132 FROM NEBULA TO NEBULA 



Now, it is quite improbable that the comet so 

 expelled would be all of one piece, but rather would 

 it be in the form of a coarse spray ( which would speedily 

 congeal in separate particles, thus occluding its gases) 

 and, under the Newtonian law of inertia, would pro- 

 ceed as a single unit indefinitely onward, with a uni- 

 form motion in a straight line, until deflected by an 

 extraneous force. PTowever, the instant of the comet's 

 liberation into an independent body becomes the sig- 

 nal for a coalition of all the gravitational forces in 

 the universe to teach it the way it should go. Its mo- 

 tion, both as to velocity and direction, being in its in- 

 ception both chance and arbitrary, offends from instant 

 to instant against the uniform law of gravitation. The 

 comet cuts across current, as it were, from the shiggish 

 drift of Neptune's path to that of flying Mercury, and 

 thence is flung back and outward again by the great 

 gravitational maelstrom whose chastening hand it can 

 never escape, and must ultimately obey by falling into 

 the orderly orbit for which it is predestined. 



The comet, thus summarily ejected, in endeavoring 

 to regain and maintain its disturbed equilibrium no 

 sooner enters that state than it is whisked out of it 

 again by its projectile momentum, and by its conse- 

 quent shifting relative to the comparatively stationary 

 forces acting upon it from without. This anomalous 

 condition causes the comet's component particles to 

 collide with each other with ever increasing frequency 

 and violence as they near the sun, the center of great- 

 est disturbance, until they shatter and become in- 

 tensely heated, thereby liberating more and more of 

 their imprisoned gases and so giving rise to those re- 

 markable phenomena of glowing nuclei, jets, envelopes, 

 coma, and tail with which we are now familiar. The 

 shape, length, and position of the tail are the ordinary 

 effect of gravitational equilibrium. 



