350 
THE WELDON RANGE-FINDER. 
To test the auxiliary base glass:—Having got your other two 
OBJECT 
glasses on these poles—accurately laid—find some point X where the 
object P can be seen through the open shutter of A’s glass, and where 
the glass of B is seen reflected along the same line, then AX should 
= j- of AB, or T i(y the range. This glass requires careful adjustment. 
With it ranges may be taken considerably under a minute. 
For the auxiliary base we have, so far, made shift with a reel some¬ 
what similar to the one I have described, but not so broad, and of 
greater diameter, capable of holding a tape 40 yds. long. This is 
marked every yard in red, and again every 10 yds. in black, thus— 
A SMALL 
PIECE OF WOOD 
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Every yard represents 100 yds. range, the black figures representing 
tens of yards. Three men should use the instruments when the 
auxiliary base glass is used. The auxiliary base-finder gives the end 
of the tape to the angle-finder, and runs off to the latter's left until he 
gets the angle-finder's glass and the object in line, moving right or left 
as required. The angle-finder holds the end of the tape in the same 
hand as he holds the glass, while the auxiliary base-finder lets the tape 
slip through his hands until he gets the reflection of the glass of the 
distant base-finder and the object seen through the angle-finder's 
shutter to coincide. This, with practice, can be done while the angle- 
finder and base-finder are finding the range, but it needs great 
accuracy, careful training, and very much practice-—so much so that 
men at first are never correct, particularly on a moving object. When 
the angle-finder calls out “ correct" the auxiliary base-finder looks 
at his tape and reads off the range. 
In this country it is very difficult to get satisfactory work from trades¬ 
men, and I have made the tapes myself for the auxiliary base-finder, by 
