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RANGE-FINDERS. 
of the observer at the left end of the base, and advance if the reflection 
falls to the left; when working on the left of a base, retire if the 
reflection falls to the left , and advance if it falls to the right: the 
distant object or apex of the triangle being always considered the 
front. 
When the object is ill-defined, it may be necessary for one man 
alone to form the triangle OAB. In this case No. 1 directs his 
telescope on the object, and places himself at A, so that he sees some 
well-defined object, JD, on horizon (or otherwise) coinciding with 0. 
He points out the object, JD , to No. 2, who takes No. l’s place at A, 
while the latter finds B, by looking at No. 2 and moving backwards or 
forwards, being kept in line with I) by signs from No. 2. No. 3 now 
assists No. 1 as before. 
Other modifications become necessary with reduced numbers, but 
need not be described here, beyond stating that iron rods with marks 
or discs on their heads take the place of men. Three such rods 
should form part of a complete equipment, so that one man can work 
unassisted. 
Opinions may differ as to the merits or demerits of a system of 
range-finding depending upon constant angles and bases, and such 
systems do undoubtedly break down now and again on unfavourable 
ground ; but many practical artillerymen will consider that the perfect 
simplicity of such systems more than compensates for the occasional 
difficulties encountered, which practice will make ever fewer. 
Remarks on Major Weldon’s Range-finder. 
In his description of the prism used to measure the constant angle, 
Major Richardson observes that the angle of the prism opposite the 
silvered face is carefully ground to 88° 34' 3"but we are not 
told anything about the other two angles of the prism, and the natural 
inference is that they are equal. It may therefore be worth while to 
point out that one base angle must be half the apex angle. The three 
angles will be 88° 34' 8", 44° 17' 1*", and 47° 8' 55i"; total 180°. 
The action of the prism is shown in annexed figure; the line EP 
Fig. 2. 
P 
