,is ,mars ,habitable8 ,a ,,critical ,,examination ,,of ,,professor ,,percival ,,lowell',s ,,book ,,mars ,,and ,,its ,,canals1 ,,with ,,an ,,alternative ,,explanation ,,by ,,alfred ,,russel ,,wallace ,f4,r4,s41 ,,etc4 ,,preface4 ,this small volume was commenced as a review article on ,professor ,percival ,lowell's book1 ,mars and its ,canals1 with the object of showing that the large amount of new and interesting facts contained in this work did not invalidate the conclusion ,i had reached in #aijb1 and stated in my book on ,man's ,place in the ,universe1 that ,mars was not habitable4 ,but the more complete presentation of the opposite view in the volume now under discussion required a more detailed examination of the various physical problems involved1 and as the subject is one of great1 popular1 as well as scientific interest1 ,i determined to undertake the task4 ,this was rendered the more necessary by the fact that in ,july last ,professor ,lowell published in the ,philosophical ,magazine an elaborate mathematical article claiming to demonstrate that1 notwithstanding its much greater distance from the sun and its excessively thin atmosphere1 ,mars possessed a climate on the average equal to that of the south of ,england1 and in its polar and sub-polar regions even less severe than that of the earth4 ,such a contention of course required to be dealt with1 and led me to collect information bearing upon temperature in all its aspects1 and so enlarging my criticism that ,i saw it would be necessary to issue it in book form4 ,two of my mathematical friends have pointed out the chief omission which vitiates ,professor ,lowell's mathematical conclusions--that of a failure to recognise the very large conservative and cumulative effect of a dense atmosphere4 ,this very point however ,i had already myself discussed in ,chapter ,,vi41 and by means of some remarkable researches on the heat of the moon and an investigation of the causes of its very low temperature1 ,i have1 ,i think1 demonstrated the incorrectness of ,mr4 ,lowell's results4 ,in my last chapter1 in which ,i briefly summarise the whole argument1 ,i have further strengthened the case for very severe cold in ,mars1 by adducing the rapid lowering of temperature universally caused by diminution of atmospheric pressure1 as manifested in the well-known phenomenon of temperate climates at moderate heights even close to the equator1 cold climates at greater heights even on extensive plateaux1 culminating in arctic climates and perpetual snow at heights where the air is still far denser than it is on the surface of ,mars4 ,this argument itself is1 in my opinion1 conclusive2 but it is enforced by two others equally complete1 neither of which is adequately met by ,mr4 ,lowell4 ,the careful examination which ,i have been led to give to the whole of the phenomena which ,mars presents1 and especially to the discoveries of ,mr4 ,lowell1 has led me to what ,i hope will be considered a satisfactory physical explanation of them4 ,this explanation1 which occupies the whole of my seventh chapter1 is founded upon a special mode of origin for ,mars1 derived from the ,meteoritic ,hypothesis1 now very widely adopted by astronomers and physicists4 ,then1 by a comparison with certain well-known and widely spread geological phenomena1 ,i show how the great features of ,mars--the 'canals' and 'oases'--may have been caused4 ,this chapter will perhaps be the most interesting to the general reader1 as furnishing a quite natural explanation of features of the planet which have been termed 'non-natural' by ,mr4 ,lowell4 ,incidentally1 also1 ,i have been led to an explanation of the highly volcanic nature of the moon's surface4 ,this seems to me absolutely to require some such origin as ,sir ,george ,darwin has given it1 and thus furnishes corroborative proof of the accuracy of the hypothesis that our moon has had an unique origin among the known satellites1 in having been thrown off from the earth itself4 ,i am indebted to ,professor ,j4 ,h4 ,poynting1 of the ,university of ,birmingham1 for valuable suggestions on some of the more difficult points of mathematical physics here discussed1 and also for the critical note 7at the end of ,chapter ,v47 on ,professor ,lowell's estimate of the temperature of ,mars4 ,,broadstone1 ,,dorset1 ,october #aijg4 ,,table ,,of ,,contents4 ,,chapter ,i4 ,,early ,,observers ,,of ,,mars1 --,mars the only planet the surface of which is distinctly visible --,early observation of the snow-caps and seas --,the 'canals' seen by ,schiaparelli in #ahgg --,double canals first seen in #ahha --,round spots at intersection of canals seen by ,pickering in #ahib --,confirmed by ,lowell in #ahid --,changes of colour seen in #ahib and #ahid --,existence of seas doubted by ,pickering and ,barnard in #ahid4 ,,chapter ,,ii4 ,,mr4 ,,lowell',s ,,discoveries ,,and ,,theories1 --,observatory at ,flagstaff1 ,arizona --,illustrated book on his observations of ,mars --,volume on ,mars and its canals1 #aijf --,non-natural features --,the canals as irrigation works of an intelligent race --,a challenge to the thinking world --,the canals as described and mapped by ,mr4 ,lowell --,the double canals --,dimensions of the canals --,they cross the supposed seas --,circular black spots termed oases --,an interesting volume4 ,,chapter ,,iii4 ,,the ,,climate ,,and ,,physiography ,,of ,,mars1 --,no permanent water on ,mars --,rarely any clouds and no rain --,snow-caps the only source of water --,no mountains1 hills1 or valleys on ,mars --,two-thirds of the surface a desert --,water from the snow-caps too scanty to supply the canals --,miss ,clerke's views as to the water-supply --,description of some of the chief canals --,mr4 ,lowell on the purpose of the canals --,remarks on the same --,mr4 ,lowell on relation of canals to oases and snow-caps --,critical remarks on the same4 ,,chapter ,,iv4 ,,is ,,animal ,,life ,,possible ,,on ,,mars8 --,water and air essential for animal life --,atmosphere of ,mars assumed to be like ours --,blue tint near melting snow the only evidence of water --,fallacy of this argument --,dr4 ,johnstone ,stoney's proof that water-vapour cannot exist on ,mars --,spectroscope gives no evidence of water4 ,,chapter ,v4 ,,temperature ,,of ,,mars--,,mr4 ,,lowell',s ,,estimate1 --,problem of terrestrial temperature --,ice under recent lava --,tropical oceans ice-cold at bottom --,earth's surface-heat all from the sun --,absolute zero of temperature --,complex problem of planetary temperatures --,mr4 ,lowell's investigation of the problem --,abstract of ,mr4 ,lowell's paper --,critical remarks on ,mr4 ,lowell's paper4 ,,chapter ,,vi4 ,a ,,new ,,estimate ,,of ,,the ,,temperature ,,of ,,mars1 --,langley's determination of lunar heat --,rapid loss of heat by radiation on the earth --,rapid loss of heat on moon during eclipse --,sir ,george ,darwin's theory of the moon's origin --,very's researches on the moon's temperature --,application of these results to the case of ,mars --,cause of great difference of temperatures of earth and moon --,special features of ,mars influencing its temperature --,further criticism of ,mr4 ,lowell's article --,very low temperature of arctic regions on ,mars4 ,,chapter ,,vii4 ,a ,,suggestion ,,as ,,to ,,the ',,canals' ,,of ,,mars1 --,special features of the canals --,mr4 ,pickering's suggested explanation --,the meteoritic hypotheses of origin of planets --,probable mode of origin of ,mars --,structural straight lines on the earth --,probable origin of the surface-features of ,mars --,symmetry of basaltic columns --,how this applies to ,mars --,suggested explanation of the oases --,probable function of the great fissures --,suggested origin of blue patches adjacent to snow-caps --,the double canals --,concluding remarks on the canals4 ,,chapter ,,viii4 ,,page ,,summary ,,and ,,conclusion1 --,the canals the origin of ,mr4 ,lowell's theory --,best explained as natural features --,evaporation difficulty not met by ,mr4 ,lowell --,how did ,martians live without the canals --,radiation due to scanty atmosphere not taken account of --,three independent proofs of low temperature and uninhabitability of ,mars --,conclusion4 ,,chapter ,i4 ,,early ,,observers ,,of ,,mars4 ,few persons except astronomers fully realise that of all the planets of the ,solar system the only one whose solid surface has been seen with certainty is ,mars2 and1 very fortunately1 that is also the only one which is sufficiently near to us for the physical features of the surface to be determined with any accuracy1 even if we could see it in the other planets4 ,of ,venus we probably see only the upper surface of its cloudy atmosphere4#a ,as regards ,jupiter and ,saturn this is still more certain1 since their low density will only permit of a comparatively small proportion of their huge bulk being solid4 ,their belts are but the cloud-strata of their upper atmosphere1 perhaps thousands of miles above their solid surfaces1 and a somewhat similar condition seems to prevail in the far more remote planets ,uranus and ,neptune4 ,it has thus happened1 that1 although as telescopic objects of interest and beauty1 the marvellous rings of ,saturn1 the belts and ever-changing aspects of the satellites of ,jupiter1 and the moon-like phases of ,venus1 together with its extreme brilliancy1 still remain unsurpassed1 yet the greater amount of details of these features when examined with the powerful instruments of the nineteenth century have neither added much to our knowledge of the planets themselves or led to any sensational theories calculated to attract the popular imagination4 ,footnote #a3 ,mercury also seems to have a scanty atmosphere1 but as its mass is only one-thirtieth that of the earth it can retain only the heavier gases1 and its atmosphere may be dust-laden1 as is that of ,mars1 according to ,mr4 ,lowell4 ,its dusky markings1 as seen by ,schiaparelli1 seem to be permanent1 and they are also for considerable periods unchangeable in position1 indicating that the planet keeps the same face towards the sun as does ,venus4 ,this was confirmed by ,mr4 ,lowell in #ahif4 ,its distance from us and unfavourable position for observation must prevent us from obtaining any detailed knowledge of its actual surface1 though its low reflective power indicates that the surface may be really visible4 ,but in the case of ,mars the progress of discovery has had a very different result4 ,the most obvious peculiarity of this planet--its polar snow-caps--were seen about #bej years ago1 but they were first proved to increase and decrease alternately1 in the summer and winter of each hemisphere1 by ,sir ,william ,herschell in the latter part of the eighteenth century4 ,this fact gave the impulse to that idea of similarity in the conditions of ,mars and the earth1 which the recognition of many large dusky patches and streaks as water1 and the more ruddy and brighter portions as land1 further increased4 ,added to this1 a day only about half an hour longer than our own1 and a succession of seasons of the same character as ours but of nearly double the length owing to its much longer year1 seemed to leave little wanting to render this planet a true earth on a smaller scale4 ,it was therefore very natural to suppose that it must be inhabited1 and that we should some day obtain evidence of the fact4 ,the ,canals discovered by ,schiaparelli4 ,hence the great interest excited when ,schiaparelli1 at the ,milan ,observatory1 during the very favourable opposition of #ahgg and #ahgi1 observed that the whole of the tropical and temperate regions from #fj ,n4 to #fj ,s4 ,lat4 were covered with a remarkable network of broader curved and narrower straight lines of a dark colour4 ,at each successive favourable opposition1 these strange objects called canali 7channels7 by their discoverer1 but rather misleadingly 'canals' in ,england and ,america1 were observed by means of all the great telescopes in the world1 and their reality and general features became well established4 ,in ,schiaparelli's first map they were represented as being much broader and less sharply defined than he himself and other observers found by later and equally favourable observations that they really were4 ,discovery of the ,double ,canals4 ,in #ahha another strange feature was discovered by ,schiaparelli1 who found that about twenty canals which had previously been seen single were now distinctly double1 that is1 that they consisted of two parallel lines1 equally distinct and either very close together or a considerable distance apart4 ,this curious appearance was at first thought to be due to some instrumental defect or optical illusion2 but as it was soon confirmed by other observers with the best instruments and in widely different localities it became in time accepted as a real phenomenon of the planet's surface4 ,round ,spots discovered in #ahib4 ,at the favourable opposition of #ahib1 ,mr4 ,w4 ,h4 ,pickering noticed that besides the 'seas' of various sizes there were numerous very small black spots apparently quite circular and occurring at every intersection or starting-point of the 'canals4' ,many of these had been seen by ,schiaparelli as larger and ill-defined dark patches1 and were termed seas or lakes2 but ,mr4 ,pickering's observatory was at ,arequipa in ,peru1 about #hjjj feet above the sea1 and with such perfect atmospheric conditions as were1 in his opinion1 equal to a doubling of telescopic aperture4 ,they were soon detected by other observers1 especially by ,mr4 ,lowell in #ahid1 who thus wrote of them3 ,scattered over the orange-ochre groundwork of the continental regions of the planet1 are any number of dark round spots4 ,how many there may be it is not possible to state1 as the better the seeing1 the more of them there seem to be4 ,in spite1 however1 of their great number1 there is no instance of one unconnected with a canal4 ,what is more1 there is apparently none that does not lie at the junction of several canals4 ,reversely1 all the junctions appear to be provided with spots4 ,plotted upon a globe they and their connecting canals make a most curious network over all the orange-ochre equatorial parts of the planet1 a mass of lines and knots1 the one marking being as omnipresent as the other4 ,changes of ,colour recognised4 ,during the oppositions of #ahib and #ahid it was fully recognised that a regular course of change occurred dependent upon the succession of the seasons1 as had been first suggested by ,schiaparelli4 ,as the polar snows melt the adjacent seas appear to overflow and spread out as far as the tropics1 and are often seen to assume a distinctly green colour4 ,these remarkable changes and the extraordinary phenomena of perfect straight lines crossing each other over a large portion of the planet's surface1 with the circular spots at their intersections1 had such an appearance of artificiality that the idea that they were really 'canals' made by intelligent beings for purposes of irrigation1 was first hinted at1 and then adopted as the only intelligible explanation1 by ,mr4 ,lowell and a few other persons4 ,this at once seized upon the public imagination and was spread by the newspapers and magazines over the whole civilised world4 ,existence of ,seas doubted4 ,at this time 7#ahid7 it began to be doubted whether there were any seas at all on ,mars4 ,professor ,pickering thought they were far more limited in size than had been supposed1 and even might not exist as true seas4 ,professor ,barnard1 with the ,lick thirty-six inch telescope1 discerned an astonishing wealth of detail on the surface of ,mars1 so intricate1 minute1 and abundant1 that it baffled all attempts to delineate it2 and these peculiarities were seen upon the supposed seas as well as on the land-surfaces4 ,in fact1 under the best conditions these 'seas' lost all trace of uniformity1 their appearance being that of a mountainous country1 broken by ridges1 rifts1 and canyons1 seen from a great elevation4 ,as we shall see later on these doubts soon became certainties1 and it is now almost universally admitted that ,mars possesses no permanent bodies of water4 ,,chapter ,,ii4 ,,mr4 ,,percival ,,lowell',s ,,discoveries ,,and ,,theories4 ,the ,observatory in ,arizona4 ,in #ahid1 after a careful search for the best atmospheric conditions1 ,mr4 ,lowell established his observatory near the town of ,flagstaff in ,arizona1 in a very dry and uniform climate1 and at an elevation of #gcjj feet above the sea4 ,he then possessed a fine equatorial telescope of #ah inches aperture and #bf feet focal length1 besides two smaller ones1 all of the best quality4 ,to these he added in #ahif a telescope with #bd inch object glass1 the last work of the celebrated firm of ,alvan ,clark ,sons1 with which he has made his later discoveries4 ,he thus became perhaps more favourably situated than any astronomer in the northern hemisphere1 and during the last twelve years has made a specialty of the study of ,mars1 besides doing much valuable astronomical work on other planets4 ,mr1 ,lowell's recent ,books upon ,mars4 ,in #aije ,mr4 ,lowell published an illustrated volume giving a full account of his observations of ,mars from #ahid to #aijc1 chiefly for the use of astronomers2 and he has now given us a popular volume summarising the whole of his work on the planet1 and published both in ,america and ,england by the ,macmillan ,company4 ,this very interesting volume is fully illustrated with twenty plates1 four of them coloured1 and more than forty figures in the text1 showing the great variety of details from which the larger general maps have been constructed4 ,non-natural ,features of ,mars4 ,but what renders this work especially interesting to all intelligent readers is1 that the author has here1 for the first time1 fully set forth his views both as to the habitability of ,mars and as to its being actually inhabited by beings comparable with ourselves in intellect4 ,the larger part of the work is in fact devoted to a detailed description of what he terms the ',non-natural ,features' of the planet's surface1 including especially a full account of the ',canals1' single and double2 the ',oases1' as he terms the dark spots at their intersections2 and the varying visibility of both1 depending partly on the ,martian seasons2 while the five concluding chapters deal with the possibility of animal life and the evidence in favour of it4 ,he also upholds the theory of the canals having been constructed for the purpose of 'husbanding' the scanty water-supply that exists2 and throughout the whole of this argument he clearly shows that he considers the evidence to be satisfactory1 and that the only intelligible explanation of the whole of the phenomena he so clearly sets forth is1 that the inhabitants of ,mars have carried out on their small and naturally inhospitable planet a vast system of irrigation-works1 far greater both in its extent1 in its utility1 and its effect upon their world as a habitation for civilised beings1 than anything we have yet done upon our earth1 where our destructive agencies