506 Prof. Helmholtz on the Interaction of Natural Forces. 



attraction of the planets towards the sun, and as vis viva of their 

 motion, and find by this how much of the force has been con- 

 verted into heat. 



The result of this calculation * is, that only about the 454th 

 part of the original mechanical force remains as such, and that 

 the remainder, converted into heat, would be suflScient to raise 

 a mass of water equal to the sun and planets taken toge- 

 ther, not less than 28 millions of degrees of the Centigrade 

 scale. For the sake of comparison, I will mention that the 

 highest temperature which we can produce by the oxyhydi'Ogeu 

 blowpipe, which is sufficient to fuse and vaporize even platina, 

 and which but few bodies can endure, is estimated at about 

 2000 degrees. Of the action of a temperature of 28 millions 

 of such degrees we can form no notion. If the mass of our 

 entire system were pure coal, by the combustion of the whole of 

 it only the 3500th pai-t of the above quantity wiould be gene- 

 rated. This is also clear, that such a great development of heat 

 must have presented the greatest obstacle to the speedy union 

 of the masses, that the greater part of the heat must have been 

 diffused by radiation into space, before the masses could form 

 bodies possessing the present density of the sun and planets, 

 and that these bodies must once have been in a state of fiery 

 fluidity. This notion is corroborated by the geological phseno- 

 mena of our planet ; and with regard to the other planetary 

 bodies, the flattened form of the sphere, which is the form of 

 equilibrium of a fluid mass, is indicative of a former state of 

 fluidity. If I thus permit an immense quantity of heat to dis- 

 appear without compensation from our system, the principle of 

 the conservation of force is not thereby invaded. Certainly for 

 oui* planet it is lost, but not for the universe. It has proceeded 

 outwards, and daily proceeds outwards into infinite space ; and 

 we know not whether the medium which transmits the undula- 

 tions of light and heat, possesses an end where the rays must 

 I'eturn, or whether they eternally pursue their way through infi- 

 nitude. 



The store of force at present possessed by our system is also 

 equivalent to immense quantities of heat. If our earth were by 

 a sudden shock brought to rest in her orbit, — which is not to be 

 feared in the existing arrangement of our system — by such a 

 shock a quantity of heat would be generated equal to that pro- 

 duced by the combustion of fourteen such earths of solid coal. 

 Making the most unfavourable assumption as to its capacity for 

 heat, that is, placing it equal to that of water, the mass of the 

 earth would thereby be heated 11200 degrees ; it would therefore 

 be quite fused and for the most part reduced to vapour. If then 

 * See note at the end. 



