet to which geometrical analysis had directed the telescope1 and that its discovery by ,galle must be regarded as a happy accident40#ab ,he proved this first by showing that ,leverrier's two fundamental propositions1-- #a4 ,that the disturber's mean distance must be between #ce and #cg4i astronomical units2 #b4 ,that its mean longitude for ,january #a1 #ahjj1 must have been between #bdc and #beb1-- were incompatible with ,neptune4 ,either alone might be reconciled with the observations1 but not both4 #ab ,proc4 ,amer4 ,acad41 ,vol4 ,i1 p4 #fe et seq4 ,in justification of his assertion that the discovery was a happy accident1 he showed that three solutions of the problem ,leverrier had set himself were possible1 all equally complete and decidedly different from each other1 the positions of the supposed planet being #abj apart4 ,had ,leverrier and ,adams fallen upon either of the other two1 ,neptune would not have been discovered4#ac ,he next showed that at #ce4c astronomical units1 an important change takes place in the character of the perturbations because of the commensurability of period of a planet revolving there with that of ,uranus4 ,in consequence of which1 a planet inside of this limit might equally account for the observed perturbations with the one outside of it supposed by ,leverrier4 ,this ,neptune actually did4 ,from not considering wide enough limits1 ,leverrier had found one solution1 ,neptune fulfilled the other4#ad ,and ,bode's law was responsible for this4 ,had ,bode's law not been taken originally as basis for the disturber's distance1 those two great geometers1 ,leverrier and ,adams1 might have looked inside4 #ac ,proc4 ,amer4 ,acad41 ,vol4 ,i1 p4 #add4 #ad ,proc4 ,amer4 ,acad41 ,vol4 ,i1 p4 #ccb4 ,this more general solution1 as ,peirce was careful to state1 does not detract from the honor due either to ,leverrier or to ,adams4 ,their masterly calculations1 the difficulty of which no one who has not had some experience of the subject can appreciate1 remain as an imperishable monument to both1 as does also ,peirce's to him4 ,,chapter ,v ,,formation ,,of ,,planets ,in our first two chapters we saw what sign-posts in the sky there are pointing to the course evolution of a solar system probably follows1 and secondly1 what evidence there is that our system took this road4 ,we now come to a question not so easy to precise1--the actual details of the journey4 ,it is always difficult to descend from a glittering panoramic survey to particular path-finding4 ,the obstacles loom so much larger on a near approach4 ,most men shy at decisions and shun self-committal to any positive course1 but when it comes to constructing a cosmogony1 few at all qualified hesitate to frame one if the old does not suit4 ,the safety in so doing lies in the fact that nothing in particular happens if it refuses to work4 ,its absurdity is promptly shown up1 it is true1 by some one else4 ,for there is almost as good a trade in exposing cosmogonies as in constructing them4 ,but no special opprobrium attaches to failure1 because everybody has failed1 from ,laplace down1 or up1 as you are pleased to consider it4 ,besides it is really not so easy to do1 as one is tempted to believe before his book is published4 ,then only does the difficulty dawn1 with a speed and clarity inversely proportional to the previous relation of the critic to the author4 ,for the author himself is apt to be blind4 ,with the fatal fondness of a parent for his offspring it is rare for the defects to be so glaringly apparent to their perpetrator4 ,at the worst he considers them venial faults which can be glossed away4 ,attacking the subject in this judicial spirit1 the reader can hardly expect me to satisfy him with a cosmogony entirely home-made1 but at best to pursue a happy middle course between creator and critic1 advocating only such portions as happen to be my own1 while sternly exposing the mistakes of others4 ,in undertaking the hazardous climb toward the origin of things two qualities are necessary in the explorer3 a quick eye for possibilities and a steady head in testing them4 ,without the discernment to perceive relations no ascent to first principles is possible2 and without the support of quantitative criterion1 one is in danger of becoming giddy from one's own imagination4 ,congruities must first hint at a path2 physical laws then determine its feasibility4 ,an eye for congruities is the first essential4 ,for congruity alone accuses an underlying law4 ,it is the analogic that with logic leads to great generalizations4 ,certain concords of the sort in the motions of the planets were what suggested to ,laplace his system of the world4 ,with the uncommon sense of a mathematician he perceived that such accordances were not necessitated by the law of gravitation1 and on the other hand1 could not be due to chance4 ,the laws of probability showed millions to one against it4 ,one of these happy harmonies was that all the large planets revolved about the ,sun in substantially the same plane2 another that they all travelled in the same sense 7direction74 ,had they been unrelated bodies at the start1 such agreement in motion was mathematically impossible4 ,their present consensus implied a common origin for all4 ,in other words1 the solar system must have grown to be what it is1 not started so4 ,this basic fact we may consider certain4 ,but from it we would fain go on to find out how it evolved4 ,to do so the same process must be followed4 ,considering1 then1 our solar system from this point of view1 one cannot but be struck by some further congruities it presents4 ,these are not quite those that inspired ,laplace1 because of discoveries since1 and demand in consequence a theory different from his4 ,the out about constructing a theory is that fresh facts will come along and knock for admission after the door is shut4 ,they prove irreconcilables because they were not consulted in advance4 ,the consequence is that since ,laplace's time new relations have come to light1 and some supposed concords have had to be given up2 so that were he alive to-day he would himself have formulated some other scheme4 ,two1 however1 are still as true3 that the planets all revolve in the same plane and in the same sense1 and that sense that of the ,sun's rotation4 ,but so general a congruity as this points only to an original common moment of momentum and is equally explicable however that motion was brought about4 ,it seems quite compatible with an original shock4 ,to say that it was caused by a disruption is simply to go one step farther back than ,laplace4 ,if1 then1 such a catastrophe did occur as the meteorites aver1 we may perhaps draw some interesting inferences about it from the present state of the system4 ,in a very close approach such as we must suppose for the disruption1 one within ,roches' limit of #b4e diameters1 the stranger1 supposing him of equal size1 would sweep from one side of the former ,sun to the other in about two hours1 and the brunt of the disrupting pull occur within that time4 ,that the former ,sun was rotating slowly seems established by the time1 twenty-eight days1 it now takes to go round4 ,in which case the orbits of the masses which were to form the planets would all lie in about the same plane1--the plane of the tramp's approach4 ,if there were exceptions1 they should be found in the innermost4 ,for such should partake most largely of the ,sun's own original rotation and travel therefore most nearly in its plane4 ,and as a fact ,mercury1 the ,benjamin1 does differ from the others by revolving in a plane inclined some #g to their mean1 agreeing in this with the ,sun's own rotation1 with whose plane it was probably originally coincident 7digression from it now being due to secular retrogression of the planets' nodes7 see ,,note #d4 ,from the relations which advance has left unchanged we pass to those phenomena which seemed to present congruities in ,laplace's day1 but which have since proved void owing to subsequent detection of exceptions4 ,time prevents my making the catalogue complete1 but the reader shall be shown enough to satisfy him of the problem's complexity and to whet his desire for further research--on the part1 preferably1 of others4 ,illustration3 ,,chart ,,showing ,,increasing ,,tilts ,,of ,,the ,,major ,,planets4 ,first comes1 then1 the rotations of the planets upon their axes1 which ,laplace supposed to be all in the same direction1 counter to the hands of a clock2 for the heavens mark time oppositely from us4 ,all those within and including ,saturn1 the only ones he knew1 turn1 indeed1 in the same sense that they travel round the ,sun4 ,but ,uranus departs from that direction by a right angle1 wallowing rather than spinning in his orbit2 while ,neptune goes still farther in idiosyncratic departure and actually turns in the opposite direction4 ,here1 then1 ,laplace's congruity breaks down1 but in its place a little attention will show that a new one has arisen4 ,for ,saturn's tilt is #bg and ,jupiter's #c1 so that with the major planets there is revealed a systematic righting of the planetary axes from inversion through perpendicularity to directness as one proceeds inward toward the ,sun4 ,another congruity supposed to exist a century ago was the exemplary agreement of all the satellites to follow in their planetary circuits the pattern set them by their primaries round the ,sun4 ,but as man has penetrated farther into space and photographic plates have come to be employed1 satellites have been revealed which depart from this orderly arrangement4 ,this is the case with the ninth1 the outermost1 satellite of ,saturn and with the eighth1 the outermost1 of ,jupiter4 ,but1 as before1 the breaking down of one congruity seems but the establishing of another4 ,it appears that only the most distant satellites are permitted such unconformity of demeanor4 ,for departure from the supposed orthodoxy occurs in both instances where the distance is most1 and does not occur in the case of all the other satellites found since ,laplace's day1 eleven in number1 nearer their planets4 ,a third congruity formerly believed in has suffered a like fate2 to wit1 that satellites always moved in or near the equatorial plane of their primary4 ,all those first discovered did2 the four large ones of ,jupiter1 the main ones of ,saturn1 and probably those of ,uranus and ,neptune4 ,even the satellites of ,mars conformed4 ,iapetus alone seemed to make exception1 and that by a glossable amount4 ,but this orderliness1 too1 has been disposed of1 only1 like the others1 to experience a resurrection in a different form4 ,illustration ,on examining more precisely the inclinations of these orbits some years ago1 an interesting relation between them and the distances of the satellites from their primaries forced itself on my notice4 ,the tilt increased as the distance grew4 ,the only exceptions were very tiny bodies occupying a sort of asteroidal relation to the rest4 ,a diagram will make this clear4 ,the kernel of it dates from the lectures then delivered before the ,massachusetts ,institute of ,technology in #aija4 ,the interesting thing now about it is that the congruity there pointed out has been conformed to by every satellite discovered since1--the sixth1 seventh1 and eighth of ,jupiter and the ninth and tenth of ,saturn4 ,it is evident that we already know enough of the geniture of our system to prophesy something about it and have the prophecy come true4 ,closely connected with the previous relation is a fourth concordance clearly of mechanical origin1 the relation of the orbital eccentricities of the satellites to their distances from their respective planets4 ,the satellites pursue more and more eccentric orbits according as they stand removed from planetary proximity4 ,a fifth congruity is no less striking4 ,all the satellites of all the planets that we can observe well enough to judge of turn the same face always to their lords4 ,that the ,moon does so to the ,earth is a fact of everyday knowledge1 and the telescope hints that the same respectful regard is paid by ,jupiter's and ,saturn's retinues to them4 ,what is still more remarkable1 ,mercury and ,venus turn out to observe the like vassal etiquette with reference to the ,sun4 ,and it will be noticed that they stand to him the nearest of his court4 ,here1 then1 is a law of proximity which points conclusively to some well-established force4 ,last is a remarkable congruity which study disclosed to me likewise some years ago1 and which has received corroboration in discoveries since4 ,this congruity is the peculiar arrangement of the masses in the solar system4 ,consider first the way in which the several planets1 as respects size1 stand ordered in distance from the sun4 ,nearest to him is ,mercury1 the smallest of all the principal ones4 ,venus and the ,earth follow1 each larger than the last2 then comes ,mars1 of distinctly less bulk1 and so to the asteroids1 of almost none4 ,after this the mass rises again to its maximum in ,jupiter1 and then subsequently falls through ,saturn to ,uranus and ,neptune4 ,here we mark a more or less regular gradation between mass and position1 a curve in which there are two ups and downs1 the outer swell being much the larger1 though the inner1 too1 is sufficiently pronounced4 ,now turn to ,saturn and his family1 which is the most numerous of the secondary systems and that having the greatest span4 ,under ,saturn's wing1 as it were1 is the ring1 itself a congeries of tiny satellites4 ,then comes ,mimas1 the smallest of the principal ones2 then ,enceladus1 a little larger2 then ,tethys1 the biggest of the three4 ,next stands ,dione1 smaller than ,tethys4 ,then the mass increases with ,rhea1 reaching its culmination in ,titan1 after which it declines once more4 ,strangely reproductive this of the curve we marked in the arrangement of the planets themselves1 even to the little inner rise and fall4 ,illustration3 ,,masses ,,of ,,planets ,,and ,,satellites4 ,striking as such analogous ordering is1 it is not all4 ,for1 scanning the ,jovian system1 we find the main curve here again2 ,ganymede1 the ,jupiter or ,titan of the system1 standing in the same medial position as they4 ,lastly1 taking up ,uranus and his family of satellites1 the same order is observable there4 ,titania1 the largest1 is posted in the centre4 ,thus the order in which the little and the big are placed with reference to their controlling orb is the same in the solar system and in that of every one of its satellite families4 ,method here is unmistakable4 ,nor is it easy to explain unless the cause in all was like4 ,that the rule in the placing of the planets should be faithfully observed by them in the ordering of their own domestic retinues1 is not the least strange feature of the arrangement4 ,it argues a common principle for both4 ,not less significant is the secondary hump in their distribution1 denoting recrudescence farther in of the primary procedure shown without4 ,one point to be particularly noticed in these latter-day congruities is that they are not simply general concords like the older ones--the fact that the planets move in one plane or in the same sense in that plane--but detailed placings1 ordered according to the distances of the planets from the ,sun or of the satellites from the planets4 ,they are thus not simply of the combinative but of the permutative order of probabilities1 a much higher one2 in other words1 the chance that they can be due to chance is multiplicately small4 ,thus just as these analogies are by so much more remarkable1 so are they by so much more cogent4 ,they tell us not only of an evolution1 but they speak of the very manner of its work4 ,they do not simply generalize1 they specify the mode of action4 ,the difficulty is to understand their language4 ,it is a case of celestial hieroglyphics to which we lack the key4 ,in attempting now to discover how all this came about we notice first that the system could not have originated in the beautifully simple way suggested by ,laplace1 because of several impossibilities in the path4 ,if rings were shed1 as he supposed1 from a symmetric contracting mass1 they should have resulted in something even more symmetric than we observe to-day4 ,in the next place they could not1 it would appear1 even if formed1 have collected into planets4 ,nor could there have been an original 8fire-mist0 with which as a stock in trade ,laplace thriftily endowed his nebula to start with--the necessity for which has been likened to our supposed descent from monkeys2 but which in truth is as misty a conception of the facts in the one case as it is a monkeying with them in the other4 ,darwin's theory distinctly avers that we were not descended from monkeys2 and ,laplace's fire-mist under modern examination evaporates away4 ,it is an interesting outcome of modern analysis that the very fact which suggested the annular genesis of planets to ,laplace1 the rings of ,saturn1 should now probably be deemed a striking instance of the reverse4 ,far from its being an exemplar in the heavens of the pristine state of the solar system1 we may now see in it a shining pattern of how the devolution of bodies comes about4 ,for instead of typifying an unfortunate set of particles which untoward circumstance has prevented from coalescing into a single orb1 it almost certainly represents the distraught state to which a once more compact congeries of them has been brought by planetary interference4 ,for to just such fate must the stresses in it caused by ,saturn have eventually led4 ,disruption inevitable to such a group the observation of comets demonstrates is daily taking place4 ,when a comet passes round the ,sun or near a planet1 the partitive pulls of the body tend to dismember it1 and the same is a fortiori true of matter circulating round a planet as relatively near as the meteoric particles that constitute ,saturn's rings4 ,starting as a congeries1 it was pulled out more and more into a ring until it became practically even throughout4 ,and the very action that produced it tends to keep it as surprisingly regular as we note to-day4 ,no1 the planets probably were otherwise generated and may have looked in their earlier stages as the knots in the spiral nebul do to-day4 ,but this does not mean that we can detail the process see ,,note #e4 ,taking now the congruities for guide1 we proceed to see what they affirm or negative4 ,laplace1 when he ventured on his exposition of the system of the world1 did so 8with the mistrust which everything which is not the direct outcome of observation or calculation must inspire40 ,to all who know how even figures can lie this caution will seem well timed4 ,the best we can do to keep our heads steady is to lay firm hold at each step on the great underlying principles of physics4 ,one of these is the conservation of the moment of momentum4 ,this expression embodies one of the grandest generalizations of cosmic mechanics4 ,the very phrase is fittingly sonorous1 with something of that religious sublimity which the dear old lady said she found such a consolation in the biblical word ,mesopotamia4 ,indeed the idea is grand for its very simplicity4 ,momentum means the quantity of motion in a body4 ,it is the speed into the number of particles or the mass4 ,moment of momentum denotes the rotatory power of it round an axis4 ,now the curious and interesting thing about this quantity is that it can neither be diminished nor increased4 ,it is an abstraction from which nothing can be abstracted--but results4 ,it is the one unalterable thing in a universe of change4 ,what it was in the beginning in a system1 that it forever remains4 ,because of this unchangeableness we can use it very effectively for purposes of deduction4 ,one of these is in connection with that other great principle of physics1 the conservation of energy4 ,by the mutual action of particles on one another1 by contraction1 by tidal pulls1 and so on1 some energy of motion is constantly being changed into heat and thus dissipated away4 ,energy of motion1 therefore1 is slowly being lost to the system1 and the only stable state for the bodies composing it is when their energy of motion has decreased to the minimum consistent with the initial moment of momentum4 ,this principle we shall find very fecund in its application4 ,it means that our whole system is evolving in a way to lessen its energy of motion while keeping its quantity of motion unchanged4 ,the universe always does a thing with the least possible expenditure of force and gets rid of its superfluous energy by parting with it to space4 ,philosophers may wrangle over its being the best possible of worlds1 but it is incontrovertibly mechanically the laziest1 which a pessimistic friend of mine says proves it the best4 ,now this generalization finds immediate use in explaining certain features of the solar system4 ,in looking over the congruities it will be seen that deviation from the principal plane of the system or departure from a circular orbit is always associated with smallness in size4 ,the insignificant bodies are the erratic ones4 ,now it has been shown mathematically in several different ways that when small particles collect into a larger mass1 the collisions tend to make the resultant orbit of the combination both more circular and more conformant to the general plane than its constituents4 ,but we may see this more forthrightly by means of the general principle enunciated above4 ,for in fact both results are direct outcomes of the conservation of moment of momentum4 ,given a certain moment of momentum for the system1 the total energy of the bodies is least when they all move in one plane4 ,this is evident at once because the components of motion at right angles to the principal plane add nothing to the moment of momentum of the system4 ,it is also least when the bodies all revolve in circles about the centre of gravity4 ,the circle has some interesting properties which almost justify the regard paid to it by the ancients as the only perfect figure4 ,it encloses the maximum area for a given periphery1 so that according to the old legends1 if one were given as much land as he could enclose with a certain bull's hide1 he should1 after cutting the hide into strips1 arrange these along the circumference of a circle4 ,now this property of the circle is intimately connected with the fact that a body revolving in a circle has the greatest moment of momentum for the least expenditure of energy4 ,for under the same central force all ellipses of the same longest diameters--major axes these are technically called--are described in the same time1 and with the same energy1 and of all such1 the circle encloses the greatest area1 which area measures the moment of momentum see ,,note #f4 ,given a certain moment of momentum1 