ON SOME NEW TELEMETERS, OR RANGE-FINDERS. 509 
instrument, should the angles set out by the instruments be different 
from those aimed at, may be made by moving the assistant observer’s 
instrument along the scale. Fasteners can then be arranged which can- 
not hold it in a wrong place at any subsequent time. It will be at once 
seen that the scale will not require to be at all a nice piece of workman- 
ship. Hrrors which would be quite inadmissible in an ordinary folding 
two-foot rule would be inappreciable in this scale. It will be evident, 
also, that observations can be made by means of this instrument with very 
great rapidity, and that, as any movement of either observer will cause a 
slight apparent motion of the object relatively to the scale, a mean value 
can be taken, thus ensuring considerable accuracy. It would require 
considerable telescopic power to enable the range to be read toone or two 
Fig. 13. Fig, 14. 
0 
if 7 &910l2 16 
| Pb aba datubbtd 
yards at 1,000 yards, but the instrument will give indications much 
within the requirements of the infantry service with great rapidity, while 
-the instrument is quite incapable of derangement. 
Although this instrument is not quite so good as the preceding one 
for the most accurate observations possible on a fixed object, yet for 
military purposes, where the objects to be fired at are in motion to or 
from the observers, it becomes just as accurate as the instrument first 
described when, as would ordinarily be the case, the guns are sighted for 
a particular range, say 1,000 yards, and the order to fire is given when 
_the enemy has reached this range as indicated by the particular object in 
the enemy’s ranks agreed upon by the two observers coinciding with 
the 1,000-yard mark as seen by the chief observer. 
The third of the range-finders now to be referred to is a modification 
of the last one. The instruments carried by both observers again set 
out constant angles. The assistant observer’s instrument in this case 
carries a mark, while the chief observer’s instrument is attached to a 
scale (a reciprocal scale as before), which, however, in this case is narrow, 
and graduated for reading only from close quarters. Fig. 15 shows the 
arrangement, A being the assistant observer’s instrument, bearing a mark 
