THE ROYAL ARTILLERY INSTITUTION. 
331 
It now remains to make a few remarks upon the parts of the gun- 
carriage in detail. 
The wheels and axletree are of sufficient importance to be treated 
of by themselves, and it need only here be mentioned, with regard to the 
destructive action of the gun upon the carriage, and axletree in par¬ 
ticular, that, looking at their inertia, the weight of the wheels should 
be a minimum (as well as for mobility). 
The scantling of the parts has been arrived at from experience and 
experiment, as well as from scientific considerations; being always kept 
at a minimum consistent with proper strength, for the sake of mobility, 
which consideration in the following remarks is understood to be kept 
in view. 
The wooden axletree bed, hitherto used, served as a convenient means 
of securing the axletree to the carriage body, more particularly in 
wooden gun-carriages; it also distributed the load in travelling, and the 
strain in firing, more uniformly over the axletree, serving by this means, 
and by its own additional strength, to admit of the axletree being 
made lighter than it otherwise could be. 
In iron carriages, however, it gives no additional facility of con¬ 
struction, and though it has the advantage of assisting the axletree to 
some extent, it is a questionable advantage; so that in this case it 
would appear to be a superfluous, and it may even be said to be a 
faulty form of construction—a compound axletree, as it were, being 
made of two substances differing so much in elasticity as wood and iron, 
and further, the material having the greatest elasticity placed to receive 
the pressure or blow; in fact, the iron may be broken before the full 
strength of the wood has been called into play. For this reason, it is 
probable that in iron carriages of the future it will be dispensed with, 
and the axletree modified. 
In form, the bed is of the same section throughout, but not 
rectangular; because while the upper surface is parallel to, and the 
sides perpendicular to, the under surfaces of the brackets into which it 
is housed, its under surface must be such as to be parallel to the ground 
when the trail is upon the limber-hook, in order that the lower surface 
of the axletree may be parallel to the same—that being the position of 
the axletree for which the lead and hollow are calculated. 
The dimensions of the bed depend entirely upon the axletree; its 
length—in which direction the fibre should run—being the same as that 
of the body of the axletree; its depth being regulated by the height con¬ 
sidered necessary to be given to the axis of the gun (which is governed 
by the general rule that the gun should be able to fire over a parapet 
3 ft. 6 ins. high at 5° depression); and its width such that it may be 
able to retain a good hold upon the axletree without giving way itself* 
The height of the brackets must be at a minimum consistent with 
the maximum elevation and depression necessary for the gun—-viz.; 
about 15° elevation; or 10° depression; being given when required—and 
also to give (in wooden gun-carriages) room for sufficient depth of 
housing over the axletree bed* 
The depth must be kept, as stated, at a minimum; because the 
deeper the brackets, the stronger, and.therefore heavier, they must be 