then the energy is least when the bodies all move in one plane and all travel in circles in that plane4 ,as energy is constantly being dissipated while any alteration among the bodies is going on1 to coplanarity and circularity of path all the bodies must tend1 if by collision they be aggregated into larger masses4 ,as in the present state of our system the small bodies travel out of the general plane in eccentric ellipses while the big ones travel in it in approximate circles1 the facts indicate that the origin of the larger masses was due to development by aggregation out of smaller particles4 ,the next principle is of a different character4 ,half a century ago celestial mechanics dealt with bodies chiefly as points4 ,the ,earth was treated as a weighted point1 and so was the ,sun4 ,this was possible because a sphere acts upon outside bodies as if all its mass were collected at its centre1 and the ,sun and many of the planets are practically spheres4 ,but when it came to nicer questions of their present behavior and especially of their past career1 it grew necessary to take their shape into account in their mutual effects4 ,one of the results was the discovery of the great rle played in evolution by tidal action4 ,inasmuch as the planets are not perfectly rigid bodies1 each is subject to tidal deformation by the other1 the outside being pulled more than the centre on one side and less on the other4 ,bodily tides are thus raised in it analogous to the surface tides we see in the ocean1 only vastly greater1 and these in turn act as a brake on its rotation4 ,now the retrograde motions occurring in the outermost parts of all the systems1 principal and subsidiary1 only and always there3 the retrograde rotations of ,neptune and ,uranus1 the retrograde revolutions of the ninth satellite of ,saturn and of the eighth of ,jupiter1 point to something fundamental4 ,for when we consider that it is precisely in its outer portions that any forces shaping the development of the system have had less time to produce their effect1 we perceive that apparent abnormality now is really survival of the original normal state1 only to be found at present in what has not been sufficiently forced to change4 ,it suggests that the pristine motion of the constituents of the scattered agglomerations which went to form the planets was retrograde1 and that their present direct rotations and the direct revolutions of most of their satellites have been imposed by some force acting since4 ,let us inquire if there be a force competent to this end1 and what its mode of action4 ,let us see how tidal action would work4 ,tidal force would raise bulges1 and these1 not being carried round with the planet's rotation except to a certain distance1 due to viscosity1 must necessarily act as brakes upon the planet's spin4 ,in consequence of the friction they would thus exert1 energy of motion must be lost4 ,so long1 then1 as tidal forces can come into play1 the energy of the system is capable of decrease4 ,according to the last principle we considered1 the system cannot be in stable equilibrium until this superfluous energy is lost or until tidal forces become inoperative1 which cannot be till all the bodies in the system turn the same face to their respective centres of attraction4 ,to see this more clearly1 take the case of a retrograde spin of a planet as compared with a direct one4 ,the energy of the planet's spin is the same in both cases1 because energy depends on the square of a quantity2 to wit1 that of the velocity1 and is therefore independent of sign4 ,not so the moment of momentum4 ,for this depends on the first power of the speed1 and if positive in the one case1 must be negative in the other4 ,the moment of momentum of the whole system1 then1 is less in the former case1 since the moment of momentum of the retrograde rotation must be subtracted from1 that of the direct rotation be added to1 that of the rest of the system4 ,for a given initial moment of momentum with which the system was endowed at the start1 there is1 then1 superfluous energy in the first state which can be got rid of through reduction to the second4 ,nature1 according to her principles of least exertion1 avails herself of the chance of dispensing with it1 and a direct rotation results4 ,sir ,robert ,ball first suggested this argument4 ,tidal action accomplishes the end4 ,in checking up a body rotating contrary to the general consensus of spin1 its first effect is to start to turn the axis over4 ,for the body is in dynamical unstable equilibrium with regard to the rest of the system4 ,the righting would continue1 practically to the exclusion of any diminution at first of the spin1 until the body had turned over in its plane so that the spin became direct4 ,as the force increases greatly with nearness to the ,sun1 the effect would be most marked on the nearer1 and most so on the biggest1 bodies4 ,this would account for the otherwise strange gradation from retrograde to direct in the tilts of the axes of the outer planets1 and also for the present tilts of all the inner ones4 ,related to the initial retrograde rotations of the planets1 and in a sense survivals from an earlier state of things1 are two of the latest discoveries of motions in the solar system1 the retrograde orbital movements of the ninth satellite of ,saturn and the eighth of ,jupiter4 ,considered so anomalous as scarcely at first to be believed1 it has been stated that they directly contradict the theory of ,laplace4 ,this is true2 in the same sense and no more in which they directly contradict the contradictor1 one of the latest theories4 ,for neither theory has anything to explain them as the result of law4 ,that they cannot be the sport of indifferent chance seems evidenced by their occupying similar external positions in their respective systems4 ,as the product of a law we must regard them1 and to find that law we now turn4 ,suppose the planet originally to have been rotating backward1 or in the direction of the hands of a clock4 ,at this time the satellite1 which may never have formed a part of its mass1 was travelling backward too1 according to what we have said4 ,then under the friction of the tides raised on the planet by the ,sun1 the planet proceeded to turn over4 ,it continued to do so until it spun direct4 ,during this process there was no passage through zero of its moment of momentum considered with regard to itself1 and therefore no difficulty on that score of supposing that it successively generated satellites at all degrees of inclination4 ,that its children are of the nature of adopted waifs1 ,babinet's criterion 7#ahfa7 would seem to imply4 ,but it must be remembered that the ,sun has been slowing up the planet's rotation now for ons4 ,as it turned over1 its tidal bulges tended to carry over with it such satellites as it already had4 ,this effect was much greater on the nearer ones1 both because they were nearer and because they were much larger than the outer4 ,so that the nearer kept with the planet1 the others lagged proportionately behind4 ,this suggests itself to account for the facts1 but the subject involves so much that is uncertain that ,i submit the hypothesis with the distrust which ,laplace has so eminently bespoken4 ,i advance in its favor only the three striking facts3 that a steady progression in their tilts of rotation is observable from ,neptune to ,jupiter and a substantially accordant one from ,mars to ,mercury2 secondly1 that the satellites turn their faces to their primaries1 as likewise do ,mercury and ,venus to the ,sun2 and1 thirdly1 that the orbits of the satellites of all the planets are themselves tilted in accordance with what it would require see ,,note #g4 ,after the axial spins have been made over to the same sense1 the second consequence of tidal action in the case of two bodies revolving about their common centre of gravity is to slow down both spins until first the smaller and then the larger turn the same face to each other and remain thus constant ever after4 ,now such is precisely the pass to which we observe the satellites of the planets have come4 ,all that we can be sure of now turn the same face always to their primary4 ,the ,moon was the first to betray her attitude1 because the one we can best note4 ,on scrutiny1 however1 ,jupiter's satellites1 so far as we can make out1 do the like2 and ,saturn's1 too4 ,and a very proper attitude it is1 this regard paid to compelling attraction4 ,thus one of the congruities we noticed stands accounted for4 ,the satellites could hardly have been at first so observant2 time has brought about this unfailing recognition of their lords4 ,of the peculiar massing of the bodies in the family of the ,sun1 and the still stranger copying of it in their own domestic circles1 little can as yet be said in interpretation4 ,that the planetary families and their ancestral group should agree is not the least strange part of the affair4 ,it shows that none of them was fortuitous1 but that at the formation of all some common principle presided1 apportioning the aggregations to their proper place4 ,but it is such fine print of the system's history as at present to preclude discernment4 ,so much for the details we may deduce of the method of our birth4 ,we perceive unmistakably that our solar system grew to be what it is1 and that it developed by agglomeration of its previously shattered fragments into the planets we behold to-day1 but exactly how the process progressed we are as yet unable to precise4 ,we are1 however1 as what ,i have mentioned and tabled show1 every day accumulating data which will enable an eventual determination probably to be reached4 ,from the fact of agglomeration1 the essence of the affair1 we turn to the traces it has left upon its several offspring4 ,just as the continued existence to-day of meteorites in statu quo informs us of a previous body from which our nebula sprang2 so a physical characteristic of our own earth at the present time shows it to have evolved from that nebula--even though we cannot make out all the steps4 ,of its having done so1 we are far more sure than of how it did4 ,that primitive man perceived that somewhere below him was a fiery region which was not an agreeable abode1 is plain from his consigning to such ,tophet those whose religious tenets did not square with his own4 ,that his conception of it was not strictly scientific is evidenced by his not realizing that to bury his enemies was the way to make them take the first step of the journey thither4 ,indeed1 the vindictive venting of his notions clearly indicates their source as volcanic1 rather than bred of a general disapproval of a downward descent either in silicates or sin4 ,it was not till man began to bore into the ,earth for metallic or potable purposes that he brought to light the generic fact that it was everywhere hotter as one went down4 ,and this not only in a very regular1 but in a most speedy1 manner4 ,the temperature increased in a really surprising way #a ,f4 for every sixty-five feet of descent4 ,as the rise continued unabated to the limit of his borings1 becoming very unpleasant at its end1 it was clear that at a depth of thirty-five miles even so refractory a substance as platinum must melt1 and practically all the ,earth except a thin crust be molten or even gaseous4 ,now heat1 like money1 is easy to dissipate but hard to acquire1 as primitive man was the first to realize4 ,it does not come without cause4 ,being a mode of motion1 other motion must have preceded it from which it sprang4 ,so much the doctrine of the conservation of energy teaches us1 a doctrine considered now to have been the great scientific heirloom of the nineteenth century to the twentieth1 yet which in its day caused the death of its first discoverer1 ,mayer1 of a broken heart from non-recognition2 its second1 ,helmholtz1 was refused publication by the leading ,berlin physical magazine of the time4 ,so quick is man to delay his own advance4 ,the only conceivable motion for thus heating the ,earth as a whole was the falling together of its parts4 ,the present heat of the ,earth1 then1 accuses the concourse of particles in the past to its formation1 or in other words proves that the ,earth was evolved out of material originally more sparcely strewn4 ,it does so not only in a generic but in a most particular manner1 for the heat is distributed just where it would be by such a process4 ,it is greater to-day within1 increasingly1 because when the globe began to cool1 the surface necessarily cooled first and established a regular gradient of heat from core to cuticle4 ,it is possible to test this qualitative inference quantitatively and see if the falling together of the meteorites was equal to the task4 ,knowing the mechanical equivalent of heat1 what we do is to calculate the quantity of motion involved and then evaluate it in heat4 ,as we are unaware of the exact law of density of the ,earth1 and are ignorant of how much was radiated away in the process1 the problem is a little like estimating the fortune of a man when we do not know the stocks in which he has invested1 and ignore how much he has spent the while4 ,we only know what he would have been worth had he followed our advice in the matter of investments and lived as frugally as we recommended4 ,for here1 too1 we are obliged to make certain assumptions4 ,nevertheless the figure obtained in the case of the planets' stores of heat is so enormous as to leave a most ample margin for dissipation4 ,had the ,earth contracted from a fairly generous expansion to its present state under the probable law of density suggested by ,laplace in another connection1 the heat developed would have been enough to raise the whole globe to #afj1jjj ,f4 if of iron1 #ij1jjj ,f4 if of stone4 ,as #aj1jjj ,f4 would have sufficed for the ,earth to have kept up its past1 to say nothing of its present1 state1 we are justified of our deduction4 ,nor is the ,earth the only body in the system which thus argues itself evolved by the falling together of its present constituents4 ,in the larger planets ,jupiter and ,saturn we seem to see the heat1 far as we are away4 ,for the cherry hue they disclose between their brighter belts proves to come from greater absorption there of the green and blue rays of the spectrum1 indicating a greater depth of atmosphere traversed4 ,thus these parts lie at a lower level1 and their ruddy hue is just what they should show were they still glowing with a dull red heat4 ,illustration3 ,,spectrogram ,,of ,,jupiter1 ,,moon ,,comparison4 ,,lowell ,,observatory4 ,v4 ,m4 ,,slipher4 ,heat is not only the end of the beginning1 it is the beginning of the end as well4 ,it is both the result of the evolving of definite bodies out of the agglomeration of matter-strewn space1 and the cause of the higher evolution of those globes themselves4 ,for the acquisition of heat is the necessary preface to all that follows4 ,heat is a body's evolutionary capital whose wise expenditure through cooling down makes all further advance to higher products possible4 ,a body too small to have acquired it must remain forever lifeless1 as dead as the meteorites themselves that enter our air as mere inert bits of stone or iron4 ,curiously enough1 heat both must have been and then must have been lost4 ,like the loss of fortune or of friends sometimes in the ennobling of character1 it is through its passing away that its effects are realized4 ,for in cooling down from a once heated condition1 that train of events occurs which we most commonly particularize as evolution4 ,so far in our survey the march of advance has been through masses of matter1 a molar evolution2 from this point on it passes into its minute constituents and becomes a molecular one4 ,the one is the necessary prelude to the other4 ,up to this great turning-point in the history of each member of a solar system we have been busied with the acquisition of heat1 though we may not have been aware of it the while4 ,all the motions we have studied tended to that end4 ,during these three chapters1 ,i1 ,,ii1 ,v1 we have been gradually rising in our point of view until we stand at the temperature pinnacle of the whole process4 ,in the next three we are to descend upon the other side4 ,the slope we have come up was of necessity barren2 the one we are to go down brings us to verdure and the haunts of men4 ,coming from the causes above1 we reach at each step effects more and more related to ourselves which those causes will help us to explain4 ,,chapter ,,vi ,a ,,planet',s ,,history ,self-sustained ,stage ,up to this point in our retrospective survey the long course of evolution has taken one line1 that of dynamical separation of the system's parts with subsequent reunitement of them according to the laws of celestial mechanics4 ,of this action ,i have submitted the reader my brief3 departing in it from common-law practice1 in which the cause of action is short and the brief long4 ,and ,i have1 ,i trust1 guarded against his appealing on exceptions4 ,from this point on we have two kinds of development to follow3 the one intrinsic1 the chemical2 the other incidental1 the physical4 ,not that1 in a way1 the one is divorcible from the other4 ,for the physical makes possible the chemical by furnishing it the conditions to act4 ,but in another sense1 and that which is most thrust upon our notice1 the two are independent4 ,thus oceans and land1 hills and valleys1 clouds and blue sky1 as we know them1--everything1 pretty much1 which we associate with a world1--are not universal1 inevitable1 results of planetary evolution1 but resultant1 individual1 characteristics of our particular abode4 ,they are as much our own as the peculiar arithmetic of waiters is theirs1 or as used to be the sobriety of the country doctor's horse--his and no other's4 ,our whole geologic career is essentially earthly4 ,not that its fundamental laws are not of universal application1 but the kaleidoscopic patterns they produce depend on the little idiosyncrasies of the constituents and the mode in which these fall together4 ,our everyday experiences we should find quite changed1 could we alight on ,venus or on ,mars4 ,on the other hand1 the chemical changes which follow a body's acquisition of heat1 setting in the moment that heat has reached its acme and starts to decline1 are as universal as the universe itself4 ,they are conditioned1 it is true1 by the body's size and by the position that body occupied in the primal nebula1 but they depend directly upon the degree of heat the body had attained4 ,the larger the planet1 the higher the temperature it reached and the fuller its possibilities4 ,even the planets are born to their estate4 ,thus the little meteorites live their whole waking life during the few seconds they spend rushing through our air4 ,for then only does change affect their otherwise eternally inert careers4 ,that the time is too short for any important experience is evident on their faces4 ,heat is most intimately associated with the very constitution of matter4 ,it is1 in fact1 merely the motion of its ultimate particles1 and plays an essential part in their chemical relations4 ,just as a certain discreet fervor and sufficient exposure for attraction to take1 make for matrimony1 so with the little molecules1 a suitable degree of warmth and a propitious opportunity similarly conduce to conjunction2 too fiery a temperament resulting in a vagabondage preventative of settled partnership and too cold a one in permanent celibacy4 ,you may think the simile a touch too anthropomorphic1 but it is a most sober statement of fact4 ,indeed1 it is more than probable that in some dull sense they feel the impulse1 though not the need of expressing it in verse4 ,that metals can remember their past states seems to have been demonstrated by ,bose1 and is certainly in keeping with general principles as we know them to-day4 ,for memory is the partial retention of past changes1 rendering those changes more facile of repetition4 ,a high degree of heat1 then1 makes chemical union impossible1 because the great speeds at which the molecules are rushing past each other prevents any of them being caught4 ,lack of speed is equally deterrent4 ,nor is it wholly or even principally1 perhaps1 a movement of the whole which is here concerned1 but a partitive throbbing of the molecule itself4 ,certain it is that great cold is as prohibitive of chemic combination as great heat4 ,phosphorus1 which evinces such avidity for oxygen at ordinary temperatures as to have got its name from the way it publishes the fact1 at very low ones shows a coolness for its affinity amounting to absolute unconcern4 ,thus only within a certain range of temperature does chemical combination occur4 ,to remain above or below this is to stay forever immortally dead4 ,to get hot enough in the first place1 and then subsequently to cool1 are therefore essential processes to a body which is to know evolutionary advance4 ,to pen the history of the solar system and leave out of it all mention of its most transcendentally wonderful result1 the chemical evolution attendant upon cooling1 would be to play 8,hamlet0 with ,hamlet left out4 ,for the thing which makes the second half of the great cosmic drama so inconceivably grand is the building up of the infinitely little into something far finer than the infinitely great4 ,the mechanical action that first tore a sun apart1 and then whirled the fragments into the beautifully symmetric system we behold to-day1 is of a grandeur which is at least conceivable2 the molecular one that1 beginning where the other left off1 built up first the diamond and then humanity is one that passes our power to imagine4 ,that out of the aggregation of meteorites should come man1 a being able to look back over his own genesis1 to be cognizant of it1 as it were1 from its first beginnings1 is almost to prove him immanent in it from the start4 ,fortunate it is that his powers should seem more limited than his perceptions1 and the more so as he goes farther1 else he had been but the embodiment of conceit4 ,we must sketch1 therefore1 the steps in this marvellous synthesis2 hastily1 for ,i have already spoken of it elsewhere in print and repetitions dull appreciation1--in the appreciative1--though we have the best of precedents for believing that1 even in science1 to be dull and iterative insures success2 the dulness passing for wisdom and the iteration tiring opposition out4 ,in the ,sun all substances are in their elemental state4 ,though its materials are the same as the ,earth's1 we should certainly not feel at home there1 even if we waived the question of comfort1 for we should recognize nothing we know4 ,we talk glibly of elements as if we had personal acquaintance with them1 man's innate snobbery cropping out4 ,for to the chemist alone are