350 
POPULAR SCIENCE REVIEW. 
CLASSIFICATION OF COMETS. 
By RICHARD A. PROCTOR, B.A., Cambridge, 
AUTHOR OE “SATRUN,” (i THE SUN,” ETC. 
S OME of the facts of science are stranger than any fictions which 
even the liveliest imagination could devise. So strange 
are they that even the student of science who has been engaged 
in the work of mastering them is scarely willing to admit them in 
their full significance, or to accept all the inferences which are 
directly or indirectly deducihle from them. This, true in all 
departments of science, is especially noteworthy in astronomy ; 
and perhaps there is no branch of astronomy in which it is more 
strikingly seen than in that which relates to comets. During 
the last quarter of a century discoveries of the most surprising 
nature have been made respecting these mysterious bodies; 
relations have been revealed which bring them into association 
with other objects once regarded as of a totally different nature, 
and the path seems opened towards results yet more amazing, 
by which, more than by any others which even astronomy has 
disclosed, we seem brought into the presence of infinite space 
and infinite time The earth on which we live — nay, our solar 
system itself — seems reduced to utter insignificance compared 
with the tremendous dimension’s of comet-traversed space ; while 
all the eras of history, and even those which measure our earth’s 
existence, seem as mere seconds compared with the awful 
time-intervals to which we are introduced by the study of 
cometic phenomena. 
One of the most interesting points suggested by the recent 
cometic discoveries is the question, how comets are to be 
classified. That they are not all of the same order is mani- 
fest, whether we consider their size, or the shape and extent 
of their orbits. But precisely as in zoological classifica- 
tion mere size or development is considered a much less 
important point than some really characteristic difference of 
structure, or even than a difference of distribution, so in classi- 
fying comets it would be unsatisfactory in the extreme could we 
