631 
KEMAKKS ON THE 
WELDON RANGE FINDER, 
BY 
LIEUT. A. H. RUSSELL, U.S.A., 
Under the direction of Col. T. T. S. Laidley, American Ordnance Department » 
(reprinted by permission.) 
A prism instrument made in London in the manner described by 
Major Bichardson, B.A., accompanied bis paper on the Weldon Bange 
Finder. It will be referred to hereafter as prism No. 1. 
This instrument, when tested, would not give the required reflection 
of 88° 34' 3", but gave a variable angle greater than 90°, showing that 
its construction was faulty, and the description given in the above 
paper incomplete. The theory and use of the instrument are, however, 
correctly given. 
Another prism was, therefore, prepared, differing from prism No. 1 
in the following particulars :— 
While No. 1 was so constructed that the two base angles were equal, 
as shown in Fig. 4, (A B C = A C B,) No. 2 was required to have one 
Fig. 4 Fig. 7. 
of these angles equal to one-half the third angle; or A B C = A C. 
The course of light in the prism is indicated in Fig. 7, which shows 