they observable entities4 ,no one but he has ever beheld calcium or silicon1 or magnesium1 or manganese1 and most of us would certainly not know these everyday elements if we met them on the street4 ,of all the substances composing the ,earth's crust1 or the air above1 or the water beneath1 practically the only elements with which we are personally familiar are iron1 copper1 and carbon1 and these only in minute quantities and in that order of acquisition2 which accounts for the stone1 iron1 and bronze ages of man1 ending we may add with the graphite or lead-pencil age of early education4 ,yet that elementary substances once existed here we have evidence4 ,we find such in volcanic vents4 ,that the ,earth was once as hot on its surface as it now is underneath1 we know from the condition of the plutonic rocks where sedimentary strata have not covered them up4 ,volcanoes and geysers are our only avenues now to that earlier state of things4 ,from these pathways to the past1 and only from them1 do we find elementary substances produced to-day1--hydrogen1 sulphur1 chlorine1 oxygen1 and carbon4#ae ,we are thus made aware that once the ,earth was simple1 too1 on the surface as well as deeper down4 ,a side-light1 this1 to what we knew must have been the case4 #ae ,geikie1 8,geology10 pages #he1 #hf1 and #aca-acf4 ,from its primordial state1 the least complex compounds were evolved first4 ,as the heat lessened1 higher and higher combinations became possible4 ,and this is why the more complex molecules are so unstable1 the organic ones the most4 ,since they are not possible at all under much stir of their atomic constituents1 it shows that the bond between them must be feeble--and1 therefore1 easily broken by other causes besides heat4 ,to the instability of the organic molecule is due its power2 and to cooling1 the possibility of its expression4 ,illustration3 ,,lowell ,,observatory ,,spectrogram ,,showing ,,water-,,vapor ,,in ,,the ,,atmosphere ,,of ,,mars1 ,,january #aijh4--,v4 ,m4 ,,slipher4 ,for the steps in the chemical process from ,sun to habitable ,earth we must look to the spectroscope2 not in its older field1 the blue end of the spectrum1 but in that which is unfolding to our view in ,dr4 ,slipher's ingenious hands1 the extension of the observable part of it into the red4 ,for at that end lie the bands due to planetary absorption4 ,here we have already secured surprising results as to the atmospheres of the various planets4 ,we have not only found positive evidence of water-vapor in the atmosphere of ,mars1 but we have detected strange envelopes in the major planets which show a constitution different from that of the ,sun on the one hand1 and of the ,earth on the other4 ,that size and position are for much in these peculiarities1 ,i have already shown you2 but something1 too1 is to be laid at the door of age4 ,the major planets are not so advanced in their planetary history as is our ,earth2 and ,dr4 ,slipher's spectrograms of them disclose what is now going on in that prefatory1 childish stage4 ,these spectrograms are full of possibilities1 and it is not too much to say that chemistry may yet be greatly indebted to the stars4 ,compounds1 the strange unknown substances there revealed by their spectral lines1 may be cryptic as yet to us4 ,some of the elements missing in ,mendeleff's table may be there1 too4 ,helium was first found in the ,sun2 coronium still awaits detection elsewhere4 ,so with these spectral lines of the outer planets4 ,it looks as if chemistry had been a thought too previous in making free for others with what should have been their names1 ,zenon and ,uranium4 ,for we may yet have to speak of ,dion and ,varunium4 ,from the chemical aspect of evolution we pass to its physical side2 from the indirectly to the directly visible results4 ,here again1 to learn what happened after the sunlike stage1 we must turn to the major planets4 ,for the cooling which induced both physical and chemical change has there progressed less far1 inasmuch as a large globe takes longer to cool than a small one4 ,to the largest planets1 then1 we should look for types of the early planetary stages to-day4 ,almost as soon as the telescope was directed to ,jupiter1 among the details it disclosed were the ,jovian belts 7in the year #afcj71 dark streaks ruling the planet's disk parallel to its equator4 ,they are of the first objects advertised as visible in small glasses to-day1 vying with the craters in the ,moon as purchasable wonders of the sky4 ,as the belts were better and better seen1 features came out in them which proved more and more interesting4 ,cassini1 in #afib1 noticed that the markings travelled round ,jupiter and those nearest his equator the quickest4 ,sir ,william ,herschel thought them due to ,jovian trade-winds1 the planet's swift rotation making up for deficiency of sun2 why1 does not appear4 ,modern study of the planet shows that the bright longitudinal layers between the dark belts are unquestionably belts of cloud4 ,their behavior indicates this1 and their intrinsic brightness bears it out4 ,for they are of almost exactly that albedo4 ,whether they are the kind of cloud with which we are familiar1 clouds of water-vapor1 we are not yet sure4 ,but whatever their constitution1 their conduct is quite other than is exhibited by our own4 ,in the first place1 they are of singular permanence for clouds4 ,the fleeting forms we know as such assume in the ,jovian air a stability worthy of ,jove himself4 ,in their general outlines1 they remain the same for years at a time4 8,constant as cloud0 would be the proper poetic simile there4 ,but while remaining true to themselves1 they prove to be in slow1 unequal shift with one another4 ,thus ,jupiter's official day differs according to the watch of the particular belt that times it4 ,spots in different latitudes drift round lazily in appearance1 swiftly in fact1 those near the equator as a rule the fastest4 ,nor is there any hard and fast latitudinal law2 it is a go-as-they-please race in which one belt passes its neighbor at a rate sometimes of four hundred miles an hour4 ,the mean day is #i #ee long4 ,illustration3 ,,jupiter ,,and ,,its 8,,great ,,red ,,spot0--,a ,,drawing ,,by ,,dr4 ,,lowell1 ,,april #ab1 #g #j-e1 #aijg4 ,illustration3 ,,jupiter ,,and ,,its 8,,great ,,red ,,spot0--,a ,,drawing ,,by ,,dr4 ,,lowell1 ,,april #ab1 #g #bh-db1 #aijg4 ,a side-light is cast upon the ,jovian state of things by the 8great red spot10 which has been more or less visible for thirty years1 and which takes five minutes longer than the equatorial band to travel round4 ,its tint bespoke interest in what might be its atmospheric horizon4 ,yet it betrayed no sign of being either depressed or exalted with regard to the rest of the surface4 8,in #ahia10 as ,miss ,clerke puts it1 8an opportunity was offered of determining its altitude relative to a small dark spot on the same parallel1 by which1 after months of pursuit1 it was finally overtaken4 ,an occultation appeared to be the only alternative from a transit2 yet neither occurred4 ,the dark spot chose a third4 ,it coasted round the obstacle in its way1 and got damaged beyond recognition in the process40 ,it thus astutely refused to testify4 ,illustration3 ,,sun ,,spots--,,after ,,bond4 ,now1 this exclusiveness on the part of the 8great red spot0 really offers us an insight to its character4 ,clearly it was no void1 but occupied space with more than ordinary persistency4 ,as it was neither above nor below the dark spot and shattered that spot on approach1 which its former surroundings had not done1 its force must have been due to motion4 ,this can be explained by its being formed of a vast uprush of heated vapor from the interior4 ,in short1 it was a sort of baby elephant of a volcano1 or geyser1 occurring as befits its youth in fluid1 not solid1 conditions1 but fairly permanent1 nevertheless--a bit of kindergarten ,jovian geology4 ,this estimate of it is concurred in by ,dr4 ,slipher's spectrogram of the dark and light belts respectively4 ,for in the spectrum of the dark one we see the distinctive ,jovian bands intensified as if the light had traversed a greater depth of ,jovian air4 ,its color1 a cherry red1 abets the conclusion--that in such places we look down into the fiery1 chaotic turmoil so incessantly going on4 ,illustration3 ,,photograph ,,of ,a ,,sun ,,spot--,,after ,,the ,,late ,m4 ,,janssen4 ,it is of interest to note that we have prototypes of this sort of extraterrestrial cyclone in the ,sun4 ,his spots are probably local upsettings of atmospheric equilibrium1 using the word atmospheric in the widest possible sense4 ,just as our storms are the mildest examples of the like expostulation at the impossibility of keeping up a too long continued decorum4 ,only that with us the ,earth is not so much to blame as the ,sun2 while both ,jupiter and the ,sun are themselves responsible for their condition4 ,thus we have1 in the very depth of their negation1 warrant from the dark belts of ,jupiter that the bright ones are cloud4 ,but also that they are not clouds ordered as ours4 ,the ,jovian clouds pay no sort of regard to the ,sun4 ,in orbital matters ,jupiter obeys the ruler of the system2 but he suffers no interference from him in his domestic affairs4 ,his cloud-belts behave as if the ,sun did not exist4 ,day and night cause no difference in them2 nor does the ,jovian year4 ,they come when they will2 last for months1 years1 decades2 and disappear in like manner4 ,they are sui ,jovis1 caused by vertical currents from the heated core and strung out in longitudinal procession by ,jupiter's spin4 ,they are self-raised1 not sun-raised1 condensations of what is vaporized below4 ,jove is indeed the cloud-compeller his name implies4 ,yet ,jupiter emits no light1 unless the cherry red of his darker belts be considered its last lingering glow4 ,he is thus on the road from ,sun to world1 and his present appearance informs us that this incubation takes place under cloud4 ,the like is true of ,saturn1 in fainter replica1 even to the cherry hue4 ,in one way ,saturn visibly asserts his independence beyond that possible by ,jupiter4 ,for ,jupiter's equator lies almost in the plane of his orbit1 and on a hasty view the ,sun might be credited with the ordering of the belts1 as was indeed long the case4 ,but ,saturn's inclination to his orbital plane is #bg2 yet his belts fit his figure as neatly as his rings1 and never get displaced1 no matter how his body be turned4 ,uranus and ,neptune are in the same self-centred attitude at present as the faint traces of belts on their disk1 otherwise of the same albedo as cloud1 lead us to conclude4 ,yet both their densities and their situation give us to believe them further advanced than the giant planets1 and still they lie wrapped in cloud4 ,these planets1 then1 are quite unbeholden to the ,sun for all their present internal economies4 ,what goes on under that veil of clouds with which they discreetly hide their doings from the too curious astronomic eye--we can only conjecture4 ,but we discern enough to know that it is no placid uneventfulness4 ,that it will continue1 too1 we are assured4 ,for whether these clouds are largely water-vapor now1 or not1 to watery ones they must come as the last of all the wrappers they will eventually put off4 ,the major planets are the only ones at the present moment in this self-centred and self-sustained stage4 ,their great size has kept them young4 ,in the smaller terrestrial planets we could not expect to witness any such condition to-day4 ,if they experienced an ebullient youth1 they have long since outgrown it4 ,only by rummaging their past could we find evidence on the point1 and this1 distance both in time and space bars us from doing4 ,there is but one body into whose foretime career we could hope to peer with the slightest prospect of success--our own ,earth4 ,illustration3 ,,the ,,volcano ,,colima1 ,,mexico1 ,,march #bd1 #aijc--;,,jos ,,maria ,,arreola1 ,,per ,,frederick ,,starr4 ,illustration3 ,,jukes ,,butte1 ,a ,,denuded ,,laccolith1 ,,as ,,seen ,,from ,,the ,,northwest--,,gilbert4 ,illustration3 ,,ideal ,,section ,,of ,a ,,laccolith--,,gilbert4 ,whether our ,earth was ever hot enough at the surface to vaporize those substances which now form the ,jovian or ,saturnian clouds1 we do not know2 but that it was once hot enough to vaporize water we are perfectly certain4 ,and this from proof both of what did exist and of what did not4 ,that the surface temperature was at onetime in the thousands of degrees ,fahrenheit1 the ,plutonic magma underlying all the sedimentary rocks of the ,earth amply shows4 ,reversely1 the absence of any effect of water until we reach these sedimentary deposits1 testifies that during all the earlier stages of the ,earth's career water as such was absent1 and as water subsequently appeared1 it is clear that the conditions did not at first allow it to form4 ,we are sure1 therefore1 that there was a time when water existed only as steam1 and very possibly a period still anterior to that when it did not exist at all1 its constituent hydrogen and oxygen not having yet combined4 ,there was certainly an era1 then1 in the morning of the ages1 when the ,earth wore her cloud-wrapper much as ,jupiter his now4 ,that the seas were not once and yet are to-day1 affords proof positive that at some intermediate period they began to be4 ,avery long intermediate one it must have been1 too1--all the time it took the ,earth to cool from about #bjjj ,c4 to #ajj ,c4 ,not till after the temperature had fallen to the latter figure in the outer regions of the atmosphere could clouds form1 and not till it had done so at the solid surface could the steam be deposited as water4 ,reasoning thus presents us with a picture of our ,earth as a vast seething caldron from which steam condensing into cloud was precipitated upon a heated layer of rock1 to rise in clouds of steam again4 ,the solid surface had by this time formed1 thickening slowly and more or less irregularly1 and into its larger dimples the water settled as it grew1 deepening them into the great ocean basins of to-day4 ,we see the process with as much certainty and considerably more comfort than if1 in the ,french sense1 we had assisted at it4 ,presence of mind now thus amply makes up for absence of body then4 ,passing on evolutionarily we reach more and more tolerable conditions and solid ground in fact1 as well as theory4 ,thus the crust hardened and cooled1 while the oceans still remained uncomfortably hot4 ,for water requires much more heat to warm it to a given temperature than rock1 about four and a half times as much4 ,it has therefore by so much the more to lose1 and is proportionally long in the losing4 ,these hot seas must have produced a small universe of cloud1 and as the conditions were the same all over the ,earth1 we can see easily with the mind's eye that we could not have seen at all with the bodily one1 had we occupied the land in those very early days4 ,to be quite shut out from curious sight without1 was hardly made up for by not being able to see more than dimly within4 ,any one who has stood on the edge of a not-extinct crater when the wind was blowing his way1 will have as good a realization of the then state of things as he probably cares for4 ,now this astronomic drawing of the then ,earth1 which by its lack of detail allows of no doubt whatever1 permits us to offer help in the elucidation of some of their phenomena to our geologic colleagues4 ,we are the more emboldened to do so in that they have themselves appealed to astronomy for diagnosis1 and accepted nostrums devised by themselves4 ,it is always better in such cases to call in a regular practitioner4 ,not that he is necessarily more astute1 but that he knows what will not work4 ,it was in the matter of the paleologic climate that they were led to consult astronomy4 ,the singular thing about paleologic times was the combination of much warmth with little light2 and the not less singular fact that these conditions were roughly uniform over the whole ,earth4 ,from this universality it was clear1 as ,de ,lapparent1 their chief spokesman1 puts it1 that nothing local could explain the fact4 ,it was something which demanded a cause common to the globe4 ,it thus fell properly within the province of astronomy4 ,for if we are to draw any line between the spheres of influence of the two sciences1 it would seem to lie where totality ends and provincialism begins4 ,i use this not as a pejorative1 but simply to part local color from one universal drab4 ,in the ,earth's general attributes1--its size1 shape1 and weight1--we must have recourse to astronomy to learn the facts4 ,not less so for those principal causes which have shaped its general career2 we surrender it only at the point where everyday interest begins1 when those causes that led it through its uninviting youth give way to effects which in the least concern humanity at large4 ,between the mere aggregation of matter into planetary bodies1 of which nebular hypotheses treat1 and the specific transformation of plants and animals upon their surfaces with which organic evolution is concerned1 lies a long history of development1 which1 beginning at the time the body starts to cool1 continues till it become1 for one cause or another1 again an inert mass4 ,in this period is contained its career as a world4 ,planetology ,i have ventured to call the brand of astronomy which deals with this evolution of worlds4 ,it treats of what is general and cosmic in that evolution1 as geology treats of what is terrestrial and specific in the history of one member of the class1 our own ,earth4 ,the two do not interfere1 as the one faces questions in time and space to which the other remains perforce a stranger4 ,if the picture by the one be fuller of detail1 the canvas of the other permits of the wider perspective4 ,certain events in the history of our ,earth can only be explained by astronomy1 as geologists have long since recognized4 ,it is these that fall into our present province4 ,geologists1 however1 have applied astronomy according to their own ideas4 ,either they called in aurists1 so to speak1 when what they needed was an oculist1 or they went to books for their drugs1 which they then administered themselves--a somewhat dangerous practice4 ,thus they began by displacing the ,earth's axis in hope of effecting a result2 not realizing that this would only shift the trouble1 not cure it2 in fact1 make it rather worse4 ,they next tried what ,de ,lapparent1 one of the most brilliant geologists of the age1 calls 8a variation in the eccentricity of the ecliptic#af joined to precession of the equinoxes10--a startling condition unknown to astronomy which does not deal in eccentric planes1 whatever such geometric anomalies may be1 but by which its coiner evidently means a change in the eccentricity of the orbit1 as the context shows4 ,its effect on the ,earth1 as he wisely points out1 would be to reduce its extremities to extremes4 ,to get out of his quandary he then embraced a brilliant suggestion of a brother geologist1 ,m4 ,blandet4 ,m4 ,blandet conceived the idea1 and brought it forth unaided1 that all that was necessary was a sun big enough to look down on both poles of the ,earth at once4 ,to get this he travelled back to the time when1 in ,laplace's cosmogony1 the ,sun filled the whole orbit of ,mercury4 ,this conception1 which1 ,de ,lapparent remarks1 8might1 at the time of its apparition1 have disconcerted spirits accustomed to consider our system as stable10--an apparition which we may add would certainly continue to disconcert them1--he says seems to him quite in harmony with that system's genesis4 ,that it labors under two physical impossibilities1 one on the score of the ,sun1 the other on that of the ,earth1 and that in this case two negatives do not make an affirmative1 need not be repeated here1 as the reader will find it set forth at length elsewhere1#ag together with what ,i conceive to be the only explanation of paleothermal times which will work astronomically--presently to be mentioned4 ,but before ,i do so1 it is pertinent to record two things that have come to my notice since4 ,one is that in rereading ,faye's 8,origine du ,monde10 ,i came upon a passage in which it appears that ,m4 ,blandet had actually consulted ,faye about his hypothesis1 and that ,faye had shown him its impossibility on much the same grounds as those above referred to2 which1 however1 did not deter ,m4 ,blandet from giving it to the world nor ,de ,lapparent from god-fathering the conception4 #af 8,abrg de ,geologie10 ,de ,lapparent4 #ag 8,mars as the ,abode of ,life10 ,macmillan1 #aijh4 ,faye1 meanwhile1 developed his theory of the origin of the world1 and by it explained the greater heat and lesser light of paleologic times compared with our own1 thus3 ,the ,earth evolved before the ,sun4 ,in paleologic times the ,sun was still of great extent1--an ungathered-up residue of nebula that had not yet fallen together enough to concentrate1 not a contracting mass from which the planets had been detached1--and was in consequence but feebly luminous and of little heating effect2 so that there were no seasons on ,earth and no climatic zones4 ,the ,earth itself supplied the heat felt uniformly over its whole surface4 ,this differs from my conception1 as the reader will see presently1 in one vital point--as to why the ,earth was not heated by the ,sun4 ,in the first place ,faye's sun has no raison d'tre2 and in the second no visible means of existence4 ,if its matter were not already within the orbit of the ,earth at the time1 there seems no reason why it should ever get there2 and if there1 why it should have been so loath to condense4 ,we cannot admit1 ,i think1 any such juvenility in the ,sun at the time the ,earth was already so far advanced as geology shows it to have been in paleologic times4 ,for the ,earth had already cooled below the boiling-point of water4 ,illustration3 ,,tree ,,fern4 ,to understand the problem from the ,earth's point of view1 let us review the facts with which geology presents us4 ,the flora of paleologic times1 as we see both at their advent in the ,devonian and from their superb development in the ,carboniferous era1 consisted wholly of forms whose descendants now seek the shade4#ah ,tree ferns1 sigillaria1 equiset1 and other gloom-seeking plants composed it4 ,that some tree fern survivals to-day can bear the light does not invalidate the racial tendency4 ,we have plenty of instances in nature of such adaptability to changed conditions4 ,in fact1 the dying out and deterioration of most of the order shows that the conditions have changed4 ,and these plants1 grown to the dimensions of trees1 inhabited equally the tropic1 the temperate1 and the frigid zones as we know them now4 ,lastly1 