THE HEA7 OF THE SUN. 3 



this globe by a dissolution of the bond of attraction 

 between the earth and sun. 



There is, however, another aspect of the earth's relation 

 to the sun which requires such close attention that it must 

 necessarily form the chief subject with which we have to 

 deal. For the preservation of life on this earth it is not 

 only necessary that the distance of our globe from the sun 

 shall never greatly alter from what it is at present, but also 

 that the present amount of the radiation from the source 

 of heat shall continue without perceptible variation. These 

 considerations introduce questions which do not admit of 

 being summarily disposed of. They involve some problems 

 that are not at all simple. Indeed, it is only in modern 

 times that the subject has become properly understood. 

 We have here to consider not alone some matters of 

 primary significance as regards the continuance of life on 

 this earth, but also various scientific problems of the 

 highest interest and importance. I therefore propose to 

 discuss how it comes to pass that the sun's power to radiate 

 heat to the earth is maintained at a rate which appears to 

 be constant. 



There seems to be sufficient reason for the belief that 

 the heat at present emitted from the sun is neither greater 

 nor less to any sensible extent than that which our lumi- 

 nary used to dispense ages ago. Where the vine and the 

 olive now grow, the vine and the olive were growing 

 twenty centuries back. We must not, however, place too 

 strong a reliance on what seems an obvious deduction from 

 such a fact. Darwin has taught us how by natural selec- 

 tion an organism can continue to preserve its adaptation 

 to the environment notwithstanding the gradual change 



