THE PLANET MARS.

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nearly as the numbers 5, 6, and 7 ; i.e. it would sometimesbe increased, and sometimes diminished, by a sixth part of itsmean intensity.

But such a variation is not excessive. We need, therefore,only take into consideration the average amount of light orheat which the planet receives. And the habitability ofMars , as far as this point is concerned, really depends uponthe answer that may be given to the following query:—Can we suppose that beings such as ourselves, if there be noother obstacle, could exist with somewhat less than one-halfof the solar light or heat that we enjoy? We think thatthe answer must certainly be, Yes !

When we consider how readily man can adapt himself to anarctic or to a tropical climate ; when we compare the averagetemperature in which a Greenlander, or an Esquimaux , can becontented, with that in which the Papuan, or Central Africannegro delights ; we are inclined to think, that it would needno very great modification of bodily constitution to enable aman to live on Mars ; especially if there were something inits atmosphere, or in its physical conditions, which mightprevent the cold from being so great as it otherwise would be.

And it has been suggested that this must be so, becausethe snow-caps do not extend by any means so far from thepoles as we should have expected would be the case, when weremember that the greater distance of Mars from the Sun, ifin other respects it resembled the Earth , is such as wouldproduce an average temperature upon its equator no greaterthan that which is found in about 62° of north or southterrestrial latitude.

At the same time we must confess, that we perceive no signsupon Mars of any specially dense atmosphere, heavily ladenwith vapours, such as might retain, and (so to say) hoard upthe heat received. The mists, or clouds, which we see are ingeneral thin and transitoiy; and other observations of variouskinds all combine to indicate, that the apparent absence offrost and snow is accompanied by a rarer, rather than by adenser, atmosphere than that of the Earth . Moreover, itwould be according to all analogy to suppose, that a globe so