ox THE INTERACTION OF NATURAL FORCES. 175 



limits of Neptune, our most distant planet. Even now 

 we discern in distant regions of the firmament nebulous 

 patches the light of which, as spectrum analysis teaches, 

 is the light of ignited gases ; and in their spectra we see 

 more especially those bright lines which are produced by 

 ignited hydrogen and by ignited nitrogen. Within our 

 system, also, comets, the crowds of shooting stars, and the 

 zodiacal light exhibit distinct traces of matter dispersed 

 like powder, which moves, however, according to the law 

 of gravitation, and is, at all events, partially retarded by 

 the larger bodies and incorporated in them. The latter 

 undoubtedly happens with the shooting stars and meteoric 

 stones which come within the range of our atmosphere. 



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 outermost planet, we should find that it would 

 require several millions of cubic miles of such matter to 

 weigh a single grain. 



The general attractive force of all matter must, how- 

 ever, impel these masses to approach each other, and to 

 condense, so that the nebulous sphere became incessantly 

 smaller, by which, according 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 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 theory origi- 

 nally gave no information. 



