88 



NATURE 



[November 22, 1894 



vapour, condensed by the cold, and carried with it successively. 

 How catrietl with it, if not by atmospheric movement ? The 

 existence of an atmosphere charged with vapour has been con- 

 firmed also by spectroscopic observations, principally those of 

 Vogel ; according to which this atmosphere must be of a com- 

 position differing little from our own, and above all viry rich in 

 aqueous vafour. This is a fact of the highest importance, 

 because from it we can rightly affirm with much probability, 

 that to water, and to no other liquid is due the seas of Mars and 

 its polar snows. When this conclusion is assured beyond all 

 doubt, another one may be derived from it, of not less import- 

 ance — that the temperature of the Arean climate, notwith- 

 standing the greater distance of that planet from the Sun, is of j 

 •he same order as the temperature of the terrestrial one. 

 Because, if it were true, as has been supposed by some ! 

 investigators, that the temperature of Mars was on the average j 

 very low (from 50' to 60' below zero 1 1, it would not be possible 

 for water vapour to be an important element in the atmosphere 

 of that planet, nor could water be an important factor in its 

 physical changes ; but would give place to carbonic acid, or to 

 some other liquid whose freezing point was much lower. 



The elements of the meteorology of Mars seem then to have 

 a close analogy to those of the Earth. But there are not lack- 

 ing, as might be expected, causes of dissimilarity. From 

 circumstances of the smallest moment, nature brings forth an 

 infinite variety in its operations. Of the greatest influence 

 must be the different arrangement of the seas and (he continents 

 upon Mars, and upon the Earth. We have already emphasised 

 the fact of the extraordinary periodical flood, which at every 

 revoluliDn of Mars inundates the northern polar region at the 

 melting of the snow. Let us now add that this inundation is 

 spread out to a great distance by means of a network of canals, 

 perhaps constituting the principal mechanism (if not the only 

 one) by which water and with its organic life) may be diffused 

 over the arid surface of the planet. Because on Mars it rains 

 very rarely, or ptrhafs tvcn, it Joi; not rain at a/I. 



The atmosphere of Mars is nearly perpetually clear, and 

 sufficiently transparent to peimit one to recognise, at any 

 moment whatever, the contours of the seas and continents, and 

 more than thai, even the minor conl'igurations. Not indeed 

 that vapours of a certain degree of opacity are lacking, but they 

 ofTer very little impediment to the study of the topography of 

 the planet. Here and there we see appear from time to lime a 

 few whitish spots, changing their position and their form, rarely 

 extending over a very wide area. They frequent by preference 

 a few regions, such as the islands of the .l/.jrir Amtrak. and on 

 the continents, the regions designated on the map with the 

 names of Klysiutii and Tempe. Their brilliancy generally 

 diminishes and disappears at the meridian hour of the place, 

 and is reinforced in the morning and evening, with very marked 

 variations. It is possible that they may be layers of cloud, 

 because the upper portions of terrestrial clouds, where they are 

 illuminated by the Sun, appear white. But various observations 

 lead us to think that we are dealing rather with a thin veil of fog, 

 instead of a true nimbus cloud, carrying storms and rain. 

 iDdecd it may be merely a temporary condensation of vapour, 

 under the form of dew or hoar-frost. 



.Vccotdingly, as fnr as we may he permitted to argue from 

 the observed faces, the climate of Mars must resemble that of a 

 clear day upon a high mountain. By day a very strong solar 

 radiation hanlly mitigated at all by mist or vapour, by night a 

 cop ous radiation from the soil towards celestial space, and 

 because of that a very marked refrigeration. Hence a climate 

 of extremes, and great change; of temperature from day to 

 night, and from one season to another. And as on the Earth 

 at altitudes of 50CO and 6ocx) metres (17,000 to 20,000 feet), 

 the vapour of the atmosphere is condensed only into the solid 

 form, proilucing those whitish masses of suspended crystals, 

 which we call cirrus clouds, so in the atmosphere of Mars, 

 it would be rarely possilile (or would even be impossible) to 

 find collections of cloud capable of producing rain of any 

 coniequence. The variation of the temperature from one 

 season 10 another would be notably increased by their long 

 I duration, and thus we c.in understand the great freezing and 

 ] melting of the snow, which is renewed in turn at the poles at 

 \cach complete revolution of the planet around the Sun. 



TorocRAriiicAL Tints. 



