178 H.. A, Newton— Origin of Comets, 
velocity. What proportion have not depends upon how fast 
the process of disintegration of comets goes on. If this process 
is very slow, the new comers on our list should form a smaller 
proportion than if the process is rapid. But it has been seen 
that in the process by which they lose velocity their orbits 
have their inclinations in general increased. This is particu- 
larly true for the inclinations between 45° and 135°, for the 
corresponding comets are more likely to pass directly across in 
front of the planets. Hence in fig. 1 we ought to expect on 
Laplace’s hypothesis as : Papi of “perturbations an increase of 
the ordinates between and 135°, at the expense of the 
ordinates between 45° os 90°. 
Again, the periodic comets form a marked group and should 
probably be treated separately. Now it is reasonable to sup- 
pose that a large part of the area between 0° and 20° lying 
below the shaded area is due also to comets of short periods. 
Of the twenty-six comets in the table whose inclinations are 
less than 20°, nine are noted as periodic and furnish the shaded 
area near A. Of seven of the remainder, viz: 1743 I, 1678, 
1585, 1766 Il, 1819 IV, 1867 I and 1847 V, the orbits com- 
puted are ellipses, mostly short ones, but the comets have not 
been certainly detected at any return. Of the other ten about 
f were not well enough observed to enable us to say 
whether their periods were short or long. It is probably sate 
to assume that the area between the curve of sines and the 
shaded area belongs, up to 20°, to comets of short period. 
hese return so frequently that their number in a list of 
observed comets is out of all proportion to their number among 
existing comets. Whatever theory of the origin of this group 
we may assume they should, because of the comparative ease 
of their being detected, not count for much in studying the 
original distribution of the inclinations. 
rrect then the curve in fig. 1 by striking ne the surplus | 
the 
area npr 20°, bringing back some of the area from 
We therefore o moncluiie, that the curve of fact 
magpie a ae the hypothesis of Laplace if 
we first make reasonable allowance for known perturbations, 
and for the —. of short 
34. Can 
plained age reasonable suppositions on Kans fore esis? rm 
think not. If the comets are from matter at a very great dis- 
tance from the sun the line AB should represent the theory, and 
the decided turn of the curve downward towards 180° seems 
Zu nee Pe Ne 
