204 H. Helmhoitz on the Interaction of Natural Forces. 



pied bj onr system, far beyond the limits of Neptune, our most 

 distant planet. Even now we perhaps see similar masses in the 

 distant regions of the firmament, as patches of nebulsej and neb- 

 ulous stars; within our system also, comets, the zodiacal light, 

 the corona of the sun during a total eclipse, exhibit remnants of 

 a nebulous substance, which is so thin that the light of the stars 

 passes through it unenfeebled and unrefracted. If we calculate 

 the density of the mass of our planetary system, according to 

 the above assumption, for the time when it was a nebulous 

 sphere, which reached to the path of the outmost planet, we 

 should find that it would require several cubic miles of such 

 matter to weigh a single grain. 



The general attractive force of all matter must, however, im- 

 pel these masses to approach each other, and to condense, so that 

 the nebulous sphere became incessantly smaller, by which, ac- 

 cording to mechanical laws, a motion of rotation originally slow, 

 and the existence of which must be assumed, would gradually 

 become quicker and quicker. By the centrifugal force which 

 must act most energetically in the neighborhood 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 liglit 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 must unfold 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 work 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 in- 

 timate contact of the different masses, condensation must have 

 taken place before the play of chemical forces began. 



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

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



py 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, 



n 