^n its general topography Mars does not present any analogy 



I the Earth. A third of its surface is occupied by the great 



Auilrale, which is strewn with many islands, and the 



continents are cut up by gulfs and ramifications of various 

 forms. To the general water system belongs an entire series 

 of small internal seas, of which the Hadriacum and the Tyr- 

 rhenum communicate with it by wide mouths, whilst the 

 Cimmerium, the Sirenum, and the Solis Lacus are connected 

 with it only by means of narrow canals. We shall notice in 

 the first four a parallel arrangement, which certainly is not 

 accidental, as also not without reason is the corresponding 

 position of the peninsulas of Ausonia, Mesperia, and Atlantis. 

 The colour of the seas of Mars is gener.ally brown, mixed with 

 grey, but not always of equal intensity in all places, nor is it 

 the same in the same place at all times. From an absolute 

 black it may descend to a light grey, or to an ash colour. Such 

 a diversity of colours may have its origin in various causes, and 

 is not without analogy also upon the Earth, where it is noted 

 that the seas of the warm zone are usually much darker th.in 

 those nearer the pole. The water of the Baltic, for example, 

 has a light, muddy colour, that is not observed in the -Mediter- 

 ranean. And thus in the seas of M.irs we see the colour become 

 darker when the sun approaches their zenith, and summer begins 

 to rule in that region. 



All of the remainder of the planet, as far as the north pole, 

 is occupied by the mass of the continents, in which, save in a 

 few areas of relatively small extent, an orange colour pre- 

 dominates, which sometimes reaches a dark red tint, and in 

 others descends to yellow and white. The variety in this 

 colouring is in part of meteorological origin, in part it may 

 depend on the diverse nature of the soil, but upon its real cause 

 it is not as yet possible to frame any very well-grounded hypo- 

 thesis. Some have thought to attribute this colouring to the 

 atmosphere of Mars, through which the surface of the planet 

 might be seen coloured, as any terrestrial object becomes red, 

 when seen through red glass. But many facts are opposed to 

 this idea, among others, that the polar snows appear always 

 of the purest white, although the r.iys of light derived from them 

 traverse twice the atmosphere of Mars under great obliquity. We 

 must then conclude that the Arean continents appear red and 

 yellow, because they are so in fact. 



Besides these dark and light regions, which we have described 

 as seas and continents, and of the nature of which there is at 

 present scarcely left any room for doubt, some others exist, 

 truly of small extent, of an amphibious nature, which some- 

 times appear yellowish like the continents, and are sometimes 

 clothed in brown (even black in certain cases), and assume the 

 appearance of seas, whilst in other cases their colour is inter- 

 mediate in lint, and leaves us in doubt to which class of regions 

 Ihey may belong. Thus, all the islands scattered through the 

 Mare Australe and the Mare F.rythra;um belong to this category, 

 so too the long peninsula called Deucalionis Kegio and Tyrrh.-e 

 Regio, and in the vicinity of the Mare ,\cidalium the regions 

 designated by the names of Baltia and Nerigos. The most 

 natural idea, and the one to which we should be led by analogy, 

 is to suppose these regions to represent huge swamps, in which 

 the variation in depth of the water produces the diversity of 

 colours. 



Not without reason, then, have we hitherto attributed to the 

 dark spots of Mars the i)art of seas, and that of continents to 

 the reddish areas which occupy nearly two-thirds of all the 

 planet, and we ^hall find later other reasons which confirm 

 this methoti of reasoning. The continents form in the northern 

 hemisphere a nearly continuous mass, the only important ex- 

 ception being the great lake called the Mare Acidalium, of 

 which the extent may vary according to the time, and which 

 is connected in some way with the inundations which we have 

 said were produced by the melting of the snow surrounding the 

 north pole. To the system of the Marc .\ci<l.-ilium undoubtedly 

 belong the temporary lake called Lacus llyperboreus and the 

 Lacus Niliacus. This last is ordinarily separated from the Mare 

 Acidalium by means of an isthmus or regular dam, of which 

 the continuity was only seen to be broken once for a 

 short time in 18S8. Other smaller dark spots are found 

 here and there in the continental area, which we may designate 

 as lakes, but they are certainly not permanent lakes like 

 ours, but are variable in appearance and size according to the 

 seasons, to the point of wholly disappearing under certain 

 circumstances. Ismenius L.acus, Lunx Lacus, Trivium Cha- 

 rontis and I'ropontis are the most conspicuous and durable 

 ones. There are also smaller ones, such as Lacus Mo ris and 

 Fons juvenile, which at their maximum size do not exceed 100 

 to 150 kilometres {Oo to 90 miles) in diameter, and are among 

 the most difficult objects upon the planet. 



.NO. i;o8, VOL. 51] 



