SCIENCE-GOSSIP. 



75 



molecular velocity of any of these gases. But 

 the critical velocity of molecules with regard to 

 Mars is as much as 3-1 miles a second, and con- 

 sequently this planet would be able to retain 

 exactly the the same gases that exist in our own 

 atmosphere. 



The climate of Mars seems to be astonishingly 

 mild and equable ; while winds, owing to the 

 flimsiness of the atmosphere, must be of the 

 weakest description. Nevertheless, it seems 

 evident that there must be a gentle upper drift of 

 moisture-laden air proceeding from the equator 

 towards the poles, and depositing its vapour in the 

 form, not of rain or snow, but of successive hoar- 

 frosts, thus giving rise to the conspicuous polar 

 ice-caps more than 2,000 miles in diameter. 



Owing to the axial tilt of Mars to its orbit being 

 very little more than ours, a similar succession of 

 seasons take place, but its far greater eccentricity 

 of orbit causes the difference between the seasons to 

 amount to seventy-four days, instead of merely eight, 

 as with us. At the present period Mars is in an 

 exactly similar condition to the earth with regard 

 to the position of the "apse-line," i.e. the line 

 joining the points of nearest approach to, and 

 farthest recession from, the sun ; the result being 

 that winter in the southern hemisphere is longer 

 than summer, and conversely in the northern 

 hemisphere. But the Martian year (6S7 days) is 

 nearly twice as long as ours, so that the heat of 

 even a short summer is sufficient to completely 

 melt the polar ice-cap, as it did in i& 



Since Mars is much smaller than the earth, it is 



clear that it must have cooled down more rapidly, 



and hence we may naturally expect to find that its 



surface, which is little more than one-fourth that 



of ours, has reached a more mature physical 



on. Now the absence of shadows at sunrise 



or sunset shows that the land on Mars must be 



singularly low, with no trace of mountain 1 



Volcanoes seem to be equally wanting : if they 



I they could not fail to be conspicuous ; 



.nee gravity at the surface is only 



nat of the earth, and since atmospheric 



resistance is likewise so much less, it is clear 



that -. an'l dust would be hurled 



to far greater heights, would spread out further, 



magnitude, 

 moon. 

 . either by 

 moan! • peaks and 



Uvdicat en seen, 



■ 

 . sometime* ca . over h 1 



of square miles. The abienoc of mow I 

 teem t 



to accommodate itself to a still contracting nucleus. 

 Tangential stresses are thus set up in the crust, 

 causing the softer and more yielding areas to be 

 ridged up and crumpled between harder resisting 

 blocks. Now, if mountains were no longer formed 

 there would cease to be any compensation for 

 atmospheric denudation, which would accordingly 

 proceed unchecked until the seas became largely 

 silted up, and the land planed down to a nearly flat 

 surface, rising by gentle gradients to a height only 

 slightly above the sea-level. This condition must 

 have been reached long ago by Mars, which exhibits 

 phenomenal flatness. 



The surface-colouration is of two tints : reddish- 

 ochre and bluish-green. The former colour pre- 

 ponderates and appears to represent extensive 

 sandv deserts traversed by the wonderful so-called 

 " canals," which have attracted so much attention 

 since their discovery some time ago by Schiaparelli. 

 But before discussing the nature of the "canals," it is 

 necessary to say that the blue-green areas, hitherto 

 termed "seas" and "gulfs," have been clearly 

 demonstrated by Mr. Lowell to contain no water, 

 for the following reasons : no glint of sunshine 

 is ever reflected from their surface ; the light 

 proceeding from them is not polarized as it would 

 be from a sheet of water ; their colour changes 

 with the seasons ; and lastly, they are intersected by 

 dark lines in direct continuation with the " canals " 

 which form so geometrical a network over the wide- 

 spread deserts. In all probability the blue-green 

 areas are the lower regions of a monotonously level 

 world, and occupy the sites of what were oceans in 

 the time when Mars could still boast of mountains 

 and rivers The sea-beds woald naturally remain the 

 most humid parts, even when they became exposed 

 to the air : for the amount of interstitial water 

 locked up in ordinary sediments amounts on an 

 average to ten per cent. It is likely that these 

 regions now represent areas clothed with vegetation. 

 The " canals " are apparently of the same blue- 

 green colour ; they proceed from dark, triangular 

 spots at the edge of the " seas," and often radiate 

 in fan like groups of four or more. They run in 

 absolutely straight lines, sometimes for more than 

 3,000 mile 1 the Eumenides-Orcus "canal"), 

 although they naturally appear i<> us as large 



m 1 reat-circli of the 



planet 1 ' om fiftet 1 thirty 



miles in breadth and cut up il land into 



large triangles. Wherever the " 1 ai al intersecti 

 a dark cin u is visible M 1 I veil points 



out that the very fact of 1 1 eting 



•it one ' bal itrong 



presumption in favour oi th en con- 



1 1 nat the 

 ..... 



rills' 

 of tii'- mo in. 1 hey annuall) 



