VELOCITY AND PRESSURE INSTRUMENTS. 
355 
I.—THE LE BOULENGJj CHRONOGRAPHS 
Principle or Action. 
Major Le Boulenge, in common with all successful inventors of instruments 
for accurately measuring the velocity of projectiles, makes use of electricity 
as his agent. 
The shot is made successively to cut two currents, and thus to demagnetise 
two electro-magnets which had previously supported two heavy bodies. The 
fall of these bodies, under the action of gravity, is the measure of the time 
taken by the shot to pass over a known distance. 
In the Navez and Navez-Leurs instruments the weight liberated by the 
shot is a pendulum oscillating in front of a graduated arc, the angle described 
by the pendulum being the measure of the time. 
In the Le Boulenge instrument, however, the weight falls freely , and 
without any disturbing influence, in a vertical direction, and the distance 
actually described by it is measured; the corresponding time being readily 
ascertained, and the velocity calculated. 
By means of a scale previously prepared, the velocity of the projectile can 
at once be read off without any calculation—-an advantage which this instru¬ 
ment possesses over all others. 
Every part of the chronograph is of metal, and it is consequently little 
influenced by changes of climate—a property which renders it peculiarly 
suitable for use in a country like India, where vulcanite and other insulating 
materials rapidly deteriorate. 
1. The Instrument. 
The Le Boulenge chronograph has been invented for two distinct purposes 
—viz., (1) for taking the velocity of projectiles, (£) for measuring any short 
intervals of time. 
The instrument is set up, when used for taking velocities, as in Plate I., 
Pig. 1. 
It consists of a hollow brass column, S, which supports two electro-magnets, 
A, B, and a small bracket, K. The column stands on a triangular base, upon 
which is fixed the “ triggerf T. (Fig. 7, Plate II.) 
The electro-magnet, A , supports a long cylindrical rod, C (Plate I., Pig. 1), 
suspended vertically and called the “ chronometer.” This rod is partially 
covered with two zinc tubes, D, E, called rr registers.” 
The electro-magnet, B, sustains a shorter rod, F (Plate I., Fig. 1), named 
the “ registrar.” 
The (c trigger,” (Plate II., Fig. 7) consists of a circular steel knife, G, fixed 
in a recess of the spring, II, by means of the screw, N, which forms an axle 
upon which it can be turned so as to bring a fresh portion of the edge 
opposite the chronometer. 
The spring, H, can be “ cocked,” or restrained, by means of the catch on 
one end of the lever, I. 
* The following description is re-written up to date from a paper published by the War Office, in 
1870, under the following title:—“Description and Use of Le Boulenge’s Chronograph. Translated 
from a Memoir by the Inventor, Captain-Commandant P. Le Boulenge, of the Belgian Artillery, 
with some additional Explanations, and the Results of Experiments made at Waltham Abbey in 
comparison with the Navez-Leurs’Instrument, by Lieut, C. Jones, R.A., Instructor Royal Gun 
Factories.” 
