26o 



NA TURE 



[January lo, 1895 



Earths anaual acti»ity. Bat there appears to be one important 

 difference here at the very ou'-et between the two planets. In 

 the else of the Earth, the r.luion of .he melun. of us polar 

 snows to the awak.nini; of surface acl.v.iy ,s 'jh'elly one of /«/ 

 hoc simply ; in the case of Mars, U seems lo be one of propter 

 iZc L well For unlike .he Ear.h, which has water to spare, 

 Mars is apparently in straits for the ari.cle. and has to draw on 

 ts polar reservoir for its annual supply. To the mel..n>; of its 

 polar cap, and lo the iranslerence of .he water thus annually set 

 U<x to eo i.s rounds, seems to depend all the phenomena upon 

 the surface of the planet. ... • u j ..„j 



The observations up .n which this deduC.on is based extend 

 over a period of more than ftve months ; from the l^t day ot 

 May 1894, to the 7th of November. They cover .he regions 

 ■from the south pole to about la.i.ude thirty degrees north. It 

 is probable that analogous changes to those recorded, differing, 

 however, in certain m.arked particulars, occur s,. .\ art.an 

 months later in the planet's northern hemisphere. \ or though 

 it is likely that the general -ys-em is one f.r the whole planet, 

 it is also likely that the distribution of the planet s surface 

 details alter* the action to some extent. -. u ij 



In order to appreciate the meaning of the changes, it should 

 be borne in mind that the vernal equinox of Mars southern 

 hemisphere occurred on A,>ril 7, 1894 ; the sum.ner solstice of 

 the same hemisphere on August 3> : and that Us autumnal 

 equinox will take place on tebruary 7. 



On the -Slst of last .Mav, therefore, it was toward the end of 

 \pril on Mars. The south polar cap was then very large, up- 

 wards of 45° across, and already in active process °\^f: 

 ine The tilt of the planet's axis towards the Earth cnabed it 

 to be well seen, and disclosed the fact that it was bordered 

 persistently by a dark ban!, broader in some places than m 

 others, but keeping pace wiih the snow's retreat. 1 he average 

 breadth of the dark band was in June, 220 miles. It was the 

 darkest marking on the disc, and was i>lue. . . v ■ •, 



As the season advanced and .he snow cap diminished, lis 

 dark girdle diminished in breadth, with fluctuations dependent, 

 doubtless, on the draining capacity of the ground. In August 

 il showed as a slender dark thread , ,_ , • t 



This formation was water, beyond a doubt ; for il was ot 

 the colour of water, it faithfully l<.llo«-ed the melting of the 

 snow, and it suhs-quen.ly vanished-three independent facts 

 mutuallv confirmatory .0 (his conclusion. ,. .u . 



That it was .he darke^^blue marking on the disc, implies that 

 it was the deepest body of water on ths planet. I hat it subse- 

 aaentlv entirely drained off, i.nplies that its depth could not have 

 been very great, lioih facts together make a fust presumption 

 in favour of its being not only the chief body of water on the 

 planet, but the only one of any size. 



This polar sea plays deui c< machina lo all that follows. 

 So soon as the melting of me snow was well under way, long 

 strai's of deeper lint than .heir surroundings made their appear- 

 ance in the midst of the dark areas. They were al.eady there 

 on the last day of May. The most conspicuous of them lay 

 between Noachis and Hellas in the Mare Ausirale, and .hence 

 through the Mare Erythoru.n lo the Ilojr-glass Sea (Syrtis 

 Major). The next most conspicuous one came down between 

 Hellas and Ansonia. Although ihese straits were very 

 dislinguishably darker than the rest of the seas through which 

 they ran, the seas themselves were men at their darkest. 1 ne 

 fact that these straits ran through the seas, suffices to raise a 

 second doubt whether (he seas be seas. The subsequent 

 behaviour of the so-called seas renders their aqualic character 



still more doubtful. , 



\t the initial stage of the Martian Nile-likc inundation, the 

 seas were at their darkest. This is probably due both to the 

 fact that some water had already found its way down from the 

 pole and also to the fact that moisture h.id been deposited there 

 on the water's journey up, and had quickened the vegetation of 

 those relatively amphibious lanris. 



For some lime Ihe dark areas continued largely unchanged in 

 appearance ; thai is, .luring the earlier and most extensive part 

 of the melting of ihe snow cap. Alter this, iheir history 

 became one long chronicle of drying up. Their lighter pans 

 ercw lighter, and their darker ones less dark, t or even to start 

 wilh Ihey were composed of every grade of linl. Indeed, one 

 of :he mo»l significant features about them w.as that at this 

 epoch il was impossible to fix any definite boundaries to the 

 s^th temperate ch.iin of islan.ls. The light areas and ihc dark 

 ones merged indistinguishably into each other. Viewed from 



the standpoint of maps of Mars, the landmarks of this whole 

 region lay obliterated by a deluge ; not directly, but indirectly. 

