EXPENDITURE AND SUPPLY. 17 



in the fireplace is the seat of a vehement chemical action. 

 The carbon which constitutes a great part of the coal is 

 uniting with the oxygen of the air, and as an incident 

 of the chemical union between these two substances 

 heat in large quantities is evolved. Hydrogen is 

 another important ingredient in the composition of 

 ordinary coal. When ignited hydrogen combines with 

 the oxygen which the air so plenteously supplies, the 

 union of the two gases produces the vapour of water, and 

 che process is accompanied by the liberation of large quan- 

 tities of heat. Thus the radiation of warmth from the 

 fireplace is the direct consequence of a chemical union 

 between different elements. It is, therefore, proper to 

 inquire whether the heat of the sun may not be sustained 

 by a somewhat similar action. Can it be that there is 

 some mighty combustion of fuel perennially in progress in 

 the sun, and that continuous radiation of heat is the con- 

 sequence ? This is a question which it is difficult to 

 answer in a simple manner. There can be no doubt that 

 chemical activities of the highest order must be in inces- 

 sant operation in the sun, but it seems impossible that any 

 appreciable proportion of the sun's radiation can be main- 

 tained by chemical action. 



Indeed we can show conclusively that no attainable 

 amount of chemical action could be adequate for the main- 

 tenance of the sun's expenditure at the rate which has 

 been current for so many centuries. In the first place it 

 is necessary that the two elementary bodies should be 

 both present in sufficient abundance, and that their 

 combination should take place with such uniformity 

 that the daily radiation shall be preserved at a nearly 



c 



