428 
MINUTES OF PROCEEDINGS OF 
tangent sight be should be inclined to the left so that the gun may be laid 
at the distance ts to the left of the target; having ab we shall get the 
required angle acb. Prom similar triangles, 
ts ab * 
but be being the length of the tangent scale, and £/Uts radius, 
Again, 
bf=zbcx cot elevation. 
ab = be tangent acb , 
ft _cot elevation b 
ts tan acb 
, T ts cot elevation 
tan acb =---; 
ft 
but as z acb is 0 , ts the deflection, and ft the range, we may write the 
equation as above, 
, n deflection , . ,. ^ 
tan 0 = —- x cot elevation.* 
range 
Tor sighting, the gun is placed under the drilling machine, and being 
previously levelled to have the breech gauge and muzzle plate adjusted to 
it, is turned over on its right side to the required angle of deflection, as shewn 
by an angular level on the trunnion. Two silk threads are stretched at one 
side of the gun, from the breech gauge to the muzzle plate, parallel to each 
other, and at the width of the socket apart. The distance of the tangent 
sight socket being then measured from the breech gauge, the arm of the 
machine is brought over the spot, and the hole is drilled. The threads are 
next fixed on the other side, and the hole is drilled. 
The hole for the centre hind sight is drilled in a similar manner. The 
sockets are then fitted in, and fixed by side screws. After this, the holes for 
the trunnion sights are drilled in the same way; but as they are not to be 
inclined at an angle, the gun must be previously re-levelled. The trunnion 
sight sockets are fixed in the bottom of the holes, and the sights “ dropped” 
over them. Up to this stage the leaf of the trunnion sight is rough, and to 
obtain the proper position of the apex, a dummy tangent sight is put in the 
gun, and a silk thread is stretched through its notch from the breech gauge 
to the muzzle plate. The leaf of the trunnion sight is then filed down to 
gauge in the “ hog-backed ” shape, and the back slope is combed or roughed, 
so as not to reflect the light to the gunner's eye when laying the gun. 
( 5 ) The vent in rifled M.L. guns does not enter near the end of the bore 
as in S.B. guns, but at a point fths the length of the service cartridge 
from the end, for it has been proved by experiment that by igniting the 
cartridge at this point, the maximum initial velocity is obtained. 
Up to 1st November, 1868, the vent bushes were the ordinary copper 
cone vents, let in perpendicularly, but at that date a new kind of vent 
(proposed by Major Palliser) was inserted in the 10-inch guns. This vent 
consisted of a steel bush, lined with copper, screwed in from the exterior, 
against a platinum tip screwed up from the interior, the tip having a flange 
# This neat formula is due to Captain R. W. Hitig, R.A. 
