554 
Proceedings of the Royal Society 
of many millions of miles in length, the occurrence of comets with 
many tails, and the observed fact that there is no definite relation 
of direction between a comet’s tail and its solar radius-vector, are 
here looked upon as due to the differences of motion of these dis- 
crete fragments relatively to the earth, in a manner somewhat 
analagous to the appearances presented by a distant flock of sea- 
birds flying in nearly one plane, and only becoming visible (as a 
long streak) when the plane of the flock passes approximately 
through the spectator’s eye. The so-called envelopes are compared 
with the curious phenomena presented by tobacco-smoke (which 
seems, however, to be emitted in a form apparently resembling thin 
continuous films of small particles of carbon), and the so-called 
“ gaseous jets,” which appear to be projected from the nucleus 
and to be repelled from the sun, are not difficult of explanation 
from the general point of view here taken. 
The investigations are mainly conducted by quaternions, and 
6how how a group of discrete masses, so small that their mutual 
•perturbations are not of great moment, except in the case of actual 
impact, gradually changes its form as it revolves about the sun ; 
independently of any hypothesis as to the cause (planetary attrac- 
tion or otherwise) by which it was first introduced into the solar 
system. 
The author had some hesitation in bringing forward this paper, 
as he did not know how far Schiaparelli, whose recent discoveries 
have been so very novel and remarkable, had carried his investiga- 
tions. The ideas here brought forward had occurred to him imme- 
diately on his being made aware (more than two years ago) of the 
identity of the orbits of the August meteorites and of Comet II., 
1862 : but they seemed so obviously to follow from that identity 
that it was only on reading Dr Tyndall’s recent speculations, which 
seem to have been well received ; and on being informed by Pro- 
fessor Newton (of Yale Coll. U.S.A.) that the questions of tails, 
envelopes, and “ gaseous jets ” had been treated by Schiaparelli 
as proving the existence of a repulsive force (such as seems to have 
been admitted by Bessel and others, who observed Halley’s comet 
on the occasion of its last return), that he ventured to produce to 
the Society an explanation so apparently simple, yet so inconsistent 
with what appears to be held by the majority of astronomers. The 