 Probably the region was in various stages of vegetal fertility in 

 consequence of a comparatively small body of water then 

 inundating it. The colour of the dark areas w-as then, and is 

 now, to my eye, a bluish-green ; quite unmistakably so. Ihis 

 tint Gradually faded out to give place to orange-yellow. 



The first marked sign of change was ihe reappearance of 

 Hesperia ; this took place in July. It was not till the end of 

 October, on the 30 h, that Atlantis was caught sight of. 

 About the same time Ihe straits between the islands Zanthus. 

 Scamander, Ascanias and Simois, came out saliently dark, a 

 darkness due to contrast. . , • . 



Meanwhile the history of Hesperia continued to be instruc- 

 tive From having been invisible in June, and conspicuous in 

 August, it returned in October to a mid-position betweeii the 

 two Vacillating as these fluctuations may seem at first sight, 

 they will all be found to be due to one progressive change in 

 , he same direction, a change that showed itself hr^t in 

 Hesperia itself, and then in the regions round about it. !■ rom 

 lune to August, Hespeiia changed from a previous blue green, 

 indistinguishable from its surroundings, to yellow, the parts 

 adiacent remaining much as before. In consequence the 

 peninsula stood out in marked contrast to the sl.U deep b ue- 

 Lreen regions by its side. Later the surroundings themselves 

 faded, and their change had the effect of once more partially 

 obliterating Hesperia. . ,, , .- j n ,1,. 



While Hesperia was thus causing itself to be noticed all he 

 rest of the south temperate zone, as we may call it lor 

 ider.liftcali-n's sake, was unobtrusively pursuing the same 

 course Whereas in June all that part of the disc cn^Prising 

 ihelwoThvle, Argvre II. and like latitudes was chiefly blue- 

 nreen by October it had become chiefly yellow. The separate 

 identity of these islands became then for the first time apparent. 

 Still further south, what had been first snow and then water 

 turned to yellow land. This metamoM'hosis went on ti , on 

 October 13, the remains of the snow-cap entirely, or practically 

 entirely, disappeared-the first complete disappearance of U on 

 record After this event the whole south polar region was one 



'"^Tow.ard 'the end of October a strange and, for observational 

 purposes, distressing phenomenon took place. What remained 

 o the more southern dark regions proceeded unexpected y to 

 fade in lint throughout. This was first noticeable m the C m- 

 merium Sea ; then in the Sea of the Sirens, and in November 

 ^Te M.are Erythr..um ab.ut the Lake of the Sun. T his fading 

 sleadily progressed until it got so far that in ,,oor seeing he 

 rnarkings were almost imperceptible, and the planet presented 

 a nearly uniform yellow disc. . . 



Now' this fading out of the dark areas is a highly significan 

 fact, with a direct bearing upon their conslitiuion. For U is not 

 simply Ihat portions of the pl.anel's su.f.ice have changed tint. 

 buTthat, taking the disc in its entirely Ihe amount of the blue- 

 green upon it has diminished, and that of 'he orange-ye o« 

 hroporliona.ely increased. Mars appears more Martian .u" 

 he did in June. Now, if the blue-green areas represent water 

 where has this water gone? Nowherconthev.sibled.se. Ilia. 

 Ts certain. For in that case Ihe amount of Ihe dark areas should 

 no'be perceptibly lessened-which 1. is. Nor can it all very 

 well have gine to that part of the planet that -^ "J''^" f °"> 

 view For Schiaparelli's observations in .S82 go to show iha 

 ^e northern snow-cap forms lale-one month aJUr the vernal 

 equinox of Ihe northern hemisphere on that year. Smcc. here- 

 ?ore. the water fails to piove an Mi, presumption .^ 'nsiantly 

 a sid in favour of Ihe il.erna.e hypothesis, that the bluegreen 

 areas represent vegetation, fertilised by a co"M>aralively small 

 amount of water whose direct presence or absences " 't "'V 

 perceptible lo us, but whose indirect effects are. F «r vegetalioa 

 might change from green to yellow without requiring any cor- 



"Tow Th^u^^'J^s^ffi^ofTh'/water may not be traced by 

 i.s amount. Ih'-cre isa'fur.hc'r change which has la.e ly appeared «" 

 the disc which hints al what lias become oi it I he canals have 

 darkened. What is more. Iheir darkening has P»rsued a per 

 fccily .lehnile course, proceeding steadily from south to no th^ 



•riie r.llowing observ.tiions show, first ih.al 'he canals are not 

 eq«.ally visible at all limes ; and secondly, that ihe.r invisibiUty 

 is a matter of the Martian seasons. , ■„ i„„,i The 



In June the canals wc.e very f.a.nt markings '"d"''- "i= 

 least faini were those in Ihe Soils l.acus region. As the planet 



NO. 



I315. VOL. 51] 



