HABITABILITY OF OTHER WORLDS. 133 



The Moon, in the absence of air and water, must be without inhabitants akin 

 to ourselves. Though the Moon has passed through the successive phases of a 

 cooling globe, I cannot think the violence which must have reigned on its surface 

 before synchronistic times would have permitted the existence of an organic being. 

 Nor, since the synchronistic period began, have the conditions, as far as we can 

 judge, been endurable. The fortnightly alternations of extreme heat and extreme 

 cold must prove fatal to all organic life with which we are acquainted. It is 

 pleasant to think of kindred beings on a neighboring world, though we might not 

 by any possibility open intercourse with them. It is pleasant even to believe that 

 the Moon may have been inhabited in a former planetary period. It creates a 

 sense of relation to distant parts of the universe to believe that other beings may 

 even have lived there and passed away. To know that the lunar surface is a 

 wild scene of desolation, and to know that only the unconscious forces of inor- 

 ganic nature have ever interrupted the oppressive silence of the planetary soli- 

 tude, seems to sunder a bond of sympathy with the universe, and isolate man- 

 kind on an island rock where no message can ever arrive. But it is better to 

 know the truth than to indulge in fancy. The Moon is probably no more unin- 

 habitable in the present period than it has been during its entire history. ^ 



Mars, according to the scientific indications, presents conditions more nearly 

 approximating the demands of habitibility than any other planet besides the earth. 

 It seems almost certain, however, that the meridian of its habitable phase is 

 passed. The Sun's apparent diameter from Mars is two thirds his size seen from 

 the earth, and his light and heat are only three-eighths as much as the earth re- 

 ceives. As the intensity of gravity on the surface of Mars is only three-eighlhs 

 the intensity of gravity on the earth, many diverse conditions would be introduced. 

 A man of ordinary agility would be able to leap over a wall twelve feet high. If 

 on the earth a strong man is able to support 26 pounds in his palm at arm's 

 length, and his arm is equivalent to four pounds in his palm, he might be forty- 

 two-feet high before the weight of his arm would become too great for him to 

 extend it; but on the planet Mars, such a man might be 109 feet in height. 2 



1 In my brochure, entitled Geology of the Stars, speaking of tlie comparatively rapid succes- 

 sion of lunar periods, I said : " The zoic age of the Moon was reached while yet our world re- 

 mained, perhaps, in a glowing condition. Its human period was passing while the Eozoon was 

 solitary occupant of our primeval ocean." Mr. Fisk in his Cosmic Philosophy (i, 400, note), has 

 cited this as " an example of the too hasty kind of inference which is often drawn in discussing 

 the question of life upon other planets." Mr. Fisk misapprehends, for it is not stated that hu- 

 man beings ever lived, or could have lived, upon the Moon. The allusion is simply to that stage 

 of lunar evolution which corresponded to the human stage in terrestrial evolution. 



2 If !<; = the total weight a strong man's arm can support, including weight of arm and 

 load, and p -= weight of arm, and ?i= number of times greater, in any dimension, the arm is 



which could bear no load, then n = — (Young's Mechanics, Williams' ed., p. 113), and if g' = gravi- 



P ''■V 



ty on any planet compared with gravity on the earth, then, on that planet n = . 



1^9' 



Now, if we assume that a man can raise 26 pounds at arm's length, and that his arm is 

 equal to 4 pounds in his palm, then n = 7.5; and if a strong man's height is 68 inches, the height 

 of a man on the earth who could barely extend his arm— since his height is proportional to his 



