THE ROYAL ARTILLERY INSTITUTION. 
329 
is specified, the carriage standing on the level, and the gun laid at any 
angle of elevation or depression. From the symmetry of the gun and 
carriage with regard to the vertical plane through their longitudinal 
axes,* we can further take the whole of the forces to be spoken of as 
acting in that plane. Taking, then, the single force applied at the 
bottom of the bore, we may conceive it resolved into two components— 
one horizontal, the other vertical. Now, a proportion only of this single 
force, or its components, is transmitted from the gun to the carriage ; 
part—depending in amount upon the weight and thickness of metal of 
the gun—being expended upon the former. 
Again, of the proportion transmitted to the carriage, the whole is not 
expended upon the carriage, but a small part transmitted to, and 
expended upon, the ground—the amount depending upon the nature of 
the latter. Now, the gun is supported upon, or attached to, the carriage 
at two points—viz., the trunnion holes, and the bearing of the elevating 
screw on the trail; but the attachment is not rigid, for the gun is 
moveable about the axis of its trunnions, and is hinged to the elevating 
screw, the latter being also moveable in a vertical plane round its 
bearing on the trail. 
Taking, therefore, a certain horizontal and vertical force as transmitted 
from the gun to the carriage, we see, from the nature of the connection 
between the two latter, that the horizontal component will be applied at 
the trunnion holes, and the vertical component partly at the trunnion 
holes and partly at the bearing of the elevating screw—mainly, however, 
at the latter. The horizontal component decreases as the angle of 
elevation or depression with the horizontal at which the gun is fired 
increases. It exerts itself upon the carriage in two ways—viz., in 
giving’ it a motion of translation to the rear, and a twist or tendency to 
constrained motion about the point of the trail, as that point may be 
regarded for the instant as fixed. Hence, to render the effect of this 
component as little hurtful to the carriage as may be, the latter should 
in itself oppose the motion of translation as little as possible; which 
amounts to saying that its inertia, and consequently its weight, should 
be a minimum (the latter we have already seen mobility also demands ); 
while to reduce the twisting strain to a minimum, the trunnion holes 
should be as low as other considerations will admit. The vertical com¬ 
ponent will act in an upward or downward direction, according as the 
gun is fired at an angle of depression or elevation with the horizontal, 
and will increase with the angle. If upward, it will tend to tear the 
carriage asunder ; if downward, to crush it—the latter being that which 
tells most upon the carriage, on account of the resistance of the ground 
upon which the carriage bears. The body of the carriage is supported 
upon the ground at two points—viz., the axletree arms and the point 
of the trail; when, therefore, the blow of discharge is transmitted to 
the carriage, if the vertical component act downward, we shall have at 
these points certain resistances called into play, that at the arms being 
* It is not only convenient, but necessary that these axes should lie in the same vertical plane, 
to prevent the carriage receiving a twist horizontally. 
