96 W. A. Norton on Comets. 
upon the normal condition of things, would seem to be modified 
and made more conspicuous, in some instances, by a sudden dis 
continuance, at a certain point on the side of the nucleus, of the 
ejection of luminous matter. ee 
I have indicated on a previous occasion (in a paper read before 
the American Philosophical Society, in 1848) the cause of the 
curvature of the tail, and of the deviation of its general dire 
tion from direct opposition to the sun; on the theory of tle 
particles being separately driven off by the repulsive force of the 
sun. The theory of the development of the tail is so intimately 
associated with that of the head—the two Bvede being m 
fact but two different parts of one general Pp. : 
it will be proper here to notice a particular phenomenon igs | 
aa to find its explanation in the views now presen 
.—<> poe se 
recede to a greater distance from the base, AB, of the head, 
pass it on their descent with much greater perpendicular ve 
oe etcies go to the interior of the tail, the others to the mar 
gi . ; 
in succession, or crowd upon the lines ‘ere by. ae re 
and separa This 
particles on the preceding side of the tai 
those traced by th i 
effect should be more marked as the comet recedes from hee ‘ 
of the orbit, the contrast was less conspicuous, 1d : 
dispersion of nebulous matter toward the end of a 
