404 
LAYING GUNS BY TELESCOPE. 
fired, and the projectile either hits or misses the mark. It generally 
misses, either owing to error in the deflection given, or in judging the 
range, or any other cause connected with the cartridge, the projectile, 
or the gun. The "layer,” or the No. 1, must then endeavour to 
correct the deflection; to obtain this correction he should lay the gun 
on the same point as before, and, as far as possible , in the same manner , 
and then move the deflection scale until the eye-hole, the fore-sight, 
and the point of impact of the projectile are in line. If the "layer” 
has taken the same kind of sight on both occasions, he will have rectified 
the deflection. But it often happens that during this operation a 
gunner does not lay twice in the same manner, and in that case, of 
course, the correction is not exact. 
Thus, for example, a gunner laying on the object, P, has directed 
the line of sight on the point, b, two metres to the left, and the first 
graze of the projectile is at P, six metres to the left of the object. In 
this case the real correction should be 6 m — 2 ra = 4 m . 
But let us suppose that the gunner, thinking he is laying in the same 
manner, lays the next round on b', three metres to the right of the 
0 m _ y object; to correct his deflection he takes the 
distance between P and V , that is 6 nl 4 - 3 m =9 m . 
3 oh Thus he makes an error of 9 m — 4 = 5, and 
if he lays the next round with mathematical 
accuracy he will strike at five metres to the 
right of the object. 
Thus, if the first graze is at P (35 metres 
to the left of P), by laying with the same 
elevation and deflection as before on the 
object, P, but using the telescope, I shall 
place the gun in the same position as when 
the first round was fired. Then, if I move 
the deflection-scale so as to bring the optical 
axis of the telescope on P, the point of graze, 
and afterwards lay the gun, with the deflec¬ 
tion thus found, on the object, P, the second 
shot—other conditions being the same-will 
fall in the direction of the object. 
It is necessary and sufficient, in order to 
correct the deflection with a gun that shoots 
straight, to lay the first two rounds in the 
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27ft 
f 
Eg.l. 
same manner. 
Suppose, for example, that wishing to 
strike the object, P, in Fig. 2, I lay the 
first round, even very badly, and direct the 
line of sight on b, 25 metres to the left 
of the object. If I can, before firing, 
and without moving the gun, place upon 
the fore-sight and tangent-scale a telescope 
with its optical axis directed on the object, 
P, and capable of being always directed with 
accuracy, I can correct the error in direc¬ 
tion, 
