1872.] Meteoric Astronomy. bAz 
Thus a test of the interplanetary nature of meteoric 
systems is at once afforded, and a test of a remarkably 
effective nature. For owing to the earth’s rotation the star- 
sphere appears, to rotate ; and thus the part of the heavens 
whence a meteor shower seems to proceed is continually 
changing its place with respect tothe horizon. Jf, notwith- 
standing this continual change of apparent place, a certain 
region of the stellar heavens continue to be that whence a 
meteor shower seems to come, the evidence is so much 
the stronger, because the test is applied under continually 
varying conditions. 
In the case of both the meteor systems referred to, the 
test confirms the result already deduced. The meteors of 
each system seem to come from a definite region of the 
heavens,—or rather from a definite point of the star sphere. 
In the case of the August meteors this point lies towards 
the north-eastern part of the constellation Perseus, or, more 
exactly, the R.A. of the point is about 3 h. 24 m., its north 
declination about 55°. The November meteors appear to 
come from a point in the constellation Leo, between the 
stars « and € of that constellation, or, more exactly, the R.A. 
of the point is about 9 h. 52 m., its north declination about 
24. These points are called the ‘‘radiant points” of the 
meteor systems, and because of the position of those points 
the August meteors are commonly called the Perseides, 
while the November meteors are called the Leonides. 
It would be necessary to enter at this point on a consider- 
ation of the appearances actually presented by the August 
and November shooting-stars during any considerable 
display, if it were my present purpose to give a full account 
of what is known respecting meteors ; but I wish at present 
to restrict the reader’s attention as far as possible to the 
cosmical aspect of the subject. 
The test here considered becomes, after it has served this 
direction &' M' indefinitely produced, is the point of the heavens from which 
that meteor seems to proceed. But the directions E’E' and ME’ are constant, 
and the proportion of EE’ to M E’ is constant; therefore the direction EM or 
©£'m’ is also constant. Hence every meteor of the system must appear to 
proceed from the point s’ on the celestial sphere. 
In reality every meteor of the system travels parallel to Mm, and therefore is 
proceeding (at the time of crossing the earth’s track) as if froma point s on 
the celestial sphere in the direction E’ m indefinitely produced. 
Since the visible part of a meteor’s course in our atmosphere is a straight 
line (approximately) directed from one and the same point of the heavens (so far 
as a given meteor system is concerned), it follows that wherever the observer 
may be, that course must appear to be such that if produced backwards it 
would pass through that part of the heavens. 
