PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 515 



of a perpetual motion might be possible, because it is known that all 

 energies, be their names what they may, can only be converted into 

 work in equivalent amounts and that the reconversion of heat into work 

 is only partially possible. 



Through resistances to motion a portion of the kinetic energy is al- 

 ways transformed into heat ; if such resistance should exist in free space 

 the energy resulting from gravitation would in part be converted into 

 heat. Laplace (1799-1825) assumed an absolutely void universe for the 

 endless duration of the planetary system ; according to the present 

 condition of science, we are obliged to assume (on account of the radia- 

 tion of light and heat) that the universe is tilled with an imponderable, 

 exceedingly rare, and extraordinarily elastic substance, termed tether. 



The tenuity of this assumed rather is so great that as yet the result 

 of its resistance as manifested in retardation has been perceptible only 

 in the course of Encke's comet, but in no other celestial body. What 

 would be the effects of a medium which would retard the motion of the 

 celestial bodies ! First, instead of the lost kinetic energy there would 

 be heat ; then, the attraction of the central body being supposed to be 

 unimpaired, the tangential motion of the planetary bodies would be 

 diminished through the resistance of the medium ; the effect of the at- 

 tractive force of the sun would be manifested in a greater degree, i. e., 

 these celestial bodies would disclose the existence of a resisting medium 

 by their contracting orbits and an increased velocity. This seems to 

 be really so in the case of Encke's comet, according to recent observa- 

 tions ; and the final fate of this comet may be its precipitation into the 

 sun.* 



J. R. Mayer (1848) assumed such a precipitation of innumerable bodies 

 (asteroids), in order to explain whence the sun obtained the supply 

 of heat which it is constantly radiating. In such a precipitation of 

 asteroids into the sun the energy of the mechanical motion would be 

 transformed into the energy of heat of sufficient intensity to account for 

 the unimpaired conservation of the sun's heat. Helmholtz explains the 

 supply of the sun's radiation differently, in calculating that a continu- 

 ous condensation of the sun, whose origin was a cosmic nebula, would 

 preserve its heat for an incalculable period of time. 



As with the heat of the sun, so the internal heat of the earth is ex- 

 plained by J. Ii. Mayer, by the precipitating of smaller bodies upon 

 each other; by Eelmholtz, by the condensation of the earth from an 

 originally cosmic nebula, both basing their respective calculations upon 

 the mechanical equivalent of heat. The result of such calculations 

 teaches that on the basis of the above hypotheses incomparably higher 

 degrees and greater amounts of heat come into action than from any 

 known combustion or chemical combination, and that consequently in 

 regard to the sun, on the assumption of the above hypotheses, the heat 



"[That the observed acceleration of bincke's cornel is really due to an atherial resist- 

 ance (as is so commonly assumed), appears to be extremely improbable. — Ed. ] 