no annual rings of growth are to be found on them4#ai ,in other words1 they grew right on1 day in1 day out4 ,the climate1 then1 was as continuous as it was widespread4 #ah ,de ,lapparent1 ,dana1 ,geikie1 passim4 #ai ,de ,lapparent4 ,on the other hand1 astronomy and geology both assert that the seas were warm4#bj ,from this it follows that a vastly greater evaporation must have gone on then than now1 and that a welkin of cloud must thus inevitably have been formed4 #bj ,de ,lapparent1 ,dana1 ,geikie1 passim4 ,now put the two facts together1 and you have the solution4 ,the climate was warm and equable over the whole globe because a thick cloud envelope shut off the ,sun's heat1 the heat being wholly supplied from the steamy seas4 ,at the same time1 by the same means the light was necessarily so tempered as to produce exactly that half-light the ferns so dearly love4 ,one and the same cause thus answers the double riddle of greater warmth and less light in those old days than is now the case4 ,and here comes in the second find ,i spoke of above1 in the person of some old trilobites who stepped in unexpectedly in corroboration4 ,it has long been known--though its full significance seems to have escaped notice--that in #ahgb ,m4 ,barrande made the discovery that many species of trilobites of the ,cambrian and lower ,silurian1 the two lowest1 and therefore the oldest1 strata of paleozoic times1 and distant relative of our horseshoe crabs1 were blind4 ,what is yet more significant1 the most antediluvian were the least provided with eyes4 ,thus in the primordial strata1 one-fourth of the whole number of species were eyeless1 in the next above one-fifth1 and in the latest of all one two-hundredth only4#ba ,furthermore1 they testify to the difficulty of seeing1 in two distinct ways1 some by having no eyes and some colossal ones1 strenuous individuals increasing their equipment and the lazy letting it lapse4 ,it seems more than questionable to attribute this blindness to a deep-sea habitat1 as ,suess does in describing them1 for they lived in what geologists agree were shallow seas on the site of ,bohemia to-day4 ,besides1 trilobites never had abyssal proclivities2 for they are found preserved in littoral deposits1 not in deep-sea silt4 ,muddy water may have had some hand in this1 but muddy water itself testifies to great commotion above and torrential rains4 ,so the light in those seas was not what it became later1 or would be now4 ,thus these trilobites were antelucan members of their brotherhood1 and this accuses a lack of light in those earlier eras even greater than in ,carboniferous times1 which is just where it ought to be found if the theory is true4 #ba ,suess1 8,the ,face of the ,earth10 p4 #bac4 ,i trust this conception may prove acceptable to geologists1 for it seems imperative from the astronomic side that something of the sort must have occurred4 ,and it is just as well1 if not better1 to view it thus in the light of the dawn of geologic history as to remain in the dark about it altogether4 ,nescience is not science--whether hyphenized or apart2 for the whole object of science is to synthesize and explain4 ,its body of learning is but the letter1 cordination the spirit1 of its law4 ,nevertheless1 the unpardonable impropriety of a new idea1 ,i am aware1 is as reprehensible as the atrocious crime of being a young man4 ,yet the world could not get on without both4 ,time is a sure reformer and will render the most hardened case of youth senile in the end4 ,so even a new idea may grow respectable at last4 ,and it is really as well to make its acquaintance while it still has vigor in it as to wait till it is old and may be embraced with impunity4 ,boasted conservatism is troglodytic1 and usually proves a self-conferred euphuism for dull4 ,for conservatism proceeds from slowness of apprehension4 ,it may be necessary for certain minds to be in the rear of the procession1 but it is of doubtful glory to find distinction in the fact4 ,thus the youth of a world1 like the babyhood of an individual1 is passed screened from immediate contact from without4 ,that this is the only way that life can originate on a planet we cannot say1 but that it is away in which it does occur1 our own ,earth attests1 and that1 moreover1 it is the way with all planets of sufficient size1 the present aspect of the major planets shows4 ,it may well be that with celestial bodies as with earthly species1 some swaddle their young1 others cast them forth to take their chance1 and that those that most protect them rear the higher progeny in the end4 ,what glories in evolution thus await the giant planets when they shall have sufficiently cooled down1 we can only dimly imagine4 ,but we can foresee enough to realize that we are not the sum of our solar system's possibilities1 and by studying the skies read there a future more wonderful than anything we know4 ,,chapter ,,vii ,a ,,planet',s ,,history ,sun-sustained ,stage ,two stages have characterized the surface history of the ,earth1--stages which may be likened to the career of the chick within and without the egg4 ,in the first of them the ,earth lay screened from outside influence under a thick shell of cloud1 indifferently exclusive of the cold of space or of the heating beams of the ,sun4 ,motherless1 the warmth of its own body brooded over it1 keeping its heat from dissipating too speedily into space1 and so fostering the life that was quickening upon its surface4 ,the second stage began when the egg-shell broke and the chick lay exposed to the universe about it1 to get its living no longer from its little world within1 but from the greater one without4 ,one and the same event ended the old life to make possible the new4 ,so soon as the cloud envelope was pierced1 both the ,earth's own heat escaped and the ,sun's rays were permitted to come in4 ,it is not surprising that under such changed conditions development itself should have changed1 too4 ,in fact1 the transformation was marked4 ,that its epochal character has failed to impress itself generally on geologists1 is perhaps because they look too closely1 missing the march of events in the events themselves1 and because1 too1 of the gradual nature of its processional change4 ,we can recall only ,de ,lapparent as having particularly signalled it2 although not only in its cause1 but for its effects1 it should have delimited two great geologic divisions of time4 ,illustration3 ,,earth ,,as ,,seen ,,from ,,above--,,photographed ,,by ,,dr4 ,,lowell ,,at ,,an ,,altitude ,,of #eejj ,,feet4 ,astronomy and geology are each but part of one universal history4 ,the tale each has to tell must prove in keeping with that of the other4 ,if they seem at variance1 it behooves us very carefully to scan their respective stories to find the flaw where the apparent incongruity slipped in4 ,each1 too1 fittingly supplements the other1 and especially must geology look to astronomy for its initial data1 since astronomy deals with the beginning of our own ,earth4 ,that study of our ,earth in its entirety falls properly within the province of astronomy1 is not only deducible from its relationship to the other planets1 but demonstrable from the cosmic causes that have been at work upon it1 and the inadequacy of anything but cosmic laws to explain them4 ,the ablest geologists to-day are becoming aware of this1--we have one of them at the head of the geology department of the ,institute1--while from the curious astronomy at second hand which gets printed in geologic text-books1 by eminent men at that1 dating from some time before the flood1--of modern ideas1--it seems high time that the connection should be made clear4 ,for1 after all1 our ,earth too is a heavenly body1 in spite of man's doing his best to make it the reverse4 ,it has some right to astronomic regard1 even if it is our own mother4 ,at the same time it is quite puerile to consider the universe as bounded by our terrestrial backyard4 ,if man took himself a thought less importantly1 he might perceive the humor of so circumscribed a view4 ,like children we play at being alone in the universe1 and then go them one better by believing it too4 ,i shall1 of course1 not touch on any matters purely geologic1 for fear of committing the very excesses ,i deplore2 mentioning only such points as astronomy has information on1 and which1 by the sidelights it throws1 may help to illuminate the subject4 ,thus it certainly is interesting and may to many be a new point of view1 that the changes introduced when paleologic times passed into neologic ones were in their fundamental aspects essentially astronomic2 which shows how truly astronomic causes are woven into the whole fabric of the ,earth4 ,for it was then only1 terrestrially speaking1 that the year began4 ,the orbital period had existed1 of course1 from the time the ,earth first made the circuit of the ,sun4 ,but the year was more a succs d'estime on the ,sun's part than one of popular appreciation4 ,as the ,sun could not be seen and worked no striking effects upon the ,earth1 the annual round had no recognizable parts1 and one revolution lapsed into the next without demarcation4 ,only with the clearing of the sky did the seasons come in3 to register time by stamping its record on the trees4 ,before that1 summer and winter1 spring and autumn1 were unknown4 ,climate1 too1 made then its first appearance2 climate1 named after the sunward obliquity of the ,earth1 and seeming at times to live down to that characterization4 ,weather there had been before2 pejoratively speaking1 nothing but weather4 ,for the downpours in paleologic times must have been exceeded in numbers only by their force4 ,one dull perpetual round of rain was the programme for the day1 with absolutely no hope of a happy clearance to-morrow4 ,it was the golden age only for weather prophets whose prognostications could hardly go wrong4 ,with climate1 however1 it was a very different matter4 ,with polyp corals building reefs almost to the pole 7#ha #ej71bb as far north nearly as man has yet by his utmost efforts succeeded in getting1 while their fellows were busy at the like industry in the tropics1 it is clear that latitude was laughed at and climate even lacked a name4 #bb ,dana4 8,geology40 ,another astronomic feature1 then for the first time disclosed1 was the full significance of the day and the revelation of its cause4 ,while the ,earth brooded under perpetual cloud1 there could have been but imperfect recognition of day and night4 ,or perhaps we may put it better by saying that the standard of both was greatly depressed1 dull days alternating with nights black as pitch4 ,but the moment the ,sun was let in1 all this changed1 though not in a twinkling4 ,the change came on most gradually4 ,we can see in our mind's eye the first openings in the great welkin permitting the ,earth its initial peeps of the world beyond1 and how quickly and tantalously they shut in again like a mid-storm morning which dreams of clearing only to find how drowsy it still is4 ,but eventually the clouds parted afresh and farther1 and the ,earth began to open its eyes to the universe without4 ,the cause of the clearing1 of course1 was the falling temperature of the seas4 ,evaporation went on much less fast as the heat of the water lessened4 ,the whole round of aquatic travel from ocean to air1 and back to ocean again1 proceeded at an ever slackening pace4 ,and here1 if it so please geologists1 may be found a reconciling of their demands for time to the relative pittance astronomy has been willing to dole them out1 a paltry #ej or #ajj millions of years1 which like all framers of budgets they have declared utterly insufficient4 ,for in early times the forces at work were greater1 and by magnifying the means you quicken the process and contract the ,earth's earlier eras to reasonable limits4 ,upon these various astronomic novelties1 the ,earth on thus awakening looked for the first time4 ,such regard altered for good its own internal relations4 ,the wider outlook made impossible the life of the narrower that preceded it4 ,a totally changed set of animals and plants arose1 to whom the cosmos bore a different aspect4 ,the ,earth ceased to be the self-centred spot it seemed before4 ,as long ago as this had the idea that our globe was the centre of the universe been cosmically exploded4 ,the ,earth knew it if man did not4 ,illustration3 ,,tracks ,,of ,,sauropus ,,prim,,vus 7 74 ,i4 ,,lea4--,,dana1 8,,manual ,,of ,,geology40 ,its denizens responded4 ,the organisms that already inhabited it proceeded to change their character and crawl out upon the land4 ,for in ,devonian times the ,earth was the home of fishes4 ,the land was not considered a fit abode by anything but insects1 and not over-good by them4 ,but it looked different when the ,sun shone4 ,some maritime dwellers felt tempted to explore1 and proceeded in the shape of amphibians to spy out the land4 ,they have left very readable accounts of their travels in footnotes by the way4 ,as one should always inspect the original documents1 ,i will reproduce the footnotes of one early explorer4 ,it is one of the few copies we have1 as the type is worn out4 ,but it tells a pretty full story as it stands4 ,the ripple-marks show that a sea beach it was which the discoverer trod in his bold journey of a few feet from home and friends1 and the pits in the sandstone that it was raining at the time of his excursion4 ,no ,columbus or ,hakluyt could have left a record more precise or more eminently trustworthy4 ,the pilgrims found it so good that their eventual collaterals1 the great reptiles1 actually took possession of the land and held it for many centuries by right of eminent domain4 ,yet throughout the time of these bold adventurers1 their skies were only clearing1 as the pitting of the sandstone eloquently states4 ,it was not till the chalk cliffs of ,dover were being laid down that we have evidence that seasons had fully developed1 in the shape of the first deciduous trees4#bc ,cryptogams1 cycads1 and1 finally1 conifers had in turn represented the highest attainments of vegetation1 and the last of these had already recognized the seasons by a sort of half-hearted hibernation or annual moulting2 deeming it wise not to be off with the old leaves before they were on with the new4 ,but finally the most advanced among them decided unreservedly to accept the winter and go to sleep till spring4 ,the larches and ginkgo trees are descendants of the leaders of this coniferous progressive party4 ,at the same time color came in4 ,we are not accustomed to realize that nature drew the ,earth in grays and greens1 and touched it up with color afterward4 ,only the tempered tints of the rocks and the leaden blue of the sea1 subdued by the disheartening welkin overhead to a dull drab1 enlivened their abode for the oldest inhabitants4 ,but with ,tertiary times entered the brilliantly petalled flowers4 ,beginning with yellow1 these rose through a chromatic scale of beauty from white through red to blue4#bd ,they decked themselves thus gaudily because the ,sun was there to see by1 as well as eyes to see4 ,for without the ,sun those unconscious horticulturists1 the insects1 could not have exercised their pictorial profession4 #bc ,dana1 ,geikie1 ,de ,lapparent4 #bd ,cf4 ,grant ,allen4 ,to the entering of the ,sun upon the scene this wondrous revolution was due2 and once entered1 it became the dominant factor in the ,earth's organic life4 ,we are in the habit of apostrophizing the ,sun as the source of all terrestrial existence4 ,it is true enough to-day1 and has been so since man entered on the scene4 ,but it was not always thus4 ,there was a time when the ,sun played no part in the world's affairs4 ,as its heat is now all-important1 it becomes an interesting matter to determine the laws governing its amount4 ,that summer is hotter than winter we all know from experience1 pleasurable or painful as the case may be4 ,this is due to the fact that the ,sun is above the horizon for a greater number of hours in summer and passes more directly overhead4 ,but not so many people are aware that on midsummer day1 so far as the ,sun is concerned1 the north pole should be the hottest place on earth4 ,that ,arctic explorers1 who have got within speaking acquaintance of it1 assure us it is not so1 shows that something besides the direct rays of the ,sun is involved4 ,indeed1 we learn as much from the extensively advertised thermometers of winter resorts which1 judiciously placed1 beguile the stranger to sojourn where it is just too cold for comfort4 ,the factor in question is the blanketing character of our air4 ,now a blanket may keep heat out as well as keep it in4 ,our air acts in both capacities4 ,it is by no means simply a storer of heat1 as many people seem to suppose2 it is a heat-stopper as well4 ,what it really is is a temporizer1 a buffer to ease the shocks of sudden change like those comfortable1 phlegmatic souls who reduce all emotion to a level4 ,for the heating power of the ,sun1 even at the ,earth's distance away1 is much greater than appears4 ,knowledge of this we owe most to ,langley1 and then to ,very1 who continued his results to yet a finer determination1 the best we have to-day4 ,in consequence we have learnt that the amount of heat we should receive from the ,sun1 could we get above our air1--the solar constant1 as it is called1--would be over three times what it is on the average in our latitude at the surface1 and is rising still1 so to speak4 ,for as man has gone higher he has found his inferences rising too1 and the limit would seem to be not yet4 ,we see then that the air to which we thought ourselves so much indebted1 actually begins its kindly offices by shutting off two-thirds of what was coming to us4 ,as it plays1 however1 something of the same trick to what tries to escape1 we are really somewhat beholden to it after all4 ,but not so much as has been thought4 ,we used to be told that the ,moon's temperature even at midday hardly rose above freezing1 but ,very has found it about #cej ,f41 which even the most chilly of souls might find warm4 ,by the late afternoon1 however1 he would need his overcoat1 and no end of blankets subsequently1 for during the long lunar night of fourteen days the temperature must fall appallingly low1 to -#cjj ,f4 or less4 ,as the determination of temperature is a vital one1 not only to any organic existence1 but even to inorganic conditions upon a planet1 it behooves us to look carefully into the question of the effective heat received from the ,sun4 ,until recently the only criterion in the case was assumed to be distance from the illuminating source1 about as efficient a mode of computation as estimating a ,russian army by its official roll4 ,for as we saw in our own case1 not all that ought to ever gets to the front1 to say nothing of what is lost there4 ,yet on this worse than guesswork astronomic text-books still assert as a fact that the temperature of other bodies--the ,moon and ,mars1 for example--must be excessively low4 ,let us now examine into this most interesting problem4 ,it is intricate1 of course1 but ,i think you will find it more comprehensible than you imagine4 ,indeed1 ,i shall be to blame if you do not4 ,for if one knows his subject1 he can always explain it1 in untechnical language1 technical terms being merely a sort of shorthand for the profession4 ,the physical processes involved can be made clear without difficulty1 although their quantitative evaluation is less forthrightly demonstrable4 ,let me1 then1 give you an epitome of my investigation of the subject4 ,illustration3 ,,adventures ,,of ,a ,,heat ,,ray4 ,consider a ray of light falling on a surface from the ,sun4 ,a part of it is reflected2 that is1 is instantly thrown off again4 ,by this part the body shines and makes its show in the world1 but gets no good itself4 ,another part is absorbed2 this alone goes to heat the body4 ,now if the visible rays were all that emanated from the ,sun1 it would be strictly true1 and a pretty paradox for believers in the efficacy of distance1 that what heated the planet was precisely what seemed not to do so4 ,unfortunately there are also invisible rays1 and these1 too1 are in part reflected and in part absorbed1 and their ratio is different from that of the visible ones4 ,to appreciate them1 ,langley invented the bolometer1 in which heat falling on a strip of metal produces a current of electricity registered by a galvanometer4 ,by thus recording the heat received at different parts of the spectrum and at different heights in our atmosphere1 he was able to find how much the air cut off4 ,very has since determined this still more accurately4 ,by thus determining the depletion in the invisible part of the spectrum joined to what astronomy tells us of the loss in the visible part1 we have a value for the whole amount4 ,by knowing1 then1 the immediate brightness of a planet and approximately the amount of atmosphere it owns1 we are enabled to judge how much heat it actually receives4 ,this proves to be1 in the case of ,mars1 more than twice as much as distance alone would lead us to infer4 ,the second question is how much of this it retains4 ,the temperature of a body at any moment is the balance struck between what it receives and what it radiates4 ,if it gets rid of a great deal of its income1 it will clearly be less hot than if it is miserly retentive4 ,to find how much it radiates we may take the difference in temperature between sunset and sunrise1 since during this interval the ,earth receives no heat from the ,sun4 ,in the same way the efficacy of different atmospheric blankets may be judged4 ,thus the ,earth parts with nine centigrade degrees' worth of its store on clear nights1 and only four degrees' worth on cloudy ones1 before morning4 ,this is at sea-level4 ,by going up a high mountain we get another set of depletions1 and from this a relative scale for different atmospheric blankets4 ,this is the principle1 and we only have to fill out the skeleton of theory with appropriate numbers to find how warm the body is4 ,in doing so1 we light on some interesting facts4 ,thus clouds reflect #gb per cent of the visible rays1 letting through only #bh per cent of them4 ,we feel chilly when a cloud passes over the ,sun4 ,on the other hand1 slate reflects only #ah per cent of the visible rays1 absorbing all the rest4 ,this is why slate gets so much hotter in the ,sun than chalk1 and why men wear white in the tropics4 ,white1 indeed1 is the best color to clothe one's self in the year around1 except for the cold effect it has on the imagination1 for it keeps one's own heat in as well as keeping the ,sun's out4 ,the modest1 self-obliterating1 white winter habit of the polar hares not only enables them to keep still and escape notice1 but keeps them warm while