THE ROYAL ARTILLERY INSTITUTION. 
485 
Having liad occasion to undertake the superintendence of shot and 
shell practice, and to organise for the first time a system of competition 
with heavy guns at sea ranges, I became impressed with the want of 
some means of accurately recording practice, and constructed the multi¬ 
plying alidade for the purpose of instructing the eye and testing the 
powers of the pointers in laying guns of position. 
The use and value of it were sufficiently demonstrated to me in the 
result of the competition at Shoeburyness, in August, 1866—one of the 
detachments I took up, which was trained with it, having some thirty 
points above the highest average of some eight days* practice during that 
competition. Since that time some improvements increasing the 
facilities in its use have been made, while the first principle of its 
construction remains the same. 
The application of this instrument for recording practice 
on occasions of artillery competitions, suggests some im¬ 
portant means for getting over difficulties that always present 
themselves from the - want of this or some other effectual 
mode of measuring range and deflection of artillery fire at 
floating targets; so as to obviate the necessity for a constant 
reference to the arbitrary decisions of an umpire, formed of 
necessity on some empirical law or rule of thumb, inconsistent 
with the just appreciation of the relative value of the practice 
of competing detachments. 
The merit of the alidade consists in its power of measuring 
the exceedingly small angular distance of a shot falling near 
a target moored, it may be, at 1800 yds. or 2000 yds. from the 
observer, and of bringing back the result of the observation 
to the hand of the observer, to be spotted on the register 
with a considerable multiplying power with the greatest 
facility and despatch. 
The simple principle of the construction of this instrument 
may shortly be described as follows :—When the alidade is in 
collimation and aligned on the target C the index is at zero, but 
on measuring a distance to the right or left a triangle ABB 
is formed, of which one side BB , as extended from the cross 
wires at B to the index at B, forms the exterior angle ABE\ 
equal to the interior opposite angles at A and B; or in other 
words, in the case where the sides AB, BB are equal, the 
angle ABE formed by the line of the index is double the 
angle BAB to be measured; much more then, as in the case 
of the present construction, where the angle at B has been 
designedly increased, does it multiply the result, which has 
been calculated as most convenient for the size of register of 
ranges between 1500 and 1800 yds. The instrument for the 
use of the range party is of simpler construction, with an angular 
measurement on a more restricted scale. 
March, 1871.. 
