22 IN STARRY REALMS. 



age no visible decline has taken place in the intensity of 

 the solar radiation. Here again is a question which we 

 may submit to calculation. We have first of all to deter- 

 mine the heat which could be generated by a body of, let 

 us say, one pound in weight, falling into the sun after 

 having been attracted thither from a very great distance. 

 The result is not a little startling ; it shows us that such a 

 body in the course of its friction through the sun's atmo- 

 sphere might generate as much heat as could be produced 

 by the combustion of many times its own weight of coal 

 consumed under the most favourable conditions. 



The stern rules of arithmetic enable us to pronounce 

 decisively on the issue as to whether the influx of meteors 

 can be entertained as an adequate source for the supply of 

 sun heat. We can estimate the quantity of heat which 

 would be contributed by a single meteor a pound in mass. 

 This determines the total mass of meteors that would 

 have to be entrapped in the sun's atmosphere every day 

 if the current expenditure of sun heat had to be defrayed 

 from this source alone. We are able to avoid expressing 

 the answer in millions of tons by the fortunate circum- 

 stance that the moon happens to present a unit of suitable 

 magnitude for the purpose. 



Suppose that the moon were to be entirely crushed into 

 fragments, which were permitted to rain down upon the 

 sun after the manner of meteors, then it can be shown 

 that the total quantity of heat generated by this influx 

 would be sufficient to maintain the sun's expenditure at 

 the present rate for about a year. Stated in this way, we 

 are enabled to decide at once as to the plausibility of the 

 supposition that the meteoric source of supply is sufficient 



