148 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



terrestrial, though we know that the Martian atmosphere is highly 

 attenuated, and if we were suddenly set down upon that planet's 

 surface we should certainly suffocate for lack of air. Water is 

 probably scarce upon that planet in similar degree. However, these 

 facts do not militate strongly against animal life upon that planet, 

 for such life would undoubtedly be developed with respiratory and 

 other organs adapted to their environment. A solution of the Mar- 

 tian problems, as to a. possible counterpart of terrestrial man on 

 that planet, is apparently not now hopeful, but present-day failures 

 may be the prelude to future successes, and I prefer to offer no dis- 

 couragement. 



The planet Venus, only a shade smaller than the earth, and but two 

 thirds as far from the sun as we, presents a similar but apparently 

 more difficult problem. We know that it has extensive atmosphere, 

 no doubt comparable with that of the earth, but concerning the pres- 

 ence of water we are justified in making no statement other than 

 we remain in apparently total ignorance. If Schiaparelli was right, 

 as he appears to have been, that Venus always presents the same face 

 to the sun, just as the moon always turns the same hemisphere toward 

 the earth, then one hemisphere of Venus undoubtedly remains in- 

 tensively hot in perpetuity, and the other hemisphere, in perpetual 

 darkness and excessively low temperature. Can the twilight zone 

 between the hemispheres of day and night offer abode and comfort 

 to living forms, vegetable and animal? We have found no answer 

 to this question, and we know not how to progress to the solution. 



Are the moon and Mercury inhabited? Certainly not by such 

 forms of life as we are familiar with, for neither object has an 

 appreciable atmosphere. Both bodies undoubtedly suffer from ex- 

 tremes of heat and cold, without the protecting blanket of atmos- 

 phere with which the earth is blessed. The other planets, Jupiter, 

 Saturn, Uranus, and Neptune, may be dismissed as uninhabitable by 

 life forms of our acquaintance. There seems no reason to doubt that 

 these great bodies, from four to eleven times the earth in diameter, 

 are still devoid of solid footing for man or beast, such as the rock 

 and soil strata afford upon the earth. 



Have astronomers been able to prove that planets revolve around 

 other suns than ours? No, the distances of the nearest stars pre- 

 clude that possibility to our means in hand. Such planets would 

 need to be manyfold brighter than Jupiter, the greatest of our 

 planets, and our great telescopes would need multiplication many 

 times in diameter to let us see them as attendants of their suns. We 

 are able to prove, and have proved, however, the existence of hun- 

 dreds of bodies, in distant space, whose rays of light we have not 

 perceived. The spectrograph has shown with certainty that, of the 

 naked-eye stars, one in four on the average is not the single star 



