10 THE POPULAR SCIENCE MONTHLY. 



not renewable ; and we must look, for the only power we know which 

 can replace coal, to those regions of the earth now desolated by solar 

 heat, and to which future empire may probably tend. 



We have considered the past and the present of our study ; for its 

 future, lies the solution of all the great problems I have already al- 

 luded to, but these questions are so interlocked that the complete 

 answer to one will probably not be given till we are nearly ready to 

 answer all. 



I have spoken of the fallacy of the popular impression of the result 

 of our study as enabling us to predict the weather, or to anticipate the 

 character of coming harvests. Repeating my belief that we as yet 

 know nothing here, or next to nothing, I yet do not mean to dispai'age 

 the object of such researches, nor even to deny the possibility of their 

 ultimate success. We can look forward, among other fair dreams for 

 our science's future, to a time when it will enable us to predict the 

 years of plenty or play the part of a beneficent Providence, by warn- 

 ing in season against those of famine, which have cost in our time so 

 many million lives in China and in India. These are, I repeat, still 

 dreams only, but we may call them hopes if we will — hopes of which 

 increased knowledge may deprive us, but of which we can not say it 

 may not bring fruition. 



There remains among the greatest problems of the future of our 

 science the all-important one to the whole human race of -the future 

 constancy of the sun's heat, of which we have, it seems to me, no 

 assurance of the present rate of supply. We have, it is true, every 

 assurance that in the contraction of the solar mass and in the supply 

 of meteoric matter, we have heat to warm the human race for periods 

 almost beyond limit ; but we learn also that this heat is tempered to 

 us by a solar envelope, which seems to be, as far as we know, in con- 

 ditions which do not favor stability. It is constantly being added to 

 by eruptions from within the sun, caused by we know not what, and 

 constantly diminished by some counter-process which we understand 

 as little. When we consider that the thickening of this solar atmos- 

 phere would bring back the age of ice, or its thinning carry our polar 

 regions to tropical temperature, and when we remember that rhyth- 

 mical action, not uniformity, seems to be the law of nature here, we 

 can feel no certainty of the future constancy of the solar heat, nor of 

 our protection against such changes as seem to have befallen other 

 suns in space, and against which we are powerless to guard. 



But such considerations of our ignorance and helplessness, while 

 they may prevent us from any undue pride in what our science has al- 

 ready attained, may teach us renewed confidence from the very brevity 

 of our life. These green fields around us were once covered with gla- 

 cial ice, and the change has been absolute from that condition to the 

 one of to-day. Yet in the lifetime of any one of the thousands of 

 insect generations which have succeeded each other in these fields. 