they wait4 ,astronomically1 the effect is equally striking4 ,mars1 for example1 owing to being cloudless and of a duller hue1 turns out to have a computed mean temperature nearly equal to the ,earth's1--a theoretic deduction which the aspect of the planet most obligingly corroborates4 ,it thus enjoys a comparatively genial old age4 ,for what is specially instructive in planetary economy is that1 on the whole1 clear skies add more by what they let in than they subtract by what they let out4 ,if the ,earth had no clouds at all1 its mean temperature would be higher than it is to-day4 ,thus as a planet ages a beneficent compensation is brought about1 the ,sun's heat increasing as its own gives out4 ,not that the foreign importation1 however slight the duty levied on it by the air1 ever fully makes up for the loss of the domestic article1 but it tempers the refrigeration which inevitably occurs4 ,the subject of refrigeration leads us to one of the most puzzling and vexed problems of geology3 how to account for the great ,ice ,age of which the manifest sign manuals both in ,europe and in ,america have so intrigued man since he began to read the riddle of the rocks4 ,upon this1 also1 planetology throws some light4 ,if ,i needed an apology to the geologists for seeming again to trespass on their particular domain1 ,i might refer to the astrocomico expositions put forward to account for the great ,ice ,age4 ,we can all remember ,croll's 8,climate and ,time10 a book which can hardly be overpraised for its title and which had things worth reading inside1 too4 ,it had in consequence no inconsiderable vogue at one time4 ,it undertook to account for glacial epochs on astronomic principles4 ,it called in such grand cosmic conditions and dealt in such imposing periods of time that it fired fancy and almost compelled capitulation by the mere marshalling of its figurative array4 ,secular change in the eccentricity of the ,earth's orbit1 combined with progression in the orbital place of the winter's solstice1 was supposed to have induced physical changes of climate which accentuated the snowfall in the northern hemisphere and so caused extensive and permanent glaciation there4 ,in other words1 long1 cold winters followed by short1 hot summers in one hemisphere were credited with accumulating a perpetual snow sheet1 such as short1 warm winters and long1 cold summers could not effect4 ,illustration3 ,,mars4 ,,north ,,polar ,,cap4 ,,south ,,polar ,,cap4 ,at maximum full extent of white ,at maximum white ,at minimum inner circle ,at minimum nothing ,now it so happens that these astronomic conditions affecting the ,earth several thousand years ago1 are in process of action on one of our nearest planetary neighbors at the present time4 ,the orbit of ,mars is such that its present eccentricity is greater than what the ,earth ever can have had1 and the winter solstice of the planet's southern hemisphere falls within #bc of its aphelion point4 ,we have then the conditions for glaciation if these are the astronomic ones supposed1 and we should expect a southern polar cap1 larger at its maximum and still more so1 relatively1 at its minimum1 than in the opposite hemisphere4 ,let us now look at the facts1 for we have now a knowledge of the ,martian polar caps exceeding in some respects what we know of our own4 ,the accompanying diagrams exhibit the state of things at a glance1 the maximum and minimum of each cap being represented in a single picture and the two being placed side by side4 ,it will be observed that the southern cap outdoes its antipodal counterpart at its maximum1 showing that the longer1 colder winter has its effect in snow or hoar-frost deposition4 ,but1 on the other hand1 instead of excelling it at its minimum1 which it should do to produce permanent glaciation1 it so far falls short of its fellow that during the last opposition at which it could be well observed1 it disappeared entirely4 ,the short1 hot summer1 then1 far exceeded in melting capacity that of the longer but colder one4 ,let us now suppose the precipitation to be increased1 the winters and summers remaining both in length and temperature what they were before4 ,the amount of snow which a summer of given length and warmth can dispose of is1 roughly speaking1 a definite quantity4 ,for it depends to a great extent only on its amount of heat4 ,the summer precipitation may be taken as offsetting itself in the two hemispheres alike4 ,if1 then1 the snowfall in the winter be for any reason increased daily in both1 a time will come when the deposition due the longer winter of the one will exceed what its summer can melt relatively to the other1 and a permanent glaciation result in the hemisphere so circumstanced4 ,increased precipitation1 then1 not eccentricity of orbit1 is the real cause of an ,ice ,age4 ,and this astronomic deduction we owe not to theoretic conclusions1 for which we lack the necessary quantitative data1 but wholly to study of our neighbor in space4 ,had any one informed our geologic colleagues that they must look to the sky for definite information about the cause of an ,ice ,age1 they would probably have been surprised4 ,with this ,martian information1 received some years ago1 it is pleasing now to see that ,earthly knowledge is gradually catching up4 ,for that increased precipitation could account for it1 the evidence of pluvial eras in the equatorial regions1 contemporaneous with glacial periods1 indicates4 ,but another and probably the chief factor involved was not a generally increased precipitation1 potent as that would be1 but an increased snow deposit due to temporary elevation of the ground4 ,illustration3 ,,glacial ,,map ,,of ,,eurasia--,,after ,,james ,,geikie4 ,illustration3 ,,map ,,showing ,,the ,,glaciated ,,area ,,of ,,north ,,america--,,the ,,arrows ,,indicating ,,the ,,direction ,,of ,,ice ,,movement--,,chamberlin ,,and ,,salisbury4 ,for it now appears that there was no glacial epoch4 ,our early ideas inculcated by text-books at school received a rude shock when it appeared that the glacial epoch was not1 as we had been led to believe1 a polar phenomenon at all1 but a local affair which on the face of it had nothing to do with the pole4 ,for investigation has disclosed that instead of emanating from the pole southward1 it proceeded from certain centres1 descending thence in all directions1 north as much as south4 ,thus there was a centre in ,norway in #fe ,n4 lat4 and another in ,scotland in #ef ,n4 ,in ,north ,america there were three--the ,labradorian in latitude #ed ,n41 the ,kerwatin to the northwest of ,hudson's ,bay in latitude #fb ,n41 and the ,cordilleran along the ,pacific coast in latitude #eh ,n4 ,on the other hand1 northern ,siberia1 the coldest region in the world1 was not glaciated4 ,that the ice flowed off these centres proves them to have been higher than the sides4 ,but we have further evidence of their then great height from the fact that dead littoral shells have been dredged from #accc fathoms in the ,north ,atlantic1 and the prolongation under water of the fiords of ,norway and of land valleys in ,north ,america witness to the same subsidence since4 ,but evidence refuses to stop here4 ,the ,alps were then more glaciated than they are now4 ,so was ,kilimanjaro and ,ruwenzori on the equator2 and finally at the same time more ice and snow existed round about the south pole than is the case to-day4 ,now this is really going too far even for the most ardent believers in the force of eccentricity4 ,for if the astronomic causes postulated were true1 they must have produced just the opposite action at the antipodes1 to say nothing of the crux of being equally effective at the equator4 ,the theory lies down like the ass between two burdens4 ,whichever load it chooses to saddle1 it must perforce abandon the other4 ,so it turns out that the ,ice ,age was not an ,ice ,age at all but an untoward elevation of certain spots1 and is to be relegated to the same limbo of exaggeration of a local incident into a world-wide cataclysm as the deluge4 ,that some geologists will still cling to their former belief ,i doubt not2 for as the philosophic old lady remarked3 8,there always have been two factions on every subject4 ,just as there are the suffragists and anti-suffragists now1 so there were slaveholders and the anti-slavery people in my time2 and even in the days of the deluge1 there were the diluvians who were in favor of a flood and the antediluvians who were opposed to it40 ,a tale which has a peculiarly scientific moral1 as in science anti and ante seem often interchangeable terms4 ,when ,i began the course of lectures that resulted in this volume1 ,i labored under the apprehension that an account of cosmic physics might prove dull4 ,it soon threatened to prove too startling4 ,i therefore hasten to reassure the timid by saying that we are outgrowing ice ages and probably deluges4 ,elevations of the ,earth's crust are likely to be less and less pronounced in the future1 and meanwhile such as exist are being slowly worn down4 ,secondly1 the ,sun is sure to continue of much the same efficiency for many ons to come4 ,and lastly1 the essential ingredient of both prodigies1 water1 is daily becoming more scarce4 ,to this latter point we now turn1 and perhaps when it is explained to him the reader may think that he has been rescued from one fate only to fall into the hands of another4 ,geology is necessarily limited in its scope to what has happened2 planetology is not so circumscribed in its domain4 ,it may indulge in prognostication of the future1 and find countenance for its conclusions in the physiognomy of other worlds4 ,thus one of the things which it foresees is the relative drying up of our abode4 ,to those whose studies have never led them off this earth1 the fact that the oceans are slowly evaporating into space may seem as incredible as would1 to one marooned on a desert island1 the march of mankind in the meantime4 ,we live on an island in space1 but can see something of the islands about us1 and our conception of what is coming to our limited habitat can be judged most surely by what we note has happened to others more advanced than ourselves4 ,just as we look at ,jupiter to perceive some likeness of what we once were1 the real image of which has travelled by this time far into the depths of space beyond possibility of recall1 so must we look to the ,moon or ,mars if we desire to see some faint adumbration of the pass to which we are likely to come4 ,for from their lack of size they should have preceded us on the road we are bound to travel4 ,now1 both these worlds to-day are water-lacking1 in whole or part2 the ,moon practically absolutely so1 ,mars so far as any oceans or seas are concerned4 ,we should do wisely then to take note4 ,but we have more definite information than simply their present presentments4 ,for both bear upon their faces marks of having held seas once upon a time4 ,they were once1 then1 more as we are now4 ,we cannot of course be sure1 as we are unable to get near enough to scan their surfaces for signs of erosive action4 ,but so far as we can make out1 past seas best explain their appearance4 ,illustration3 ,,the ,,moon--,,photographed ,,at ,,the ,,lowell ,,observatory4 ,so sealike1 indeed1 was their look that the first astronomers to note them took them unhesitatingly for water expanses4 ,thus the moment the telescope brought the ,moon near enough for map making of it we find the dark patches at once designated as seas4 ,the ,sea of ,serenity1 the ,sea of ,showers1 the ,bay of ,rainbows1 speak still of what once was supposed to be the nature of the dark1 smooth1 lunar surfaces they name4 ,suggestively1 indeed1 in an opera glass do they seem to lap the land4 ,the ,lake of ,dreams fore-shadowed what was eventually to be thought of them4 ,with increasing optical approach the substance evaporated1 but the form remained4 ,it was speedily evident that there was no water there2 yet the semblance of its repository still lurked in those shadows and suggests itself to one scanning their surfaces to-day4 ,if they be not old sea bottoms1 they singularly mimic the reality in their smooth1 sloping floors and their long1 curving lines of beach4 ,their strange uniformity shows that something protected them from volcanic fury while the rest of the lunar face was being corrugated4 ,this preservative points to some superincumbent pressure which can have been no other than water4 ,lava-flows on such a scale seem inadmissible4 ,what these surfaces show and what they do not show alike hint them sea bottoms once upon a time4 ,in the strange chalk-like hue of the lunar landscape they look like plaster of ,paris death-masks of the former seas4 ,a like history fell to the lot of the surface features of ,mars4 ,there too1 as soon as the telescope revealed them and their permanency of place1 the dark patches upon the planet's face were forthrightly taken for seas1 and were so called3 the ,sea of the ,sirens and the ,great ,red ,sea4 ,such they long continued to be deemed4 ,the seas of ,mars held water in theory centuries after the idea of the lunar had vanished into air4 ,at last1 ruthless science pricked the pretty bubble analogy had pictured4 ,being so much farther off than the ,moon1 it was much later that their true character came out4 ,come out it has1 though1 within the last few years4 ,lines--some of the so called canals--have been detected crossing the seas1 lines persistent in place4 ,this has effectually disposed of any water in them4 ,but here again something of semblance is left behind4 ,they are still the darkest portions of the planet1 and their tint changes in places with the progress of the planet's year4 ,that their color is that of vegetation1 and that its change obeys the seasons1 stamp it for vegetation in fact4 ,thus these regions must be more humid than the rest of ,mars4 ,they must1 therefore1 be lower4 ,that they are thus lower and possess a modicum of water to-day marks them out for the spots where seas would be1 were there any seas to be4 ,as we know of a vera causa which has for ages been tending to deplete them1 extrapolation from what is now going on returns them the water they have lost and rehabilitates their ancient aquatic character4 ,to the far-sight of inference1 seas they again become in the morning of the ages long ago when ,mars itself was young4 ,nor is this the end of the evidence4 ,when we compare quantitatively the areas occupied by the quondam seas on ,mars and on the ,moon1 we find reason to increase our confidence in our deduction4 ,for the smaller body1 the ,moon1 should have had less water relatively1 at the time when the seas there were laid down1 than the larger1 ,mars4 ,because from the moment its mass began to collect1 it was in process of parting with its gases1 water-vapor among the rest1 and1 as we shall see more in detail in the next chapter1 it had from the start less hold on them than ,mars4 ,its oceans1 therefore1 should have been less extensive than the ,martian ones4 ,this is what the present lunar ,mare seem to attest4 ,they are less extended than the dark areas of ,mars4 ,a fact which becomes the more evident when we remember that the ,moon has long turned the same face to the ,earth4 ,her shape1 therefore1 has been that of an egg1 with the apex pointing toward our world4 ,here the water would chiefly collect4 ,the greater part of the seas she ever had should be on our side of her surface1 the one she presents in perpetuity to our gaze4 ,it is to the heavens that we must look for our surest information on such a cosmic point1 because of the long perspective other bodies give us of our own career4 ,less conclusive1 because dependent upon less time1 is any evidence our globe can offer4 ,yet even from it we may learn something2 if nothing else1 that it does not contradict the story of the sky4 ,to it1 therefore1 we return1 quickened in apprehension by the sights we have elsewhere seen4 ,the first thing our sharpened sense causes us to note is the spread of deserts even within historic times4 ,just as deserts show by their latitudinal girdling of the ,earth their direct dependence upon the great system of planetary winds1 as meteorologists recognizingly call them1 so a study of the fringes of these belts discloses their encroachment upon formerly less arid lands4 ,the southern borders of the ,mediterranean reveal this all the way from ,carthage to ,palestine4 ,the disappearance of their former peoples1 leaving these lands but scantily inhabited now1 points to this2 because other regions1 as ,india1 which still retain a waterful climate1 are as populous as ever4 ,much of this is doubtless due to the overthrow of dynasties and the ensuing lapse of irrigation1 but query3 ,is it all8 ,for we have still more definite information in the drying up of the streams which have left the aqueducts of ,carthage without continuation1 as much to water on the one hand as to its drinkers on the other4 ,men may leave because of lack of water1 but water does not leave because of dearth of men to drink4 ,recent search around the ,caspian by ,huntington has disclosed the like degeneration due to encroaching desertism there4 ,indeed1 it is no chance coincidence that just where all the great nations thrived in the morning of the historic times should be precisely where populous peoples no longer exist4 ,for neither increasing cold nor increasing heat is responsible for this1 seeing that no general change has occurred in either4 ,nor were they particularly exposed to extermination by northern hordes of barbarians4 ,egypt as a world power died a natural death1 and ,babylonia too2 but the common people died of thirst1 indirect and unconscious and not wholly of their own choosing4 ,prehistoric records make this conclusion doubly sure1 by lengthening the limit of our observation4 ,both extinct flora and extinct fauna tell the same tale4 ,in the neighborhood of ,cairo petrified forests attest that ,egypt was not always a wiped slate1 while the unearthed animals of the ,fayum bear witness to water where no water is to-day4 ,illustration3 ,,petrified ,,bridge1 ,,third ,,petrified ,,forest1 ,,near ,,adamana1 ,,arizona--,,photograph ,,by ,,harvey4 ,anywhere we wander along these girdling belts we find the same story written for us to read4 ,the great deserts of ,new ,mexico and ,arizona show castellated structures far beyond the means of its present ,indian population to inhabit4 ,yet this retrenchment occurred long before the white man came with his exterminating blight on everything he touched4 ,nor have we reason to suppose that it arose in consequence of invasion by other alien hordes4 ,individual communities may thus indeed have perished as the preservation of their domiciles intact leads us to infer1 but all did not thus vanish from off the ,earth4 ,here again humanity died or moved away because nature dried the sources of its supply4 ,and here1 as elsewhere1 we find prehistoric record in the rocks of a once more smiling state of things1 strengthening the testimony we deduce from man4 ,the forests1 crowning now only the greater heights1 are but the shrinking residues of what once clothed the land4 ,the well-named ,arid ,zone is becoming more so every day4 ,if from the land evidence of drying up we turn to the marine1 we see the same shrinkage at work4 ,it has even been discovered in a lowering of the ocean bed1 but as this may so easily be disputed1 we turn to one aspect of the situation which cannot so easily be gainsaid1--the bodies of water that have been cut off4 ,that the ,dead ,sea1 the ,caspian1 the ,great ,salt ,lake1 are slowly but surely giving way to land1 is patent4 ,if the climate at least were not more arid than before this could not occur2 but more than this1 if the ocean were not on the whole shrinking1 there would be no tendency to leave such arms of itself behind to shrivel up4 ,that the ocean basins are deepening is possible1 but we know of one depletion which is not replaced--evaporation into space2 and of another bound to come--withdrawal into fissures when the earth shall cease to be too hot4 ,this gradual withdrawal of the water may seem an unpleasant one to contemplate1 but like most things it has its silver lining in the hope it holds out that sometime there shall be no more sea4 ,those of us who detest the constant going down to the sea in ships hardly more than the occasional going down with them1 can take a crumb of comfort in the thought4 ,unfortunately it partakes of a somewhat far-off realization in our distant descendants1 coming a little too late to be of material advantage to ourselves4 ,but let me not leave the reader wholly disconsolate4 ,for another thought we can take with us in closing our sketch of so much of the ,earth's life as brings it well down to to-day1--the thought that it has grown for us a steadily better place to contemplate from the earliest eras to the present time4 ,indeed1 with innate prescience we forbore to appear till the prospect did prove pleasing4 ,finally1 we may palliate prognostication by considering that if its future seem a thought less attractive1 we1 at least1 shall not be there to see4 ,,chapter ,,viii ,,death ,,of ,a ,,world ,everything around us on this ,earth we see is subject to one inevitable cycle of birth1 growth1 decay4 ,nothing that begins but comes at last to end4 ,not less is this true of the ,earth as a whole and of each of its sister planets4 ,though our own lives are too brief even to mark the slow nearing to that eventual goal1 the past history of the ,earth written in its rocks and the present aspects of the several planets that circle similarly round the ,sun alike assure us of the course of aging as certainly as if time1 with all it brings about1 passed in one long procession before our very eyes4 ,death is a distressing thing to contemplate under any circumstances1 and not less so to a philosopher when that of a whole world is concerned4 ,to think that this fair globe with all it has brought forth must lapse in time to nothingness2 that the generations of men shall cease to be1 their very records obliterated1 is something to strike a chill into the heart of the most callous and numb endeavor at its core4 ,that ons must roll away before that final day is to the mind of the far-seeing no consolation for the end4 ,not only that we shall pass1 but that everything to show we ever were shall perish too1 seems an extinction too overpowering for words4 ,but vain regret avails not to change the universe's course4 ,what is concerns us and what will be too4 ,from facing it we cannot turn away4 ,we may alleviate its poignancy by the thought that our interest is after all remote1 affecting chiefly descendants we shall never know1 and commend to ourselves the altruistic example so nobly set us by doctors of medicine