are perhaps more prominent than those of an improving and recuperative character4 ,a ,challenge to the ,thinking ,world4 ,this volume is therefore in the nature of a challenge1 not so much to astronomers as to the educated world at large1 to investigate the evidence for so portentous a conclusion4 ,to do this requires only a general acquaintance with modern science1 more especially with mechanics and physics1 while the main contention 7with which ,i shall chiefly deal7 that the features termed 'canals' are really works of art and necessitate the presence of intelligent organic beings1 requires only care and judgment in drawing conclusions from admitted facts4 ,as ,i have already paid some attention to this problem and have expressed the opinion that ,mars is not habitable1#b judging from the evidence then available1 and as few men of science have the leisure required for a careful examination of so speculative a subject1 ,i propose here to point out what the facts1 as stated by ,mr4 ,lowell himself1 do not render even probable much less prove4 ,incidentally1 ,i may be able to adduce evidence of a more or less weighty character1 which seems to negative the possibility of any high form of animal life on ,mars1 and1 a fortiori1 the development of such life as might culminate in a being equal or superior to ourselves4 ,as most popular works on ,astronomy for the last ten years at least1 as well as many scientific periodicals and popular magazines1 have reproduced some of the maps of ,mars by ,schiaparelli1 ,lowell1 and others1 the general appearance of its surface will be familiar to most readers1 who will thus be fully able to appreciate ,mr4 ,lowell's account of his own further discoveries which ,i may have to quote4 ,one of the best of these maps ,i am able to give as a frontispiece to this volume1 and to this ,i shall mainly refer4 ,footnote #b3 ,man's ,place in the ,universe p4 #bfg 7#aijc74 ,the ,canals as described by ,mr4 ,lowell4 ,in the clear atmosphere of ,arizona1 ,mr4 ,lowell has been able on various favourable occasions to detect a network of straight lines1 meeting or crossing each other at various angles1 and often extending to a thousand or even over two thousand miles in length4 ,they are seen to cross both the light and the dark regions of the planet's surface1 often extending up to or starting from the polar snow-caps4 ,most of these lines are so fine as only to be visible on special occasions of atmospheric clearness and steadiness1 which hardly ever occur at lowland stations1 even with the best instruments1 and almost all are seen to be as perfectly straight as if drawn with a ruler4 ,the ,double ,canals4 ,under exceptionally favourable conditions1 many of the lines that have been already seen single appear double--a pair of equally fine lines exactly parallel throughout their whole length1 and appearing1 as ,mr4 ,lowell says1 clear cut upon the disc1 its twin lines like the rails of a railway track4 ,both ,schiaparelli and ,lowell were at first so surprised at this phenomenon that they thought it must be an optical illusion1 and it was only after many observations in different years1 and by the application of every conceivable test1 that they both became convinced that they witnessed a real feature of the planet's surface4 ,mr4 ,lowell says he has now seen them hundreds of times1 and that his first view of one was 'the most startlingly impressive' sight he has ever witnessed4 ,dimensions of the ,canals4 ,a few dimensions of these strange objects must be given in order that readers may appreciate their full strangeness and inexplicability4 ,out of more than four hundred canals seen and recorded by ,mr4 ,lowell1 fifty-one1 or about one eighth1 are either constantly or occasionally seen to be double1 the appearance of duplicity being more or less periodical4 ,of 'canals' generally1 ,mr4 ,lowell states that they vary in length from a few hundred to a few thousand miles long1 one of the largest being the ,phison1 which he terms 'a typical double canal1' and which is said to be #bbej miles long1 while the distance between its two constituents is about #acj miles4#c ,the actual width of each canal is from a minimum of about a mile up to several miles1 in one case over twenty4 ,a great feature of the doubles is1 that they are strictly parallel throughout their whole course1 and that in almost all cases they are so truly straight as to form parts of a great circle of the planet's sphere4 ,a few however follow a gradual but very distinct curve1 and such of these as are double present the same strict parallelism as those which are straight4 ,footnote #c3 ,this is on the opposite side of ,mars from that shown in the frontispiece4 ,canals extend across the ,seas4 ,it was only after seventeen years of observation of the canals that it was found that they extended also into and across the dark spots and surfaces which by the earlier observers were termed seas1 and which then formed the only clearly distinguishable and permanent marks on the planet's surface4 ,at the present time1 ,professor ,lowell states that this curious triangulation has been traced over almost every portion of the planet's surface1 whether dark or light1 whether greenish1 ochre1 or brown in colour4 ,in some parts they are much closer together than in others1 forming a perfect network of lines and spots1 so that to identify them all was a matter of extreme difficulty4 ,two such portions are figured at pages #bdg and #bef of ,mr4 ,lowell's volume4 ,the ,oases4 ,the curious circular black spots which are seen at the intersections of many of the canals1 and which in some parts of the surface are very numerous1 are said to be more difficult of detection than even the lines1 being often blurred or rendered completely invisible by slight irregularities in our own atmosphere1 while the canals themselves continue visible4 ,about #ahj of these have now been found1 and the more prominent of them are estimated to vary from #ge to #ajj miles in diameter4 ,there are however many much smaller1 down to minute and barely visible black points4 ,yet they all seem a little larger than the canals which enter them4 ,where the canals are double1 the spots 7or 'oases' as ,mr4 ,lowell terms them7 lie between the two parallel canals4 ,no one can read this book without admiration for the extreme perseverance in long continued and successful observation1 the results of which are here recorded2 and ,i myself accept unreservedly the substantial accuracy of the whole series4 ,it must however always be remembered that the growth of knowledge of the detailed markings has been very gradual1 and that much of it has only been seen under very rare and exceptional conditions4 ,it is therefore quite possible that1 if at some future time a further considerable advance in instrumental power should be made1 or a still more favourable locality be found1 the new discoveries might so modify present appearances as to render a satisfactory explanation of them more easy than it is at present4 ,but though ,i wish to do the fullest justice to ,mr4 ,lowell's technical skill and long years of persevering work1 which have brought to light the most complex and remarkable appearances that any of the heavenly bodies present to us1 ,i am obliged absolutely to part company with him as regards the startling theory of artificial production which he thinks alone adequate to explain them4 ,so much is this the case1 that the very phenomena1 which to him seem to demonstrate the intervention of intelligent beings working for the improvement of their own environment1 are those which seem to me to bear the unmistakable impress of being due to natural forces1 while they are wholly unintelligible as being useful works of art4 ,i refer of course to the great system of what are termed 'canals1' whether single or double4 ,of these ,i shall give my own interpretation later on4 ,,chapter ,,iii4 ,,the ,,climate ,,and ,,physiography ,,of ,,mars4 ,mr4 ,lowell admits1 and indeed urges strongly1 that there are no permanent bodies of water on ,mars2 that the dark spaces and spots1 thought by the early observers to be seas1 are certainly not so now1 though they may have been at an earlier period2 that true clouds are rare1 even if they exist1 the appearances that have been taken for them being either dust-storms or a surface haze2 that there is consequently no rain1 and that large portions 7about two-thirds7 of the planet's surface have all the characteristics of desert regions4 ,snow-caps the only ,source of ,water4 ,this state of things is supposed to be ameliorated by the fact of the polar snows1 which in the winter cover the arctic and about half the temperate regions of each hemisphere alternately4 ,the maximum of the northern snow-caps is reached at a period of the ,martian winter corresponding to the end of ,february with us4 ,about the end of ,march the cap begins to shrink in size 7in the ,northern ,hemisphere71 and this goes on so rapidly that early in the ,june of ,mars it is reduced to its minimum4 ,about the same time changes of colour take place in the adjacent darker portions of the surface1 which become at first bluish1 and later a decided blue-green2 but by far the larger portion1 including almost all the equatorial regions of the planet1 remain always of a reddish-ochre tint4#d ,footnote #d3 ,in #ahij at ,mount ,wilson1 ,california1 ,mr4 ,w4,h4 ,pickering's photographs of ,mars on ,april #ith showed the southern polar cap of moderate dimensions1 but with a large dim adjacent area4 ,twenty-four hours later a corresponding plate showed this same area brilliantly white2 the result apparently of a great ,martian snowfall4 ,in #ahhb the same observer witnessed the steady disappearance of #a1fjj1jjj square miles of the southern snow-cap1 an area nearly one-third of that hemisphere of the planet4 ,the rapid and comparatively early disappearance of the white covering is1 very reasonably1 supposed to prove that it is of small thickness1 corresponding perhaps to about a foot or two of snow in north-temperate ,america and ,europe1 and that by the increasing amount of sun-heat it is converted1 partly into liquid and partly into vapour4 ,coincident with this disappearance and as a presumed result of the water 7or other liquid7 producing inundations1 the bluish-green tinge which appears on the previously dark portion of the surface is supposed to be due to a rapid growth of vegetation4 ,but the evidence on this point does not seem to be clear or harmonious1 for in the four coloured plates showing the planet's surface at successive ,martian dates from ,december #cjth to ,february #bast1 not only is a considerable extent of the south temperate zone shown to change rapidly from bluish-green to chocolate-brown and then again to bluish-green1 but the portions furthest from the supposed fertilising overflow are permanently green1 as are also considerable portions in the opposite or northern hemisphere1 which one would think would then be completely dried up4 ,no ,hills upon ,mars4 ,the special point to which ,i here wish to call attention is this4 ,mr4 ,lowell's main contention is1 that the surface of ,mars is wonderfully smooth and level4 ,not only are there no mountains1 but there are no hills or valleys or plateaux4 ,this assumption is absolutely essential to support the other great assumption1 that the wonderful network of perfectly straight lines over nearly the whole surface of the planet are irrigation canals4 ,it is not alleged that irregularities or undulations of a few hundreds or even one or two thousands of feet could possibly be detected1 while certainly all we know of planetary formation or structure point strongly towards some inequalities of surface4 ,mr4 ,lowell admits that the dark portions of the surface1 when examined on the terminator 7the margin of the illuminated portion71 do look like hollows and may be the beds of dried-up seas2 yet the supposed canals run across these old sea-beds in perfect straight lines just as they do across the many thousand miles of what are admitted to be deserts--which he describes in these forcible terms3 ,pitiless as our deserts are1 they are but faint forecasts of the state of things existent on ,mars at the present time4 ,it appears1 then1 that ,mr4 ,lowell has to face this dilemma--,only if the whole surface of ,mars is an almost perfect level could the enormous network of straight canals1 each from hundreds to thousands of miles long1 have been possibly constructed by intelligent beings for purposes of irrigation2 but1 if a complete and universal level surface exists no such system would be necessary4 ,for on a level surface--or on a surface slightly inclined from the poles towards the equator1 which would be advantageous in either case--the melting water would of itself spread over the ground and naturally irrigate as much of the surface as it was possible for it to reach4 ,if the surface were not level1 but consisted of slight elevations and expressions to the extent of a few scores or a few hundreds of feet1 then there would be no possible advantage in cutting straight troughs through these elevations in various directions with water flowing at the bottom of them4 ,in neither case1 and in hardly any conceivable case1 could these perfectly straight canals1 cutting across each other in every direction and at very varying angles1 be of any use1 or be the work of an intelligent race1 if any such race could possibly have been developed under the adverse conditions which exist in ,mars4 ,the ,scanty ,water-supply4 ,but further1 if there were any superfluity of water derived from the melting snow beyond what was sufficient to moisten the hollows indicated by the darker portions of the surface1 which at the time the water reaches them acquire a green tint 7a superfluity under the circumstances highly improbable71 that superfluity could be best utilised by widening1 however little1 the borders to which natural overflow had carried it4 ,any attempt to make that scanty surplus1 by means of overflowing canals1 travel across the equator into the opposite hemisphere1 through such a terrible desert region and exposed to such a cloudless sky as ,mr4 ,lowell describes1 would be the work of a body of madmen rather than of intelligent beings4 ,it may be safely asserted that not one drop of water would escape evaporation or insoak at even a hundred miles from its source4 #e ,footnote #e3 ,what the evaporation is likely to be in ,mars may be estimated by the fact1 stated by ,professor ,j4,w4 ,gregory in his recent volume on ',australia' in ,stanford's ,compendium1 that in ,north-,west ,victoria evaporation is at the rate of ten feet per annum1 while in ,central ,australia it is very much more4 ,the greatly diminished atmospheric pressure in ,mars will probably more than balance the loss of sun-heat in producing rapid evaporation4 ,miss ,clerke on the ,scanty ,water-supply4 ,on this point ,i am supported by no less an authority than the historian of modern astronomy1 the late ,miss ,agnes ,clerke4 ,in the ,edinburgh ,review 7of ,october #ahif7 there is an article entitled ',new ,views about ,mars1' exhibiting the writer's characteristic fulness of knowledge and charm of style4 ,speaking of ,mr4 ,lowell's idea of the 'canals' carrying the surplus water across the equator1 far into the opposite hemisphere1 for purposes of irrigation there 7which we see he again states in the present volume71 ,miss ,clerke writes3 ,we can hardly imagine so shrewd a people as the irrigators of ,thule and ,hellas#f wasting labour1 and the life-giving fluid1 after so unprofitable a fashion4 ,there is every reason to believe that the ,martian snow-caps are quite flimsy structures4 ,their material might be called snow souffl1 since1 owing to the small power of gravity on ,mars1 snow is almost three times lighter there than here4 ,consequently1 its own weight can have very little effect in rendering it compact4 ,nor1 indeed1 is there time for much settling down4 ,the calotte does not form until several months after the winter solstice1 and it begins to melt1 as a rule1 shortly after the vernal equinox4 7,the interval between these two epochs in the southern hemisphere of ,mars is #agf days47 ,the snow lies on the ground1 at the outside1 a couple of months4 ,at times it melts while it is still fresh fallen4 ,thus1 at the opposition of #ahha-hb the spreading of the northern snows was delayed until seven weeks after the equinox3 and they had1 accordingly1 no sooner reached their maximum than they began to decline4 ,and ,professor ,pickering's photographs of ,april #ith and #ajth1 #ahij1 proved that the southern calotte may assume its definitive proportions in a single night4 ,footnote #f3 ,areas on ,mars so named4 ,no attempt has yet been made to estimate the quantity of water derivable from the melting of one of these formations2 yet the experiment is worth trying as a help towards defining ideas4 ,let us grant that the average depth of snow in them1 of the delicate ,martian kind1 is twenty feet1 equivalent at the most to one foot of water4 ,the maximum area covered1 of #b1djj1jjj square miles1 is nearly equal to that of the ,united ,states1 while the whole globe of ,mars measures #ee1ejj1jjj square miles1 of which one-third1 on the present hypothesis1 is under cultivation1 and in need of water4 ,nearly the whole of the dark areas1 as we know1 are situated in the southern hemisphere1 of which they extend over1 at the very least1 #ag1jjj1jjj square miles2 that is to say1 they cover an area1 in round numbers1 seven times that of the snow-cap4 ,only one-seventh of a foot of water1 accordingly1 could possibly be made available for their fertilisation1 supposing them to get the entire advantage of the spring freshet4 ,upon a stint of less than two inches of water these fertile lands are expected to flourish and bear abundant crops2 and since they completely enclose the polar area they are necessarily served first4 ,the great emissaries for carrying off the surplus of their aqueous riches1 would then appear to be superfluous constructions1 nor is it likely that the share in those riches due to the canals and oases1 intricately dividing up the wide1 dry1 continental plains1 can ever be realised4 ,we have assumed1 in our little calculation1 that the entire contents of a polar hood turn to water2 but in actual fact a considerable proportion of them must pass directly into vapour1 omitting the intermediate stage4 ,even with us a large quantity of snow is removed aerially2 and in the rare atmosphere of ,mars this cause of waste must be especially effective4 ,thus the polar reservoirs are despoiled in the act of being opened4 ,further objections might be taken to ,mr4 ,lowell's irrigation scheme1 but enough has been said to show that it is hopelessly unworkable4 ,it will be seen that the writer of this article accepted the existence of water on ,mars1 on the testimony of ,sir ,w4 ,huggins1 which1 in view of later observations1 he has himself acknowledged to be valueless4 ,dr4 ,johnstone ,stoney's proof of its