Maintenance of the Sun's Heat. 465 



action the repulsion of heat, are mainly produced by the reaction 

 of the atoms, due to their inertia and impenetrability. It is plain, 

 however, from this reasoning, that there must be an original and 

 independent source of undulations. Now obviously such a supply 

 may be conceived to be furnished to the sun by undulations ema~ 

 nating from the stains. We have ocular evidence that stars trans- 

 mit light-undulations, and it is quite possible that they originate 

 others not sensible to the sight. Also, according to our pre- 

 liminary hypothesis respecting the constitution of bodies, the 

 sun must be regarded as atomically constituted throughout. 

 Hence the stellar-undulations, of whatever kind, entering his 

 vast body, have their effects multiplied to an incalculable amount 

 by the reaction of the immense number of atoms. This is the 

 theoretical explanation of the sun's internal heat. The continual 

 generation of new undulations both maintains the heat, and sup- 

 plies the loss resulting from the continual propagation of undu- 

 lations from the body of the sun. If the external supply be con- 

 stant, the sun's internal heat must eventually be constant also. 

 For if at any time the loss of undulations by emanation exceeded 

 the supply by internal generation, the heat would decline, and 

 the atoms of the sun being brought closer together by the con- 

 sequent contraction, the generation of undulations would increase 

 till it became adequate to the supply of the loss. So if at any 

 time the generation of undulations and the internal heat were in 

 excess, the supply would be diminished by the expansion of the 

 mass. Hence the sun's heat will be constant so long as the calorific 

 action of the universe is constant. 



In a previous communication entitled a " Theory of Molecular 

 Forces," contained in the Philosophical Magazine for February 

 1860, I have shown how the waves propagated from the indivi- 

 dual atoms of a body constitute by their aggregation compound 

 waves of different orders, the highest of which is the order of 

 gravity-undulations. It is under this form of compound undu- 

 lations that the above-mentioned loss by emanation takes place. 



This theory is not complete unless an explanation be given of 

 the origin of the light-undulations which come from stars. In- 

 asmuch as our sun is a star, the inquiry is the same as that of 

 ascertaining the origin and generation of the sun's light. Solar 

 light is always accompanied by heat — the latter being due to 

 direct vibrations, and the other to transverse. But this heat is 

 to be regarded in its origin and effects as quite distinct from the 

 internal heat above treated of. Observations of the sun's disc 

 seem to indicate that the solar rays which are at once light- 

 bearing and heat-bearing, come chiefly from the upper superficial 

 boundary of a stratum of cloudy matter, which, with occasional 

 interruptions in the form of spots, perpetually surrounds the 



