332 
MINUTES OF PEOCEEDINGS OF 
in themselves; and again, because the higher they are, the less will be 
the stability of the system. 
The thickness of the bracket should be at a minimum consistent with 
strength. Its length must be such as to afford secure attachment to the 
trail in wooden carriages; in iron carriages, the brackets and trail are 
in one. 
With regard to the position of the trunnion holes in the brackets, it 
is ruled by the consideration that it must not be so far back as to make 
the weight on the limber hook—the position of which is, in a measure, 
fixed by other things—excessive, but such as easiness of lift in 
unlimbering demands ; and, so far as it may be taken into account, of 
correct distribution of the load on the fore and hind axles. At the same 
time, the position of the trunnions must not be so far forward as that 
when the carriage is unlimbered and gun fired, the trail would rebound 
from the ground, and the system turn over to the front. Neither 
should the weight on the limber-hook be so little as in travelling over 
rough ground, or up an incline, to cause a succession of heavy blows by 
the trail against the key securing it. In practice, in gun-carriages for 
the lighter field guns, the axis of the trunnions—the gun being 
unlimbered and on the level—and the axis of the axletree of the carriage 
are very nearly in the same vertical plane; which with the construction 
of the trail, &c., causes the point of the trail to press upon the ground 
with a force equal to about half its own weight. 
In the carriages for the heavier guns, it is found impossible to com¬ 
bine the required conditions in one set of trunnion holes, and it becomes 
necessary to have one set for the gun in travelling, and another in 
firing. 
The dimensions of the trail are fixed as follows :—Its length chiefly 
depends upon the influence it has upon the recoil when the gun is fired, 
and therefore upon the extent to which it is considered desirable to 
check that recoil ; bearing in mind, as before mentioned, that the more 
the recoil is checked, the greater will be the destructive effect upon the 
carriage. In this view, experience has shown that the angle which the 
trail makes with the ground should not exceed 22°. Setting this point 
aside^ the length of the trail must be sufficient to prevent any danger 
of the gun and carriage turning over to the rear about its point on 
firing. Minor considerations which affect the length of the trail are, 
that it must be long enough to admit of easy access between the fore 
and hind wheels, and not so long as to make the fore and hind axles 
unnecessarily far apart. As we have seen, it is where the elevating 
screw is supported that the greatest breaking strain comes upon the 
trail, and where, therefore, its cross section must be the greatest; 
depending not only upon the amount of the blow communicated through 
the elevating screw—which is exceedingly difficult to calculate—but also 
upon the distance from the elevating screw to the point of the trail* 
Towards the point of the trail, though the cross section may be 
decreased with reference to the blow on the elevating screw, it must 
be such as to be able to withstand any lateral strain the trail may be 
iiable to be exposed to; for instance, the jamming of the fore wheel 
against it in locking, and also any twisting strain in going over rough 
ground. 