absence1 derived from the molecular theory of gases1 had not then been made public4 ,description of some of the ,canals4 ,at the end of his volume ,mr4 ,lowell gives a large chart of ,mars on ,mercator's projection1 showing the canals and other features seen during the opposition of #aije4 ,this contains many canals not shown on the map here reproduced 7see frontispiece71 and some of the differences between the two are very puzzling4 ,looking at our map1 which shows the north-polar snow below1 so that the south pole is out of the view at the top of the map1 the central feature is the large spot ,ascraeeus ,lucus1 from which ten canals diverge centrally1 and four from the sides1 forming wide double canals1 fourteen in all4 ,there is also a canal named ,ulysses1 which here passes far to the right of the spot1 but in the large chart enters it centrally4 ,looking at our map we see1 going downwards a little to the left1 the canal ,udon1 which runs through a dark area quite to the outer margin4 ,in the dark area1 however1 there is shown on the chart a spot ,aspledon ,lucus1 where five canals meet1 and if this is taken as a terminus the ,udon canal is almost exactly #bjjj miles long1 and another on its right1 ,lapadon1 is the same length1 while ,ich1 running in a slightly curved line to a large spot 7,lucus ,castorius on the chart7 is still longer4 ,the ,ulysses canal1 which 7on the chart7 runs straight from the point of the ,mare ,sirenum to the ,astraeeus ,lucus is about #bbjj miles long4 ,others however are even longer1 and ,mr4 ,lowell says3 ,with them #bjjj miles is common2 while many exceed #bejj2 and the ,eumenides-,orcus is #cedj miles from the point where it leaves ,lucus ,phoeniceus to where it enters the ,trivium ,charontis4 ,this last canal is barely visible on our map1 its commencement being indicated by the word ,eumenides4 ,the ,trivium ,charontis is situated just beyond the right-hand margin of our map4 ,it is a triangular dark area1 the sides about #bjj miles long1 and it is shown on the chart as being the centre from which radiate thirteen canals4 ,another centre is ,aquae ,calidae situated at the point of a dark area running obliquely from #ee to #ce ,n4 latitude1 and1 as shown on a map of the opposite hemisphere to our map1 has nearly twenty canals radiating from it in almost every direction4 ,here at all events there seems to be no special connection with the polar snow-caps1 and the radiating lines seem to have no intelligent purpose whatever1 but are such as might result from fractures in a glass globe produced by firing at it with very small shots one at a time4 ,taking the whole series of them1 ,mr4 ,lowell very justly compares them to a network which triangulates the surface of the planet like a geodetic survey1 into polygons of all shapes and sizes4 ,at the very lowest estimate the total length of the canals observed and mapped by ,mr4 ,lowell must be over a hundred thousand miles1 while he assures us that numbers of others have been seen over the whole surface1 but so faintly or on such rare occasions as to elude all attempts to fix their position with certainty4 ,but these1 being of the same character and evidently forming part of the same system1 must also be artificial1 and thus we are led to a system of irrigation of almost unimaginable magnitude on a planet which has no mountains1 no rivers1 and no rain to support it2 whose whole water-supply is derived from polar snows1 the amount of which is ludicrously inadequate to need any such world-wide system2 while the low atmospheric pressure would lead to rapid evaporation1 thus greatly diminishing the small amount of moisture that is available4 ,everyone must1 ,i think1 agree with ,miss ,clerke1 that1 even admitting the assumption that the polar snows consist of frozen water1 the excessively scanty amount of water thus obtained would render any scheme of world-wide distribution of it hopelessly unworkable4 ,the very remarkable phenomena of the duplication of many of the lines1 together with the darkspots--the so-called oases--at their intersections1 are doubtless all connected in some unknown way with the constitution and past history of the planet2 but1 on the theory of the whole being works of art1 they certainly do not help to remove any of the difficulties which have been shown to attend the theory that the single lines represent artificial canals of irrigation with a strip of verdure on each side of them produced by their overflow4 ,lowell on the ,purpose of the ,canals4 ,before leaving this subject it will be well to quote ,mr4 ,lowell's own words as to the supposed perfectly level surface of ,mars1 and his interpretation of the origin and purpose of the 'canals'3 ,a body of planetary size1 if unrotating1 becomes a sphere1 except for solar tidal deformation2 if rotating1 it takes on a spheroidal form exactly expressive1 so far as observation goes1 of the so-called centrifugal force at work4 ,mars presents such a figure1 being flattened out to correspond to its axial rotation4 ,its surface therefore is in fluid equilibrium1 or1 in other words1 a particle of liquid at any point of its surface at the present time would stay where it was devoid of inclination to move elsewhere4 ,now the water which quickens the verdure of the canals moves from the pole down to the equator as the season advances4 ,this it does then irrespective of gravity4 ,no natural force propels it1 and the inference is forthright and inevitable that it is artificially helped to its end4 ,there seems to be no escape from this deduction4 ,water only flows downhill1 and there is no such thing as downhill on a surface already in fluid equilibrium4 ,a few canals might presumably be so situated that their flow could1 by inequality of terrane1 lie equatorward1 but not all4444,now it is not in particular but by general consent that the canal-system of ,mars develops from pole to equator4 ,from the respective times at which the minima take place1 it appears that the canal quickening occupies fifty-two days1 as evidenced by the successive vegetal darkenings1 to descend from latitude #gb north to latitude #j1 a journey of #bfej miles4 ,this gives for the water a speed of fifty-one miles a day1 or #b4a miles an hour4 ,the rate of progression is remarkably uniform1 and this abets the deduction as to assisted transference4 ,but the fact is more unnatural yet4 ,the growth pays no regard to the equator1 but proceeds across it as if it did not exist into the planet's other hemisphere4 ,here is something still more telling than travel to this point4 ,for even if we suppose1 for the sake of argument1 that natural forces took the water down to the equator1 their action must there be certainly reversed1 and the equator prove a dead-line1 to pass which were impossible 7pp4 #cgd-e74 ,i think my readers will agree with me that this whole argument is one of the most curious ever put forth seriously by an eminent man of science4 ,because the polar compression of ,mars is about what calculation shows it ought to be in accordance with its rate of rotation1 its surface is in a state of 'fluid equilibrium1' and must therefore be absolutely level throughout4 ,but the polar compression of the earth equally agrees with calculation2 therefore its surface is also in 'fluid equilibrium'2 therefore it also ought to be as perfectly level on land as it is on the ocean surface6 ,but as we know this is very far from being the case1 why must it be so in ,mars8 ,are we to suppose ,mars to have been formed in some totally different way from other planets1 and that there neither is nor ever has been any reaction between its interior and exterior forces8 ,again1 the assumption of perfect flatness is directly opposed to all observation and all analogy with what we see on the earth and moon4 ,it gives no account whatever of the numerous and large dark patches1 once termed seas1 but now found to be not so1 and to be full of detailed markings and varied depths of shadow4 ,to suppose that these are all the same dead-level as the light-coloured portions are assumed to be1 implies that the darkness is one of material and colour only1 not of diversified contour1 which again is contrary to experience1 since difference of material with us always leads to differences in rate of degradation1 and hence of diversified contour1 as these dark spaces actually show themselves under favourable conditions to independent observers4 ,lowell on the ,system of ,canals as a whole4 ,we will now see what ,mr4 ,lowell claims to be the plain teaching of the 'canals' as a whole3 ,but last and all-embracing in its import is the system which the canals form4 ,instead of running at hap-hazard1 the canals are interconnected in a most remarkable manner4 ,they seek centres instead of avoiding them4 ,the centres are linked thus perfectly one with another1 an arrangement which could not result from centres1 whether of explosion or otherwise1 which were themselves discrete4 ,furthermore1 the system covers the whole surface of the planet1 dark areas and light ones alike1 a world-wide distribution which exceeds the bounds of natural possibility4 ,any force which could act longitudinally on such a scale must be limited latitudinally in its action1 as witness the belts of ,jupiter and the spots upon the sun4 ,rotational1 climatic1 or other physical cause could not fail of zonal expression4 ,yet these lines are grandly indifferent to such competing influences4 ,finally1 the system1 after meshing the surface in its entirety1 runs straight into the polar caps4 ,it is1 then1 a system whose end and aim is the tapping of the snow-cap for the water there semi-annually let loose2 then to distribute it over the planet's face 7p4 #cgc74 ,here1 again1 we have curiously weak arguments adduced to support the view that these numerous straight lines imply works of art rather than of nature1 especially in the comparison made with the belts of ,jupiter and the spots on the sun1 both purely atmospheric phenomena1 whereas the lines on ,mars are on the solid surface of the planet4 ,why should there be any resemblance between them8 ,every fact stated in the above quotation1 always keeping in mind the physical conditions of the planet--its very tenuous atmosphere and rainless desert-surface--seem wholly in favour of a purely natural as opposed to an artificial origin2 and at the close of this discussion ,i shall suggest one which seems to me to be at least possible1 and to explain the whole series of the phenomena set forth and largely discovered by ,mr4 ,lowell1 in a simpler and more probable manner than does his tremendous assumption of their being works of art4 ,readers who may not possess ,mr4 ,lowell's volume will find three of his most recent maps of the 'canals' reproduced in ,nature of ,october #aath1 #aijf4 ,,chapter ,,iv4 ,,is ,,animal ,,life ,,possible ,,on ,,mars8 ,having now shown1 that1 even admitting the accuracy of all ,mr4 ,lowell's observations1 and provisionally accepting all his chief conclusions as to the climate1 the nature of the snow-caps1 the vegetation1 and the animal life of ,mars1 yet his interpretation of the lines on its surface as being veritably 'canals1' constructed by intelligent beings for the special purpose of carrying water to the more arid regions1 is wholly erroneous and rationally inconceivable4 ,i now proceed to discuss his more fundamental position as to the actual habitability of ,mars by a highly organised and intellectual race of material organic beings4 ,water and ,air essential to ,life4 ,here1 fortunately1 the issue is rendered very simple1 because ,mr4 ,lowell fully recognises the identity of the constitution of matter and of physical laws throughout the solar-system1 and that for any high form of organic life certain conditions which are absolutely essential on our earth must also exist in ,mars4 ,he admits1 for example1 that water is essential1 that an atmosphere containing oxygen1 nitrogen1 aqueous vapour1 and carbonic acid gas is essential1 and that an abundant vegetation is essential2 and these of course involve a surface-temperature through a considerable portion of the year that renders the existence of these--especially of water--possible and available for the purposes of a high and abundant animal life4 ,blue ,colour the only ,evidence of ,water4 ,in attempting to show that these essentials actually exist on ,mars he is not very successful4 ,he adduces evidence of an atmosphere1 but of an exceedingly scanty one1 since the greatest amount he can give to it is-- not more than about four inches of barometric pressure as we reckon it2#g and he assumes1 as he has a fair right to do till disproved1 that it consists of oxygen and nitrogen1 with carbon-dioxide and water-vapour1 in approximately the same proportions as with us4 ,with regard to the last item--the water-vapour--there are however many serious difficulties4 ,the water-vapour of our atmosphere is derived from the enormous area of our seas1 oceans1 lakes1 and rivers1 as well as from the evaporation from heated lands and tropical forests of much of the moisture produced by frequent and abundant rains4 ,all these sources of supply are admittedly absent from ,mars1 which has no permanent bodies of water1 no rain1 and tropical regions which are almost entirely desert4 ,many writers have therefore doubted the existence of water in any form upon this planet1 supposing that the snow-caps are not formed of frozen water but of carbon-dioxide1 or some other heavy gas1 in a frozen state2 and ,mr4 ,lowell evidently feels this to be a difficulty1 since the only fact he is able to adduce in favour of the melting snows of the polar caps producing water is1 that at the time they are melting a marginal blue band appears which accompanies them in their retreat1 and this blue colour is said to prove conclusively that the liquid is not carbonic acid but water4 ,this point he dwells upon repeatedly1 stating1 of these blue borders3 ,this excludes the possibility of their being formed by carbon-dioxide1 and shows that of all the substances we know the material composing them must be water4 ,footnote #g3 ,in a paper written since the book appeared the density of air at the surface of ,mars is said to be #a_/ab of the earth's4 ,this is the only proof of the existence of water he adduces1 and it is certainly a most extraordinary and futile one4 ,for it is perfectly well known that although water1 in large masses and by transmitted light1 is of a blue colour1 yet shallow water by reflected light is not so2 and in the case of the liquid produced by the snow-caps of ,mars1 which the whole conditions of the planet show must be shallow1 and also be more or less turbid1 it cannot possibly be the cause of the 'deep blue' tint said to result from the melting of the snow4 ,but there is a very weighty argument depending on the molecular theory of gases against the polar caps of ,mars being composed of frozen water at all4 ,the mass and elastic force of the several gases is due to the greater or less rapidity of the vibratory motion of their molecules under identical conditions4 ,the speed of these molecular motions has been ascertained for all the chief gases1 and it is found to be so great as in certain cases to enable them to overcome the force of gravity and escape from a planet's surface into space4 ,dr4 ,g4 ,johnstone ,stoney has specially investigated this subject1 and he finds that the force of gravity on the earth is sufficient to retain all the gases composing its atmosphere1 but not sufficient to retain hydrogen2 and as a consequence1 although this gas is produced in small quantities by volcanoes and by decomposing vegetation1 yet no trace of it is found in our atmosphere4 ,the moon however1 having only one-eightieth the mass of the earth1 cannot retain any gas1 hence its airless and waterless condition4 ,water ,vapour cannot exist on ,mars4 ,now1 ,dr4 ,stoney finds that in order to retain water vapour permanently a planet must have a mass at least a quarter that of the earth4 ,but the mass of ,mars is only one-ninth that of the earth2 therefore1 unless there are some special conditions that prevent its loss1 this gas cannot be present in the atmosphere4 ,mr4 ,lowell does not refer to this argument against his view1 neither does he claim the evidence of spectroscopy in his favour4 ,this was alleged more than thirty years ago to show the existence of water-vapour in the atmosphere of ,mars1 but of late years it has been doubted1 and ,mr4 ,lowell's complete silence on the subject1 while laying stress on such a very weak and inconclusive argument as that from the tinge of colour that is observed a little distance from the edge of the diminishing snow-caps1 shows that he himself does not think the fact to be thus proved4 ,if he did he would hardly adduce such an argument for its presence as the following3 ,the melting of the caps on the one hand and their re-forming on the other affirm the presence of water-vapour in the ,martian atmosphere1 of whatever else that air consists 7p4 #afb74 ,yet absolutely the only proof he gives that the caps are frozen water is the almost frivolous colour-argument above referred to6 ,no ,spectroscopic ,evidence of ,water ,vapour4 ,as ,sir ,william ,huggins is the chief authority quoted for this fact1 and is referred to as being almost conclusive in the third edition of ,miss ,clerke's ,history of ,astronomy in #ahic1 ,i have ascertained that his opinion at the present time is that there is no conclusive proof of the presence of aqueous vapour in the atmosphere of ,mars1 and that observations at the ,lick ,observatory 7in #ahie71 where the conditions and instruments are of the highest order1 were negative4 ,he also informs me that ,marchand at the ,pic du ,midi ,observatory was unable to obtain lines of aqueous vapour in the spectrum of ,mars2 and that in #aije1 ,slipher1 at ,mr4 ,lowell's observatory1 was unable to detect any indications of aqueous vapour in the spectrum of ,mars4 ,it thus appears that spectroscopic observations are quite accordant with the calculations founded on the molecular theory of gases as to the absence of aqueous vapour1 and therefore presumably of liquid water1 from ,mars4 ,it is true that the spectroscopic argument is purely negative1 and this may be due to the extreme delicacy of the observations required2 but that dependent on the inability of the force of gravity to retain it is positive scientific evidence against its presence1 and1 till shown to be erroneous1 must be held to be conclusive4 ,this absence of water is of itself conclusive against the existence of animal life1 unless we enter the regions of pure conjecture as to the possibility of some other liquid being able to take its place1 and that liquid being as omnipresent there as water is here4 ,mr4 ,lowell however never takes this ground1 but bases his whole theory on the fundamental identity of the substance of the bodies of living organisms wherever they may exist in the solar system4 ,in the next two chapters ,i shall discuss an equally essential condition1 that of