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KNOWLEDGE 



[April 1, 1895. 



to the square metre. Now the earth's total superficies is 

 of about 510 millions of square kilometres ; the whole 

 atmosphere, therefore, weighs 5 quintillions, 268 quad- 

 rillions of kilogrammes — that is to say, a little less than 

 the millionth part of the weight of our terrestiial globe. 



The Martian atmosphere is incomparably lighter. 

 Gra^^ty at the surface of Mars being much feebler than at 

 the surface of our earth (0-37G), all bodies there weigh less in 

 the same proportion, and the atmosphere is in the same case. 

 If every square metre of the surface of Mars supported the 

 same atmosphere as ours, the pressure of that atmosphere 

 would be reduced in the preceding proportion ; that is to say, 

 that the barometer, instead of being at 760 millimetres at 

 the sea level, would only be at 286 millimetres. This is the 

 pressure which we find in a balloon at a height of 8000 

 metres, or on the summits of lofty mountains. At the 

 summit of Mont Blanc the pressure is one of 424 millimetres. 



It is very certain that the atmosphere of Mars is not 

 analogous to ours, and that water there is not in the same 

 condition as with us ; for if it were so, the temperature 

 at the planet's surface would be below zero, even without 

 taking into account its greater distance from the sun, and 

 we should have before our eyes a globe of ice, which is not 

 the case. On the contrary, we discover on Mars snow con- 

 fined within well-defined hmits, and these limits vary with 

 the temperature, and if we observe a Martian hemisphere 

 during its summer it has less snow at its pole than we have at 

 ours. Those patches of snow that we perceive from time to 

 time at certain points of the temperate region s are also melted. 



Both observation and calculation bring us to the 

 conclusion that this atmosphere of Mars is less dense 

 than ours, that it forms less cloud, that its currents have 

 less intensity, that its winds are never very high, and that 

 it is visited by no tempests. Its conditions as to density 

 and pressure are very difi'erent from those that prevail 

 here. On Mars, evaporation must be easy and rapid ; 

 the boiling point there is doubtless about 46' instead of 

 100°. The zero point at which water freezes is not the 

 same as on our planet. Its atmosphere cannot be either 

 chemically or physically the same as ours. 



Its mean temperature may be higher than that of the 

 earth. The effects observed correspond to a higher mean 

 degree of ambient heat relatively to the collective conditions 

 of both planets. 



We know that the atmosphere serves as a hothouse for 

 the conservation of the heat derived from the sun, and to 

 prevent its loss by radiation into space, but it is not air 

 properly speaking — the mixture of oxygen and nitrogen — 

 that possesses this property, but aqueous vapour. A 

 molecule of water vapour is 16,000 times more efficacious 

 than a molecule of dry air in preserving heat. Nor is 

 water the only body that can boast of this property. The 

 vapours of sulphuric, formic, and acetic ethers, of amylene, 

 ethyl iodide, chloroform, and carbon bisulphide possess 

 it likewise. The atmosphere of Mars, rarefied as it 

 certainly is, can hold vapours of this kind in suspension, 

 and preserve at the planet's surface a temperature equal to, 

 or even higher than the mean temperature of the earth. 



But it is scarcely necessary to imagine anything else 

 than water analogous to ours, since the Martian snow so 

 closely resembles our snow in its winter invasions and 

 summer dissolution, and by the inundations by which its 

 melting is followed, that we may look upon it as almost 

 identical with ours. 



The real difference is in the mode of circulation. On 

 Mars, oceanic evaporation does not give rise, as with us, to 

 clouds, lains, springs, and rivers. 



None of the great water-courses with which we are 

 acquainted on jVIars finds its source on terra-firma. We 



see nothing but canals running from one sea to another. 

 Every canal begins and ends either in a sea or in a lake, or 

 in another canal, or lastly at the intersection of several 

 other canals, but none of them has ever been brought to 

 an abrupt conclusion in the midst of land — a fact which is 

 of the highest importance. Moreover, they intersect each 

 other at every possible angle. 



Clouds, on the other hand, are extremely rare on Mars, 

 and perhaps they are only thin mists or light ciiTus. 

 They are certainly not clouds of rain or tempest. At the 

 time of the last opposition of 1894, at the observatory of 

 Juvisy, when we had our eyes, so to speak, constantly fixed 

 on Mars, the planet showed itself to us, as usual, perpetually 

 clear, with the exception of the 10th of October and for a few 

 days after, during which I ascertained that the Cimmerian 

 and Tyrrhenian seas were masked by a veil of clouds. These 

 veils are very rare on Mars, whereas on the earth they are 

 perpetual. There is, perhaps, not a single day in the year on 

 which the whole surface of the earth can be discovered and 

 clearly seen in space. In short, the meteorological con- 

 ditions prevailing in the two worlds are absolutely unlike. 



Furthermore, in the highly-rarefied atmosphere of Mars, 

 there are no intense winds, nothmg analogous to our trade 

 winds, or to the regime of predominant winds which govern 

 our terrestrial climates. Sometimes we can perceive very 

 long trails of snow, apparently produced by currents in a 

 tranquil atmosphere, as, for instance, those which Mr. 

 Schiaparelli observed in November and December, 1881, 

 round the north pole and extending very far ((■((/(' " The 

 Planet Mars," p. 741, fig. 263) ; but these are exceptions. 

 Fine weather is the normal state of the Martian climates. 



Of course, we must not deceive ourselves as to the 

 accuracy of our Martian knowledge. We do not see every- 

 thing. We have never seen the delicate ramifications 

 which may characterize the canals. We know neither the 

 width of the narrowest, nor the laws which govern their 

 periodical duplication ; and it was only the other day that 

 we ascertained indubitably that they transport the sea 

 waters from one point to another. Mr. Maunder was 

 perfectly right in thinking that " we cannot assume that 

 what we are able to discern is really the ultimate structure 

 of the body we are examining." This ignorance of ours 

 may hide a whole world of unknown realities. Nevertheless, 

 we may, perhaps, try to form some idea of what takes 

 place in the circulation of its waters. 



The melting of the polar snow almost always gives rise 

 to inundations over immense tracts of land, over hundreds 

 of thousands of square kilometres. The seas encroach far 

 into the interior of the lands ; the canals grow wider; fresh 

 canals, often of great magnitude, appear ; and islands, 

 peninsulas, and portions of continents become submerged. 

 Everything proves to us that the surface of the planet is 

 one immense plain, and that mountains are very rare. 



The canals may be natural grooves due to the evolution of 

 the planet itself, just as the English and the Mozambique 

 Channels are on our earth, or they may be furrows dug by 

 the inhabitants for the distribution of their waters, or they 

 may be both — that is to say, they may be natural formations, 

 rectified by intelligence. We will not attempt, as some 

 have done, to calculate the work represented by the con- 

 struction of this geometrical network, for the conditions 

 of the planet's surface, the nature of its materials, its density 

 and gravity, the muscular force, machinery, and character 

 of its humanity, are so difi'erent from terrestrial conditions 

 that there can be no analogy between them. But what is 

 certain is that these canals serve to effect the circulation 

 of water, and constitute a hydrographic system of the 

 most ingenious character. It may be objected that this 

 admirable system does not prevent inundations. No, but it 



