AUTOMATIC SIGHTING. 
273 
with the ordinary way of finding the range and laying the gun. 
Officers who have worked with the D.R.F. and P.F.know how exactly 
the instrument must be levelled in order to obtain co ect ranges, and 
this with levels that easily show difference of rr of a minute. 
How then is it possible to make a big gun on its comparatively rough 
mounting into a range-finding instrument. Of course, if you can get 
a site with a height of 200 or more feet, and are satisfied with 
moderate ranges, it can be done, but extraordinary care must be taken 
even then to have the racers, etc. very true. 
It must be remembered that in firing with an automatic sight, the 
errors given under the headings (a) and (b) might be in the opposite 
direction and counteract one another, and good shooting would result; 
on the other hand they might be in the same direction when the results 
would be deplorable. 
“ So far I have only given the theoretical conditions on which the 
automatic sight is based, the methods of carrying them into practice 
have been various. The one that perhaps will be most easily under¬ 
stood is the Italian sight tried in 1878-79. In this a rack G fixed to 
A 
the carriage, revolves a pinion H in a fitting attached to thej'gun. 
Fixed to the pinion are three cams E } for use at low, mean and high 
tide. The tangent scale A sliding up and down freely in a socket B 
fixed to the gun has its lower end resting on one of these cams. The 
cams being cut to a proper curve it follows that when the gun is 
elevated or depressed the pinion H is revolved by the rack G, and^the 
sight raised or lowered to the proper height to fulfil the conditions 
given in Fig. 1. This arrangement is rather inconvenient for the 
“ layer,” as he has to raise and lower his head tor every movementjof 
the gun. 
I had tried some experiments at Gibraltar in 1876 on the same lines 
but found the racers too much out of truth to admit of any accuracy. 
