Maintenance of the Sun's Heat. 461 



bodies descending in spiral courses to the sun's surface, and 

 supposes that these bodies constitute by their aggregate visibility 

 the phenomenon of the zodiacal light. This theory appears, 

 however, to have been subsequently abandoned for the most 

 part, if we may judge from statements made by Professors 

 Thomson and Tait in the article " On Energy " (in the Number 

 of ' Good Words' for October 1862), which on another account 

 is now attracting the attention of men of science. The authors 

 there admit that an explanation which "supposes the loss by 

 radiation at present not to be compensated by fresh influx 

 of meteoric matter''' is probably the true one. According 

 to this explanation, the sun "must be at present in the con- 

 dition of a heated body cooling. But being certainly liquid 

 for a great depth all round his surface, if not throughout, 

 the superficial parts must sink by becoming heavier as they 

 contract through cooling. The currents thus produced, bring- 

 ing fresh portions from below to the surface, and keeping all the 

 liquid thoroughly stirred up, must distribute the loss of heat 

 very equably throughout the whole liquid mass, and so prevent 

 the surface from cooling quickly, as it certainly would do if the 

 superficial stratum were solid.' J This new theory has apparently 

 not satisfied Sir John Herschel, who, in an article " On the Sun " 

 contained in the Number of the same publication for April 1863, 

 has suggested that the permanence of the sun's light and heat 

 might possibly be accounted for by attributing a species of vita- 

 lity to Nasmyth's f willow-leaves.' 



I will not disguise that I have cited the above views because 

 in my opinion they give evidence of themselves, without the 

 necessity of any argument, that the problem of the sun's heat 

 has not yet been solved, and justify the course I am about to 

 take of attempting the solution of it on entirely different prin- 

 ciples. The investigation which I now proceed to enter upon 

 will rest, first, on the hypothetical constitution of matter which 

 I have already so frequently enunciated, viz. that all visible and 

 tangible substances consist of discrete inert atoms of spherical 

 form and constant magnitude ; and secondly, on the mathema- 

 tical theory of heat which I have expounded in the Philosophical 

 Magazine for March 1859. This theory assumes that the force 

 of heat is due to the dynamical action of the direct vibrations of 

 the sether, the laws of the vibrations being inferred by mathe- 

 matical reasoning applied to the medium on hydrodynamical 

 principles, and on the supposition that it is a continuous and 

 perfect fluid varying in pressure proportionally to variations of 

 its density. 



Before applying the above principles to the present problem, 

 an instance of the dynamical action of aerial vibrations will be 

 Phil. Mag. S. 4. Vol. 25. No. 170. June 1863. 2 I 



