548 



SCIENCE 



[N. S. Vol. LII. No. 1354 



land, where water can be stored in high level 

 reservoirs and, passing through water wheels 

 at lower levels, be made to generate electric 

 power for lighting, for heating and for the 

 running of motors, it is the sun's energy 

 which is transformed to meet the needs of 

 men. The sun's rays evaporate the surface 

 waters of the oceans, lakes, streams and lands ; 

 the winds, generated by the unequal solar 

 heating of our atmosphere, transport some of 

 the water vapor to the high moimtains, where 

 it is deposited as rain or snow. It is merely 

 the descent of these waters to the lower levels 

 that is controlled by man and transformed 

 into electric power for his own purposes. 



It would take more than two billion earths 

 placed side by side to form a continuous 

 spherical shell around our sun at distance 

 equal to the earth's distance, and thus to 

 receive the total output of solar heat. There- 

 fore less than one two-billionth part of that 

 output falls upon the earth. The earth's 

 share of solar energy, expressed in horse-power 

 or other familiar units, is too great to set 

 down in figures. If you should happen to 

 own 250 acres of land in one of the tropical 

 deserts of the earth, you will be interested to 

 know that your quota of the solar energy, 

 near the middle of a summer day, is falling 

 upon your tract of land at the rate of about 

 one-million horse-power — more than enough 

 heat and power to supply all the needs of this 

 great city — and this is but two thirds of the 

 Sim's good intentions toward you, for some 

 40 per cent, of the energy is intercepted by 

 the atmosphere overlying yom* farm, and re- 

 turned forthwith to outer space. 



Tour neighbor's tract of 250 acres is also 

 receiving solar energy at the rate of one mil- 

 lion horse power. Figuring backward, if one 

 farm area receives a million horse power, and 

 there are more than a hundred million such 

 farm areas on the earth turned toward the 

 sun at one time, and the whole earth inter- 

 cepts less than one two-billionth of the sun's 

 energy output, is it any wonder that sun wor- 

 ship became one of the recognized religions? 

 Accurate knowledge saves us from that, but it 



is becoming in us to give the sun our due 

 respect. 



A great problem ahead of the scientific 

 world is the storage of the sun's beneficent 

 heat rays for release as needed. Astronomers 

 are seeking intently for the sources of the 

 sun's outpouring of energy: how can the sun 

 maintain the supply for tens of millions of 

 years, as it undoubtedly is doing? One im- 

 portant source has been found — the sun's own 

 gravitation which tries constantly to pull 

 every particle of its material to the sim's 

 center — but another and greater source seems 

 to await discovery. Does any one say, since 

 the supply of solar energy will surely meet 

 our needs for ten or a himdred million years, 

 why look further for the cause? Why not let 

 it go at that? This selfish spirit, if applied 

 to all subjects, would retrograde our civiliza- 

 tion. Even the possession of the truth is 

 not so potent for good as the desire to know 

 the truth, and the struggle to discover it. 

 Practically, a knowledge of the origin of the 

 sun's heat may be the key for locking up 

 great quantities of it on summer days and im- 

 loeking it when and where needed. 



Who is not interested in Mars, a planet 

 much smaller than the earth, a little over four 

 thousand miles in diameter, which revolves 

 around the sun in somewhat less than two 

 years, at an average distance from the sun 

 fifty per cent, greater than the earth's dis- 

 tance? Mars is literally one of the earth's 

 brothers, and we should be sincerely interested 

 in his welfare. Does life exist on that planet? 

 Almost certainly there is vegetable life. We 

 have no reason to doubt it. Certain areas of 

 the planet change in color as the climatic 

 seasons come and go, very much as we should 

 expect if these colors were controlled by the 

 natural stages of vegetable life. However, in 

 precaution, I should guard against the draw- 

 ing of the conclusion that vegetable life on 

 Mars has actually been proved to exist. I 

 can merely say that we see no reason to doubt 

 its existence. Is there animal life on Mars? 

 There probably is, but we have no positive 

 evidence that such is the case. If the phys- 

 ical conditions on the planet as to water, air 



