THE ROYAL ARTILLERY INSTITUTION. 
115 
Description of Drawings» 
Eig. 1 is a general view of camera and apparatus attached, the same 
letters have reference to the same parts in each of the figures:— 
A, rotating disc, shewn as set before taking a photograph, with the solid 
part opposite the lenses indicated by dotted lines; b, the spiral spring 
wound up; e, the catch on armature, and pin set to prevent rotation (see 
Eig. 3); c } an electro-magnet; d 3 armature of magnet, on which is placed the 
catch e 3 and pin for liberating the disc; f a flexible spring to support the 
armature, &c.; g 3 a plate of brass to act as a stop when in contact with the 
catch e 3 in which position the holes ii are opposite the lenses, and the 
camera open; M, are binding screws in connection with thejmagnet, to 
which the wires from the galvanic battery to the gun are attached, forming 
an unbroken communication with the magnet in the circuit. 
When the gun is to be fired, and photograph taken, communication is made 
with the galvanic battery; at that instant c is magnetized and attracts d towards 
it, withdrawing the pin, and bringing the catch e close to the disc; rotation 
commences, and continues until the stop g abuts against the catch e } where 
it is held, and thus the camera is open for an instant of time until contact 
is broken by the discharge of the gun; c is then demagnetized, the armature 
and catch return to their original position, g passes under the catch (see 
Eig 3), rotation is completed, and the camera closed. 
To adapt this arrangement to photograph projectiles in flight, a second 
electro-magnet K, is used (Eig. 2) with a spring armature of thin iron l, 
which presses on the binding screw h 3 and completes the circuit of the 
magnet C 3 when K is not in action, but when so, it attracts the armature 
from the binding screw Ji 3 cutting off the current from G; it will thus 
appear that the magnetization of one magnet follows the demagnetization of 
the other, the spring l acting in two capacities, as a conductor in conveying 
the current by the binding screw h to magnet C, and as an armature to 
magnet K } thus controlling the action of the former. 
To take a projectile in flight it is necessary that a wire screen be used 
(similar to that in experiments with the Navez instrument), the wires in 
connection with the galvanic battery having magnet K in circuit, and 
armature l in contact, consequently not touching the binding screw h*, 
when the wire screen is broken by shot passing through it, K is 
demagnetized, l returns to Ji and completes the circuit with C f the disc A is 
set in motion as before described, showing the trajectory of the shot during 
the time the camera was open, this time being determined may approximately 
measure the time of flight. 
To take impact of projectiles the same arrangement is used, the wire 
screen being placed in front of object to be fired at, and at such distance 
that the camera may be fully open at that instant of time. 
The two latter uses have not been practically tested in consequence of 
this season of the year being unfavourable for instantaneous photographs, 
but it may fairly be assumed that the arrangement that can take a shot 
in its highest velocity is also capable of doing so when much reduced. 
[vol. v,] 
16 
