Sun- Heat, 37 



ered down upon its surface. Estimates have 

 been carefully made, and we are gravely in- 

 formed of the probable amount of combustive 

 material required to supply the sun's demands 

 for given periods. It is said that the coal- 

 fields of Pennsylvania, which would supply 

 the world's consumption for centuries, would 

 keep the sun's rate of emission for consid- 

 erably less than y,-^^ part of a second. 

 POUILLET estimated the quantity of heat 

 emitted by the sun per hour to be equal to 

 the supply of a layer of anthracite coal ten 

 feet thick, spread over the whole surface of 

 the sun. 



The theory advocated by HELMHOLTZ, and 

 by many other scientists, of " the gradual 

 contraction of the solar orb," and that of 

 SECCHI, " the dissociation of compound bodies 

 in the sun's substance," are attempts after a 

 more consistent philosophy. 



The foregoing theories pre-suppose the 

 sun to be a glowing fiery mass, from which, 

 in all directions, issue radiations of heat and 

 light into space. Of this enormous quantity 

 of radiated heat, the earth is supposed to 



receive but ^<nnr,<hnr,<nnr P art - 



MEYER observes : " A general law of 

 nature which knows no exception is the fol- 



