*1872.] Meteoric Astrononvy. 145 
roth, §’ the point on the heavens towards which she 
is travelling at the moment. Let E/ be a line directed 
towards the radiant point of the August meteors, which hes 
about 4o from &’. Then E’m perpendicular to E/ represents 
the least possible velocity for the meteors (where EE’ repre- 
sents the earth’s velocity). Coming from the direction of a 
point, s, in the heavens, with this velocity they would seem 
to radiate from 3, E'S being drawn parallel to El, since 
a meteor which was at m when the earth was at E would 
meet the earth at £’.. Again, if we take Em’, equal to the 
diameter of a square of which EF’ is a side (that is equal to 
Ek), this line will represent the greatest velocity a meteor 
crossing the earth’s orbit can possibly have, if it 1s tra- 
velling in a closed orbit. This gives the direction, s’m’E’, 
along which an August meteor would actually travel, on the 
supposition that it has this maximum velocity. We may 
fairly assume that the meteors are not arriving on a course 
intermediate to mz’ and EE’, because then their relative 
velocity would fall much too far below the velocities esti- 
mated by Secchi, Newton, Herschel, and others. 
From some point on the arc ss’ upon the celestial vault, 
therefore, the August meteors are certainly travelling; and 
with some velocity intermediate to the velocities represented 
by the lines m’r’ and me’, where EE’ represents a velocity of 
185 miles per second. Moreover, the reader is not to 
suppose that the figure deals with hypothetical relations, 
and does not admit of being at once and definitely inter- 
preted. ’ represents a real point on the heavens, a point 
on the ecliptic close by the star 6 Arietis, towards which, 
as already mentioned, the earth is actually travelling on 
August roth. This point can at once be found on a 
celestial globe. 4, again, is a known point, the radiant 
of the August meteors (already indicated), and about 39° 
from 3%. It can, of course, be found on a globe, since its 
R.A. and declination have been given. Now let the end ofa 
cord be held down on a globe at the point corresponding to 
>’, and let the string be stretched over the globe across the 
point corresponding to ¥, so as to pass beyond &. It will 
indicate the position of the arc, s’s, on the celestial 
sphere. It will lie in a circular arc of which 2% 3’ will 
represent 39. And if we take points on it corresponding to 
* Because if v be the velocity, it can be shown that a body moving in a 
circle at a distance (d) from the sun, the velocity in a parabolic orbit will be 
V2.v, at a distance (d) from the sun. The earth’s orbit is near enough toa 
circle to render this relation applicable ; moreover, on August roth, the earth 
is nearly at her mean distance from the sun. 
GL. 11. (N.S:) U 