temperature1 which affords a still more conclusive and even crushing argument against the suitability of ,mars for the existence of organic life4 ,,chapter ,v4 ,,the ,,temperature ,,of ,,mars--,,mr4 ,,lowell',s ,,estimate4 ,we have now to consider a still more important and fundamental question1 and one which ,mr4 ,lowell does not grapple with in this volume1 the actual temperatures on ,mars due to its distance from the sun and the atmospheric conditions on which he himself lays so much stress4 ,if ,i am not greatly mistaken we shall arrive at conclusions on this subject which are absolutely fatal to the conception of any high form of organic life being possible on this planet4 ,the ,problem of ,terrestrial ,temperatures4 ,in order that the problem may be understood and its importance appreciated1 it is necessary to explain the now generally accepted principles as to the causes which determine the temperatures on our earth1 and1 presumably1 on all other planets whose conditions are not wholly unlike ours4 ,the fact of the internal heat of the earth which becomes very perceptible even at the moderate depths reached in mines and deep borings1 and in the deepest mines becomes a positive inconvenience1 leads many people to suppose that the surface- temperatures of the earth are partly due to this cause4 ,but it is now generally admitted that this is not the case1 the reason being that all rocks and soils1 in their natural compacted state1 are exceedingly bad conductors of heat4 ,a striking illustration of this is the fact1 that a stream of lava often continues to be red hot at a few feet depth for years after the surface is consolidated1 and is hardly any warmer than that of the surrounding land4 ,a still more remarkable case is that of a glacier on the south-east side of the highest cone of ,etna underneath a lava stream with an intervening bed of volcanic sand only ten feet thick4 ,this was visited by ,sir ,charles ,lyell in #ahbh1 and a second time thirty years later1 when he made a very careful examination of the strata1 and was quite satisfied that the sand and the lava stream together had actually preserved this mass of ice1 which neither the heat of the lava above it at its first outflow1 nor the continued heat rising from the great volcano below it1 had been able to melt or perceptibly to diminish in thirty years4 ,another fact that points in the same direction is the existence over the whole floor of the deepest oceans of ice-cold water1 which1 originating in the polar seas1 owing to its greater density sinks and creeps slowly along the ocean bottom to the depths of the ,atlantic and ,pacific1 and is not perceptibly warmed by the internal heat of the earth4 ,now the solid crust of the earth is estimated as at least about twenty miles in average thickness2 and1 keeping in mind the other facts just referred to1 we can understand that the heat from the interior passes through it with such extreme slowness as not to be detected at the surface1 the varying temperatures of which are due entirely to solar heat4 ,a large portion of this heat is stored up in the surface soil1 and especially in the surface layer of the oceans and seas1 thus partly equalising the temperatures of day and night1 of winter and summer1 so as greatly to ameliorate the rapid changes of temperature that would otherwise occur4 ,our dense atmosphere is also of immense advantage to us as an equaliser of temperature1 charged as it almost always is with a large quantity of water-vapour4 ,this latter gas1 when not condensed into cloud1 allows the solar heat to pass freely to the earth2 but it has the singular and highly beneficial property of absorbing and retaining the dark or lower-grade heat given off by the earth which would otherwise radiate into space much more rapidly4 ,we must therefore always remember that1 very nearly if not quite1 the whole of the warmth we experience on the earth is derived from the sun4#h ,footnote #h3 ,professor ,j4,h4 ,poynting1 in his lecture to the ,british ,association at ,cambridge in #aijd1 says3 ,the surface of the earth receives1 we know1 an amount of heat from the inside almost infinitesimal compared with that which it receives from the sun1 and on the sun1 therefore1 we depend for our temperature4 ,in order to understand the immense significance of this conclusion we must know what is meant by the whole heat or warmth2 as unless we know this we cannot define what half or any other proportion of sun-heat really means4 ,now ,i feel pretty sure that nine out of ten of the average educated public would answer the following question incorrectly3 ,the mean temperature of the southern half of ,england is about #dh ,f4 ,supposing the earth received only half the sun-heat it now receives1 what would then be the probable mean temperature of the ,south of ,england8 ,the majority would1 ,i think1 answer at once--,about #bd ,f4 ,nearly as many would perhaps say--#dh ,f4 is #af above the freezing point2 therefore half the heat received would bring us down to #h above the freezing point1 or #dj ,f4 ,very few1 ,i think1 would realise that our share of half the amount of sun-heat received by the earth would probably result in reducing our mean temperature to about #ajj ,f4 below the freezing point1 and perhaps even lower4 ,this is about the very lowest temperature yet experienced on the earth's surface4 ,to understand how such results are obtained a few words must be said about the absolute zero of temperature4 ,the ,zero of ,temperature4 ,heat is now believed to be entirely due to ether-vibration1 which produces a correspondingly rapid vibration of the molecules of matter1 causing it to expand and producing all the phenomena we term 'heat4' ,we can conceive this vibration to increase indefinitely1 and thus there would appear to be no necessary limit to the amount of heat possible1 but we cannot conceive it to decrease indefinitely at the same uniform rate1 as it must soon inevitably come to nothing4 ,now it has been found by experiment that gases under uniform pressure expand #a_/bgc of their volume for each degree ,centigrade of increased temperature1 so that in passing from #j ,c4 to #bgc ,c4 they are doubled in volume4 ,they also decrease in volume at the same rate for each degree below #j ,c4 7the freezing point of water74 ,hence if this goes on to-#bgc ,c4 a gas will have no volume1 or it will undergo some change of nature4 ,hence this is called the zero of temperature1 or the temperature to which any matter falls which receives no heat from any other matter4 ,it is also sometimes called the temperature of space1 or of the ether in a state of rest1 if that is possible4 ,all the gases have now been proved to become1 first liquid and then 7most of them7 solid1 at temperatures considerably above this zero4 ,the only way to compare the proportional temperatures of bodies1 whether on the earth or in space1 is therefore by means of a scale beginning at this natural zero1 instead of those scales founded on the artificial zero of the freezing point of water1 or1 as in ,fahrenheit's1 #cb below it4 ,only by using the natural zero and measuring continuously from it can we estimate temperatures in relative proportion to the amount of heat received4 ,this is termed the absolute zero1 and so that we start reckoning from that point it does not matter whether the scale adopted is the ,centigrade or that of ,fahrenheit4 ,the ,complex ,problem of ,planetary ,temperatures4 ,now if1 as is the case with ,mars1 a planet receives only half the amount of solar heat that we receive1 owing to its greater distance from the sun1 and if the mean temperature of our earth is #fj ,f41 this is equal to #eea ,f4 on the absolute scale4 ,it would therefore appear very simple to halve this amount and obtain #bge4e ,f4 as the mean temperature of that planet4 ,but this result is erroneous1 because the actual amount of sun heat intercepted by a planet is only one condition out of many that determine its resulting temperature4 ,radiation1 that is loss of heat1 is going on concurrently with gain1 and the rate of loss varies with the temperature according to a law recently discovered1 the loss being much greater at high temperatures in proportion to the #dth power of the absolute temperature4 ,then1 again1 the whole heat intercepted by a planet does not reach its surface unless it has no atmosphere4 ,when it has one1 much is reflected or absorbed according to complex laws dependent on the density and composition of the atmosphere4 ,then1 again1 the heat that reaches the actual surface is partly reflected and partly absorbed1 according to the nature of that surface--land or water1 desert or forest or snow-clad--that part which is absorbed being the chief agent in raising the temperature of the surface and of the air in contact with it4 ,very important too is the loss of heat by radiation from these various heated surfaces at different rates2 while the atmosphere itself sends back to the surface an ever varying portion of both this radiant and reflected heat according to distinct laws4 ,further difficulties arise from the fact that much of the sun's heat consists of dark or invisible rays1 and it cannot therefore be measured by the quantity of light only4 ,from this rough statement it will be seen that the problem is an exceedingly complex one1 not to be decided off-hand1 or by any simple method4 ,it has in fact been usually considered as 7strictly speaking7 insoluble1 and only to be estimated by a more or less rough approximation1 or by the method of general analogy from certain known facts4 ,it will be seen1 from what has been said in previous chapters1 that ,mr4 ,lowell1 in his book1 has used the latter method1 and1 by taking the presence of water and water-vapour in ,mars as proved by the behaviour of the snow-caps and the bluish colour that results from their melting1 has deduced a temperature above the freezing point of water1 as prevalent in the equatorial regions permanently1 and in the temperate and arctic zones during a portion of each year4 ,mr4 ,lowell's ,mathematical ,investigation of the ,problem4 ,but as this result has been held to be both improbable in itself and founded on no valid evidence1 he has now1 in the ,london1 ,edinburgh1 and ,dublin ,philosophical ,magazine of ,july #aijg1 published an elaborate paper of #ae pages1 entitled ,a ,general ,method for ,evaluating the ,surface-,temperatures of the ,planets2 with special reference to the ,temperature of ,mars1 by ,professor ,percival ,lowell2 and in this paper1 by what purports to be strict mathematical reasoning based on the most recent discoveries as to the laws of heat1 as well as on measurements or estimates of the various elements and constants used in the calculations1 he arrives at a conclusion strikingly accordant with that put forward in the recently published volume4 ,having myself neither mathematical nor physical knowledge sufficient to enable me to criticise this elaborate paper1 except on a few points1 ,i will here limit myself to giving a short account of it1 so as to explain its method of procedure2 after which ,i may add a few notes on what seem to me doubtful points2 while ,i also hope to be able to give the opinions of some more competent critics than myself4 ,mr4 ,lowell's ,mode of ,estimating the ,surface-temperature of ,mars4 ,the author first states1 that ,professor ,young1 in his ,general ,astronomy 7#ahih71 makes the mean temperature of ,mars #bbc4f absolute1 by using ,newton's law of heat being radiated in proportion to temperature1 and #cfc abs4 7-#if ,f47 by ,dulong and ,petit's law2 but adds1 that a closer determination has been made by ,professor ,moulton1 using ,stefan's law1 that radiation is as the _/#dth power of the temperature1 whence results a mean temperature of-#ca ,f4 ,these estimates assume identity of atmospheric conditions of ,mars and the ,earth4 ,but as none of these estimates take account of the many complex factors which interfere with such direct and simple calculations1 ,mr4 ,lowell then proceeds to enunciate them1 and work out mathematically the effects they produce3 7#a7 ,the whole radiant energy of the sun on striking a planet becomes divided as follows3 ,part is reflected back into space1 part absorbed by the atmosphere1 part transmitted to the surface of the planet4 ,this surface again reflects a portion and only the balance left goes to warm the planet4 7#b7 ,to solve this complex problem we are helped by the albedoes or intrinsic brilliancy of the planets1 which depend on the proportion of the visible rays which are reflected and which determines the comparative brightness of their respective surfaces4 ,we also have to find the ratio of the invisible to the visible rays and the heating power of each4 7#c7 ,he then refers to the actinometer and pyroheliometer1 instruments for measuring the actual heat derived from the sun1 and also to the ,bolometer1 an instrument invented by ,professor ,langley for measuring the invisible heat rays1 which he has proved to extend to more than three times the length of the whole heat-spectrum as previously known1 and has also shown that the invisible rays contribute #fh per cent1 of the sun's total energy4#i ,footnote #i3 ,for a short account of this remarkable instrument1 see my ,wonderful ,century1 new ed41 pp4 #adc-ade4 7#d7 ,then follows an elaborate estimate of the loss of heat during the passage of the sun's rays through our atmosphere from experiments made at different altitudes and from the estimated reflective power of the various parts of the earth's surface--rocks and soil1 ocean1 forest and snow--the final result being that three-fourths of the whole sun-heat is reflected back into space1 forming our albedo1 while only one-fourth is absorbed by the soil and goes to warm the air and determine our mean temperature4 7#e7 ,we now have another elaborate estimate of the comparative amounts of heat actually received by ,mars and the ,earth1 dependent on their very different amounts of atmosphere1 and this estimate depends almost wholly on the comparative albedoes1 that of ,mars1 as observed by astronomers being #j4bg1 while ours has been estimated in a totally different way as being #j4ge1 whence he concludes that nearly three-fourths of the sun-heat that ,mars receives reaches the surface and determines its temperature1 while we get only one-fourth of our total amount4 ,then by applying ,stefan's law1 that the radiation is as the #dth power of the surface temperature1 he reaches the final result that the actual heating power at the surface of ,mars is considerably more than on the ,earth1 and would produce a mean temperature of #gb ,f41 if it were not for the greater conservative or blanketing power of our denser and more water-laden atmosphere4 ,the difference produced by this latter fact he minimises by dwelling on the probability of a greater proportion of carbonic-acid gas and water-vapour in the ,martian atmosphere1 and thus brings down the mean temperature of ,mars to #dh ,f41 which is almost exactly the same as that of the southern half of ,england4 ,he has also1 as the result of observations1 reduced the probable density of the atmosphere of ,mars to #b-a_/b inches of mercury1 or only one-twelfth of that of the ,earth4 ,critical ,remarks on ,mr4 ,lowell's ,paper4 ,the last part of this paper1 indicated under pars4 #d and #e1 is the most elaborate1 occupying eight pages1 and it contains much that seems uncertain1 if not erroneous4 ,in particular1 it seems very unlikely that under a clear sky over the whole earth we should only receive at the sea-level #j4bc of the solar rays which the earth intercepts 7p4 #afg74 ,these data largely depend on observations made in ,california and other parts of the southern ,united ,states1 where the lower atmosphere is exceptionally dust-laden4 ,till we have similar observations made in the tropical forest-regions1 which cover so large an area1 and where the atmosphere is purified by frequent rains1 and also on the prairies and the great oceans1 we cannot trust these very local observations for general conclusions affecting the whole earth4 ,later1 in the same article 7p4 #agj71 ,mr4 ,lowell says3 ,clouds transmit approximately #bj per cent4 of the heat reaching them3 a clear sky at sea-level #fj per cent4 ,as the sky is half the time cloudy the mean transmission is #ce per cent4 ,these statements seem incompatible with that quoted above4 ,the figure he uses in his calculations for the actual albedo of the earth1 #j4ge1 is also not only improbable1 but almost self-contradictory1 because the albedo of cloud is #j4gb1 and that of the great cloud-covered planet1 ,jupiter1 is given by ,lowell as #j4ge1 while ,zollner made it only #j4fb4 ,again1 ,lowell gives ,venus an albedo of #j4ib1 while ,zollner made it only #j4ej and ,mr4 ,gore #j4fe4 ,this shows the extreme uncertainty of these estimates1 while the fact that both ,venus and ,jupiter are wholly cloud-covered1 while we are only half-covered1 renders it almost certain that our albedo is far less than ,mr4 ,lowell makes it4 ,it is evident that mathematical calculations founded upon such uncertain data cannot yield trustworthy results4 ,but this is by no means the only case in which the data employed in this paper are of uncertain value4 ,everywhere we meet with figures of somewhat doubtful accuracy4 ,here we have somebody's 'estimate' quoted1 there another person's 'observation1' and these are adopted without further remark and used in the various calculations leading to the result above quoted4 ,it requires a practised mathematician1 and one fully acquainted with the extensive literature of this subject1 to examine these various data1 and track them through the maze of formulae and figures so as to determine to what extent they affect the final result4 ,there is however one curious oversight which ,i must refer to1 as it is a point to which ,i have given much attention4 ,not only does ,mr4 ,lowell assume1 as in his book1 that the 'snows' of ,mars consist of frozen water1 and that therefore there is water on its surface and water-vapour in its atmosphere1 not only does he ignore altogether ,dr4 ,johnstone ,stoney's calculations with regard to it1 which ,i have already referred to1 but he uses terms that imply that water-vapour is one of the heavier components of our atmosphere4 ,the passage is at p4 #afh of the ,philosophical ,magazine4 ,after stating that1 owing to the very small barometric pressure in ,mars1 water would boil at #aaj ,f41 he adds3 ,the sublimation at lower temperatures would be correspondingly increased4 ,consequently the amount of water-vapour in the ,martian air must on that score be relatively greater than our own4 ,then follows this remarkable passage3 ,carbon-dioxide1 because of its greater specific gravity1 would also be in relatively greater amount so far as this cause is considered4 ,for the planet would part1 caeteris paribus1 with its lighter gases the quickest4 ,whence as regards both water-vapour and carbon-dioxide we have reason to think them in relatively greater quantity than