who1 on the demise of others at which--and possibly to which--they have themselves assisted1 show a fortitude not easily surpassed1 a fortitude extending even to their bills4 ,if they can act thus unshaken at sight of their contemporaries1 we should not fall behind them in heroism toward posterity4 ,having in our last chapter run the gantlet of the geologists1 we are in some sort fortified to face death--in a world--in this4 ,the more so that we have some millenniums of respite before the execution of the decree4 ,by the death of a planet we may designate that stage when all change on its surface1 save disintegration1 ceases4 ,for then all we know as life in its manifold manifestations is at an end4 ,to this it may come by many paths4 ,for a planet1 like a man1 is exposed to death from a variety of untoward events4 ,of these the one least likely to occur is death by accident4 ,this1 celestially speaking1 is anything which may happen to the solar system from without1 and is of the nature of an unforeseen catastrophe4 ,our ,sun might1 as we remarked1 be run into4 ,for so far as we know at present the stars are moving among themselves without any too careful regard for one another4 ,the swarm may be circling a central ,sun as ,andr states1 but the individual stars behave more like the random particles of a gas with licensed freedom to collide2 whereas we may liken the members of the solar system to molecules in the solid state held to a centre from which they can never greatly depart4 ,their motions thus afford a sense of security lacking in the universe at large4 ,such an accident1 a collision actual or virtual with another sun1 would probably occur with some dark star2 of which we sketched the ultimate results in our first chapter4 ,the immediate ones would be of a most disastrous kind4 ,for prefatory to the new birth would be the dissolution to make such resurrection possible4 ,destruction might come direct1 or indirectly through the ,sun4 ,for though the ,sun would be the tramp's objective point1 we might inadvertently find ourselves in the way4 ,the choice would be purely academic2 between being powdered1 or deorbited and burnt up4 ,so remote is this contingency that it need cause us no immediate alarm1 as ,i carefully pointed out4 ,but so strong is the instinct of self-preservation and so pleasurable the sensation of spreading appalling news1 that the press of ,america1 and incidentally ,europe1 took fire1 with the result1 so ,i have been written1 that by the time the pictured catastrophe reached the ,pacific 8it had assumed the dimensions of a first magnitude fact40 ,this is the first way in which our world may come by its death4 ,it is possible1 but unlikely4 ,for our ,earth1 long before that1 is morally certain to perish otherwise4 ,the second mode is one1 incident to the very constitution of our solar system4 ,it follows as a direct outcome of that system's mechanical evolution1 and may be properly designated1 therefore1 as due to natural causes4 ,it might be diagnosed as death by paralysis4 ,for such it resembles in human beings1 palsy of individual movement afflicting a planet instead of a man4 ,tidal friction is the slow undermining cause2 a force which is constantly at work in the action of every body in the universe upon every other4 ,as we previously explained1 the pull of one mass upon another is inevitably differential4 ,not only is the second drawn in its entirety toward the first1 falling literally as it circles round1 but the nearer parts are drawn more than the centre and the centre more than those farthest away4 ,we may liken the result to a stretched rotating rubber ball1 with1 however1 one important difference1--that each layer is more or less free to shear over the others4 ,the bulge1 solicited by the rotation to keep up1 by the disturber to lag behind1 is torn two ways1 and the friction acts as a break upon the body's rotation1 tending first to turn it over if it be rotating backward and then to slow it down till the body presents the same face in perpetuity to its primary4 ,the tides are the bulge1 not simply those superficial ones which we observe in our oceans1 and know to be so strong1 but substantial ones of the whole body which we must conceive thus as egg-shaped through the action that goes on--the long diameter of the egg pointing somewhat ahead of the line joining its centre to the distorting mass4 ,all the bodies in the solar system are thus really egg-shaped1 though the deformation is so slight as to escape detection observationally4 ,the knowledge is an instance of how much more perceptive the brain is than the eye4 ,for we are certain of the fact1 and yet to see it with our present means is impossible1 and may long remain so4 ,two concomitant symptoms follow the friction of the tidal ans3 a shift of the plane in which the rotation takes place1 and a loss of speed in the spin itself4 ,the first tends to bring the plane of rotation down to the orbital plane1 with rotation and revolution in the same sense4 ,this effect takes place quicker than the other1 and in consequence different stages may be noted in the creeping paralysis by which the body is finally overcome4 ,loss of seasons characterizes the first4 ,for the coincidence of the two planes means invariability in the ,sun's declination throughout the year for a given latitude4 ,this reduces all its days to one dead level in which summer and winter1 spring and autumn1 are always and everywhere the same4 ,there is thus a return at the end of the planet's career to an uneventful condition reminiscent of its start2 a senility in planets comparable to second childhood in man4 ,in large planets this outgrowing of seasons occurs before they have any1 while the planet is yet cloud-wrapped4 ,such planets know nothing of some attributes of youth1 like those unfortunate men who never were boys2 just as reversely the meteorites are boys that never grew up4 ,for if the planet be large1 the action of the tidal forces is proportionately more powerful2 while on the other hand the self-aging of the planet is greatly prolonged1 and thus it may come about that the former process outstrips the latter to the missing of seasons entirely4 ,this is sure to be the case with ,jupiter1 as the equator has already got down to within #c of the orbit1 and threatens to be the case with ,saturn4 ,these bodies1 then1 when they shall have put off their swaddling clothes of cloud1 will wake to climates without seasons2 globes where conditions are always the same on the same belts of latitude1 and on which these alter progressively from equator to pole4 ,variety other than diurnal is thus excluded from their surfaces and from their skies4 ,for the ,sun and stars will rise always the same1 in punctual obedience only to the slowly shifting year4 ,the next stage of deprivation is the parting with the day4 ,although the day disappears1 the result is too much day or too little1 depending on where you choose to consider yourself upon the afflicted orb4 ,for tidal friction proceeds to lengthen the twenty-four or other hours first to weeks1 then months1 then years1 and at last to infinity2 thus bringing the sun to a stock-still on the meridian1 to flood one side of the world with perpetual day and plunge the other in eternal night4 ,which of these two hemispheres would be the worse abode1 is matter of personal predilection2 dust or glacier1 deserts both4 ,everlasting unshielded noon would cause a wind circulation from all points of the enlightened periphery to the centre1 whence a funnel-shaped current would rise to overflow back into the antipodes1 thence to return by the horizon again4 ,as the night side would be several hundred degrees at least colder than the noon one1 all the moisture would be evaporated on the sunlit hemisphere1 to be carried round and deposited as ice on the other1 there to stay4 ,life would be either toasted or frapp4 ,a ,sahara backed by polar regions would be the obverse and the reverse of the shield4 ,illustration3 ,october #ae1 #ahif4 ,illustration3 ,february #ab1 #ahig4 ,illustration3 ,march #bf1 #ahig4 ,,venus--,,drawings ,,by ,,dr4 ,,lowell ,,showing ,,agreement ,,at ,,different ,,distances4 ,the reader may deem the picture a fancy sketch which possibly may not appeal to him4 ,nevertheless1 it not only is possible1 but one which has overtaken our nearest of neighbors4 ,to this pass the ,mater ,amorum1 ,venus herself1 has already been brought4 ,she betrays it by the wrinkles which modern observation has revealed upon her face4 ,innocent critics1 with a gallantry one would hardly have credited them1--which shows how one may wrong even the humblest of creatures1--have denied the existence of these marks of age1 on the chivalrous a priori assumption that it could not possibly be true because never seen before4 ,their negation1 in nave ignorance of the facts1 partakes the logic of the gallant captain1 who1 when asked by a lady to guess her age1 replied3 8',pon my word1 ,i haven't the slightest idea10 hastily adding1 8,but you don't look it60 ,less commendable than this conventional nescience1 but unfortunately more to the point1 is the evidence of prying scientific curiosity4 ,shrewdly divined as much as detected by ,schiaparelli1 made more certain by the crow's-feet disclosed at ,flagstaff1 and corroborated by the testimony of the spectroscope there1 her isochronism of rotation and revolution lies beyond a doubt4 ,attraction to her lord has conquered at last her who was the cynosure of all4 ,venus1 in her old age1 stares forever at the ,sun1 and we all know how ill an aging beauty can support a garish light4 ,mercury has been brought to a like pass4 ,this was evident even before the facts came out about ,venus1 for ,venus1 true to her instincts1 shields herself with a veil of air which largely baffles man's too curious gaze4 ,mercury1 on the other hand1 offers no objection to observation4 ,when looked for at the proper time1 his markings are quite distinct1 dark1 broken lines suggesting cracks4 ,schiaparelli1 again1 was the first to perceive the true state of the case1 and his observations were independently confirmed and extended at ,flagstaff in #ahif4 ,in so doing the latter disclosed a very interesting fact4 ,it was evident that the markings held in general a definite fixed position upon the illuminated part of the disk1 showing that the planet kept the same face always to the ,sun4 ,but systematic observation1 continued day after day for weeks1 disclosed a curious shift1 which1 though slight1 was unmistakable4 ,upon thought the cause suggested itself1 and on being subjected to calculation proved equal to such accounting4 ,in this singular systematic sway stood revealed the libration in longitude caused by the eccentricity of the planet's orbit4 ,illustration3 ,,diagram ,,of ,,libration ,,in ,,longitude ,,due ,,to ,,rotation4 ,illustration3 ,mercury4 ,effect of ,libration ,rotation #hh days4 ,mercury revolves about the ,sun in an ellipse more eccentric than that of any other principal planet4 ,at times he is half as far off again from him as he is at others4 ,when near1 he travels faster than when far4 ,for both reasons1 nearness and speed1 his angular revolution about the ,sun varies greatly from point to point according to where he finds himself in his orbit4 ,his rotation1 however1 is necessarily uniform4 ,for even the ,sun has no power at once to change the enormous moment of momentum of his axial spin4 ,in consequence1 at times his angular velocity of revolution gains on his rotation1 at other times loses1 both coming out together at the end of a complete ,mercurial year4 ,the result is a superb rhythmic oscillation1 a true mercurial pendulum compensated by celestial laws to perfect isochronism of swing4 ,the outward sign of this shows in the movement of the markings4 ,to observers in space like ourselves1 the planet seems to sway his head as he travels along his orbit4 ,for weeks he turns his face1 as shown by the markings on it1 more and more over to the left2 then turns it back again as far over to the right4 ,it is as if he were looking furtively around as he hastens over his planetary path4 ,venus1 of course1 is equally subject to this law of distraction1 but owing to the almost perfect circularity of her orbit she is less visibly affected4 ,in fact1 it is not possible to detect her lapse from a fixed regard to the ,sun4 ,at most it is no more than a glance out of the corner of her eyes--her slight deviation from perfect rectitude of demeanor4 ,knowledge of the laws governing such action alone permits us to recognize its occurrence4 ,mercury and ,venus are the only planets as yet that turn a constant face to their overruling lord4 ,the reason for this appears when one goes into the matter analytically4 ,the tidal force is not the direct pull of the ,sun on a particle of the body1 but the difference in the pulls upon a particle at the centre and one at the circumference4 ,being differential1 it depends directly upon the radius of the distorted body and inversely upon the third power of its distance away4 ,as the space through which the force acts is proportional to the force itself1 the effect is as the squares of the quantities mentioned1 or1 inversely1 as the sixth power of the distance and as the square of the body's radius4 ,the result thus proves greatest on the planets nearest to the ,sun1 and diminishes rapidly as we pass outward from him4 ,if1 then1 the solar force had had time enough to produce its effects1 it would be first in ,mercury and then in ,venus that it should be seen4 ,and this is precisely where we observe it4 ,the ,moon presents us a well-known case of such filial regard1 resulting in permanent incompetency of action on its own account4 ,it turns always the same face to us1 following us about with the mute attention of a dog to its master4 ,here again the libration may be detected1 for no dog but makes excursions on the road4 ,this case differs from those of ,mercury and ,venus in that the body to which the regard is paid is not also the dispenser of light and warmth4 ,in consequence1 though the side of the ,moon with which we are presented remains always the same1 we do not always see it2 the light creeping over it with the progress of the lunation1 from new to full4 ,on this account the worst that happens to our ,moon in its old age is that its day becomes its month4 ,illustration3 ,,moon--,,full ,,and ,,half1 ,,photographed ,,at ,,the ,,lowell ,,observatory4 ,our ,moon is not peculiar in having its day and its month the same4 ,on the contrary1 it is now the rule with satellites thus to protract their days4 ,so far as we can observe1 all the large satellites of ,jupiter turn the same face to him2 those of ,saturn pay him a like regard2 while about those of ,uranus and ,neptune we are too far off to tell4 ,their direct respect for their primary1 with only secondary recognition of the ,sun1 keeps them from the full consequences of their fatal yielding to attraction4 ,it is bad enough to have the day half a month long1 but worse to have one that never ends1 or1 still worse1 perpetual night4 ,in our diagnosis of the cause of death in planets1 we now pass from paralysis to heart failure4 ,for so we may speak of the next affection which ends in their taking off1 since it is due to want of circulation and lack of breath4 ,it comes of a planet's losing first its oceans and then its air4 ,to understand how this distressing condition comes about1 we must consider one of the interesting scientific legacies of the nineteenth century to the twentieth3 the kinetic theory of gases4 ,illustration3 ,,illustrating ,,molecular ,,motion ,,in ,a ,,gas 7,,black ,,molecules ,,here ,,considered ,,at ,,rest74 ,the kinetic theory of gases supposes them to be made up of minute particles all alike1 which are perfectly elastic and are travelling hither and thither at great speeds in practically straight lines4 ,in consequence1 these are forever colliding among themselves1 giving and taking velocities with bewildering rapidity1 resulting in a state of confusion calculated to drive a computer mad4 ,somebody has likened a quiet bit of air to a boiler full of furious bees madly bent on getting out4 ,the simile flatters the bees4 ,to follow the vicissitudes of any one molecule in this hurly-burly would be out of the question2 still more1 it would seem1 that of all of them at once4 ,yet no less ,herculean a task confronts us4 ,to find out about their motions1 we are therefore driven to what is called the statistical method of inquiry1--which is simply a branch of the doctrine of probabilities4 ,it is the method by which we learn how many people are going to catch cold in ,boston next week when we know nothing about the people1 or about colds1 or about catching them4 ,at first sight it might seem as if we could never discover anything in this hopelessly ignorant way1 and as if we had almost better call in a doctor4 ,but in the multitude of colds--not of counsellors--lies wisdom4 ,so in other things not hygienic4 ,as you cannot possibly divine1 for instance1 what each boy in town is going to do during the year1 nor what is his make of mind1 how can you say whether he will accidentally discharge a firearm and shoot his playmate or not6 ,and yet if you take all the boys of ,boston1 you can predict to a nicety how many will thus let off a gun and 8not know that it was loaded40 ,in this only genuine method of prophecy1 complete ignorance of all the actual facts1 we are able without knowing anything whatever about each of the molecules to predicate a good deal about them all4 ,to begin with1 the pressure a gas exerts upon the sides of a vessel containing it must be the bombardment the sides receive from the little molecules2 and the heating due this rain of blows1 or the temperature to which the vessel is raised1 must measure their energy of translation4 ,on this supposition it is found that the laws of ,avogadro and of ,boyle are perfectly accounted for1 besides many more properties of gases which the theory explains1 and as nothing yet has been encountered seriously contradicting it1 we may consider it as almost as surely correct as the theory of gravitation4 ,to three great geniuses of the last century we owe this remarkable discovery--,clausius1 ,clerk ,maxwell1 and ,boltzmann4 ,by determining the density of a gas at a given temperature and under a given pressure1 we can find by the statistical method the average speed of its molecules4 ,it depends on the most probable distribution of their energy4 ,for hydrogen at the temperature of melting ice1 and under atmospheric pressure1 this speed proves to be a little over a mile a second--a speed1 curiously enough1 which is to that of light almost exactly as centimetres to miles4 ,but some of the molecules are going at speeds much above the mean2 fewer and fewer as the speed gets higher4 ,just how many there are for any assigned speed1 we can calculate by the same ingenious application of unknown quantities4 ,illustration3 ,,distribution ,,of ,,molecular ,,velocities ,,in ,a ,,gas4 ,these speeds have been found for a temperature of freezing1 and as the speed varies as the square root of the absolute temperature1 we might suppose that when an adventurous or lucky molecule arrived at practically the limit of the atmosphere1 where the cold is intense1 it would become numbly sluggish4 ,but let us consider this4 ,when we enclose a gas in a cooler vessel1 the molecules bombard the sides more than they are bombarded back4 ,in consequence1 they lose energy2 as we say1 are cooled4 ,but in free air if a molecule be fortunate enough to elude its neighbors1 there is nothing to take away its motion but the ether through radiation1 and this is a very slow process4 ,thus the escaping fugitive must arrive at the confines of the air with the speed it had at its last encounter4 ,we reach1 then1 this result3 ,in space there is no such thing as temperature2 temperature being simply the aggregate effect of molecular temperament4 ,the reason we should consider it uncommonly cold up there is that fewer molecules would strike us4 ,quantity1 therefore1 in our estimation replaces quality1--a possible substitution which also accounts for some reputations1 literary or otherwise4 ,the only forces which could affect this lonely molecule would be the heating by the ,sun1 the repellent force of light1 and gravity4 ,now the speed which gravity on the ,earth can control is #f4i miles a second4 ,it can impart this to a body falling freely to it from infinite space1 and can therefore annul it on the way up1 and no more4 ,if1 then1 any of the molecules reach the outer boundary of the air going at more than this speed1 they will pass beyond the ,earth's power to restrain4 ,they will become little rovers in space on their own account1 and dart off on interstellar travels of their own4 ,this extension of the kinetic theory and of the consequent voyages of the molecules is due to ,dr4 ,johnstone ,stoney1 who has since1 humorously enough1 tried to stop the very balls he set rolling4 ,first thoughts are usually the best1 after all4 ,as among the molecules some are already travelling at speeds in excess of this critical velocity1 molecules must constantly be attaining to this emancipation1 and thus be leaving the ,earth for good4 ,in consequence there is a steady drain upon its gaseous covering4 ,furthermore1 as we know from comets' tails1 the repellent power of the light-waves1 what we may call the levity of light1 much exceeds upon such volatile vagrants the heat excitement or even the gravity of the ,sun1 so that we arrive at this interesting conclusion--their escape is best effected under cover of the night4 ,again1 the heavier the gas1 the less its molecular speed at a given temperature1 because its kinetic energy which measures that temperature is one-half the molecule's mass into the square of its speed4 ,thus their ponderosity prevents as many of them from following their more agile cousins of a different constitution4 ,so that the lighter gases are sooner gone4 ,water-vapor leaves before oxygen4 ,nor is there any escape from this escape of the gases4 ,it may take excessively long1 but go they must until a solitary individual who happens to have had the wrong end of the last collision is alone left hopelessly behind4 ,another factor also is concerned4 ,the smaller the planet1 the lower the utmost velocity it can control1 and the quicker1 therefore1 it must lose its atmosphere4 ,for a greater number of molecules must at every instant reach the releasing speed4 ,thus those bodies that are little shall1 perforce1 have less to cover themselves withal4 ,now this inevitable depletion of their atmospheric envelopes1 the aspects of the various planets strikingly attest4 ,they do so in most exemplary fashion1 according to law4 ,the