Prof. Helmholtz on the Interaction of Natural Forces. 505 



must act most energetically in the neighbourhood of the equator 

 of the nebulous sphere^ masses could from time to time be torn 

 away, which afterwards would continue their courses separate 

 from the main mass, forming themselves into single planets, or, 

 similar to the great original sphere, into planets with satellites 

 and rings, until finally the principal mass condensed itself into 

 the sun. With regard to the origin of heat and light this view 

 gives us no information. 



When the nebulous chaos first separated itself from other 

 fixed star masses, it must not only have contained all kinds of 

 matter which was to constitute the future planetary system, but 

 also, in accordance with our new law, the whole store of force 

 which at one time miist imfold therein its wealth of actions. 

 Indeed in this respect an immense dower was bestowed in the 

 shape of the general attraction of all the particles for each other. 

 This force, which on the earth exerts itself as gravity, acts in the 

 heavenly spaces as gi-avitation. As terrestrial gravity when it 

 draws a weight downwards performs v/ork and generates vis viva, 

 so also the heavenly bodies do the same when they draw two 

 portions of matter from distant regions of space towards each 

 other. 



The chemical forces must have been also present, ready to 

 act ; but as these forces can only come into operation by the 

 most intimate 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 equivalence 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 col- 

 lision, 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 

 commencement, the density of the nebulous matter was a vanish- 

 ing 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 ; wc can further calculate how 

 much of this work still exists in the form of mechanical force, as 

 * No necessity for a " Firemist." — Tit. 

 Phil, May. S. 4. No. 75. ^ujjpl. Vol. 11. 2 L 