in our own air at corresponding barometric pressure4 ,i cannot understand this passage except as implying that 'water-vapour and carbon-dioxide' are among the heavier and not among the lighter gases of the atmosphere--those which the planet 'parts with quickest4' ,but this is just what water-vapour is1 being a little less than two-thirds the weight of air 7#j4fbbe71 and one of those which the planet would part with the quickest1 and which1 according to ,dr4 ,johnstone ,stoney1 it loses altogether4 99 99 99 99 99 ,note on ,professor ,lowell's article in the ,philosophical ,magazine2 by ,j4,h4 ,poynting1 ,f4,r4,s41 ,professor of ,physics in the ,university of ,birmingham4 ,i think ,professor ,lowell's results are erroneous through his neglect of the heat stored in the air by its absorption of radiation both from the sun and from the surface4 ,the air thus heated radiates to the surface and keeps up the temperature4 ,i have sent to the ,philosophical ,magazine a paper in which ,i think it is shown that when the radiation by the atmosphere is taken into account the results are entirely changed4 ,the temperature of ,mars1 with ,professor ,lowell's data1 still comes out far below the freezing-point--still further below than the increased distance alone would make it4 ,indeed1 the lower temperature on elevated regions of the earth's surface would lead us to expect this4 ,i think it is impossible to raise the temperature of ,mars to anything like the value obtained by ,professor ,lowell1 unless we assume some quality in his atmosphere entirely different from any found in our own atmosphere4 ,j4,h4 ,,poynting4 ,october #ai1 #aijg4 ,,chapter ,,vi4 ,a ,,new ,,estimate ,,of ,,the ,,temperature ,,of ,,mars4 ,when we are presented with a complex problem depending on a great number of imperfectly ascertained data1 we may often check the results thus obtained by the comparison of cases in which some of the more important of these data are identical1 while others are at a maximum or a minimum4 ,in the present case we can do this by a consideration of the ,moon as compared with the ,earth and with ,mars4 ,langley's ,determination of the ,moon's ,temperature4 ,in the moon we see the conditions that prevail in ,mars both exaggerated and simplified4 ,mars has a very scanty atmosphere1 the moon none at all1 or if there is one it is so excessively scanty that the most refined observations have not detected it4 ,all the complications arising from the possible nature of the atmosphere1 and its complex effects upon reflection1 absorption1 and radiation are thus eliminated4 ,the mean distance of the moon from the sun being identical with that of the earth1 the total amount of heat intercepted must also be identical2 only in this case the whole of it reaches the surface instead of one-fourth only1 according to ,mr4 ,lowell's estimate for the earth4 ,now1 by the most refined observations with his ,bolometer1 ,mr4 ,langley was able to determine the temperature of the moon's surface exposed to undimmed sunshine for fourteen days together2 and he found that1 even in that portion of it on which the sun was shining almost vertically1 the temperature rarely rose above the freezing point of water4 ,however extraordinary this result may seem1 it is really a striking confirmation of the accuracy of the general laws determining temperature which ,i have endeavoured to explain in the preceding chapter4 ,for the same surface which has had fourteen days of sunshine has also had a preceding fourteen days of darkness1 during which the heat which it had accumulated in its surface layers would have been lost by free radiation into stellar space4 ,it thus acquires during its day a maximum temperature of only #dia ,f4 absolute1 while its minimum1 after #ad days' continuous radiation1 must be very low1 and is1 with much reason1 supposed to approach the absolute zero4 ,rapid ,loss of ,heat by ,radiation on the ,earth4 ,in order better to comprehend what this minimum may be under extreme conditions1 it will be useful to take note of the effects it actually produces on the earth in places where the conditions are nearest to those existing on the moon or on ,mars1 though never quite equalling1 or even approaching very near them4 ,it is in our great desert regions1 and especially on high plateaux1 that extreme aridity prevails1 and it is in such districts that the differences between day and night temperatures reach their maximum4 ,it is stated by geographers that in parts of the ,great ,sahara the surface temperature is sometimes #aej ,f41 while during the night it falls nearly or quite to the freezing point--a difference of #aah degrees in little more than #ab hours4#aj ,in the high desert plains of ,central ,asia the extremes are said to be even greater4#aa ,again1 in his ,universal ,geography1 ,reclus states that in the ,armenian ,highlands the thermometer oscillates between #ac ,f4 and #aab;,f4 ,we may therefore1 without any fear of exaggeration1 take it as proved that a fall of #ajj ,f4 in twelve or fifteen hours not infrequently occurs where there is a very dry and clear atmosphere permitting continuous insolation by day and rapid radiation by night4 ,footnote #aj3 ,keith ,johnston's ',africa' in ,stanford's ,compendium4 ,footnote #aa3 ,chambers's ,encyclopaedia1 ,art4 ',deserts4' ,now1 as it is admitted that our dense atmosphere1 however dry and clear1 absorbs and reflects some considerable portion of the solar heat1 we shall certainly underestimate the radiation from the moon's surface during its long night if we take as the basis of our calculation a lowering of temperature amounting to #ajj ,f4 during twelve hours1 as not unfrequently occurs with us4 ,using these data--with ,stefan's law of decrease of radiation as the #dth power of the temperature--a mathematical friend finds that the temperature of the moon's surface would be reduced during the lunar night to nearly #bjj ,f4 absolute 7equal to-#beh ,f474 ,more ,rapid ,loss of ,heat by the ,moon4 ,although such a calculation as the above may afford us a good approximation to the rate of loss of heat by ,mars with its very scanty atmosphere1 we have now good evidence that in the case of the moon the loss is much more rapid4 ,two independent workers have investigated this subject with very accordant results--,dr4 ,boeddicker1 with ,lord ,rosse's #c-;foot reflector and a ,thermopile to measure the heat1 and ,mr4 ,frank ,very1 with a glass reflector of #ab inches diameter and the ,bolometer invented by ,mr4 ,langley4 ,the very striking and unexpected fact in which these observers agree is the sudden disappearance of much of the stored-up heat during the comparatively short duration of a total eclipse of the moon--less than two hours of complete darkness1 and about twice that period of partial obscuration4 ,dr4 ,boeddicker was unable to detect any appreciable heat at the period of greatest obscuration2 but1 owing to the extreme sensitiveness of the ,bolometer1 ,mr4 ,very ascertained that those parts of the surface which had been longest in the shadow still emitted heat to the amount of one per cent4 of the heat to be expected from the full moon4 ,this however is the amount of radiation measured by the ,bolometer1 and to get the temperature of the radiating surface we must apply ,stefan's law of the #dth power4 ,hence the temperature of the moon's dark surface will be the fourth root of 7#a over #ajj7 #a over #c4b ,a of the highest temperature 7which we may take at the freezing-point1 #dia ,f4 abs471 or #aed ,f4 abs41 just below the liquefaction point of air4 ,this is about #ej lower than the amount found by calculation from our most rapid radiation2 and as this amount is produced in a few hours1 it is not too much to expect that1 when continued for more than two weeks 7the lunar night71 it might reach a temperature sufficient to liquefy hydrogen 7#fj ,f4 abs471 or perhaps even below it4 ,note ,a3 ,la,tex markup root #d of #a over #ajj #a over #c4b ,theory of the ,moon's ,origin4 ,this extremely rapid loss of heat by radiation1 at first sight so improbable as to be almost incredible1 may perhaps be to some extent explained by the physical constitution of the moon's surface1 which1 from a theoretical point of view1 does not appear to have received the attention it deserves4 ,it is clear that our satellite has been long subjected to volcanic eruptions over its whole visible face1 and these have evidently been of an explosive nature1 so as to build up the very lofty cones and craters1 as well as thousands of smaller ones1 which1 owing to the absence of any degrading or denuding agencies1 have remained piled up as they were first formed4 ,this highly volcanic structure can1 ,i think1 be well explained by an origin such as that attributed to it by ,sir ,george ,darwin1 and which has been so well described by ,sir ,robert ,ball in his small volume1 ,time and ,tide4 ,these astronomers adduce strong evidence that the earth once rotated so rapidly that the equatorial protuberance was almost at the point of separation from the planet as a ring4 ,before this occurred1 however1 the tension was so great that one large portion of the protuberance where it was weakest broke away1 and began to move around the earth at some considerable distance from it4 ,as about #a_/ej of the bulk of the earth thus escaped1 it must have consisted of a considerable portion of the solid crust and a much larger quantity of the liquid or semi-liquid interior1 together with a proportionate amount of the gases which we know formed1 and still form1 an important part of the earth's substance4 ,as the surface layers of the earth must have been the lightest1 they would necessarily1 when broken up by this gigantic convulsion1 have come together to form the exterior of the new satellite1 and be soon adjusted by the forces of gravity and tidal disturbance into a more or less irregular spheroidal form1 all whose interstices and cavities would be filled up and connected together by the liquid or semi-liquid mass forced up between them4 ,thence-forward1 as the moon increased its distance and reduced its time of rotation1 in the way explained by ,sir ,robert ,ball1 there would necessarily commence a process of escape of the imprisoned gases at every fissure and at all points and lines of weakness1 giving rise to numerous volcanic outlets1 which1 being subjected only to the small force of lunar gravity 7only one-sixth that of the earth71 would1 in the course of ages1 pile up those gigantic cones and ridges which form its great characteristic4 ,but this small gravitative power of the moon would prevent its retaining on its surface any of the gases forming our atmosphere1 which would all escape from it and probably be recaptured by the earth4 ,by no process of external aggregation of solid matter to such a relatively small amount as that forming the moon1 even if the aggregation was so violent as to produce heat enough to cause liquefaction1 could any such long-continued volcanic action arise by gradual cooling1 in the absence of internal gases4 ,there might be fissures1 and even some outflows of molten rock2 but without imprisoned gases1 and especially without water and water-vapour producing explosive outbursts1 could any such amount of scoriae and ashes be produced as were necessary for the building up of the vast volcanic cones1 craters1 and craterlets we see upon the moon's surface4 ,i am not aware that either ,sir ,robert ,ball or ,sir ,george ,darwin have adduced this highly volcanic condition of the moon's surface as a phenomenon which can only be explained by our satellite having been thrown off a very much larger body1 whose gravitative force was sufficient to acquire and retain the enormous quantity of gases and of water which we possess1 and which are absolutely essential for that special form of cone-building volcanic action which the moon exhibits in so pre-eminent a degree4 ,yet it seems to me clear1 that some such hypothetical origin for our satellite would have had to be assumed if ,sir ,george ,darwin had not deduced it by means of purely mathematical argument based upon astronomical facts4 ,returning now to the problem of the moon's temperature1 ,i think the phenomena this presents may be in part due to the mode of formation here described4 ,for1 its entire surface being the result of long-continued gaseous explosions1 all the volcanic products--scoriae1 pumice1 and ashes--would necessarily be highly porous throughout2 and1 never having been compacted by water-action1 as on the earth1 and there having been no winds to carry the finer dust so as to fill up their pores and fissures1 the whole of the surface material to a very considerable depth must be loose and porous to a high degree4 ,this condition has been further increased owing to the small power of gravity and the extreme irregularity of the surface1 consisting very largely of lofty cones and ridges very loosely piled up to enormous heights4 ,now this condition of the substance of the moon's surface is such as would produce a high specific heat1 so that it would absorb a large amount of heat in proportion to the rise of temperature produced1 the heat being conducted downwards to a considerable depth4 ,owing1 however1 to the total absence of atmosphere radiation would very rapidly cool the surface1 but afterwards more slowly1 both on account of the action of ,stefan's law and because the heat stored up in the deeper portions could be carried to the surface by conduction only1 and with extreme slowness4 ,very's ,researches on the ,moon's ,heat4 ,the results of the eclipse observations are supported by the detailed examination of the surface-temperature of the moon by ,mr4 ,very in his ,prize ,essay on the ,distribution of the ,moon's ,heat 7published by the ,utrecht ,society of ,arts and ,sciences in #ahia74 ,he shows1 by a diagram of the ',phase-curve1' that at the commencement of the ,lunar day the surface just within the illuminated limb has acquired about #a_/g of its maximum temperature1 or about #gj ,f4 abs4 ,as the surface exposed to the ,bolometer at each observation is about #a_/cj of the moon's surface1 and in order to ensure accuracy the instrument has to be directed to a spot lying wholly within the edge of the moon1 it is evident that the surface measured has already been for several hours exposed to oblique sunshine4 ,the curve of temperature then rises gradually and afterwards more rapidly1 till it attains its maximum 7of about #cj to #dj ,f47 a few hours before noon4 ,this1 ,mr4 ,very thinks1 is due to the fact that the half of the moon's face first illuminated for us has1 on the average1 a darker surface than that of the afternoon1 or second quarter1 during which the curve descends not quite so rapidly1 the temperature near sunset being only a little higher than that near sunrise4 ,this rapid fall while exposed to oblique sunshine is quite in harmony with the rapid loss of heat during the few hours of darkness during an eclipse1 both showing the prepotency of radiation over insolation on the moon4 ,two other diagrams show the distribution of heat at the time of full-moon1 one half of the curve showing the temperatures along the equator from the edge of the disc to the centre1 the other along a meridian from this centre to the pole4 ,this diagram 7here reproduced7 exhibits the quick rise of temperature of the oblique rim of the moon and the nearly uniform heat of the central half of its surface2 the diminution of heat towards the pole1 however1 is slower for the first half and more rapid for the latter portion4 ,it is an interesting fact that the temperature near the margin of the full-moon increases towards the centre more rapidly than it does when the same parts are observed during the early phases of the first quarter4 ,mr4 ,very explains this difference as being due to the fact that the full-moon to its very edges is fully illuminated1 all the shadows of the ridges and mountains being thrown vertically or obliquely behind them4 ,we thus measure the heat reflected from the whole visible surface4 ,but at new moon1 and somewhat beyond the first quarter1 the deep shadows thrown by the smallest cones and ridges1 as well as by the loftiest mountains1 cover a considerable portion of the visible surface1 thus largely reducing the quantity of light and heat reflected or radiated in our direction4 ,it is only at the full1 therefore1 that the maximum temperature of the whole lunar surface can be measured4 ,it must be considered a proof of the delicacy of the heat-measuring instruments that this difference in the curves of temperature of the different parts of the moon's surface and under different conditions is so clearly shown4 ,the ,application of the ,preceding ,results to the ,case of ,mars4 ,this somewhat lengthy account of the actual state of the moon's surface and temperature is of very great importance in our present enquiry1 because it shows us the extraordinary difference in mean and extreme temperatures of two bodies situated at the same distance from the sun1 and therefore receiving exactly the same amount of solar heat per unit of surface4 ,we have learned also what are the main causes of this almost incredible difference1 namely3 7#a7 a remarkably rugged surface with porous and probably cavernous rock-texture1 leading to extremely rapid radiation of heat in the one2 as compared with a comparatively even and well-compacted surface largely clad with vegetation1 leading to comparatively slow and gradual loss by radiation in the other3 and 7#b71 these results being greatly intensified by the total absence of a protecting atmosphere in the former1 while a dense and cloudy atmosphere with an ever-present supply of water-vapour1 accumulates and equalises the heat received by the latter4 ,the only other essential difference in the two bodies which may possibly aid in the production of this marvellous result1 is the fact of our day and night having a mean length of #ab hours1 while those of the moon are about #ad-a_/b of our days4 ,but the altogether unexpected fact1 in which two independent enquirers agree1 that during the few hours' duration of a total eclipse of the moon so large a proportion of the heat is lost by radiation renders it almost certain that the resulting low temperature would be not very much less if the moon had a day and night the same length as our own4 ,the great lesson we learn by this extreme contrast of conditions supplied to us by nature1 as if to enable us to solve some of her problems1 is1 the overwhelming importance1 first1 of a dense and well-compacted surface1 due to water-action and strong gravitative force2 secondly1 of a more or less general coat of vegetation2 and1 thirdly1 of a dense vapour-laden atmosphere4 ,these three favourable conditions result in a mean temperature of about #fj ,f4 with a range seldom exceeding #dj above or below it1 while over more than half the land-surface of the earth the temperature rarely falls below the freezing point4 ,on the other hand1 we have a globe of the same materials and at the same distance