larger1 the major planets1 as we have already remarked1 have a perfect plethora of atmosphere1 more than we at least know what to do with in the way of cataloguing yet4 ,the medium-sized1 like our own ,earth1 have a very comfortable amount2 ,mars1 an uncomfortable one1 as we consider1 and the smallest none at all4 ,all the smaller bodies of our system are thus painfully deprived so far as we can discover4 ,we are certain of it in the case of our ,moon and ,mercury1 the only ones we can see well enough to be sure4 ,in further evidence it has been shown at the ,yerkes and at ,flagstaff that no perceptible effect of air betrays itself in the spectroscopic imprint of the rings of ,saturn1 those tiny satellites of his1 and very recently a spectrogram of ,ganymede1 ,jupiter's third moon1 made at ,flagstaff for the purpose by ,mr4 ,e4 ,c4 ,slipher has proved equally void of atmospheric hint4 ,illustration3 ,,spectrogram ,,of ,,saturn--,,photographed ,,by ,,dr4 ,v4 ,m4 ,,slipher1 ,,lowell ,,observatory1 ,,october #aa1 #aijd4 ,,exposure #d ,,on 8#bg0 ,,gilt ,,edge ,,plate4 ,,long ,,camera ,,placed ,,beneath ,,the ,,slit4 ,,titanium ,,comparison ,,spectrum4 ,,enlargement ,,by ,,mr4 ,c4 ,o4 ,,lampland4 ,with the loss of water and of air1 all possibility of development departs4 ,not only must every organism die1 but even the inorganic can no longer change its state4 ,in the extinction thus not only of inhabitants but of the habitat that made them possible1 occurs a curious inversion of the order we are familiar with in the life history of organisms4 ,in planets it is the grandchildren that die first1 then the children1 and lastly their surviving parent4 ,and this is not accidental1 but inevitably consequent upon their respective origins4 ,for the offspring1 as we may spell it with a hyphen1 of any cosmic mass is of necessity smaller than that from which it issued4 ,being smaller1 it must age quicker4 ,in the natural order of events1 then1 its end must be reached first4 ,such has been the course taken1 or still taking1 by the bodies of our solar family4 ,the latest generation has already succumbed to this ebbing of vitality with time4 ,every one of the satellites of the planets--those of ,neptune1 ,uranus1 ,saturn1 ,jupiter1 and our own ,moon--is practically dead2 born so the smaller which never were alive4 ,our own ,moon carries its decrepitude on its face4 ,to all intents and purposes its life is past2 and that it had at one time a very fiery existence1 the great lunar craters amply testify4 ,it is now1 for all its flooding with radiance our winter nights1 the lifeless statue of its former self4 ,the same inevitable end1 in default of others1 is now overtaking the planetary group4 ,its approach is stamped on the face of ,mars4 ,there we see a world dying of exhaustion4 ,the signs of it are legible in the markings we descry4 ,how long before its work is done1 we ignore4 ,but that it is a matter of time only1 our study of the laws of the inexorable lead us to conclude4 ,mars has been spared the fate of ,mercury and ,venus to perish by this other form of planetary death4 ,last in our enumeration of the causes by which the end of a world may be brought about1 because the last to occur in order of time1 is the extinction of the ,sun itself4 ,certain to come and conclude the solar system's history as the abode of life1 if all the others should by any chance fail to precede it1 it fittingly forms the climax1 grand in its very quietude1 of all that went before4 ,by the same physical laws that caused our ,earth once to be hot1 the ,sun shines to-day4 ,only its greater size has given it a life and a brilliancy denied to smaller orbs4 ,the falling together of the scattered particles of which it is composed1 caused1 and still is causing1 the dazzling splendor it emits4 ,and so long as it remains gaseous1 its temperature must increase1 in spite of its lavish expenditure of heat1 as ,homer ,lane discovered forty years ago4 ,but the ,sun's store of heat1 immense as it is to-day1 and continued as it is bound to be for untold ons by means of contraction of its globe upon itself1 and possibly by other causes1 must some day give out4 ,from its present gaseous condition it must gradually but eventually contract to a solid one1 and this in turn radiate all its heat into space4 ,slowly its lustre must dim as it becomes incapable of replenishing its supply of motive power by further shrinkage in size4 ,fitfully1 probably1 like ,mira ,ceti to-day1 it will show temporary bursts of splendor as if striving to regain the brightness it had lost1 only to sink after each effort into more and more impotent senility4 ,at last some day must come1 if we may talk of days at all when the great event occurs when all days shall be blotted out1 that the last flicker shall grow extinct in the orb that for so long has made the hearth of the whole system4 ,for1 presciently enough1 the ,latin word focus means hearth1 and the body which includes within it the focus about which all the planets revolve also constitutes the hearth from which they all are lighted and warmed4 ,when this ultimate moment arrives and the last spark of solar energy goes out1 the ,sun will have reverted once more to what it was when the cataclysm of the foretime stranger awoke it into activity4 ,it will again be the dark body it was when our peering into the past first descries it down the far vista of unrecorded time4 ,ghostlike it will travel through space1 unknown1 unheralded1 till another collision shall cause it to take a place again among the bright company of heaven4 ,thus1 in our account of the career of a solar system1 we began by seeing with the mind's eye a dark body travelling incognito in space1 and a dark body we find ourselves again contemplating at the end4 ,in this kaleidoscopic biograph of the solar system's life1 each picture dissolves into its successor by the falling together of its parts to fresh adjustments of stability1 as in that instrument of pleasure which so witched our childish wonder in early youth4 ,just as when a combination had proved so pretty1 once gone1 to our sorrow no turning of the handle could ever bring it back1 so in the march of worlds no retrace is possible of steps that once are past4 ,inexorable permutations lead from one state to the next1 till the last of all be reached4 ,yet1 unlike our childhood's toy1 reasoning can conjure up beside the present picture far vistas of what preceded it and of what is yet to come4 ,hidden from thought only by the distraction of the day1 as the universe to sight lies hid by the day's overpowering glare1 both come out on its withdrawal till we wonder we never gazed before4 ,our own surroundings shut out the glories that lie beyond4 ,our veil of atmosphere cloaks them from our view4 ,but wait1 as an astronomer1 till the ,sun sinks behind the hills and his gorgeous gold of parting fades to amber amid the tender tapestry of trees4 ,the very air takes on a meaning which the flood of day had swamped4 ,seen itself1 no longer imperfectly seen through1 it wakes to semi-sentient existence1 a spirit come to life aloft to shield us from the too immediate vacancy of space4 ,the perfumes of the soil1 the trees1 the flowers1 steal out to it1 as the twilight glow itself exhales to heaven4 ,in the hushed quiet of the gloaming ,earth holds her breath1 prescient of a revelation to come4 ,then as the half-light deepens1 the universe appears4 ,one by one the company of heaven stand forth to human sight4 ,venus first in all her glory brightens amid the dying splendor of the west1 growing in lustre as her setting fades4 ,from mid-heaven the ,moon lets fall a sheen of silvery light1 the ghostly mantle of her ghostlike self1 over the silent ,earth4 ,eastward ,jupiter1 like some great lantern of the system's central sweep1 swings upward from the twilight bow to take possession of the night4 ,beyond lies ,saturn1 or ,uranus perchance dim with distance1 measuring still greater span4 ,all in order in their several place the noble cortge of the ,sun is exposed to view1 seen now by the courtesy of his withdrawal1 backgrounded against the immensity of space4 ,great worlds1 these separate attendants1 and yet as nothings in the void where stare the silent stars1 huge suns themselves with retinues unseen1 so vast the distances 'twixt us and them4 ,no less a revelation awaits the opening of the shutters of the mind4 ,if night discloses glimpses of the great beyond1 knowledge invests it with a meaning unfolding and extending as acquaintance grows4 ,sight is human2 insight seems divine4 ,to know those points of light for other worlds themselves1 worlds the telescope approaches as the years advance1 while study reconstructs their past and visions forth their future1 is to be made free of the heritage of heaven4 ,time opens to us as space expands4 ,we stand upon the ,earth1 but in the sky1 a vital portion not only of our globe1 but of all of which it1 too1 forms part4 ,to feel it is to enter upon another life2 and if to realization of its beauty1 its grandeur1 and its sublimity of thought these chapters of its history have proved in any wise the portal1 they have not been penned in vain4 ,,notes #a ,,meteor ,,orbits ,if the space of the solar system be equally filled with meteors throughout1 or if they diminish as one goes out from the ,sun according to any rational law1 their average speed of encounter with the ,earth would be nearly parabolic4 ,if they were travelling in orbits like those of the short-period comets1 that is with their aphelia at ,jupiter's orbit and their perihelia at or within the ,earth's1 their major axes would lie between #f4b and #e4b4 ,if we suppose their perihelion distances to be equally distributed according to distance1 we have for the mean a major axis of #e4g4 ,their velocity1 then1 at the point where they cross the ,earth's track would be given by #b #a v 7------ - ------ 71 #a #b4he in which #ah4e in miles per second #cdb4be1 whence v #bc4gf in miles per second4 ,suppose them to be approaching the ,earth indifferently from all directions4 ,at sunset the zenith faces the ,earth's quit2 at sunrise the ,earth's goal4 ,let be the real angle of the meteor's approach reckoned from the ,earth's quit2 the apparent angle due to compounding the meteor's velocity-direction with that of the ,earth4 ,then those approaching it at any angle #j less than that which makes #ij will be visible at sunset2 those at a greater angle1 at sunrise4 ,the angle #ja is given by the relation1 a cos ------ 1 x in which a is the ,earth's velocity1 x the meteor's1 and is reckoned from the ,earth's quit4 ,the portion of the celestial dome covered at sunset is1 therefore1 #cfj sin dd1 #j #j where is the azimuth1 #ahj #cfj that at sunrise1 sin dd4 #j ,if the meteors have direct motion only1 can never exceed #ij1 and the limits become1 #cfj for sunset1 sin dd1 #j #j #ij #cfj and for sunrise1 sin dd4 #j ,the mean inclination at sunset is #cfj sin dd1 #j #j 1 #cfj sin dd1 #j #j in which must be expressed in terms of 1 etc4 ,from this it appears that the relative number of bodies1 travelling in all directions and at parabolic speed1 which the ,earth would encounter at sunrise and sunset respectively would be3-- sunrise #e4h sunset #a4j and with the speed of the short-period comets1 sunrise #h4j sunset #a4j ,if1 however1 the bodies were all moving in the same sense as the ,earth1 i4e4 direct1 the ratios would be3-- ,,parabolic,,speed ,,of ,,short,,speed ,,of ,,actual ,,short-,,period ,,speed ,,period ,,comets ,,comets ,,about ,,jupiter ---------------------------------------- ------------------- ,sunrise #b4d #c4e #c4c ,sunset #a4j #a4j #a4j ,as the actual number encountered is between #b and #c to #a1 we see that the greater part must be travelling in the same sense as the ,earth1 since they come indifferently at all altitudes from the plane of her orbit4 #b ,,densities ,,of ,,the ,,planets ,the densities of the principal planets1 so far as we can determine them at present1 the density of water being unity1 are3-- ,mercury #c4fe ,venus #e4cf ,earth #e4ec ,moon #c4cb ,mars #c4ic -------- mean #d4cf ,jupiter #a4cc ,saturn #j4gb ,uranus #a4bb ,neptune #a4aa -------- mean #a4ji ,sun #a4ch ,the second decimal place is not to be considered as anything but an indication4 #c ,,variation ,,in ,,spectroscopic ,,shift ,in the case of a body reflecting light1 the shift differs from that for a body emitting it4 ,if the planet be on the further side of the ,sun1 the approaching rim advances both toward the ,sun and toward the ,earth1 thus doubling the shift4 ,the receding rim recedes in like manner4 ,at elongation the rims approach or recede with regard to the ,earth1 but not the ,sun1 and the shift is single as for emission4 ,at inferior conjunction rotational approach to the ,earth implies rotational recession from the ,sun1 and the two effects cancel4 #d ,,on ,,the ,,planets' ,,orbital ,,tilts ,the tilts of the plane of rotation of the ,sun and of the orbits of the several planets to the dynamical plane of the system tabulated are3-- ,sun #g ,mercury #f #ad ,venus #b #d ,earth #a #da ,mars #a #ch ,asteroids various ,jupiter #bj ,saturn #ef ,uranus #a #b ,neptune #dc where1 in the determination of that plane1 the latest values of the masses of the planets and the rotations of the ,sun1 ,jupiter1 and ,saturn have been taken into account4 ,these tilts suggest something1 doubtless1 but it is by no means clear what it is they suggest4 ,they are just as compatible with a giving off from a slowly condensing nebula as with an origin by shock4 ,the greater inclinations of ,mercury and ,venus may be due to their late birth from the central mass without the necessity of a cataclysm1 the rotation of that central mass out of the general plane being caused by the consensus of the motions of the particles from which it was formed4 ,the accordance of the larger planetary masses with the dynamical plane of the system would necessarily result from their great aggregations4 ,so that this1 too1 is quite possible without shock4 #e ,,planets ,,and ,,their ,,satellite ,,systems ,if we compute the speeds of satellites about their primaries in the solar system and compare them with the velocities in their orbits of the planets themselves1 a striking parallelism stands displayed between the several systems4 ,this is shown in the following table of them3 ,,parabolic ,,mean ,,speed1 ,,speed ,,at ,,ratio ,,speed ,,miles ,a ,,second ,,orbit ,,sat4 ,,about -------------------------------------- ,,primary ,,to of ,primary of ,satellite ,miles a ,,planet',s in ,orbit about ,primary second ,,speed ,v v ,,in ,,orbit ---------------------------------------- ------------------------ ,jupiter #h4a #aa4e ,sat4 #a #aj4g #a4cb #b #h4e #a4je #c #f4g #j4hc #d #e4a #j4fc ,saturn #f4j #h4e #a #i4j #a4ej #b #g4i #a4ca #c #h4b #a4cf #d #f4c #a4je #e #e4c #j4hi #f #c4e #j4ei #h #b4j #j4cd ,uranus #d4b #e4i #a #c4e #j4hb #b #b4i #j4gj #c #b4c #j4ed #d #b4j #j4dg ,neptune #c4d #d4h #a #b4g #j4ha ,the relations here disclosed are too systematic to be the result of chance4 ,the orbits of all these satellites have no perceptible eccentricity independent of perturbation except ,iapetus1 of which the eccentricity is about 4#jc4 ,in view of the various cosmogonies which have been advanced for the genesis of the solar system it is interesting to note what these speeds imply as to the effect upon the satellites of the impact of particles circulating in the interplanetary spaces at the time the system evolved4 ,to simplify the question we shall suppose--which is sufficiently near the truth--that the planets move in circles1 the interplanetary particles in orbits of any eccentricity4 ,taking the ,sun's mass as unity1 the distance ,r of any given planet from the ,sun also as unity1 let the planet's mass be represented by ,m and the radius of its satellite's orbit1 supposed circular1 as r4 ,we have for the space velocity of the satellite on the sunward side of the planet1 calling that of the planet in its orbit ,v and that of the satellite in its orbit round the planet v1 ,v - v 7#a_/,r7 - ,m_/r4 ,for a particle1 the semi-major axis of whose orbit is a and which shall encounter the satellite1 the velocity is v 7#b_/7,r-r7 - #a_/;a74 ,that no effect shall be produced by the impact of these two bodies1 their velocities must be equal1 or #a_/,r - ,m_/r #b_/7,r-r7 - #a_/;a ,as ,r-r a7#a e7 for the point of impact if the particle be wholly within the orbit of the planet and e the eccentricity of its orbit1 we find e #b ,,mr_/r - ,,rm_/r approx4 for the case of no action1 the other terms being insensible for the satellites in the table1 since in all r ,r_/#djj4 ,supposing1 now1 the particles within the orbit of the planet to be equally distributed according to their major axes1 then as the velocity of any one of them1 taking ,r-r ,r approx4 as unity1 is v 7#b_/a - #a_/;a71 the mean velocity of all of those which may encounter the satellite is1 at the point of collision1 77#b;a - #a7 _/ a7da ---------------------------------------- -------------------------------- da #b 7#b;a - a7 - #a_/7b7 log7#b;a - #a7 #b;a #j4ged2 that is1 just over three-quarters of the planet's speed in its orbit4 ,if we suppose the particles to be equally distributed in space1 we shall have more with a given major axis in proportion to that axis1 and our integral will become 7#b;a - #a7;a da ---------------------------------------- ------------------------ a da #h_/c 7#d;a-#a7_/h 7#b;a - a7 - 7#a_/af #b 7 log7#b;a - a7 #b a - #a_/7b #b 7 #j4gib of the planet's orbital speed4 ,the speed v1 then1 at which a satellite must be moving round the planet to have the same velocity as the average particle within the planet's orbit1 is ,v - v v4 ,this velocity is1 for the several planets3-- ,,distribution ,,of ,,distribution ,,of ,,particles ,,as ,,their ,,particles ,,equal ,,major ,,axes ,,in ,,space ------------------------------------ ,miles a second ,miles a second ---------------------------------------- ---- ,jupiter #b4j #a4f ,saturn #a4e #a4b ,uranus #a4j #j4i ,neptune #j4h #j4g ,if the satellite be moving in its orbit less fast than this1 its space-speed will exceed that of the average particle2 it will strike the particle at its own rear and be accelerated by the collision4 ,if faster1 the particle will strike it in front and retard it in its motion round its primary4 ,from the table it appears that all the large satellites of all the planets have an orbital speed round their primaries exceeding those in either column4 ,in consequence1 all of them must have been retarded during their formation by the impact of interplanetary particles and forced nearer their primaries than would otherwise have been the case2 and this whether the particles were distributed more densely toward the ,sun1 as #a_/;a1 or were equally strewn throughout4 ,for interplanetary particles whose orbits lie without the particular planet's path the mean speed is the parabolic at the planet's distance1 given in the third column of the table4 ,this is the case on either supposition of distribution4 ,the orbital speed of the satellite which shall not be affected by collisions with them is1 for the several planets3-- ,,miles ,a ,,second ---------------------- ,jupiter #c4d ,saturn #b4e ,uranus #a4g ,neptune #a4d ,all the satellites but ,iapetus have orbital speeds exceeding this1 and consequently are retarded also by these particles4 ,for particles crossing the orbit 7#b7 the mean velocity would be practically parabolic1 #a4d1 even if the distribution were as #a_/r1 r being the distance from the ,sun4 ,the effect would depend upon the angle of approach and in the mean give a greater velocity for the particle than for the satellite within the orbit1 a less one without2 retarding the satellite in both cases4 ,thus the total effect of all the particles encountering the large satellites is to retard them and to tend to make them hug their primary4 ,for retrograde satellites the velocities of impact with inside and outside particles moving direct are respectively3 ,,inside ,,outside ----------------------------- ,jupiter #b4j v v #c4d ,saturn #a4e v v #b4e ,uranus #a4j v v #a4g ,neptune #j4h v v #a4d ,in both cases the impact tends to check the satellite4 ,comparing with these the velocities of impact for direct satellites in a direct plenum3-- ,,inside ,,outside ------------------------------- ,jupiter #b4j - v #c4d - v ,saturn #a4e - v #b4e - v ,uranus #a4j - v #a4g - v ,neptune #j4h - v #a4d - v the signs being taken positive when the motion is direct1 we see that retrograde satellites would be more arrested than direct ones with the same orbital speed round the primary4 ,in a plenum of direct moving particles1 then1 the force tending to stop the satellite and bring it down upon the planet is greater for retrograde satellites than for direct ones4 ,if1 therefore1 the positions of the satellites have been controlled by the impact of interplanetary particles1 the retrograde satellites should be found nearer their planets than the direct ones4 #f ,,on ,,the ,,induced ,,circularity ,,of ,,orbits ,,through ,,collision ,since the moment of momentum is the velocity into the perpendicular upon its direction1 in the time dt it is3-- vp dt h dt rd4 ,the whole moment of momentum from perihelion to perihelion is therefore3-- #cfj rd a7#a-;e7_/#a-;e #cfj 7-e sin 7_/7#a;e cos 7 #b_/7a-;e7 tan 7#a-;e7_/7#a;etan 7_/#b77 #b;a 7#a - e71 which is twice the area of the ellipse4 ,the energy in the ellipse during an interval dt is 77mvdt 77m7#b_/r - #a_/;a7dt1 from the well-known equation for the velocity in a focal conic4 ,the integral of this for the whole ellipse is #cfj 77mv dt 777m_/h77#br - r_/a7d ma4 ,since rd 7a #a - e7_/7#a e cos 7d 7#b;a #a -e7_/7#a -e7 tan77#a -e7_/7#a e7tan 7_/#b77 and r d is given above4 ,by collision a part of this energy is lost1 being converted into heat4 ,the major axis1 a1 is1 therefore1 shortened4 ,but from the expression #b;a 7#a-;e7 for the moment of momentum we see that this is greatest when e is least4 ,if1 therefore1 a is diminished1 e must also be diminished1 or the moment of momentum would be lessened1 which is impossible4 #g ,,capture ,,of ,,satellites ,see has recently shown 7,astr4 ,nach4 ,no4 #dcda-db7 that a particle moving through a resisting medium under the attraction of two bodies revolving round one another in circles may eventually be captured by one of them though originally under the domination of both4 ,the argument consists in introducing the effect of a resisting medium upon the motion in the space permitted by ,jacobi's integral1 following ,darwin's examination of this space4 ,in the actual case of nature the effect is much more complicated1 and at present is not capable of exact solution for masses other than indefinitely small1 even supposing circular orbits