Prof. Tyndall's Notes on Scientific History. 35 



The manner in which Mayer expands his conceptions from 

 the union of atoms to the union of worlds is a remarkable illus- 

 tration of his generalizing power. After discoursing thus, he 

 goes on to say : — 



22. " The earth moves in its orbit with a mean velocity of 

 93,700'. To produce this motion by the combustion of coal, 

 fifteen times the earth's weight of coal would have to be 

 consumed, and the heat produced would be competent to raise 

 the temperature of a quantity of water equal to the earth in 

 weight 128,000°. A small portion therefore of the force with 

 which the earth moves in its orbit would suffice to dissolve all 

 mechanical connexion among its parts. Supposing a mass equal 

 to the earth in weight to lie at rest on the surface of the sun, 

 to raise that mass, place it at the earth's distance from the sun 

 (215 times the sun's radius), and to impart to it there the velo- 

 city of 93,700', would require 429 times the above quantity of coal, 

 or a quantity 6435 times the weight of the earth." 



23. (In a letter published in the Philosophical Magazine for 

 Augustl862 Mr. Joule writes as follows : — " In 1847, in a popular 

 lecture published in the l Manchester Courier,' I explained the 

 phenomena of shooting- stars, and also stated that the effect of 

 the earth falling into the sun would be to increase the tempera- 

 ture of that luminary." The foregoing passage, giving the 

 amount of the heat that would result from the falling of the 

 earth into the sun, was published by Mayer in 1845 *.) 



24. Mayer next briefly considers the case of the voltaic battery 

 and the gas battery. He then draws out a scheme of the five 

 principal forms of energy which he has been examining, and 

 under five-and-twenty separate heads he states their relations and 

 mutual conversions. "Preconceived notions," he says, "sanc- 

 tioned by time and diffusion, and not the phenomena of Nature, 

 are opposed to the propositions here laid down. While," he 

 adds, "we ascribe substantiality to motion, we must entirely 

 deny materiality to heat and electricity. I know quite well 

 that we have against us here the most deeply rooted convic- 

 tions — hypotheses canonized by the greatest authorities. With 

 the theory of imponderables we banish from science the last 

 remains of the mythology of Greece ; but we know that Nature 

 in her simple truth transcends in glory the devices of the human 

 phantasy, as much as she excels the operations of the human 

 hand." 



* It has been said that in the application of the dynamical theory of 

 heat to shooting-stars, "and some other points of celestial dynamics," 

 Mr. Joule had "at least one year's priority." (Phil. Mag. vol. xxv. p. 431.) 

 The " some other points " shrink, if I mistake not, to the point referred to 

 in the text, and the year's priority is, in reality, two years' posteriority. 

 Mr. Joule's remarks on shooting-stars shall be quoted further on. 



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