363 
THE WELDON BANGE-EINDER. 
BY 
COLONEL A. W. DRAYS ON, R.A., F.R.A.S. 
In tlie December No. of the “ Proceedings of the R.A. Institution/’ 
there is a description of a method of range-finding, said to have been 
perfected by Major Weldon, of the Madras Staff Corps. Having had 
an instrument constructed fifteen years ago by Messrs. Trougbton and 
Simms, identical with that which Major Weldon has lately invented, 
and having given both the instrument and the method a very extensive 
trial at Woolwich and Shoeburyness, before Committees, and at 
Aldershot, I consider it may be of some interest if I give the results of 
my experience connected therewith. 
Finding that persons unused to instruments had some difficulty in 
setting the index of a sextant to any given angle—such as 84° 17', 
87° 8', or 88° 34'—I consulted with Mr. Simms, of the firm of 
Troughton and Simms, as regards constructing a small instrument 
like an optical square, which should by reflection show these angles 
only. These opticians turned me out four instruments; one an optical 
square set to show 90° only, another to show 88° 34', a third 87° 8', 
and a fourth 84° 17'. 
After a long series of trials, I selected the optical square, and the 
instrument showing 87° 8', and I used these in the following 
manner:— 
The optical square was used to set off the right angle between the 
distant object and the second observer. The instrument showing 
87° 8' was used to place the second observer so that the distant object 
coincided in the object glass of the instrument, with the observer using 
the optical square. The range of the distant object was then 20 times 
the base. 
x Example : One observer stands at 0, using an optical 
/ square, the second observer moves to A , until at A he 
/ finds that 0 and X coincide in his instrument, showing 
/ 87° 8'. The range OX = 20 AO. 
/ One observer can of course do the whole of this. 
/ The base, AO, may be paced if great accuracy is not 
/ required, but it ought to be measured. 
/ For measuring I used a stout tape on a large roller, 
/ and when gunners or private soldiers used this, an error 
/ in multiplying sometimes occurred, For example, sup- 
/ pose the base was 69 yds., I have been given the range 
/ as 1280 yds. instead of 1380. To avoid this source of 
a~ o error I requested Messrs. Elliot, opticians, to construct 
for me stout tape, on which half yards were shown and numbered, so 
