TELESCOPIC SIGHT FOR FIELD GUNS. 
21 
2. The mechanism whereby elevation is given to any extent must be 
simple, independent of the gun, and not liable to unintentional 
alterations. 
3. The elevation that can be given must not be limited. 
4. The present sights must not be interfered with, the telescope being 
really supplementary, and not intended to supersede them. 
5. The whole must be simple , strong, and not liable to injury with 
ordinary usage, nor requiring constant adjustment. 
In designing the following instrument I had to consider these con¬ 
ditions ; and taking No. 3 first, I decided to fix the telescope on the 
muzzle (whence the gun would be laid) instead of at the breech; the 
No. 1 standing between the off wheel and the muzzle, and the No. 5 
elevating from his own side (where the No. 1 would himself stand if 
working the wheel). 
Taking No. 1 difficulty next, the frame of the instrument was fixed 
with regard to two possible motions by attaching it to a block fitted to 
slide into the notch of the fore sight, and with regard to a third by 
an arm which, being fixed to its other end, rested upon the chase of 
the gun. 
Nothing thus being attached permanently to the gun. No. 4 diffi¬ 
culty was obviated, and the rest lay with 
The Instrument. 
This consisted essentially of five parts :— 
(1) The telescope (one of the cross telescopes of an old Nolaffis 
range-finder). 
(2) An arm , to which the telescope was attached. 
(3) A frame, in which the arm oscillated. 
(4) A sliding rest , which ran along the upper surface of the frame, 
and on which the arm rested. 
(5) A screw shaft , whereby the sliding rest was moved along the 
frame. 
The frame is shown in Fig. 1; the only peculiarity about it was that 
the upper surface had to be flat. 
The arm (Fig. 2) was of peculiar construction. The fore part 
consisted of a block which fitted accurately between the sides of the 
frame, through which on either side axles were driven into the block. 
The upper surface of the arm had to be level, but the lower surface of 
the portion behind the block was formed in a curve. Against this 
curve the sliding rest worked, and it was of such a nature that equal 
increments of motion of the rest along the level surface of the frame 
produced equal angles of motion of the arm about the axles in the 
block. 
The screw shaft, which is also shown in Fig. 1, simply ran down the 
centre of the frame through one end, and was worked by a thumb- 
piece. The sliding rest geared upon the screw shaft, and naturally 
4 
