272 CELESTIAL DYNAMICS. 



travel more than one thousand miles towards the central 

 body. 



As cosmical masses stream from all sides in immense 

 numbers towards the sun, it follows that they must become 

 more and more crowded together as they approach thereto. 

 The conjecture at once suggests itself that the zodiacal light, 

 the nebulous light of vast dimensions which surrounds the 

 sun, owes its origin to such closely-packed asteroids. How 

 ever it may be, this much is certain, that this phenomenon is 

 caused by matter which moves according to the same laws as 

 the planets round the sun, and it consequently follows that 

 the whole mass which originates the zodiacal light is contin 

 ually approaching the sun and falling into it. 



This light does not surround the sun uniformly on all 

 sides ; that is to say, it has not the form of a sphere, but that 

 of a thin convex lens, the greater diameter of which is in the 

 plane of the solar equator, and accordingly it has to an ob 

 server on our globe a pyramidal form. Such lenticular dis 

 tribution of the masses in the universe is repeated in a re 

 markable manner in the disposition of the planets and the 

 fixed stars. 



From the great number of cometary masses and asteroids 

 and the zodiacal light on the one hand, and the existence of a 

 resisting asther on the other, it necessarily follows that pon 

 derable matter must continually be arriving on the solar sur 

 face. The effect produced by these masses evidently depends 

 on their final velocity ; and, in order to determine the latter, we 

 shall discuss some of the elements of the theory of gravitation. 



The final velocity of a weight attracted by and moving 

 towards a celestial body will become greater as the height 

 through which the weight falls increases. This velocity, how 

 ever, if it be only produced by the fall, cannot exceed a cer 

 tain magnitude ; it has a maximum, the value of which de 

 pends on the volume and mass of the attracting celestial body 



