Decembee lOj 1920] 



SCIENCE 



549 



and soil are such -that vegetable life may 

 exist, the chances are strongly in favor of 

 animal life also. However, I think we must 

 leave unanswered for the present the question 

 whether such animal life is highly intelli- 

 gent. The forests of the St. Lawrence Valley 

 and the prairies of the Mississippi Valley put 

 on their green coats in the spring and changed 

 them to brown coats in the fall, perhaps even 

 better before the coming of man than after 

 his destructive influence descended upon them. 

 If you had the means to ascend several thou- 

 sand miles above your present position, and 

 could dwell there throughout the year, you 

 would witness the formation of a polar snow 

 cap upon the earth early in the autimon. 

 The southern edge of this cap would extend 

 farther and farther to the south up to the 

 time of mid-winter. Its edge would extend 

 well down toward the southern limits of the 

 United States, to the Himalayas in Asia, and 

 so on. With the coming of spring the north 

 polar cap would decrease in size and probably 

 disappear, save as to snows on the higher 

 mountains and the possible ice and snows of 

 the immediate polar region. An observer 

 similarly situated above South America would 

 witness similar phenomena as to the south 

 polar regions; and these are indeed the phe- 

 nomena observed on the planet Mars. The 

 white polar caps on Mars was and wane with 

 the coming and going of the winter as they 

 do upon the earth. Superficially, the Mar- 

 tian conditions seem not very different from 

 the terrestrial, though we know that the Mar- 

 tian 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 un- 

 doubtedly be developed with respiratory and 

 other organs adapted to their environment. 

 A solution of the Martian 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 

 discouragement. 



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 appar- 

 ently more difficult problem. We know that 

 it has an extensive atmosphere, no doubt com- 

 parable with that of the earth, but concerning 

 the presence of water we are justified in 

 making no statement other than that we re- 

 main in apparently total ignorance. If Schi- 

 aparelli 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- 

 tensely hot in perpetuity, and the other 

 hemisphere in perpetual darkness and ex- 

 cessively 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 foimd no an- 

 swer to this question, and we know not how 

 to progress to the solution. 



Are the moon and Mercury inhabited? Cer- 

 tainly not by such forms of life as we are fa- 

 miliar with, for neither object has an appreci- 

 able atmosphere. Both bodies undoubtedly 

 suffer from extremes of heat and cold, without 

 the protecting blanket of atmosphere with 

 which the earth is blessed. The other planets, 

 Jupiter, Saturn, TJranus 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 preclude 

 that possibility to our means in hand. Such 

 planets would need to be many-fold 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 



