5CJ0 
1st screen 2:1 screen wall 
H > 73 18,7.") 85,95 
“ lu re, if, according to the rule given 
above, the tibtance on the tirst screen be 
t‘ lke P lrom the distances on the other two 
Hie remainder will be 7, and 74,2 ; and these 
numbers, it each shot kept to a vertical 
piane, ought to be in the proportion of 1 to 5, 
that being the proportion of the distances oi 
tne second screen and of the wall from the 
first. But the last number 74,2 exceeds 
what it ought to be by this analogy, by 39,2- 
so that between them there is a deviation’ 
from the vertical plane of above 39 inches 
and this too in a transit of little more than 
eighty yards. 
Bui furthe 
RIFLE. 
. , to shew that these irregu- 
larities do not depend upon any accidental 
circumstances ot the ball's fitting or not fit- 
ting the piece, there were five shot more 
made with the same quantity of powder as 
befoie ; blit with smaller bullets, which ran 
much looser hi the piece. And the hori- 
zontal distances being measured in incite 
from the trace of the first I-ihIIpi o, , 
the succeeding ones, 
follow : 
i to 2 
3 
4 
1st screen 
15.6 R 
6,4 L 
4,7 R 
12.6 R 
first bullet to 
each of 
the numbers 
were as 
2d screen 
wall 
31,1 R 
94,0 R 
12.75 L 
23,0 L 
8,5 R 
15,5 R 
24,0 R 
63.5 R 
“ Here again, on the supposed fixed position 
of the piece, tiie horizontal distance on the 
wall, between the first and third, will be found 
to be above fifteen inches less than it should 
be, if each kept to a vertical piane. And 
like irregularities, though smaller, occur in 
every other experiment. And if they are 
examined accord, ng to the third method 
set down above, and the horizontal distances 
of ilie third and fourth, for instance, are com- 
pared, these on the first and second screen, 
and on the wall, appear to be thus: 
1st screen 2d screen ■ wall 
IM 21,2 5 38,5 
“ And if the horizontal distance on the 
first screen is taken from the other two, the 
remainders will be 10,15 and 27,4; where 
the Last of them, instead of being live times 
the first, as it ought to be, is 23,35 short of it. 
So that here there is a deviation of above 23 
inches. 
“ From all these experiments the deflection 
in question sterns to be incontestably evinced. 
But to give some farther light to this subject, 
I took a barrel of the same bore with* that 
hitherto used, and bent it at about three or 
four inches from its muzzle to the left, the 
bend making an angle of 3° or 4° with the 
axis of the piece. This piece, thus bent, 
was fired with a loose ball and the same 
quantity of powder hitherto used, the screens 
of the last experiment being still continued. 
It was natural to expect tlrat if this piece was 
pointed by the general direction of its axis, 
the ball would be canted to the left of that 
direction by the bend near its mouth. But 
as the bullet, in passing through that bent 
part, would, as I conceived, be forced to roll 
upon the right-hand side of the barrel ; and 
thereby the left side of the bullet would turn 
up against the air, and would increase the 
resistance on that side ; I predicted to the 
company then present, that if the axis on 
which the bullet whirled did not shift its po- 
sition after it was separated from the piece, 
then, notwithstanding the bend of the piece 
to the left, the bullet itself might be executed 
to incurvate towards the right; and this, upon 
trial, did most remarkably happen. For one 
ol the bullets fired from this bent piece, pass- 
ed through the first screen about 1-J inch 
distant trom the trace of one of the shot 
tned from the straight piece in the last set of 
experiments. On the second screen the 
traces ot the same bullets were about three 
inches distant, the bullet from the crooked 
piece passing on both screens to the left of 
the other ; but comparing the places of these 
bullets on the wall, it appeared that the bul- 
let from the crooked piece, though it diver- 
ged from the track ot the other on the two 
screens, had now crossed that track, and was 
deflected considerably to the right of it ; so 
that it was obvious, that, though the bullet 
Irom the crooked piece might at first be 
canted to the left, and had diverged from the 
track of the other bullet, with which it was 
compared ; yet by degrees it deviated again 
to the right, and a little beyond the second 
screen crossed that track, trom which it be- 
fore diverged ; and on the wall was deflected 
fourteen inches, as I remember, on the con- 
trary side. And this experiment is not only 
the most convincing proof of the reality of 
tins deflection here contended for ; but is 
likewise the strongest confirmation, that it is 
brought about in the very manner, and by 
the very circumstances, which we have ail 
along described. 
