94: II. A. JVeivton — The Story of Bields Comet. 



the planets, it would have gone off again into outer space 

 whence it came. Some such cause robbed it of a little of its 

 momentum, and it could not quite rise out of the sun's con- 

 trolling force, but it came around again in an elliptic orbit to 

 remain thenceforth a member of the solar system. It may or 

 it may not then have been a great comet, like Donati's (in 

 1858). It was probably a small one. It may have made its 

 circuit of the sun in tens of years or in tens of thousands. 



At some time, probably in the early historic ages, it came 

 near the huge planet Jupiter. When it had gone out of his 

 reach it had just momentum enough left to go around the sun 

 in its present orbit of 6§ years. It went away from Jupiter an 

 entire and single comet. As it came near the sun, his burning 

 heat acting upon the cold rocky body of the comet cracked off 

 and scattered in every direction small angular bits. At the 

 same time a very thin vapor, shining by its own light, was set 

 free. To this vapor both comet and sun had an unaccountable 

 repulsion. It was driven off first by the comet every way. 

 But soon that which was sent toward the sun was driven back 

 again, and it went streaming off into space to form the comet's 

 tail, a process ably set forth by Professor Norton. 



This matter which made the tail of the comet never got 

 back. It had, moreover, nothing whatever to do with the 

 meteoroicl stream. The meteoroids are solid fragments. To 

 them the sun, at least, had little repulsion. The comet was so 

 small that perhaps the force with which a boy can throw a 

 stone would have sent the bits of stone entirely off the comet, 

 never to come back. Those which were shot forward from 

 the comet near P (first figure) went up along the orbit with 

 greater velocity and rose higher from the sun than the comet 

 did near D. Having a longer road to travel, they took a 

 longer time to come around to P in each circuit. On the 

 other hand, those bits which were shot backward followed the 

 comet with less velocity and could not quite rise to D, and so 

 having a shorter road to go over came sooner back to P, gain- 

 ing on the comet at each circuit. Thus the stream grew longer 

 slowly, and new fragments being thrown off at each circuit, 

 the meteoroid stream grew in length to its hundreds of millions 

 of miles. At times, the main comet has broken into two or 

 more parts, giving us the double comets of 1845 and 1852, the 

 Pogson comet of 1872, and the double meteor stream of No- 

 vember, 1872. 



