194 
MINUTES OF PBOCEEDINGS OF 
the 10 to the right of 0 may mean 91; 20 may mean 92. These mean¬ 
ings are, however, of little practical importance, as, with abase of 50 yds., 
90 on E would give a range of 11,400 yds., which is not an artillery 
range. 
Let us now start again from 0, hut try hack to the left, we see 9, this 
means 90 among the small numbers , 8 means 80, 7 70, &c., and 80 will 
mean 0 among the small numbers. 
Table. —Showing probable and possible values of particular figures on 
line E, presuming that the values in the first column are the only probable 
values. 
Probable. 
Possible. 
Figure on 
Boiler. 
Sum of 
Base angles 
of 
triangle. 
Vertical 
angle of 
triangle. 
Sum of 
Base angles 
of 
triangle. 
Vertical 
angle of 
triangle. 
1 
0 
1774° 
24° 
179|° 
1 ° 
20 
178° 
2° 
179°-48' 
12' ■ 
60 
179° 
1° 
179°-54' 
6' 
; 80 
177F 
2F 
175° 
5° 
9 to tlie 
left of 0. 
177F 
2f 
l79°-434' 
16F 
5 to the 
left of 0. 
1761 s 
3|° 
179°-37F 
224 ' 
Tests. 
The instruments scarcely ever lose their original set; when, however, 
it is considered how much will depend in action upon their absolute 
accuracy, it will be seen how necessary it is to provide tests which will 
always assure the officers of a battery that the range-finders will give the 
exact distance. 
Sun Tests. 
For an hour and a half after sunrise, or before sunset, this may 
be used without digging holes for the trails. The two guns are 
laid by their sights on the sun; the object glasses are covered with 
shutters so as only to leave a small hole through which the rays of the 
sun can enter; the size of the hole varies with the brightness of the sun, 
the smaller the safer, if the sun be distinctly visible. 
The reason for putting on the shutter is simply that the object glasses 
of the telescope are burning glasses, and if the full heat of a bright sun 
were allowed to enter it might, in some cases, spoil the test, and possibly 
destroy the wires, although this last has never yet happened. 
For the same reason a man should cover the object glass with his hand 
whenever the telescope is not actually being looked through. 
A glass shade is also put over the eye-piece or near end of the teles¬ 
cope. 
Enough light should be found in the telescope to see the wires 
distinctly when off the sun; if this cannot be done the shutter of the 
