THE 

 LONDON, EDINBURGH a.nd DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



DECEMBER 1854. 



LII. On the Mechanical Energies of the Solar System. 

 By Professor William Thomson*. 



THE mutual actions and motions of the heavenly bodies have 

 long been regarded as the grandest phsenomena of mechanical 

 energy in nature. But their light has been seen, and their heat 

 has been felt, without the slightest suspicion that we had thus a 

 direct perception of mechanical energy at all. Even after it has 

 been shown f that the almost inconceivably minute fraction of 

 the sun's heat and light reaching the earth is the source of 

 energy from which all the mechanical actions of organic life, 

 and nearly every motion of inorganic nature at its surface, are 

 derived, the energy of this source has been scarcely thought of 

 as a development of mechanical power. 



Little more than ten years ago the true relation of heat to 

 force, in every electric, magnetic, and chemical action, as well as 

 in the ordinary operations of mechanics, was pointed out J ; and 

 it is a simple corollary from this that the sun, within the 

 historical period of human observation, has emitted hundreds of 



* From the Transactions of the Royal Society of Edinburgh, vol. xxi. 

 part 1 ; read April 17, 1854. 



t Herschel's Astronomy, Edition 1833. See last Ed., § (399). 



X Joule " On the Generation of Heat in the Galvanic Circuit," com- 

 municated to the Royal Society of London, Dec. 17, 1840, and published, 

 Phil. Mag., Oct. 1841. "On the Heat evolved during the Electrolysis of 

 Water," Literary and Phil. Soc. of Manchester, 1843, vol. vii. part 3, 

 Second Series. " On the Calorific EiFects of Magneto-Electricity, and the 

 Mechanical Value of Heat," communicated to the British Association, 

 August 1843, and pubhshed, Phil. Mag., Sept. 1843. " On the Changes 

 of Temperature produced by the Rarefaction and Condensation of Air," 

 Phil. Mag. S. 4. Vol. 8. No. 54. Dec. 1854. 2 E 



