2 



SCIENCE 



[N. S. Vol. XXIX. No. 731 



the individual in estimating the number of 

 years that he may reasonably hope to live 

 would take into account death by lightning 

 — vpere that the only death, he might look 

 forward to a very long life. Neither need 

 we consider the accuracy of the forecasts 

 of the probable future of the sun any more 

 than the individual takes into account 

 probable geological and climatic changes as 

 having any bearing on his own expectancy 

 of life. The drama of human existence 

 on the earth is a fleeting show when meas- 

 ured in terms of the duration of the sun. 

 The exhaustion of our supply of fixed 

 nitrogen, a contingency discussed some 

 years ago by Sir William Crookes, and of 

 bur free oxygen which was more recently 

 suggested by Lord Kelvin are factors that 

 bring the question of the duration of 

 human activity somewhat nearer home but 

 they are still so remote as to be of no 

 immediate practical importance. Other 

 factors there are, however, that are not 

 only immediate but rapidly becoming im- 

 minent and pressing. 



At the recent conference on the con- 

 versation of resources which met at the 

 White House at the invitation of the presi- 

 dent of the United States notes of warn- 

 ing were sounded concerning the coming 

 exhaustion of coal, wood, ores and soils. 

 Whether or not we accept as exact the 

 estimates furnished by experts on that im- 

 pressive occasion, there is no doubt that -we 

 are approaching the end of our available 

 resources and that the near future will 

 have momentous problems to face. 



Certain things are clear. 



First. Unchecked wastefulness as ex- 

 hibited, for example, in the extermination 

 of the bison, in the destruction of forests, 

 in the exhaustion of the soil, in the disap- 

 pearance from our coasts and streams, that 

 once teemed with fish, of this important 

 source of food supply, in the pouring into 

 the air of an incredible amount of uniTsed 



fuel from hundreds of thousands of coke 

 ovens must cease or our ruthless exploita- 

 tion will bring disaster on generations soon 

 to come. The prevention of these and 

 countless other manifestations of indi- 

 vidual and corporate greed is a problem 

 for the economist and the law-maker 

 although they will scarcely succeed in its 

 solution without calling science to their 

 aid. 



Second. Saving and thrift offer at best 

 only a postponement of the day of distress. 

 The end of our supplies of coal and 

 petroleum must ultimately be reached. 

 Forests may be renewed and the soil re- 

 stored to its maximum fertility but the 

 problem which is presently to confront the 

 race is that of civilized existence without 

 recourse to energy stored by the slow 

 processes of nature. This problem must 

 be definitely solved before the complete ex- 

 haustion of our inherited capital. 



Third. The problem is not without con- 

 ceivable solution, since the annual acces- 

 sion of energy from the sun, did we know 

 how to utilize it without awaiting the slow 

 processes of storage employed by nature, 

 is ample for every thinkable need of the 

 future inhabitants of our planet. Esti- 

 mates of the constant o^ solar radiation 

 show that about 2.18 kilowatts of power is 

 continually received from the sun for 

 every square meter of the earth's surface 

 or over seven and a half millions of horse- 

 power per square mile. The present use 

 of power in the United States is about 

 eighty million horse-power or one horse- 

 power per capita. This quantity is likely 

 to increase more rapidly than the popula- 

 tion in the future unless curtailed by lack 

 of fuel, but it is evident that a very small 

 fraction of the sun's radiation would meet 

 all demands. 



Now abundant power is soon to be the 

 factor upon which material advancement 

 will chiefly depend. To obtain it in the 



