7 C ITALIAN FIELD GUN. 
401 
hot a steel ring 0*79 in. in width; one-half of the width being bored 
out so as to fit the shoulder when expanded by heat (shrinkage 0*008 in.), 
the other half bored out to 3*76 ins. diameter. The inside of the cast- 
iron nave (3*7 ins. in diameter) works in and bears against this steel 
ring. The bearing surface of the axle-arm is 7*22 ins. in length, mea¬ 
suring from the outside edge of the shoulder horizontally. Beyond 
this point, the metal is cut away so as to leave the cross section of the 
arm a square inscribed in the original circle. The width of the recess 
is 0*335 in., and the side of the square is 1*1 in. Into this fits a 
movable steel disk with a square cut out of it, so as to form a fork and 
to drop into the recess prepared for it in the axle-arm. The upper 
part of the disk, however, has an outward semi-circular shoulder about 
double the width of the thickness of the disk. It is kept in its place 
by a pin running through the ends of the fork just under the square 
on the axle. The outside of the nave and pipe-box runs against 
this disk; thus the wheel runs between two steel disks endwise and 
internally on the taper arm with a clearance of only 0*01 in. As, 
further, there is ample provision for oiling (such is the lubrication 
intended, as oil is more easily procured in Italy than grease), and as 
dirt is prevented from entering 'twixt nave and axle by a cap screwed 
over the end of the cast-iron nave, the wheel runs truly and easily. 
The pipe-box can suffer but little wear, inasmuch as the steel shoulders 
prevent the wheel from canting from wear, as it would were it not for 
the end support. 
The dip or hollow of the axle-arm is whereas the dish of the 
wheel is T V; consequently the lowest spoke is not perpendicular to the 
ground. This construction is justified by the following considerations:— 
Looking at the carriage from behind, and supposing the road to slope 
from right to left, the strain on the lowest spoke of the near or left 
wheel is much greater than on that on the corresponding spoke of the 
off or right wheel. It is desirable, then, to have that spoke as nearly 
vertical as possible, to resist the extra strain on it. 
If this reasoning be sound, the lowest spoke should not be vertical 
on level ground. Now, if reference be made to our text-books, it will 
be found laid down that the “ downward inclination or hollow is given 
to the arm for the purpose of bringing the lower or working spoke 
vertical, the wheels being on the level .” But both the wheel and axle 
without this arrangement are amply strong on a bad road when the 
weight acts symmetrically on both wheels of the carriage. It seems 
unnecessary in such case to make special arrangements for the better 
support of the weight; but, on the contrary, that such should be made 
when that weight bears upon one wheel more than on the other, as in 
the case of a sloping road. 
The axle-arm is in prolongation of the axis of the axle. In other 
words, it has no “lead.” 
The length of the axletree, or extreme width of the carraige (61*47 ins.), 
was adapted from the width of a pair of horses in draught. It was 
observed that when horses pull they incline towards each other, and 
when they back they incline outwards. The distance between the 
outer flanks of the horses was measured under both circumstances, and 
