20 
THE TELEGRAPH . 
bringing into use a similar system for the service of the 
English troops in Afghanistan, where it proved of great 
advantage. 
The instrument (Fig. 6) is supported by a light but firm 
tripod, has a movable disc, P, capable of a quick or slow 
motion, which is imparted by a tangential screw. A circular 
mirror, M, is supported on a foot surmounted by a semicircular 
Fig. 6. 
frame in which the mirror turns on pivots. The mirror has a 
small aperture in the centre by which a sight may be taken 
from behind. On the disc an ordinary Morse key is connected 
with the upper part of the mirror, to which its movements 
are communicated by means of a steel rod capable of adjust¬ 
ment. The apparatus can, moreover, be adjusted to suit the 
position of the sun and the place towards which the signals 
are to be transmitted. The lever of the Morse key changes the 
inclination so as to throw the reflected rays to a given point. 
The mirror may also be moved by hand and adjusted in its 
