68 W. A. Norton on the Dimensions of Donati’s Comet. 
of the comet. But each of the several envelopes, lying in regular 
succession within the outer one, is upon the present theory, the 
round summit of a similar fountain of shining nebulous matter, 
which flows on continuously past the nucleus into the depths of 
space. ‘These several conoidal streams lie, at first, one within the 
other, but at a distance from the nucleus must become more or 
less intermingled, unless each is composed of particles differently 
repelled, or attracted by the sun, from those of all the others. 
The entire luminous stream which we call the tail of the comet 
is made up of these individual streams equal in number to the 
number of separate envelopes. 
This conception, which is a necessary consequence of the Dy- 
namical Theory under discussion, accords with the notion to 
which Dr. Winnecke was conducted by his observations, with 
regard to the actual physical structure of the train of Donati’s 
comet. He intimates that these observations can only be satis- 
fied by the hypothesis of several conoidal trains enclosed one 
ithin the other. 
It should be observed that in comparing the longitudinal sec- 
tion of the tail of the comet in the plane of the orbit, as theoreti- 
cally determined, with the tail as actually observed, we have 
virtually assumed that the plane passing through the line of 
‘ sight and the general direction of the tail was perpendicular to 
it. In point of fact at the assumed date 
kh? 
dius of the nucleus, H the distance of the vertex of the envelope 
from the centre of the nucleus, p the effective repulsion of the 
nucleus, or the excess of its actual repulsion over its actual 
attraction, and & the actual repulsion of the sun. The true value 
of k is, then, the effective repulsive action of the sun, by which 
the particle is urged off into space in a hyperbolic orbit, aug- 
mented by the sun’s attraction of gravitation. In considering 
H : : 
tained the equation H=", or <="; in which r denotes the ra- 
