358 



SCIENTIFIC THOUGHT. 



the gathering up of cosmical matter which, under the 

 force of gravitation, was in rapid motion — so the heat of 

 the sun originated through the conversion of the energy 

 of this arrested motion into heat. This process of gather- 

 ing up of cosmical or meteoric matter is still going on, 

 and it makes up for the loss or expenditure of solar heat 

 through radiation. Helmholtz, in the sequel of his 

 investigation into the conservation of energy, likewise 

 takes up this problem, and while admitting to some 

 extent Mayer's theory,^ shows that even without the 

 accession of cosmical matter, the mere contraction through 

 gravitation of the gaseous substances of the sun would 

 result in a continual production of heat. His calcula- 

 tions show that the amount of this contraction, resulting 

 in a diminution of the sun's apparent diameter, would not 

 be great enough to be perceptible during historic ages. 

 The theory of Helmholtz has in general been accepted as 



which the sun's heat was kept up 

 by breakfasting anil dining on 

 meteorites. (See Wolf, ' Handbuch 

 der Astronouiie,' vol. ii. p. 433. ) It 

 is on the other side equally interest- 

 ing to see how Herbert Spencer, for 

 whom the nebular hypothesis was 

 a principal example of cosmic 

 evolution, failed to avail himself 

 of the strengthening support it re- 

 ceived through thermodynamics (see 

 ' Essays,' vol. i., " On the Nebular 

 Hypothesis," 18.58). Had Mayer 

 brought his ideas into connection 

 with I^aplace's cosmogony, he prob- 

 ably would have hit upon the 

 correcter version, the contraction 

 theorj', which it was reserved for 

 Helmholtz to propound in 18.'>4. 



^ The subject was about the same 

 time taken up by William Thomson 

 (Lord Kelvin), fii'st in a paper " On 



the Mechanical Energies of the 

 Solar System " (Trans. Edin. Roy. 

 Soc, 1854), and continued in a 

 series of papers and addresses, 

 reprinted in his mathematical, &c., 

 papers (vol. ii. ) in the 1st volume 

 of his ' Popular Addresses,' and in 

 an appendix to Thomson and Tait's 

 'Natural Philosophy.' He shows 

 that the form of the meteoric theory 

 propounded by Mayer, and inde- 

 pendently by Waterston (Brit. 

 Assoc, 1853), is as little able to 

 explain the maintenance of the 

 sun's heat through known historic 

 ages as the chemical theory of com- 

 bustion, which was alreadj- aban- 

 doned by Mayer in 1846, and finally 

 adopts Helmholtz's foi lu of the 

 meteoric theorj' as the most likely. 

 ('Pop. Lect.,' vol. i. p. 365, &c. ; p. 

 373, &c.) 