from the sun1 with a maximum temperature of freezing water1 and a minimum not very far from the absolute zero1 the monthly mean being probably much below the freezing point of carbonic-acid gas--a difference entirely due to the absence of these three favourable conditions4 ,the ,special ,features of ,mars as influencing ,temperature4 ,coming now to the special feature of ,mars and its probable temperature1 we find that most writers have arrived at a very different conclusion from that of ,mr4 ,lowell1 who himself quotes ,mr4 ,moulton as an authority who 'recently1 by the application of ,stefan's law1' has found the mean temperature of this planet to be-#ce ,f4 ,again1 ,professor ,j4,h4 ,poynting1 in his lecture on ',radiation in the ,solar ,system1' delivered before the ,british ,association at ,cambridge in #aijd1 gave an estimate of the mean temperature of the planets1 arrived at from measurements of the sun's emissive power and the application of ,stefan's law to the distances of the several planets1 and he thus finds the earth to have a mean temperature of #ag ,c4 7#fb-a_/b ,f47 and ,mars one of-#ch ,c4 7-#cf-a_/b ,f471 a wonderfully close approximation to the mean temperature of the earth as determined by direct measurement1 and therefore1 presumably1 an equally near approximation to that of ,mars as dependent on distance from the sun1 and 'on the supposition that it is earth-like in all its conditions4' ,but we know that it is far from being earth-like in the very conditions which we have found to be those which determine the extremely different temperatures of the earth1 and moon2 and1 as regards each of these1 we shall find that1 so far as it differs from the earth1 it approximates to the less favourable conditions that prevail in the moon4 ,the first of these conditions which we have found to be essential in regulating the absorption and radiation of heat1 and thus raising the mean temperature of a planet1 is a compact surface well covered with vegetation1 two conditions arising from1 and absolutely dependent on1 an ample amount of water4 ,but ,mr4 ,lowell himself assures us1 as a fact of which he has no doubt1 that there are no permanent bodies of water1 great or small1 upon ,mars2 that rain1 and consequently rivers1 are totally wanting2 that its sky is almost constantly clear1 and that what appear to be clouds are not formed of water-vapour but of dust4 ,he dwells1 emphatically1 on the terrible desert conditions of the greater part of the surface of the planet4 ,that being the case now1 we have no right to assume that it has ever been otherwise2 and1 taking full account of the fact1 neither denied nor disputed by ,mr4 ,lowell1 that the force of gravity on ,mars is not sufficient to retain water-vapour in its atmosphere1 we must conclude that the surface of that planet1 like that of the moon1 has been moulded by some form of volcanic action modified probably by wind1 but not by water4 ,adding to this1 that the force of gravity on ,mars is nearer that of the moon than to that of the earth1 and we may r reasonably conclude that its surface is formed of volcanic matter in a light and porous condition1 and therefore highly favourable for the rapid loss of surface heat by radiation4 ,the surface-conditions of ,mars are therefore1 presumably1 much more like those of the moon than like those of the earth4 ,the next condition favourable to the storing up of heat--a covering of vegetation--is almost certainly absent from ,mars except1 possibly1 over limited areas and for short periods4 ,in this feature also the surface of ,mars approximates much nearer to lunar than to earth-conditions4 ,the third condition--a dense1 vapour-laden atmosphere--is also wanting in ,mars4 ,for although it possesses an atmosphere it is estimated by ,mr4 ,lowell 7in his latest article7 to have a pressure equivalent to only #b-a_/b inches of mercury with us1 giving it a density of only one-twelfth part that of ours2 while aqueous vapour1 the chief accumulator of heat1 cannot permanently exist in it1 and1 notwithstanding repeated spectroscopic observations for the purpose of detecting it1 has never been proved to exist4 ,i submit that ,i have now shown from the statements--and largely as the result of the long-continued observations--of ,mr4 ,lowell himself1 that1 so far as the physical conditions of ,mars are known to differ from those of the earth1 the differences are all unfavourable to the conservation and favourable to the dissipation of the scanty heat it receives from the sun--that they point unmistakeably towards the temperature conditions of the moon rather than to those of the earth1 and that the cumulative effect of these adverse conditions1 acting upon a heat-supply1 reduced by solar distance to less than one-half of ours1 must result in a mean temperature 7as well as in the extremes7 nearer to that of our satellite than to that of our own earth4 ,further ,criticism of ,mr4 ,lowell's ,article4 ,we are now in a position to test some further conclusions of ,mr4 ,lowell's ,phil4 ,mag4 article by comparison with actual phenomena4 ,we have seen1 in the outline ,i have given of this article1 that he endeavours to show how the small amount of solar heat received by ,mars is counterbalanced1 largely by the greater transparency to light and heat of its thin and cloudless atmosphere1 and partially also by a greater conservative or 'blanketing' power of its atmosphere due to the presence in it of a large proportion of carbonic acid gas and aqueous vapour4 ,the first of these statements may be admitted as a fact which he is entitled to dwell upon1 but the second--the presence of large quantities of carbon-dioxide and aqueous vapour is a pure hypothesis unsupported by any item of scientific evidence1 while in the case of aqueous vapour it is directly opposed to admitted results founded upon the molecular theory of gaseous elasticity4 ,but1 although ,mr4 ,lowell refers to the conservative or 'blanketing' effect of the earth's atmosphere1 he does not consider or allow for its very great cumulative effect1 as is strikingly shown by the comparison with the actual temperature conditions of the moon4 ,this cumulative effect is due to the continuous reflection and radiation of heat from the clouds as well as from the vapour-laden strata of air in our lower atmosphere1 which latter1 though very transparent to the luminous and accompanying heat rays of the sun1 are opaque to the dark heat-rays whether radiated or reflected from the earth's surface4 ,we are therefore in a position strictly comparable with that of the interior of some huge glass house1 which not only becomes intensely heated by the direct rays of the sun1 but also to a less degree by reflected rays from the sky and those radiated from the clouds1 so that even on a cloudy or misty day its temperature rises many degrees above that of the outer air4 ,such a building1 if of large size1 of suitable form1 and well protected at night by blinds or other covering1 might be so arranged as to accumulate heat in its soil and walls so as to maintain a tolerably uniform temperature though exposed to a considerable range of external heat and cold4 ,it is to such a power of accumulation of heat in our soil and lower atmosphere that we must impute the overwhelming contrast between our climate and that of the moon4 ,with us1 the solar heat that penetrates our vapour-laden and cloudy atmosphere is shut in by that same atmosphere1 accumulates there for weeks and months together1 and can only slowly escape4 ,it is this great cumulative power which ,mr4 ,lowell has not taken account of1 while he certainly has not estimated the enormous loss of heat by free radiation1 which entirely neutralises the effects of increase of sun-heat1 however great1 when these cumulative agencies are not present4#ab ,footnote #ab3 ,the effects of this 'cumulative' power of a dense atmosphere are further discussed and illustrated in the last chapter of this book1 where ,i show that the universal fact of steadily diminishing temperatures at high altitudes is due solely to the diminution of this cumulative power of our atmosphere1 and that from this cause alone the temperature of ,mars must be that which would be found on a lofty plateau about #ah1jjj feet higher than the average of the peaks of the ,andes6 ,temperature on ,polar ,regions of ,mars4 ,there is also a further consideration which ,i think ,mr4 ,lowell has altogether omitted to discuss4 ,whatever may be the mean temperature of ,mars1 we must take account of the long nights in its polar and high-temperate latitudes1 lasting nearly twice as long as ours1 with the resulting lowering of temperature by radiation into a constantly clear sky4 ,even in ,siberia1 in ,lat4 #fg-a_/b,n4 a cold of-#hh;,f4 has been attained2 while over a large portion of ,n4 ,asia and ,america above #fj ,lat4 the mean ,january temperature is from-#cj;,f4 to-#fj;,f41 and the whole subsoil is permanently frozen from a depth of #f or #g feet to several hundreds4 ,but the winter temperatures1 over the same latitudes in ,mars1 must be very much lower2 and it must require a proportionally larger amount of its feeble sun-heat to raise the surface even to the freezing-point1 and an additional very large amount to melt any considerable depth of snow4 ,but this identical area1 from a little below #fj to the pole1 is that occupied by the snow-caps of ,mars1 and over the whole of it the winter temperature must be far lower than the earth-minimum of-#hh;,f4 ,then1 as the ,martian summer comes on1 there is less than half the sun-heat available to raise this low temperature after a winter nearly double the length of ours4 ,and when the summer does come with its scanty sun-heat1 that heat is not accumulated as it is by our dense and moisture-laden atmosphere1 the marvellous effects of which we have already shown4 ,yet with all these adverse conditions1 each assisting the other to produce a climate approximating to that which the earth would have if it had no atmosphere 7but retaining our superiority over ,mars in receiving double the amount of sun-heat71 we are asked to accept a mean temperature for the more distant planet almost exactly the same as that of mild and equable southern ,england1 and a disappearance of the vast snowfields of its polar regions as rapid and complete as what occurs with us6 ,if the moon1 even at its equator1 has not its temperature raised above the freezing-point of water1 how can the more distant ,mars1 with its oblique noon-day sun falling upon the snow-caps1 receive heat enough1 first to raise their temperature to #cb ,f41 and then to melt with marked rapidity the vast frozen plains of its polar regions8 ,mr4 ,lowell is however so regardless of the ordinary teachings of meteorological science that he actually accounts for the supposed mild climate of the polar regions of ,mars by the absence of water on its surface and in its atmosphere4 ,he concludes his fifth chapter with the following words3 ,could our earth but get rid of its oceans1 we too might have temperate regions stretching to the poles4 ,here he runs counter to two of the best-established laws of terrestrial climatology-- the wonderful equalising effects of warm ocean-currents which are the chief agents in diminishing polar cold2 the equally striking effects of warm moist winds derived from these oceans1 and the great storehouse of heat we possess in our vapour-laden atmosphere1 its vapour being primarily derived from these same oceans6 ,but1 in ,mr4 ,lowell's opinion1 all our meteorologists are quite mistaken4 ,our oceans are our great drawbacks4 ,only get rid of them and we should enjoy the exquisite climate of ,mars--with its absence of clouds and fog1 of rain or rivers1 and its delightful expanses of perennial deserts1 varied towards the poles by a scanty snow-fall in winter1 the melting of which might1 with great care1 supply us with the necessary moisture to grow wheat and cabbages for about one-tenth1 or more likely one-hundredth1 of our present population4 ,i hope ,i may be excused for not treating such an argument seriously4 ,the various considerations now advanced1 especially those which show the enormous cumulative and conservative effect of our dense and water-laden atmosphere1 and the disastrous effect--judging by the actual condition of the moon--which the loss of it would have upon our temperature1 seem to me quite sufficient to demonstrate important errors in the data or fallacies in the complex mathematical argument by which ,mr4 ,lowell has attempted to uphold his views as to the temperature and consequent climatic conditions of ,mars4 ,in concluding this portion of my discussion of the problem of ,mars1 ,i wish to call attention to the fact that my argument1 founded upon a comparison of the physical conditions of the earth and moon with those of ,mars1 is dependent upon a small number of generally admitted scientific facts2 while the conclusions drawn from those facts are simple and direct1 requiring no mathematical knowledge to follow them1 or to appreciate their weight and cogency4 ,i claim for them1 therefore1 that they are in no degree speculative1 but in their data and methods exclusively scientific4 ,in the next chapter ,i will put forward a suggestion as to how the very curious markings upon the surface of ,mars may possibly be interpreted1 so as to be in harmony with the planet's actual physical condition and its not improbable origin and past history4 ,,chapter ,,vii4 ,a ,,suggestion ,,as ,,to ,,the ',,canals' ,,of ,,mars4 ,the special characteristics of the numerous lines which intersect the whole of the equatorial and temperate regions of ,mars are1 their straightness combined with their enormous length4 ,it is this which has led ,mr4 ,lowell to term them 'non-natural features4' ,schiaparelli1 in his earlier drawings1 showed them curved and of comparatively great width4 ,later1 he found them to be straight fine lines when seen under the best conditions1 just as ,mr4 ,lowell has always seen them in the pure atmosphere of his observatory4 ,both of these observers were at first doubtful of their reality1 but persistent observation continued at many successive oppositions compelled acceptance of them as actual features of the planet's disc4 ,so many other observers have now seen them that the objection of unreality seems no longer valid4 ,mr4 ,lowell urges1 however1 that their perfect straightness1 their extreme tenuity1 their uniformity throughout their whole length1 the dual character of many of them1 their relation to the 'oases' and the form and position of these round black spots1 are all proofs of artificiality and are suggestive of design4 ,and considering that some of them are actually as long as from ,boston to ,san ,francisco1 and relatively to their globe as long as from ,london to ,bombay1 his objection that no natural phenomena within our knowledge show such regularity on such a scale seems1 at first1 a mighty one4 ,it is certainly true that we can point to nothing exactly like them either on the earth or on the moon1 and these are the only two planetary bodies we are in a position to compare with ,mars4 ,yet even these do1 ,i think1 afford us some hints towards an interpretation of the mysterious lines4 ,but as our knowledge of the internal structure and past history even of our earth is still imperfect1 that of the moon only conjectural1 and that of ,mars a perfect blank1 it is not perhaps surprising that the surface-features of the latter do not correspond with those of either of the others4 ,mr4 ,pickering's ,suggestion4 ,the best clue to a natural interpretation of the strange features of the surface of ,mars is that suggested by the ,american astronomer ,mr4 ,w4,h4 ,pickering in ,popular ,astronomy 7#aijd74 ,briefly it is1 that both the 'canals' of ,mars and the rifts as well as the luminous streaks on the moon are cracks in the volcanic crust1 caused by internal stresses due to the action of the heated interior4 ,these cracks he considers to be symmetrically arranged with regard to small 'craterlets' 7,mr4 ,lowell's 'oases'7 because they have originated from them1 just as the white streaks on the moon radiate from the larger craters as centres4 ,he further supposes that water and carbon-dioxide issue from the interior into these fissures1 and1 in conjunction with sunlight1 promote the growth of vegetation4 ,owing to the very rare atmosphere1 the vapours1 he thinks1 would not ascend but would roll down the outsides of the craterlets and along the borders of the canals1 thus irrigating the immediate vicinity and serving to promote the growth of some form of vegetation which renders the canals and oases visible4#ac ,footnote #ac3 ,nature1 vol4 #gj1 p4 #ecf4 ,this opinion is especially important because1 next to ,mr4 ,lowell1 ,mr4 ,pickering is perhaps the astronomer who has given most attention to ,mars during the last fifteen years4 ,he was for some time at ,flagstaff with ,mr4 ,lowell1 and it was he who discovered the oases or craterlets1 and who originated the idea that we did not see the 'canals' themselves but only the vegetable growth on their borders4 ,he also observed ,mars in the ,southern ,hemisphere at ,arequipa2 and he has since made an elaborate study of the moon by means of a specially constructed telescope of #ace feet focal length1 which produced a direct image on photographic plates nearly #af inches in diameter4#ad ,footnote #ad3 ,nature1 vol4 #gj1 ,may #e1 p4xi1 supplement4 ,it is clear therefore that ,mr4 ,lowell's views as to the artificial nature of the 'canals' of ,mars are not accepted by an astronomer of equal knowledge and still wider experience4 ,yet ,professor ,pickering's alternative view is more a suggestion than an explanation1 because there is no attempt to account for the enormous length and perfect straightness of the lines on ,mars1 so different from anything that is found either on our earth or on the moon4 ,there must evidently be some great peculiarity of structure or of conditions on ,mars to account for these features1 and ,i shall now attempt to point out what this peculiarity is and how it may have arisen4 ,the ,meteoritic ,hypothesis4 ,during the last quarter of a century a considerable change has come over the opinions of astronomers as regards the probable origin of the ,solar ,system4 ,the large amount of knowledge of the stellar universe1 and especially of nebulae1 of comets and of meteor-streams which we now possess1 together with many other phenomena1 such as the constitution of ,saturn's rings1 the great number and extent of the minor planets1 and generally of the vast amount of matter in the form of meteor-rings and meteoric dust in and around our system1 have all pointed to a different origin for the planets and their satellites than that formulated by ,laplace as the ,nebular hypothesis4 ,it is now seen more clearly than at any earlier period1 that most of the planets possess special characteristics which distinguish them from one another1 and that such an origin as ,laplace suggested--the slow cooling and contraction of