pendicularly. The force of ever)' particle, which impinges 
obliquely, is refolvable into vvo, one perpendicular to the fur- 
face, and the other parallel to it. That part of the force, 
which is perpendicular to the earth’s furface, produces a pro- 
greflive motion of the whole globe. The other, which is 
parallel to the furface. contributes nothing to the progreflive 
motion, but tends to produce a rotation of the globe upon an 
axis. Hence the progreflive force of motion, communicated to 
the globe, is lefs than it would be, if all the particles ftruck the 
furface perpendicularly. It is further leflened upon another 
account, namely, that the whole of th (perpendicular force is 
not effe&ive in moving the earths ce /.ter. I find by com- 
putation that the diminution upon the whole is For the 
eafe of the mathematical reader, I fnall briefly ftate the prin- 
ciples upon which this computation of the force with which the 
earth may be (truck by light, has been framed. 
The number of particles, which are directed to the earth out 
of each emiflion, is to half the number of the whole emiflion, 
in the duplicate proportion of the chord of the fun’s horizontal 
parallax, to the chord of 90° : by the known dodtrine of Archi- 
medes. Hence, the number of the whole emiflion being deter- 
mined, the number of thofe which tend towards the earth, is 
given. And the force of each Angle particle being given, the 
fum of the forces of that given number is given; and this 
is the progreflive force which would be imprefled upon the 
earth, if all the force of each particle were effective. In what 
proportion the progref- C 
five force is diminilhed, 
on account of the vari- 
Imairine T to be the 
earth’s center and ACB 
to be half a great circle A 
I 
ous obliquities of im- 
pulie, is thus invetti- 
gated. 
an 