for the chief bodies4 ,it may1 however1 explain the curious relation shown in the arrangement of the direct and retrograde movement of satellites4 ,,index ,a ,abnormality1 the survival of original state1 #add1 #adf4 ,absorption in spectrum1 planetary1 #eb1 #afa4 of ,uranus1 #aah4 of ,jupiter1 #aeb4 of ,saturn1 #aeb4 ,achilles1 #id4 ,adams1 #aai1 #aba4 ,adams1 ,mr4 ,j4 ,c41 #abc-abf4 ,agassiz1 #da4 ,airy1 #aba1 #abc4 ,albedo1 of dark star1 #bg4 of ,mercury1 #fb1 #gc-ge4 of ,venus1 #gc-ge4 of ,moon1 #ge4 of ,jupiter1 #ajd1 #aje4 of ,saturn1 #aji4 of ,uranus1 #aaf4 of ,neptune1 #afh4 of clouds1 #aie4 ,algol1 #c4 ,american ,academy1 #abe4 ,amphibians1 first record of1 #ahh4 ,anderson1 ,dr4 ,thomas ,d41 #h1 #ab4 ,andr1 #bae4 ,andromeda1 great nebula in1 #aj1 #bj1 #ba4 constitution disclosed by spectroscope1 #de1 #dh4 ,apex of ,sun's way1 #bf4 ,arago1 #aba4 ,asteroids1 #ci1 #fj1 #fa1 #id-ajb4 domain of1 #id4 diminutive size1 #id1 #aja4 number1 #id1 #aja4 peculiar discovery of1 #ie-ih4 never formed part of a pristine whole1 #ih4 where thickest1 #ih4 formation of large planet from1 prevented1 #ih1 #ii4 mid-course between planets and comets1 #ajj4 shape of1 #aja1 #ajb4 mammoth meteorites1 #ajb4 mark transition between inner and outer planets1 #ajb4 ,atmosphere1 spectrographic study of1 #ec1 #ed1 #afa4 ,mercury deprived of1 #ga1 #ge1 #bcb4 reflecting power1 #ge4 of ,venus1 #ge4 ,moon deprived of1 #ge1 #bcb4 thin on ,mars1 #ge1 #ia1 #bcb4 of ,uranus1 enormous1 #aag1 #aah1 #bcb4 of ,neptune1 vast1 #aah1 #bcb4 of ,jupiter1 #aff1 #bcb4 depletion of1 #bca-bcc4 none on ,ganymede1 #bcb1 #bcc4 of ,saturn1 #bcb4 lacking in ,saturn's rings1 #bcb4 ,avogadro1 #bbh4 ,axes of planets1 systematic righting of1 #acb4 tilts accounted for1 #adf4 ,b ,babinet1 #adg4 ,backland1 #fh4 ,ball1 ,sir ,robert1 #ade4 ,barrande1 ,m41 #agh4 ,belopolski1 #hg4 ,bessel1 #abj1 #aba4 ,blandet1 ,m41 #age1 #agf4 ,bode1 #ie1 #aai4 ,bode's law1 #if1 #ajj1 #aai1 #abb1 #abf4 ,bolometer1 #aid4 ,bolton1 ,mr4 ,scriven1 #ajc1 #aje1 #ajf4 ,boltzmann1 #bbh4 ,bose1 #aeg4 ,bouvard1 ,alexis1 #abj1 #aba4 ,boyle1 #bbh4 ,bradley1 #fh4 ,c ,cambrian era1 #agh4 ,cambridge ,observatory1 #abc4 ,campbell1 #i4 ,carboniferous period1 #agi4 ,cassini1 #gf1 #afb4 ,celestial mechanics1 #bh1 #id1 #aee4 ,ceres1 #aja4 ,challis1 #abc4 ,chemistry1 indebted to the stars1 #afj4 ,clausius1 #bbh4 ,clerke1 ,miss1 #i1 #afd4 ,climate1 advent of1 #ahe4 ,clouds1 none on ,venus1 #ge4 of ,jupiter not ordered as ours1 #ajg1 #afc1 #afg4 ,uranus wrapped in1 #afh4 ,neptune wrapped in1 #afh4 ,earth once wrapped in1 #agj1 #aga1 #agh4 ,collision of dark star with ,sun1 #be1 #bae4 warning of1 #bf-bi4 disturbances previous to1 #bi1 #cj4 rarity of event1 #cj4 ,collisions between meteorites of a flock1 #aa1 #di4 causing light1 #di1 #ej4 ,columbus1 #ahh4 ,comets1 #cc1 #fa4 members of solar system1 #cd1 #ce4 orbits of1 #fa1 #ajj4 ,commensurability of orbital period1 #ii1 #aaa4 ,congruities of solar system1 #abh-acg4 deviations from1 #fb1 #ajj1 #aja1 #acj1 #aca1 #ada4 specify mode of evolution1 #acg4 ,convection currents1 #bai4 in atmosphere of ,venus1 #hj4 ,copeland1 ,dr4 #g4 ,copernican system1 #eh4 ,copernicus1 #fb4 ,cosmic action1 #a1 #bb1 #ahd4 ,croll1 #aif4 ,cuticle of star1 effect of impact on1 #aa4 ,d ,dana1 #agg1 #ahf1 #ahi4 ,dark stars1 origin1 #b4 number1 #b1 #be4 evidence of1 #c-e4 collision of1 #aj1 #aa4 rendered visible1 #bf4 ,darwin1 #fb1 #ach1 ,notes #beb4 ,day1 lengthened to infinity1 #gj1 #bai4 none on ,venus1 #hc4 ,jovian1 #afc4 first appreciation of1 #ahf4 coincides with month1 on satellites1 #bbe4 ,death of a planet1 defined1 #bad4 catastrophic cause1 #bae1 #baf4 due to tidal retardation of rotation1 #baf-bai4 outcome of loss of oceans and air1 #bbf1 #bcc4 caused by extinction of ,sun itself1 #bcd4 ,density1 of dark star1 #bg4 of planets1 #ea1 ,notes #bdc4 of ,mercury1 #fc1 #fd4 of ,venus1 #ij4 of ,jupiter1 #ajc1 #aag4 of ,uranus1 #aae4 ,deserts1 increase of1 on ,earth1 #bjh-baa4 ,devonian era1 #ahg4 ,dhurmsala meteorite1 #da4 ,diameter1 of ,mercury1 #fc1 #fd1 #ff1 #fg4 of ,venus1 #ij4 of ,earth1 #ij4 of ,mars1 #ia4 of satellites of ,mars1 #ib4 of ,jupiter1 #ajc4 of ,uranus1 #aae-aag4 ,dust1 in atmosphere of ,venus1 #ge4 ,e ,earth1 characteristics1 not universal1 #ij1 #ia1 #aee4 evolved from a nebula1 #adi4 internal heat1 #aej4 early surface temperature1 #afj1 #afi1 #agj4 once cloud-wrapped1 #agj1 #aga1 #agh4 solid surface formed1 #aga4 hot seas of1 #aga1 #agb4 self-sustained1 #ahb4 study of1 within province of astronomy1 #ahd4 ceased to be self-centred1 #ahg4 ,sun becomes dominant factor in organic life of1 #aij4 ,earth shine1 #hb4 ,eccentricity1 orbital1 of ,mercury1 #fc1 #fe1 #fi1 #bbb4 of asteroids1 erratic1 #ajj1 #aja4 of satellites1 increases with distance from primary1 #acd4 ,eclipsing binaries1 #c1 #d4 ,ejectum from nova1 #e1 #af4 rate of regression1 #af4 ,elemental substances1 #aei4 in ,sun1 #aei4 once in ,earth1 #afj4 discovery of1 in stars1 #afa1 #afb4 ,ellipticity1 of ,jupiter1 #ajc4 of ,saturn1 #aji4 of ,uranus1 #aae4 ,encke1 #fh4 ,energy1 conservation of1 #adj1 #aej1 #aea4 dissipation1 #adj-adb4 conditions for a minimum1 #adb4 ,eros1 fluctuation of light of1 gives evidence of form1 #aja1 #ajb4 ,evolution1 #aec4 white nebul in process of1 #di4 rounded out1 #ef4 of solar family1 #ajj4 evidence of1 in solar system1 #aag4 manner of1 lessens energy1 #ada4 ,evolution1 chemical1 #aee1 #agc4 universal1 #aef4 temperature conducive to1 #aeg1 #aeh4 attendant upon cooling1 #aeh1 #afb4 steps in1 shown by spectroscope1 #afa4 ,evolution1 physical1 #aee1 #afb4 induced by cooling1 #afb4 ,f ,fabry1 #cd4 ,fauna1 #agh1 #agi1 #ahg4 ,faye1 #age1 #agf4 ,flagstaff1 ,arizona1 #eb1 #ff1 #fh1 #gi1 #hc1 #hi1 #ib1 #ajf1 #aaj1 #bba1 #bcb4 clear and steady air of1 #ff1 #hf4 ,flamstead1 #aai4 ,fleming1 ,mrs41 #g4 ,flemming1 #abj1 #aba4 ,flora1 of paleologic times1 #agg4 ,french ,academy1 #abb4 ,g ,galle1 ,dr41 #abb1 #abc1 #abe4 ,gases1 peculiar to nebul1 #aa1 #af4 occluded in meteorites1 #db1 #dc4 in atmospheres of planets1 #ec-ee4 ,gauss1 #cd1 #if1 #ig4 ,geikie1 #afj1 #agg1 #ahi4 ,geology1 relation to astronomy1 #agc1 #agd1 #ahc1 #ahd4 scope of1 #agd1 #bjc4 ,geysers1 avenues to earlier state1 #afj4 ,goodricke1 #c4 ,h ,hakluyt1 #ahh4 ,harvard ,college ,observatory1 #h1 #ab4 ,heat1 molecular motion1 #aej1 #aeg1 #bcj4 the result of evolving1 #aec4 the preface to higher evolution1 #aec1 #aef4 laws governing amount of1 #aij4 atmosphere keeps out1 as well as stores1 #aia4 effective1 received from ,sun1 #aib-aid4 invisible rays1 #aid4 retained1 #aid-aif4 radiated1 #aid-aif4 ,heat of condensation of ,earth1 accuses concourse of particles1 #aea4 evaluated1 #aea1 #aeb4 sufficient for geologic phenomena1 #aeb4 ,hector1 #id4 ,helmholtz1 #aea4 ,hencke1 #ih4 ,herschel1 ,sir ,john1 #abb4 ,herschel1 ,sir ,william1 #if1 #aad1 #afb4 ,hertha1 periodic variability1 #ajb4 ,hipparchus1 #e4 ,holden1 #i4 ,hubbard1 ,professor1 #abd4 ,huggins1 #eb4 ,humphreys1 #aj4 ,huntington1 #bji4 ,i ,ice ,age1 #aif4 not of orbital occasioning1 #aig-aii4 increased precipitation1 the cause1 #aii1 #bjj4 a local affair1 #bjj-bjb4 ,irradiation1 affecting diameter of ,mercury1 #ff1 #fh4 ,j ,jacobi1 ,notes #beb4 ,julius1 ,professor1 #aj4 ,juno1 #aja4 ,jupiter1 #ajc-ajh4 not solid1 #ajd1 #ajg4 a semi-sun1 #aje1 #ajh1 #aeb1 #aff1 #afg4 white spots of1 #ajf4 ,jupiter1 8great red spot0 of1 #afd4 time of rotation1 #afd4 a vast uprush of heated vapor1 #afe1 #aff4 ,jupiter's belts1 secular progression1 #ajd4 rotate at different speeds1 #ajd1 #afb1 #afc4 color1 #ajd4 wisps across1 #aje1 #ajf4 bright ones1 cloud1 #afc1 #afg4 spectrographic study of1 #aff4 ,k ,kapteyn1 #ad4 ,keeler1 #ai1 #eb1 #aaj4 ,kepler1 #f4 ,kinetic theory of gases1 #bbf1 #bbh4 corollary of1 #ed4 extension of1 #bcj1 #bca4 ,kirkwood1 ,professor1 #ce4 ,l ,lagrange1 #id1 #ig4 ,lalande1 #abc1 #abd4 ,lane1 ,homer1 #bcd4 ,langley1 #aia1 #aid4 ,laplace1 #cd1 #aaj1 #abg1 #abi1 #aca1 #acb1 #ach1 #aci1 #adg1 #aeb1 #age4 ,laplacian cosmos1 #abi1 #acj4 false congruities of1 #aca-acc4 annular genesis1 disproved1 #ach1 #aci4 original 8fire-mist0 of1 impossible1 #ach4 ,lapparent1 de1 #agc-agf1 #ahc1 #ahi4 ,lemonnier1 #aae1 #aai4 ,leonard1 ,miss1 #gi4 ,leverrier1 #aai1 #aba-abf4 ,lexell1 #aae4 ,libration in longitude1 of ,mercury1 #fe1 #fi1 #gj1 #bbb1 #bbc4 causes true day1 #gj1 #ga4 of ,venus1 inappreciable1 #hc1 #bbc4 of ,moon1 #bbd4 ,lick ,observatory1 #ac1 #ad4 ,lockyer1 #dh4 ,lowell ,observatory1 #fe1 #gd4 ,m ,major planets1 gaseous1 #aag4 constitution of1 differs from ,sun or ,earth1 #afa4 types of early planetary stages1 #afb4 self-centred and self-sustained1 #afh4 ,man1 immanent1 #aei4 ,mars1 polar caps1 #aih4 canals in dark regions1 #bjf1 #bjg4 dying of exhaustion1 #bcd4 ,mass1 of ,mercury1 #fc1 #fd1 #fh4 of ,mars1 #ia4 of ,jupiter1 #ajc4 arrangement of1 in solar system1 #ace-acg1 #adh4 ,massachusetts ,institute of ,technology1 #acd1 #ahd4 ,mauvais1 #abe4 ,maxwell1 ,clerk1 #aaj1 #aac1 #bbh4 ,mayer1 #aai1 #aea4 ,mendeleff1 #afa4 ,mercury1 #fb-gc4 time of rotation and revolution the same1 #fe1 #fi4 axis stands plumb to orbit1 #gj4 turns same face to the ,sun1 #gj1 #gb1 #acd1 #bba4 surface markings1 #gb1 #bba4 color1 #gb4 ,meteorites1 #ca1 #ce1 #cf4 cosmic bodies1 #cb1 #cc4 relation to shooting-stars1 #cf4 members of solar system1 #cf4 composition1 #dj-dd1 #ee4 fused by friction with atmosphere1 #dj4 temperature1 #da1 #ee4 fragments of a dark body1 #dd4 link past to present1 #dd1 #ef1 #eg1 #acj4 ,meteors1 orbits of1 #cf1 #ci1 ,notes #bda-bdc4 visibility of1 #ch4 ,meteor-streams1 #cc1 #fa4 first recognition of1 #cd4 disintegrated comets1 #cd4 ,michelson1 #aj4 ,milham1 ,professor1 #ii4 ,mira ,ceti1 #bce4 ,mohler1 #aj4 ,molecular speeds1 gaseous1 #bbh-bca4 critical velocity1 #bcj1 #bca4 ,molecule1 organic1 power in its instability1 #afj4 ,moment of momentum1 #adj1 ,notes #bej4 cause of original1 #acj4 ,moment of momentum1 conservation of1 #adj4 applied to solar system1 #ada-adc4 ,momentum1 #adj4 ,monck1 ,mr41 #aj4 ,moon1 turns same face to ,earth1 #acd1 #bjh1 #bbd1 #bbe4 once fiery1 now dead1 #bcc1 #bcd4 ,mountains1 none on ,mars1 #ia4 ,mller1 #gc1 #gd1 #ajd1 #aje1 #aaf4 ,n ,naval ,observatory at ,washington1 #abb4 ,nebul1 origin of1 #aj1 #aa4 amorphous1 #ah1 #dd4 planetary1 #ah4 spectrum of amorphous1 #de4 ,nebul1 spiral1 #ag-be1 #dd4 evolved from disrupted stars1 #aj-ae4 relation to nov1 #ad-af4 corpuscular character of1 #ae1 #af4 knots and patches of1 #ae4 most common1 #ai1 #bj4 two-armed1 #bj1 #be4 central nucleus1 globular1 #ba4 not due to explosive action1 #bb1 #bc1 #be4 not caused by disintegration1 #bd1 #be4 cause of development1 #bd1 #be4 spectrum of1 #de-dh4 composed of flocks of meteorites1 #dh1 #di4 constitution established by spectroscope1 #di1 #ej4 ,nebular hypotheses1 #agc4 ,neologic times1 clearing of sky in1 #ahe4 ,neptune1 #aah4 rotates backward1 #aah4 owes discovery to mathematical triumph1 #aai-abf4 faint belts on1 #afh4 further advanced than giant planets1 #afh4 ,newcomb1 #fg4 ,newton1 ,professor1 #cf1 #db4 ,newton1 ,sir ,isaac1 #cd4 ,nova ,aurig1 #g1 #h1 #ab4 history chronicled by its spectrum1 #h1 #i4 ,nova ,cygni1 #g4 ,nov1 #f1 #g4 origin #e1 #aj4 first chronicled1 #e4 spectroscopic study of1 #g4 ,nova ,persei1 #g4 history of1 #ab-ae4 ,o ,oceans1 none on ,mars1 #ia4 evaporation of1 #bjd4 basins of1 on ,moon1 #bjd-bjh4 basins of1 on ,mars1 #bjf1 #bjg4 ,olbers1 #ig4 ,olmstead1 ,professor1 #cc4 ,orbital distance1 of ,mercury1 #fb4 of ,venus1 #gc4 of ,mars1 #ia4 of ,eros1 #id4 of ,saturn1 #ajh4 ,orbital tilts1 of asteroids1 erratic1 #ajj1 #aja4 of satellites of ,uranus1 #aaf4 of planets1 substantially the same1 #abi-aca1 ,notes #bdd4 deviation from rule1 by ,mercury1 #aca4 of satellites1 increase with distance from primary1 #acc1 #acd4 ,orbits1 determining factors1 #ce4 rendered more circular by collisions1 #ada-adc1 ,notes #bej1 #bea4 made more conformant to general plane by collisions1 #ada-adc4 ,orion1 great nebula in1 #ah4 ,p ,paleologic times1 much warmth and little light in1 #agb4 fallacies in geologists' expositions of1 #agd-agf4 climate continuous1 #agg1 #ahf4 seas warm1 #agg1 #agh4 explained by cloud envelope1 #agh4 corroboration of explanation1 #ahg1 #agi4 excessive rain in1 #ahe1 #ahf4 passage into ,neologic1 essentially astronomic1 #ahe4 ,pallas1 #aja4 ,parabolic speed at orbit1 ,notes #bde4 ,patroclus1 #id4 ,peirce1 #aaj1 #abe1 #abf4 ,perrine1 #ae4 ,perrotin1 #aaf4 ,perturbations1 in motion of planets1 heralding a catastrophe1 #bh1 #cj4 reflected1 #fc4 mass of planet determined by1 #fh4 of asteroids by ,jupiter1 #ih1 #ii4 restrictive action of1 #ii4 the fashioning force of planetary orbits1 #ii1 #ajj4 of rings of ,saturn by satellites1 #aaa1 #aab4 of ,uranus lead to discovery of ,neptune1 #aba-abf4 ,petersen1 ,dr41 #abc4 ,photometric determinations1 #ib1 #ic4 background1 the fundamental factor in1 #ib1 #ic4 ,piazzi1 #if4 ,pilgrim ,star1 #e1 #f4 ,planetary astronomy1 advance in1 #ei1 #fj4 ,planetology1 #bjc4 defined1 #agc1 #agd4 ,planets1 #fa4 knots in spiral nebul1 #be1 #aci4 developed by agglomeration1 #adc1 #adi1 #aea1 #aeb4 ,pliny1 #e4 ,plutonic rocks1 #afj4 ,pluvial eras1 contemporaneous with glacial1 #bjj4 ,polyp corals1 in paleologic times1 #ahf4 ,pristine motion of planetary particles1 retrograde1 #add4 superfluous energy in1 #ade4 unstable1 #ade4 ,ptolemaic system1 #eh4 ,r ,refrigeration1 tempered by loss of cloud1 #aif4 ,revolutions1 of shooting-stars1 #ci4 of asteroids1 direct like planets1 #ajj4 planetary1 in same sense1 #abi1 #acj4 outermost satellites1 retrograde1 #acb4 of satellites explained1 #adf1 #adg1 ,notes #beb4 ,ritchey1 #ad4 ,roberts1 ,dr41 #bj4 ,roche1 ,edouard1 #aaj4 ,rosse1 ,lord1 #ag4 ,rotation of planets1 #aca1 #acb4 systematic righting of axes1 #acb4 initially1 retrograde1 #adf4 ,rotation period1 of ,venus1 spectrographically determined1 #hc1 #he-ij4 of ,mars1 spectrographically determined1 #hh1 #hi4 of ,jupiter1 spectrographically determined1 #hi4 of ,uranus1 #aaf4 ,royal ,observatory1 ,edinburgh1 #g4 ,s ,satellites1 #fa4 of ,mars1 #ib4 of ,saturn1 #ajh1 #aab4 of ,uranus1 #aaf4 solid1 #aag4 of ,neptune1 #aah4 turn same face to primaries1 #acd1 #adg1 #adh1 #bbe4 latest discoveries in regard to motions of1 #adf4 origin of1 #adg4 death of1 before planet1 #bcc4 impact of interplanetary particles on1 ,notes #bdf-bej4 capture of1 ,notes #bea1 #beb4 ,saturn1 #ajh-aad4 belts of1 #aji1 #afh4 inherent light1 #aji1 #aeb4 ,saturn's rings1 #aji-aad4 mechanical marvel of1 not early appreciated1 #aaj4 discrete particles1 #aaj1 #ace4 knots upon1 #aaj-aac4 not flat1 but tores1 #aaa-aad4 show devolution--not pristine state of solar system1 #ach1 #aci4 once a congeries1 #aci4 ,schaeberle1 #i4 ,schiaparelli1 #cd1 #cf1 #fd-ff1 #fi1 #gf1 #gg1 #bba4 ,schroeter1 #fe1 #gg4 ,seasons1 loss of1 #ga1 #hc1 #bag1 #bah4 begin with clearing of sky1 #ahe4 fully developed1 #ahi4 ,see1 ,notes #bea4 ,seeliger1 #aj4 ,shooting-stars1 #cc1 #ce4 radiant of1 #cc1 #cf4 members of solar system1 #cf-dj4 tiny planets1 #ci4 ,siderite1 #cf4 ,silurian era1 #agh4 ,sirona1 periodic variability of1 #ajb4 ,sky1 cause of clearing1 #ahg4 ,slipher1 ,dr4 ,v4 ,m41 #eb1 #gi1 #hc1 #hf1 #hh1 #hi1 #aag1 #afa1 #aff4 ,slipher1 ,mr4 ,e4 ,c41 #gi1 #bcc4 ,solar constant1 #aia4 ,solar system1 evolved from a dark star1 #dd4 evidence of origin1 #ea1 #acj4 characteristics of1 #fj-fb4 evolutionarily one1 #fb4 gap in progression of orbital distances1 #ie-ajj4 bodies of1 egg-shaped1 #bag4 ,specific gravity1 of stone and iron1 #dd4 ,spectroscope1 #g1 #hd4 ,spectroscopic shift1 #hd4 determining velocity1 #c4 in ,nova ,aurig1 #i4 produced by great pressure1 #aj1 #ac4 produced by anomalous refraction1 #aj4 produced by change of density1 #aj1 #ac4 explained1 #he4 variation in1 ,notes #bdc1 #bdd4 ,spectrum1 of ,nova ,persei1 #ab1 #ac4 nebular1 #ac1 #af1 #de-dh4 peculiarities of nebular1 explained1 #ej4 photographic extension of1 #eb1 #aag1 #afa4 of major planets1 #eb1 #ec1 #afa4 of belts of ,jupiter1 #aff4 ,spiral structure1 implies rotation combined with motion out or in1 #bb4 ,stability of a system1 condition for1 #adj1 #ada4 ,stoney1 ,dr4 ,johnstone1 #bca4 ,struve1 #aji4 ,suess1 #agi4 ,sun1 original slow rotation of the1 #acj4 heat of1 #bcd1 #bce4 reversion to a dark star1 #bce1 #bcf4 ,sun spots1 #ajd1 #aff4 ,t ,temperature1 of ,moon1 #aia1 #aib4 of ,mars1 #aib1 #aid1 #aif4 defined1 #bcj4 no such thing as1 in space1 #bcj4 ,tercidina1 periodic variability of1 #ajb4 ,tertiary times1 entrance of color with1 #ahi1 #aij4 ,tidal action1 #adc-adg1 #baf-bah4 causes loss of energy1 #add4 inoperative1 #add1 #ade1 #adg4 changes retrograde rotation of planet to direct1 #ade-adg1 #bag4 on satellites1 #adg4 slows down spin1 #adh1 #bag4 brings plane of rotation down to orbital plane1 #bag4 lengthens day to infinity1 #bai4 analytically expressed1 #bbd4 greatest on planets near ,sun1 #ace1 #bbd4 ,tidal action1 disruptive1 #acj4 exemplified by spiral nebul1 #bd1 #be4 hinted at1 by meteorites1 #ee4 theory corroborated by densities of planets1 #ea4 theory corroborated by atmospheres of planets1 #eb-ee4 on comets1 #aci4 cause of ,saturn's rings1 #aci4 ,tisserand1 #fh4 ,titius1 #ie4 ,todd1 #fh4 ,trees1 deciduous1 first appearance of1 #ahi4 ,trilobites1 blindness of1 #agh1 #agi4 ,twining1 #cc4 ,tycho ,brahe1 #e4 ,u ,uranus1 #aad-aah4 history of discovery1 #aad1 #aae1 #aai4 a ball of vapor1 #aae1 #aag4 belts of1 #aae1 #aaf1 #afh4 tilt of axis to ecliptic1 great1 #aae4 spectroscopic revelations of1 #aag1 #aah4 in an early amorphous state1 #aah4 further advanced than the giant planets1 #afh4 ,v ,velocity1 of ,mercury in orbit1 #fc4 of satellites about primary1 ,notes #bde4 of major planets1 in orbit1 ,notes #bde4 ,venus1 #gc-ij4 surface markings1 #gd1 #gg1 #gi1 #hj1 #hc1 #bbj1 #bba4 brilliancy due to cloudless atmosphere1 #ge4 importance of rotation period1 #ge1 #gf4 turns same face to the ,sun1 #gg-hj1 #acd1 #bbj1 #bba4 ice on the night side1 causes ashen light1 #hb4 ,very1 ,professor1 #af1 #aia1 #aib1 #aid4 ,vesta1 #aja4 ,vogel1 #eb4 ,volcanoes1 avenues to earlier state1 #afj4 ,von ,zach1 #if4 ,w ,walker1 ,mr41 #abc1 #abd4 ,water1 becoming more scarce1 #bjc1 #bjd1 #baa4 lacking on ,moon1 #bjd4 ,water-vapor1 in atmosphere of ,jupiter1 #ec4 in atmosphere of ,mars1 #ia1 #afa4 smaller planet has less hold on1 #bjg4 ,williams1 ,mr4 ,stanley1 #ajc4 ,witt1 de1 #id4 ,wolf1 ,dr41 #ac4 ,wolf1 ,max1 #id4 ,wolf-,rayet stars1 #ac1 #dh4 ,wright1 #ac1 #dc4 ,y ,year1 of ,uranus1 #aaf4 ,yerkes ,observatory1 #bcb4 ,young1 #df4 ,,percival ,,lowell',s ,mars and ,its ,canals ,illustrated1 #hvo1 #b4ej net 8,the book makes fascinating reading and is intended for the average man of intelligence and scientific curiosity4 ,it represents mature reflection1 patient investigation and observation1 and eleven years' additional work and verification4444 ,it is the work of a scientist who has found inspiration and joy in his work2 it is full of enthusiasm1 but the enthusiasm is not allowed to influence unduly a single conclusion40--,chicago ,evening ,post4 8,it seems impossible that ,mr4 ,lowell can raise another girder more grandly impressive and expressive of the whole fabric or take another step in his scientific syllogism that will hold us any tighter in his logic4 ,he has practically reached already his #8,q4 ,e4 ,d4' ,the thing is done1 apparently1 except for filling in the detail4 ,but with his racy1 epigrammatic brilliancy of style1 his delicate1 quiet humor1 his daring scientific imagination--all held in check by instructive modesty of good breeding1 gayly throwing to the winds all professional airs and mere rhetorical bounce--his course will be no doubt as charming to the end as it has been steadily illuminating even for the illuminati40--,boston ,transcript4 8,whether or not we choose to follow the author of this book to his ultimate inferences1 he at least opens up a field of fascinating conjecture4 ,the work is written in a style as popular as the precise enumeration of the ascertained facts permits1 and if the narrative is not in all its details as entrancing as a novel1 it nevertheless transports us into a region of superlatively romantic interest40--,new ,york ,tribune4 8,no doubt the highest living authority on ,mars and things ,martian is ,prof4 ,percival ,lowell1 director of the observatory at ,flagstaff1 ,arizona1 an astronomical investigator and writer known over the entire world4 ,professor ,lowell's book1 #8,mars and ,its ,canals1' is the final word1 up to the present1 on the planet and what we know of it40--,review of ,reviews4 ,,published ,,by ,,the ,,macmillan ,,company #fd-ff ,fifth ,avenue1 ,new ,york ,,percival ,,lowell',s ,mars as the ,abode of ,life ,illustrated1 #hvo1 #b4ej net ,the book is based on a course of lectures delivered at the ,lowell ,institute in #aijf1 supplemented by the results of later observations4 ,it is1 in the large1 the presentation of the results of the author's research into the genesis and development of what we call a world2 not the mere aggregating of matter1 but the process by which that matter comes to be individual as we find it4 ,he bridges with the new science of planetology the evolutionary gap between the nebular hypothesis and the ,darwinian theory4 8,it is not only as an astronomer but as a writer that ,professor ,lowell charms the reader in this work4 ,the beguilement of the theme is well matched by the grace and literary finish of the style in which it is presented4 ,the subject is one to beget enthusiasm in its advocates1 and the author certainly is not devoid of it4 ,the warmth and earnestness of the true lover of his theme shine through the entire work so that in its whole style and illustrations it is a charming production40--,st4 ,louis ,globe ,democrat4 8,mr4 ,lowell approaches the subject by outlining the now generally accepted theory of the formation of planets and the solar system4 ,he describes the stages in the life history of a planet three of which are illustrated in the present state of the earth1 ,mars1 and the moon4 ,he tells what conditions we would expect to find on a planet in what we may call the ,martian age1 and proceeds to show how the facts revealed by observation square with the theories4 ,the book is fascinatingly readable40--,the ,outlook4 8,so attractive are the style and the illustrations that the work will doubtless draw the attention of many new readers to its fascinating subject4 ,professor ,lowell has fairly prempted that portion of the field of astronomy which interests the widest readers1 for there is no doubt that speculation regarding the possibility of life on other planets than our own has a peculiar attraction for the average human mind4444 ,for the convenience of the non-technical reader1 the body of the book has been made as simple and understandable as possible40--,philadelphia ,press4 ,,published ,,by ,,the ,,macmillan ,,company #fd-ff ,fifth ,avenue1 ,new ,york