one vast sun-mist or nebula1 besides presenting inherent difficulties--many think them impossibilities--in itself does not afford an adequate explanation of these peculiarities4 ,hence has arisen what is termed the ,meteoritic theory1 which has been ably advocated for many years by ,sir ,norman ,lockyer1 and with some unimportant modifications is now becoming widely accepted4 ,briefly1 this theory is1 that the planets have been formed by the slow aggregation of solid particles around centres of greatest condensation2 but as many of my readers may be altogether unacquainted with it1 ,i will here give a very clear statement of what it is1 from ,professor ,j4,w4 ,gregory's presidential address to the ,geological ,section of the ,british ,association of the present year4 ,he began by saying that these modern views were of far more practical use to men of science than that of ,laplace1 and that they give us a history of the world consistent with the actual records of geology4 ,he then continues3 ,according to ,sir ,norman ,lockyer's ,meteoritic ,hypothesis1 nebulae1 comets1 and many so-called stars consist of swarms of meteorites which1 though normally cold and dark1 are heated by repeated collisions1 and so become luminous4 ,they may even be volatilised into glowing meteoric vapour2 but in time this heat is dissipated1 and the force of gravity condenses a meteoritic swarm into a single globe4 ',some of the swarms are1' says ,lockyer1 'truly members of the solar system1' and some of these travel round the sun in nearly circular orbits1 like planets4 ,they may be regarded as infinitesimal planets1 and so ,chamberlain calls them 'planetismals4' ,the planetismal theory is a development of the meteoritic theory1 and presents it in an especially attractive guise4 ,it regards meteorites as very sparsely distributed through space1 and gravity as powerless to collect them into dense groups4 ,so it assigns the parentage of the solar system to a spiral nebula composed of planetismals1 and the planets as formed from knots in the nebula1 where many planetismals had been concentrated near the intersections of their orbits4 ,these groups of meteorites1 already as dense as a swarm of bees1 were then packed closer by the influence of gravity1 and the contracting mass was heated by the pressure1 even above the normal melting-point of the material1 which was kept rigid by the weight of the overlying layers4 ,now1 adopting this theory as the last word of science upon the subject of the origin of planets1 we see that it affords immense scope for diversity in results depending on the total amount of matter available within the range of attraction of an incipient planetary mass1 and the rates at which this matter becomes available4 ,by a special combination of these two quantities 7which have almost certainly been different for each planet7 ,i think we may be able to throw some light upon the structure and physical features of ,mars4 ,the ,probable ,mode of ,origin of ,mars4 ,this planet1 lying between two of much greater mass1 has evidently had less material from which to be formed by aggregation2 and if we assume--as in the absence of evidence to the contrary we have a right to do--that its beginnings were not much later 7or earlier7 than those of the earth1 then its smaller size shows that it has in all probability aggregated very much more slowly4 ,but the internal heat acquired by a planet while forming in this manner will depend upon the rate at which it aggregates and the velocity with which the planetismals' fall into it1 and this velocity will increase with its mass and consequent force of gravity4 ,in the early stages of a planet's growth it will probably remain cold1 the small amount of heat produced by each impact being lost by radiation before the next one occurs2 and with a small and slowly aggregating planet this condition will prevail till it approaches its full size4 ,then only will its gravitative force be sufficient to cause incoming matter to fall upon it with so powerful an impact as to produce intense heat4 ,further1 the compressive force of a small planet will be a less effective heat-producing agency than in the case of a larger one4 ,the earth we know has acquired a large amount of internal heat1 probably sufficient to liquefy its whole interior2 but ,mars has only one-ninth part the mass of the earth1 and it is quite possible1 and even probable1 that its comparatively small attractive force would never have liquefied or even permanently heated the more central portions of its mass4 ,this being admitted1 ,i suggest the following course of events as quite possible1 and not even improbable1 in the case of this planet4 ,during the whole of its early growth1 and till it acquired nearly its present diameter1 its rate of aggregation was so slow that the planetismals falling upon it1 though they might have been heated and even partially liquefied by the impact1 were never in such quantity as to produce any considerable heating effect on the whole mass1 and each local rise of temperature was soon lost by radiation4 ,the planet thus grew as a solid and cold mass1 compacted together by the impact of the incoming matter as well as by its slowly increasing gravitative force4 ,but when it had attained to within perhaps #ajj1 perhaps #ej miles1 or less1 of its present diameter1 a great change occurred in the opportunity for further growth4 ,some large and dense swarm of meteorites1 perhaps containing a number of bodies of the size of the asteroids1 came within the range of the sun's attraction and were drawn by it into an orbit which crossed that of ,mars at such a small angle that the planet was able at each revolution to capture a considerable number of them4 ,the result might then be that1 as in the case of the earth1 the continuous inpour of the fresh matter first heated1 and later on liquefied the greater part of it as well perhaps as a thin layer of the planet's original surface2 so that when in due course the whole of the meteor-swarm had been captured1 ,mars had acquired its present mass1 but would consist of an intensely heated1 and either liquid or plastic thin outer shell resting upon a cold and solid interior4 ,the size and position of the two recently discovered satellites of ,mars1 which are believed to be not more than ten miles in diameter1 the more remote revolving around its primary very little slower than the planet rotates1 while the nearer one1 which is considerably less distant from the planet's surface than its own antipodes and revolves around it more than three times during the ,martian day1 may perhaps be looked upon as the remnants of the great meteor-swarm which completed the ,martian development1 and which are perhaps themselves destined at some distant period to fall into the planet4 ,should future astronomers witness the phenomenon the effect produced upon its surface would be full of instruction4 ,as the result of such an origin as that suggested1 ,mars would possess a structure which1 in the essential feature of heat-distribution1 would be the very opposite of that which is believed to characterise the earth1 yet it might have been produced by a very slight modification of the same process4 ,this peculiar heat-distribution1 together with a much smaller mass and gravitative force1 would lead to a very different development of the surface and an altogether diverse geological history from ours1 which has throughout been profoundly influenced by its heated interior1 its vast supply of water1 and the continuous physical and chemical reactions between the interior and the crust4 ,these reactions have1 in our case1 been of substantially the same nature1 and very nearly of the same degree of intensity throughout the whole vast eons of geological time1 and they have resulted in a wonderfully complex succession of rock-formations--volcanic1 plutonic1 and sedimentary--more or less intermingled throughout the whole series1 here remaining horizontal as when first deposited1 there upheaved or depressed1 fractured or crushed1 inclined or contorted2 denuded by rain and rivers with the assistance of heat and cold1 of frost and ice1 in an unceasing series of changes1 so that however varied the surface may be1 with hill and dale1 plains and uplands1 mountain ranges and deep intervening valleys1 these are as nothing to the diversities of interior structure1 as exhibited in the sides of every alpine valley or precipitous escarpment1 and made known to us by the work of the miner and the well-borer in every part of the world4 ,structural ,straight ,lines on the ,earth4 ,the great characteristic of the earth1 both on its surface and in its interior1 is thus seen to be extreme diversity both of form and structure1 and this is further intensified by the varied texture1 constitution1 hardness1 and density of the various rocks and debris of which it is composed4 ,it is therefore not surprising that1 with such a complex outer crust1 we should nowhere find examples of those geometrical forms and almost world-wide straight lines that give such a remarkable1 and as ,mr4 ,lowell maintains1 'non-natural' character to the surface of ,mars1 but which1 as it seems to me1 of themselves afford prima facie evidence of a corresponding simplicity and uniformity in its internal structure4 ,yet we are not ourselves by any means devoid of 'straight lines' structurally produced1 in spite of every obstacle of diversity of form and texture1 of softness and hardness1 of lamination or crystallisation1 which are adverse to such developments4 ,examples of these are the numerous 'faults' which occur in the harder rocks1 and which often extend for great distances in almost perfect straight lines4 ,in our own country we have the ,tyneside and ,craven faults in the ,north of ,england1 which are #cj miles long and often #bj yards wide2 but even more striking is the great ,cleveland ,dyke--a wall of volcanic rock dipping slightly towards the south1 but sometimes being almost vertical1 and stretching across the country1 over hill and dale1 in an almost perfect straight line from a point on the coast ten miles north of ,scarborough1 in a west-by-north direction1 passing about two miles south of ,stockton and terminating about six miles north-by-east of ,barnard ,castle1 a distance of very nearly #fj miles4 ,the great fault between the ,highlands and ,lowlands of ,scotland extends across the country from ,stonehaven to near ,helensburgh1 a distance of #abj miles2 and there are very many more of less importance4 ,much more extensive are some of the great continental dislocations1 often forming valleys of considerable width and length4 ,the ,upper ,rhine flows in one of these great valleys of subsidence for about #ahj miles1 from ,mulhausen to ,frankfort1 in a generally straight line1 though modified by denudation4 ,vaster still is the valley of the ,jordan through the ,sea of ,galilee to the ,dead ,sea1 continued by the ,wady ,arabah to the ,gulf of ,akaba1 believed to form one vast geological depression or fracture extending in a straight line for #djj miles4 ,thousands of such faults1 dykes1 or depressions exist in every part of the world1 all believed to be due to the gradual shrinking of the heated interior to which the solid crust has to accommodate itself1 and they are especially interesting and instructive for our present purpose as showing the tendency of such fractures of solid rock-material to extend to great lengths in straight lines1 notwithstanding the extreme irregularity both in the surface contour as well as in the internal structures of the varied deposits and formations through which they pass4 ,probable ,origin of the ,surface-features of ,mars4 ,returning now to ,mars1 let us consider the probable course of events from the point at which we left it4 ,the heat produced by impact and condensation would be likely to release gases which had been in combination with some of the solid matter1 or perhaps been itself in a solid state due to intense cold1 and these1 escaping outwards to the surface1 would produce on a small scale a certain amount of upheaval and volcanic disturbance2 and as an outer crust rapidly formed1 a number of vents might remain as craters or craterlets in a moderate state of activity4 ,owing to the comparatively small force of gravity1 the outer crust would become scoriaceous and more or less permeated by the gases1 which would continue to escape through it1 and this would facilitate the cooling of the whole of the heated outer crust1 and allow it to become rather densely compacted4 ,when the greater portion of the gases had thus escaped to the outer surface and assisted to form a scanty atmosphere1 such as now exists1 there would be no more internal disturbance and the cooling of the heated outer coating would steadily progress1 resulting at last in a slightly heated1 and later in a cold layer of moderate thickness and great general uniformity4 ,owing to the absence of rain and rivers1 denudation such as we experience would be unknown1 though the superficial scoriaceous crust might be partially broken up by expansion and contraction1 and suffer a certain amount of atmospheric erosion4 ,the final result of this mode of aggregation would be1 that the planet would consist of an outer layer of moderate thickness as compared with the central mass1 which outer layer would have cooled from a highly heated state to a temperature considerably below the freezing-point1 and this would have been all the time contracting upon a previously cold1 and therefore non-contracting nucleus4 ,the result would be that very early in the process great superficial tensions would be produced1 which could only be relieved by cracks or fissures1 which would initiate at points of weakness--probably at the craterlets already referred to--from which they would radiate in several directions4 ,each crack thus formed near the surface would1 as cooling progressed1 develop in length and depth2 and owing to the general uniformity of the material1 and possibly some amount of crystalline structure due to slow and continuous cooling down to a very low temperature1 the cracks would tend to run on in straight lines and to extend vertically downwards1 which two circumstances would necessarily result in their forming portions of 'great circles' on the planet's surface--the two great facts which ,mr4 ,lowell appeals to as being especially 'non-natural4' ,symmetry of ,basaltic ,columns4 ,we have however one quite natural fact on our earth which serves to illustrate one of these two features1 the direction of the downward fissure4 ,this is1 the comparatively common phenomenon of basaltic columns and ',giant's ,causeways4' ,the wonderful regularity of these1 and especially the not unfrequent upright pillars in serried ranks1 as in the palisades of the ,hudson river1 must have always impressed observers with their appearance of artificiality4 ,yet they are undoubtedly the result of the very slow cooling and contraction of melted rocks under compression by strata below and above them1 so that1 when once solidified1 the mass was held in position and the tension produced by contraction could only be relieved by numerous very small cracks at short distances from each other in every direction1 resulting in five1 six1 or seven-sided polygons1 with sides only a few inches long4 ,this contraction began of course at the coolest surface1 generally the upper one2 and observation of these columns in various positions has established the rule that their direction lengthways is always at right angles to the cooling surface1 and thus1 whenever this surface was horizontal1 the columns became almost exactly vertical4 ,how this applies to ,mars4 ,one of the features of the surface of ,mars that ,mr4 ,lowell describes with much confidence is1 that it is wonderfully uniform and level1 which of course it would be if it had once been in a liquid or plastic state1 and not much disturbed since by volcanic or other internal movements4 ,the result would be that cracks formed by contraction of the hardened outer crust would be vertical2 and1 in a generally uniform material at a very uniform temperature1 these cracks would continue almost indefinitely in straight lines4 ,the hardened and contracting surface being free to move laterally on account of there being a more heated and plastic layer below it1 the cracks once initiated above would continually widen at the surface as they penetrated deeper and deeper into the slightly heated substratum4 ,now1 as basalt begins to soften at about #adjj ,f4 and the surface of ,mars has cooled to at least the freezing-point--perhaps very much below it--the contraction would be so great that if the fissures produced were #ejj miles apart they might be three miles wide at the surface1 and1 if only #ajj miles apart1 then about two-thirds of a mile wide4#ae ,but as the production of the fissures might have occupied perhaps millions of years1 a considerable amount of atmospheric denudation would result1 however slowly it acted4 ,expansion and contraction would wear away the edges and sides of the fissures1 fill up many of them with the debris1 and widen them at the surfaces to perhaps double their original size4#af ,footnote #ae3 ,the coefficient of contraction of basalt is #j4jjjjjf for #a ,f41 which would lead to the results given here4 ,footnote #af3 ,mr4 ,w4,h4 ,pickering observed clouds on ,mars #ae miles high2 these are the 'projections' seen on the terminator when the planet is partially illuminated4 ,they were at first thought to be mountains2 but during the opposition of #ahid1 more than #djj of them were seen at ,flagstaff during nine months' observation4 ,usually they are of rare occurrence4 ,they are seen to change in form and position from day to day1 and ,mr4 ,lowell is strongly of opinion that they are dust-storms1 not what we term clouds4 ,they were mostly about #ac miles high1 indicating considerable aerial disturbance on the planet1 and therefore capable of producing proportional surface denudation4 ,suggested ,explanation of the ',oases4' ,the numerous round dots seen upon the 'canals1' and especially at points from which several canals radiate and where they intersect--termed 'oases' by ,mr4 ,lowell and 'craterlets' by ,mr4 ,pickering may be explained in two ways4 ,those from which several canals radiate may be true craters from which the gases imprisoned in the heated surface layers have gradually escaped4 ,they would be situated at points of weakness in the crust1 and become centres from which cracks would start during contraction4 ,those dots which occur at the crossing of two straight canals or cracks may have originated from the fact that at such intersections there would be four sharply-projecting angles1 which1 being exposed to the influence of alternate heat and cold 7during day and night7 on the two opposite surfaces1 would inevitably in time become fractured and crumbled away1 resulting in the formation of a roughly circular chasm which would become partly filled up by the debris4 ,those formed by cracks radiating from craterlets