22 
TELESCOPIC SIGHT FOR FIELD GUNS. 
equal turns of tlie screw shaft (or thumb-piece) produced equal 
motions of the rest along the frame; this produced equal angles of 
motion of the arm or equal angles of elevation. 
Fig. 1. 
(Scale f.) 
Fig. 3. 
Sliding rest. 
Fig. 2. 
I arranged the curve on the lower surface of the arm so that 10 
complete turns of the screw gave 1° of elevation, and I graduated the 
surface of the frame with divisions corresponding to the motion of 
the rest due to one turn of the shaft; I divided the circumference of 
the thumb-piece into sis parts, and I was able thus to give eleva¬ 
tions to 1'. 
The form of the block which was to fit into the slot of the muzzle 
swell was a D, which slid over the fore sight and between the sides of 
the slot. This D was rivetted on to the fore end of the frame. 
The hind rest for the frame was simply a plate, curved at its lower 
edge, to rest on the surface of the chase of the gun, and was so 
arranged as to shut up against the frame when the instrument was 
not in use. 
There is no necessity for any deflecting arrangement (though I had 
made one) ; for I found that with the horizontal cross-wire of the 
telescope, to keep your elevation correct you could lay to the right or 
left of the target, and with better results than by giving deflection in 
the ordinary way. 
In rivetting the D block on to the frame, the axis of the elevating 
arm was inclined at the 1° 30' given to the tangent sight, and the axis 
of the telescope thereby caused to move in the same plane as the line 
of sight does, or rather in one parallel to it. 
I was only able to fire six rounds to judge of the accuracy of my 
instrument. Of these, two were rendered useless as records by the 
time fuzes bursting short (I had no percussion) ; another (the second 
round) was incorrectly laid, owing to an incorrect signal from the 
range party, but fell almost exactly as far from the previous one as I 
had given elevation for. Of the remainder, one fell within 15, another 
35, and another 5 yds. of the target, against 70, 50, and 70 of previous 
