THE ROYAL ARTILLERY INSTITUTION. 
425 
upwards are to have no preponderance, and as this is practically impossible, 
it is further stated that anything under 3 cwt. will be considered as none. 
The actual weight of each gun is taken by means of a strong steelyard, to 
the short arm of which the gun is slung by the trunnions. 
( 3 ) The object of lining is to enable us to adjust the sights and elevating 
plates. The line of metal is the first line required, and is obtained as in 
cast-iron guns, by finding the axis of the gun and a line parallel to it along 
the top of the gun, but the process is much more refined and accurate. The 
gun is placed on a horizontal iron table, and being levelled across the 
trunnions and along the bore, is carefully scotched up. Instead of using a 
wooden batten to find the axis, a centering block, capable of being pressed 
out so as to fit tightly in the bore, is pushed home to the breech end. Trom 
the very centre of this block, a silk thread is extended through a plate on 
the muzzle to an iron upright (plumbed) stand, some feet in front of the 
gun. The stand is then moved to the right or left until the thread grazes 
the centre point on the muzzle plate. 
A “ breech gauge,” provided with a vertical slide, having been fixed 
horizontally on the cascable, another silk thread is stretched from the stand 
to the breech slide so as to pass through a point in the muzzle plate in the 
same vertical plane as the lower thread, and just high enough to clear the 
breech of the gun. This gives the position of the line of metal, which is 
accordingly marked for about 1^ inch in length at the extreme end of the 
cylindrical part of the breech. 
Yertical and horizontal lines are marked on the face of the muzzle along the 
slots in the plate, and short horizontal lines are marked on the right side of the 
muzzle, and on both sides of the breech, by means of a scribing block, the movable 
arm of which was adjusted to the horizontal slot, the block resting on the table. 
The horizontal and vertical axes are cut, as usual, on the right trunnion. 
(4) M.L. guns are sighted like B.L. guns on both sides, and with the same 
kind of tangent sights; but M.L. guns have in addition short centre, hind, and 
fore sights. They have therefore three pairs of sights attached to the gun, 
and besides these there is a wood scale for use on board ship. 
The tangent scale has a flat steel bar, graduated on three sides, viz. on 
one of its narrow sides in degrees, on the other in yards, and on one of its 
flat sides in tenths of inch of fuze corresponding to the range scale. 
Tor guns with less than 40 inches radius, the tangent bar is equally 
divided for degrees; but for those natures with a longer radius, the 9-inch 
for example, the degree divisions regularly increase from 1° upwards. 
Each degree is graduated into six divisions of ten minutes each. Tor a 
smaller number of minutes than ten, there is a screw collar on the land 
service pattern, which can he turned round until the required number is in 
line with & fleur-de-lis marked on the sight; this was considered unnecessary 
by the naval authorities, “ as the tangent bar can be set to eye to within 
2' or 3', which corresponds to about 16 or 24 yards of range—an insignificant 
quantity when compared with unavoidable errors arising from other sources.” 
But in all other respects the L.S. and S.S. tangent sights are identical. 
The range scale is marked in hundred of yards corresponding to full 
charges, and must be found most useful in active service, as the enemy's 
distance being known, it is only necessary to elevate directly and bore the 
fuze for the corresponding range. 
