What We Learn from the Sun 



the worlds which circle around him have need 

 of it in other words for countless ages yet to 

 come? 



Now there are two ways in which the solar 

 energies might be maintained. The mere con- 

 traction of the solar substance, Helmholtz tells 

 us, would suffice to supply such enormous quan- 

 tities of heat, that if the heat actually given out 

 by the sun were due to this cause alone, there 

 would not, in many thousands of years, be any 

 perceptible diminution of the sun's diameter. 

 Secondly, the continual downfall of meteors 

 upon the sun would cause an emission of heat. 

 But though the sun's increase of mass from this 

 cause would not be rendered perceptible in 

 thousands of years, either by any change in his 

 apparent size or by changes in the motions of his 

 family cf worlds, yet the supply of heat obtain- 

 able in this way can be but small compared with 

 the sun's emission of heat. This follows from 

 the limits between which Leverrier has shown 

 that the total mass of the meteors of our system 

 must certainly lie. 



It seems far from unlikely that both these 

 processes are in operation at the same time. 

 Certainly the latter is, for we know, from the 

 motions of the meteoric bodies which reach the 

 earth, that myriads of these bodies must con- 

 tinually fall upon the sun. If the corona and 

 zodiacal light are really due to the existence of 

 flights of meteoric systems circling around the 

 sun, or to the existence in his neighborhood of 



