90 Life Conditions in other Worlds. 



hundred times colder because he receives nine hundred times 

 less. He says, " The feeble sunshine on a remote planet may 

 be retained and accumulated on its surface in the same way, 

 and (for the same reason) that a very slight amount of sun- 

 shine, or even the dispersed heat of a clouded day, suffices to 

 maintain the interior of a greenhouse at a high temperature." 



The amount of force that can be exerted by a given weight 

 of muscular fibre appears to differ very much in terrestrial 

 creatures, and so does the amount of strength and cohesion of 

 bodies of nearly the same density. None of our larger 

 terrestrial animals exhibit, on their scale, anything approaching 

 to the strength which insects manifest on a smaller scale ; and 

 if we compare the action and continuous motion of cilia in 

 animalcules * with the minute portions of matter that are 

 concerned in keeping them going, we are led to conceive that, 

 in some other worlds, considerable locomotive powers may 

 exist in larger creatures not cumbered by our weight of flesh 

 and bone. 



The relation of density to cohesion varies exceedingly in 

 substances we are acquainted with. Compare, for example, the 

 solidity of a bamboo with the mobility, and in that sense 

 weakness, of the much heavier body, water; the tenacity of 

 gold, so great that a single grain may be drawn into five 

 hundred feet of wire, with the brittleness that may be com- 

 municated to the same metal by combining it with small 

 quantities of certain other substances, so as not materially to 

 change its specific gravity. 



It is reasonable to suppose that in* planets differing ma- 

 terially in size and density from our own, and also in the 

 quantity of solar heat and light which they receive, the 

 cohesion of substances within a' certain range of density may 

 vary much more than they do on the earth, and we must 

 therefore be cautious in our guesses as to how much firmness 

 or weakness may exist in the surface materials of the various 

 planetary worlds. 



Recent remarks have shown us that terrestrial life exists 

 under a wider range of conditions than was supposed. On 

 mountain heights, where the atmosphere is half, or less than 

 half, what it is at the sea level, life still appears, and even so 

 highly organized a creature as a condor can soar for hours 

 together 18,000 feet above the sea level, and can live and 

 breed at 10,000 to 15,000 feet elevation. At 18,480 feet the 

 atmospheric pressure is reduced one-half. Dr. Wallich, who has 

 importantly added to and confirmed what was previously 

 known of life at great sea depths, tells us that the Ehizopods 



* Ciliary motion is not occasioned by muscles — no one knows how it is pro- 

 duced, and it is found in plants as well as in animals. 