would also be subject to the same process of rounding off to an even greater extent2 and thus would be produced the 'oases' of various sizes up to #ej miles or more in diameter recorded by ,mr4 ,lowell and other observers4 ,probable ,function of the ,great ,fissures4 ,mr4 ,pickering1 as we have seen1 supposes that these fissures give out the gases which1 overflowing on each side1 favour the growth of the supposed vegetation which renders the course of the canals visible1 and this no doubt may have been the case during the remote periods when these cracks gave access to the heated portions of the surface layer4 ,but it seems more probable that ,mars has now cooled down to the almost uniform mean temperature it derives from solar heat1 and that the fissures--now for the most part broad shallow valleys--serve merely as channels along which the liquids and heavy gases derived from the melting of the polar snows naturally flow1 and1 owing to their nearly level surfaces1 overflow to a certain distance on each side of them4 ,suggested ,origin of the ,blue ,patches4 ,these heavy gases1 mainly perhaps1 as has been often suggested1 carbon-dioxide1 would1 when in large quantity and of considerable depth1 reflect a good deal of light1 and1 being almost inevitably dust-laden1 might produce that blue tinge adjacent to the melting snow-caps which ,mr4 ,lowell has erroneously assumed to be itself a proof of the presence of liquid water4 ,just as the blue of our sky is undoubtedly due to reflection from the ultra-minute dust particles in our higher atmosphere1 similar particles brought down by the 'snow' from the higher ,martian atmosphere might produce the blue tinge in the great volumes of heavy gas produced by its evaporation or liquefaction4 ,it may be noted that ,mr4 ,lowell objects to the carbon-dioxide theory of the formation of the snow-caps1 that this gas at low pressures does not liquefy1 but passes at once from the solid to the gaseous state1 and that only water remains liquid sufficiently long to produce the blue colour' which plays so large a part in his argument for the mild climate essential for an inhabited planet4 ,but this argument1 as ,i have already shown1 is valueless4 ,for only very deep water can possibly show a blue colour by reflected light1 while a dust-laden atmosphere--especially with a layer of very dense gas at the bottom of it1 as would be the case with the newly evaporated carbon-dioxide from the diminishing snow-cap --would provide the very conditions likely to produce this blue tinge of colour4 ,it may be considered a support to this view that carbonic-acid gas becomes liquid at--#adj ,f4 and solid at--#afb ,f41 temperatures far higher than we should expect to prevail in the polar and north temperate regions of ,mars during a considerable part of the year1 but such as might be reached there during the summer solstice when the snows' so rapidly disappear1 to be re-formed a few months later4 ,the ,double ,canals4 ,the curious phenomena of the 'double canals' are undoubtedly the most difficult to explain satisfactorily on any theory that has yet been suggested4 ,they vary in distance apart from about #ajj to #djj miles4 ,in many cases they appear perfectly parallel1 and ,mr4 ,lowell gives us the impression that they are almost always so4 ,but his maps show1 in some cases1 decided differences of width at the two extremities1 indicating considerable want of parallelism4 ,a few of the curved canals are also double4 ,there is one drawing in ,mr4 ,lowell's book 7p4 #bai7 of the mouths1 or starting points1 of the ,euphrates and ,phison1 two widely separated double canals diverging at an angle of about #dj from the same two oases1 so that the two inner canals cross each other4 ,now this suggests two wide bands of weakness in the planet's crust radiating probably from within the dark tract called the ',mare ,icarium1' and that some widespread volcanic outburst initiated diverging cracks on either side of these bands4 ,something of this kind may have been the cause of most of the double canals1 or they may have been started from two or more craterlets not far apart1 the direction being at first decided by some local peculiarity of structure2 and where begun continuing in straight lines owing to homogeneity or uniform density of material4 ,this is very vague1 but the phenomena are so remarkable1 and so very imperfectly known at present1 that nothing but suggestion can be attempted4 ,concluding ,remarks on the ',canals4' ,in this somewhat detailed exposition of a possible1 and1 ,i hope1 a probable explanation of the surface-features of ,mars1 ,i have endeavoured to be guided by known facts or accepted theories both astronomical and geological4 ,i think ,i may claim to have shown that there are some analogous features of terrestrial rock-structure to serve as guides towards a natural and intelligible explanation of the strange geometric markings discovered during the last thirty years1 and which have raised this planet from comparative obscurity into a position of the very first rank both in astronomical and popular interest4 ,this wide-spread interest is very largely due to ,mr4 ,lowell's devotion to its study1 both in seeking out so admirable a position as regards altitude and climate1 and in establishing there a first-class observatory2 and also in bringing his discoveries before the public in connection with a theory so startling as to compel attention4 ,i venture to think that his merit as one of our first astronomical observers will in no way be diminished by the rejection of his theory1 and the substitution of one more in accordance with the actually observed facts4 ,,appendix4 ,a ,suggested ,experiment to ,illustrate the ',canals' of ,mars4 ,if my explanation of the 'canals' should be substantially correct--that is1 if they were produced by the contraction of a heated outward crust upon a cold1 and therefore non-contracting interior1 the result of such a condition might be shown experimentally4 ,several baked clay balls might be formed to serve as cores1 say of #h to #aj inches in diameter4 ,these being fixed within moulds of say half an inch to an inch greater diameter1 the outer layer would be formed by pouring in some suitable heated liquid material1 and releasing it from the mould as soon as consolidation occurs1 so that it may cool rapidly from the outside4 ,some kinds of impure glass1 or the brittle metals bismuth or antimony or alloys of these might be used1 in order to see what form the resulting fractures would take4 ,it would be well to have several duplicates of each ball1 and1 as soon as tension through contraction manifests itself1 to try the effect of firing very small charges of small shot to ascertain whether such impacts would start radiating fractures4 ,when taken from the moulds1 the balls should be suspended in a slight current of air1 and kept rotating1 to reproduce the planetary condition as nearly as possible4 ,the exact size and material of the cores1 the thickness of the heated outer crust1 the material best suited to show fracture by contraction1 and the details of their treatment1 might be modified in various ways as suggested by the results first obtained4 ,such a series of experiments would probably throw further light on the physical conditions which have produced the gigantic system of fissures or channels we see upon the surface of ,mars1 though it would not1 of course1 prove that such conditions actually existed there4 ,in such a speculative matter we can only be guided by probabilities1 based upon whatever evidence is available4 ,,chapter ,,viii4 ,,summary ,,and ,,conclusion4 ,this little volume has necessarily touched upon a great variety of subjects1 in order to deal in a tolerably complete manner with the very extraordinary theories by which ,mr4 ,lowell attempts to explain the unique features of the surface of the planet1 which1 by long-continued study1 he has almost made his own4 ,it may therefore be well to sum up the main points of the arguments against his view1 introducing a few other facts and considerations which greatly strengthen my argument4 ,the one great feature of ,mars which led ,mr4 ,lowell to adopt the view of its being inhabited by a race of highly intelligent beings1 and1 with ever-increasing discovery to uphold this theory to the present time1 is undoubtedly that of the so-called 'canals'--their straightness1 their enormous length1 their great abundance1 and their extension over the planet's whole surface from one polar snow-cap to the other4 ,the very immensity of this system1 and its constant growth and extension during fifteen years of persistent observation1 have so completely taken possession of his mind1 that1 after a very hasty glance at analogous facts and possibilities1 he has declared them to be 'non-natural'-- therefore to be works of art--therefore to necessitate the presence of highly intelligent beings who have designed and constructed them4 ,this idea has coloured or governed all his writings on the subject4 ,the innumerable difficulties which it raises have been either ignored1 or brushed aside on the flimsiest evidence4 ,as examples1 he never even discusses the totally inadequate water-supply for such worldwide irrigation1 or the extreme irrationality of constructing so vast a canal-system the waste from which1 by evaporation1 when exposed to such desert conditions as he himself describes1 would use up ten times the probable supply4 ,again1 he urges the 'purpose' displayed in these 'canals4' ,their being all so straight1 all describing great circles of the 'sphere1' all being so evidently arranged 7as he thinks7 either to carry water to some 'oasis' #bjjj miles away1 or to reach some arid region far over the equator in the opposite hemisphere6 ,but he never considers the difficulties this implies4 ,everywhere these canals run for thousands of miles across waterless deserts1 forming a system and indicating a purpose1 the wonderful perfection of which he is never tired of dwelling upon 7but which ,i myself can nowhere perceive74 ,yet he never even attempts to explain how the ,martians could have lived before this great system was planned and executed1 or why they did not first utilise and render fertile the belt of land adjacent to the limits of the polar snows--why the method of irrigation did not1 as with all human arts1 begin gradually1 at home1 with terraces and channels to irrigate the land close to the source of the water4 ,how1 with such a desert as he describes three-fourths of ,mars to be1 did the inhabitants ever get to know anything of the equatorial regions and its needs1 so as to start right away to supply those needs8 ,all this1 to my mind1 is quite opposed to the idea of their being works of art1 and altogether in favour of their being natural features of a globe as peculiar in origin and internal structure as it is in its surface-features4 ,the explanation ,i have given1 though of course hypothetical1 is founded on known cosmical and terrestrial facts1 and is1 ,i suggest1 far more scientific as well as more satisfactory than ,mr4 ,lowell's wholly unsupported speculation4 ,this view ,i have explained in some detail in the preceding chapter4 ,mr4 ,lowell never even refers to the important question of loss by evaporation in these enormous open canals1 or considers the undoubted fact that the only intelligent and practical way to convey a limited quantity of water such great distances would be by a system of water-tight and air-tight tubes laid under the ground4 ,the mere attempt to use open canals for such a purpose shows complete ignorance and stupidity in these alleged very superior beings2 while it is certain that1 long before half of them were completed their failure to be of any use would have led any rational beings to cease constructing them4 ,he also fails to consider the difficulty1 that1 if these canals are necessary for existence in ,mars1 how did the inhabitants ever reach a sufficiently large population with surplus food and leisure enabling them to rise from the low condition of savages to one of civilisation1 and ultimately to scientific knowledge8 ,here again is a dilemma which is hard to overcome4 ,only a dense population with ample means of subsistence could possibly have constructed such gigantic works2 but1 given these two conditions1 no adequate motive existed for the conception and execution of them--even if they were likely to be of any use1 which ,i have shown they could not be4 ,further ,considerations on the ,climate of ,mars4 ,recurring now to the question of climate1 which is all-important1 ,mr4 ,lowell never even discusses the essential point--the temperature that must necessarily result from an atmospheric envelope one-twelfth 7or at most one-seventh7 the density of our own2 in either case corresponding to an altitude far greater than that of our highest mountains4#ag ,surely this phenomenon1 everywhere manifested on the earth even under the equator1 of a regular decrease of temperature with altitude1 the only cause of which is a less dense atmosphere1 should have been fairly grappled with1 and some attempt made to show why it should not apply to ,mars1 except the weak remark that on a level surface it will not have the same effect as on exposed mountain heights4 ,but it does have the same effect1 or very nearly so1 on our lofty plateaux often hundreds of miles in extent1 in proportion to their altitude4 ,quito1 at #icej ft4 above the sea1 has a mean temperature of about #eg ,f41 giving a lowering of #bc from that of ,manaos at the mouth of the ,rio ,negro4 ,this is about a degree for each #djj feet1 while the general fall for isolated mountains is about one degree in #cdj feet according to ,humboldt1 who notes the above difference between the rate of cooling for altitude of the plains--or more usually sheltered valleys in which the towns are situated--and the exposed mountain sides4 ,it will be seen that this lower rate would bring the temperature of ,mars at the equator down to #bj ,f4 below the freezing point of water from this cause alone4 ,footnote #ag3 ,a four inches barometer is equivalent to a height of #dj1jjj feet above sea-level with us4 ,but all enquirers have admitted1 that if conditions as to atmosphere were the same as on the earth1 its greater distance from the sun would reduce the temperature to-#ca ,f41 equal to #fc below the freezing point4 ,it is therefore certain that the combined effect of both causes must bring the temperature of ,mars down to at least #gj or #hj;below the freezing point4 ,the cause of this absolute dependence of terrestrial temperatures upon density of the air-envelope is seldom discussed in text-books either of geography or of physics1 and there seems to be still some uncertainty about it4 ,some impute it wholly to the thinner air being unable to absorb and retain so much heat as that which is more dense2 but if this were the case the soil at great altitudes not having so much of its heat taken up by the air should be warmer than below1 since it undoubtedly receives more heat owing to the greater transparency of the air above it2 but it certainly does not become warmer4 ,the more correct view seems to be that the loss of heat by radiation is increased so much through the rarity of the air above it as to more than counterbalance the increased insolation1 so that though the surface of the earth at a given altitude may receive #aj per cent4 more direct sun-heat it loses by direct radiation1 combined with diminished air and cloud-radiation1 perhaps #bj or #be per cent4 more1 whence there is a resultant cooling effect of #aj or #ae per cent4 ,this acts by day as well as by night1 so that the greater heat received at high altitudes does not warm the soil so much as a less amount of heat with a denser atmosphere4 ,this effect is further intensified by the fact that a less dense cannot absorb and transmit so much heat as a more dense atmosphere4 ,here then we have an absolute law of nature to be observed operating everywhere on the earth1 and the mode of action of which is fairly well understood4 ,this law is1 that reduced atmospheric pressure increases radiation1 or loss of heat1 more rapidly than it increases insolation or gain of heat1 so that the result is always a considerable lowering of temperature4 ,what this lowering is can be seen in the universal fact1 that even within the tropics perpetual snow covers the higher mountain summits1 while on the high plains of the ,andes1 at #ae1jjj or #af1jjj feet altitude1 where there is very little or no snow1 travellers are often frozen to death when delayed by storms2 yet at this elevation the atmosphere has much more than double the density of that of ,mars6 ,the error in ,mr4 ,lowell's argument is1 that he claims for the scanty atmosphere of ,mars that it allows more sun-heat to reach the surface2 but he omits to take account of the enormously increased loss of heat by direct radiation1 as well as by the diminution of air-radiation1 which together necessarily produce a great reduction of temperature4 ,it is this great principle of the prepotency of radiation over absorption with a diminishing atmosphere that explains the excessively low temperature of the moon's surface1 a fact which also serves to indicate a very low temperature for ,mars1 as ,i have shown in ,chapter ,,vi4 ,these two independent arguments--from alpine temperatures and from those of the moon--support and enforce each other1 and afford a conclusive proof 7as against anything advanced by ,mr4 ,lowell7 that the temperature of ,mars must be far too low to support animal life4 ,a third independent argument leading to the same result is ,dr4 ,johnstone ,stoney's proof that aqueous vapour cannot exist on ,mars2 and this fact ,mr4 ,lowell does not attempt to controvert4 ,to put the whole case in the fewest possible words3 ,all physicists are agreed that1 owing to the distance of ,mars from the sun1 it would have a mean temperature of about-#ce ,f4 7 #def ,f4 abs47 even if it had an atmosphere as dense as ours4 7#b7 ,but the very low temperatures on the earth under the equator1 at a height where the barometer stands at about three times as high as on ,mars1 proves1 that from scantiness of atmosphere alone ,mars cannot possibly have a temperature as high as the freezing point of water2 and this proof is supported by ,langley's determination of the low maximum temperature of the full moon4 ,the combination of these two results must bring down the temperature of ,mars to a degree wholly incompatible with the existence of animal life4 7#c7 ,the quite independent proof that water-vapour cannot exist on ,mars1 and that therefore1 the first essential of organic life--water--is non-existent4 ,the conclusion from these three independent proofs1 which enforce each other in the multiple ratio of their respective weights1 is therefore irresistible--that animal life1 especially in its higher forms1 cannot exist on the planet4 ,mars1 therefore1 is not only uninhabited by intelligent beings such as ,mr4 ,lowell postulates1 but is absolutely ,,uninhabitable4