“ To prevent this irregularity, rifled bar- 
rels are made use of ; and here it happens, 
that, when the piece is fired, tiie zone of the 
bullet follows the sweep of the rifles; and 
thereby, besides its progressive motion, ac- 
quires a circular motion round the axis of 
the piece, which circular motion will be 
continued to the bullet, after its separation 
from the piece ; by which means a bullet 
discharged from a rifled barrel is constantly 
made to whirl round an axis, which is coinci- 
dent with the line of its flight. Ami hence 
it follows, that the resistance on the foremost 
surface of the bullet is equally distributed 
round the pole of its circular motion ; and 
acts with an equal effort on every side of the 
line ot direction ; so that (his resistance can 
produce no deviation from that line. And 
(which is still of more importance), if by the 
casual irregularity of the foremost surface of 
the bullet, or by any other accident, the re- 
sistance should he stronger on one side of 
the pole of the circular motion than on the 
other; yet, as the place, where this greater 
resistance acts, must perpetually shift its 
position round the line in which the bullet 
flies, the deflection, which this inequality 
would occasion, it it acted constantly with 
the same given tendency, is now continually 
rectified by the various and contrary ten- 
dencies of that disturbing force, during the 
course of one revolution. 
I his perpetual correction of a deflective 
effort on the foremost surface of the bullet, 
in consequence of the revolution of the bul- 
let round the line of its direction, may per- 
haps be exemplified, by considering what 
happens to a castle-top, whilst it spins upon 
its point. For it will be easily acknowledg- 
ed, that this, without its revolving motion, 
could not continue for the least portion of 
time in that situation. And if we examine 
how this happen-?, vre shall find, that, thnuab 
its centre of gravity is not exactly over the 
point it spins on, yet that inequality cannot 
instantly bring it to the ground according to 
its natural eiiort ; because, during one revo- 
lution, the centre of gravity preponderates oil 
every side ot the top ; and thereby raises it 
as much in one p'a e, as it depressed it in 
another. And this reasoning (supposing 
that the tendency of the centre of gra- 
vity ot the top to descend, be analogous to 
tiie action ot the unequal resistance on the 
tovcinost surface of a bullet fired from a 
rifled barrel) will easily explain how, not- 
withstanding that inequality, the bullet keeps 
true to its track without deflection. And 
what is here advanced, is farther confirmed 
by the general practice with regard to ar- 
rows. I 1 or it is well known to every archer, 
Inat the feathers of an arrow are placed in ,* 
spiral form, so as to make the arrow spin 
round its axis; without which it would be 
obvious to the eye, that the arrow undu- 
lated in the air, and did not keep accurately 
to its direction. And it is owing to the same 
principle, that every school-boy finds himself 
under the necessity of making his shuttle- 
cock spin, before he can depend upon the 
truth of its flight. 
This is the general theory of the motion 
of bullets discharged from rilled pieces ; and 
it is found by experiment, that their actual 
motions correspond very well with these 
speculations. For the exactness which those 
w ho are dextrous in the use of these pieces 
attain to, is indeed wonderful ; and that at 
such distances, that it the bullets were fired 
from the common pieces, in which the custo- 
mary aberration takes place, not one in 
twenty of them could ever be traced. 
“ i his may suffice as to the general idea 
of the form and convenience of a rifled piece; 
and here it will be expedient to insert some 
experiments, by which it will appear, how 
well it answers the purpose I have men- 
tioned above ; I mean that of keeping the 
ball fo its regular track, by preventing that 
deflection, which, as we have seen, takes 
place in the bullets fired from common pie- 
ces. 1 
“ And first I considered, that in conse- 
quence of the reasoning about the manner 
in which it produces this effect ; it should 
follow, that the same hemisphere of the bul- 
let which lies foremost in the piece, must 
continue foremost during the whole course 
of its flight. 
. “ To examine this particular, I took a 
rifled barrel carrying a bullet of six to 
the pound ; but instead of its leaden bullet, 
I used a wooden one of the same size, made 
°f a soft springy wood, which bent itself 
easily into the rifles without breaking. And, 
firing the piece thus loaded against a wall at 
such a distance, as the bullet might not he 
shivered by the blow ; l always found, tin t 
the same surface, which lay foremost in the 
piece, continued foremost without any sen- 
sible deflection, during the time of its flight. 
And this was easy to be observed, bv ex- 
amining the bullet; as both the marks of the 
rifles, and the part that impinged on the 
wall, were sufficiently apparent. 
“ Now, as these wooden bullets were hi t 
the sixteenth part of the weight of those 
of lead; I conclude, that if there had been 
any unequal resistance or defective power. 
