HERMANN VON HELMHOLTZ 291 



contact of the different masses, condensation must have taken place 

 before the play of chemical forces began. 



Whether a still further supply of force in the shape of heat was 

 present at the commencement we do not know. At all events, by 

 aid of the law of the eqliivalence of heat and work, we find in the 

 mechanical forces, existing at the time to which we refer, such a rich 

 source of heat and light, that there is no necessity whatever to take 

 refuge in the idea of a store of these forces originally existing. 

 When through condensation of the masses their particles came into 

 collision, and clung to each other, the vis viva of their motion would 

 be thereby annihilated, and must reappear as heat. Already in old 

 theories, it has been calculated that cosmical masses must generate 

 heat by their collision, but it was far from anybody's thought to make 

 even a guess at the amount of heat to be generated in this way. At 

 present we can give definite numerical values with certainty. 



Let us make this addition to our assumption; that, at the com- 

 mencement, the density of the nebulous matter was a vanishing 

 quantity, as compared with the present density of the sun and planets ; 

 we can then calculate how much work has been performed by the 

 condensation; we can further calculate how much of this work still 

 exists in the form of mechanical force, as 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 converted 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 re- 

 mainder, converted into heat, would be sufficient to raise a mass of 

 water equal to the sun and planets taken together, not less than twenty- 

 eight 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 oxyhydrogen blowpipe, which is sufficient to fuse 

 and vaporize even platina, and which but few bodies can endure, is 

 estim.ated at about two thousand centigrade degrees. Of the action 

 of a temperature of twenty-eight 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 part of the 

 above quantity would be generated. This is also clear, that such a 

 development of heat must have presented the greatest obstacle to the 



