366 
VELOCITY AND PRESSURE INSTRUMENTS. 
Instruments. 
12-pr. 
Henry Rifle. 
Difference 'between 
the mean velocities 
given by each 
instrument. 
Mean 
velocity at 
105 ft. 
Mean 
difference 
of velocity. 
Mean 
velocity at 
105 ft. 
Mean 
difference 
of velocity. 
12-pr. 
Henry 
Rifle. 
Navez-Leurs. 
1004-9 
8-88 
1259-3 
6-11 
■) 
[■ 4-0 
2-2 
Le Boulenge. 
1000-9 
8-69 
1261-5 
6-12 
5 
From the above calculation it appears that the mean differences of velocity 
as shown by each instrument (for similar descriptions of powder) are practi¬ 
cally equal, though the mean velocity given by the Navez-Leurs instrument 
is in one case greater and in the other case less than that obtained by the 
Le Boulenge chronograph. 
This variation at different parts of the scale is no doubt due to a slight 
error in the constant used in the preparation of the tables for one of the 
instruments; and the fact that the Navez-Leurs instrument had been in con¬ 
stant use for some years without any re-adjustment, is amply sufficient to 
account for so small a discrepancy in a velocity of nearly 1300 ft. a second. 
The accordance between the mean differences of velocity is most remark¬ 
able, when we consider that the mechanical construction of the two instruments 
is totally dissimilar ; it proves that they are equally accurate in their working, 
while, at the same time, it justifies the assumption that their results are both 
trustworthy. 
The object of the above experiment was to test the reliability of the 
Le Boulenge instrument with a view to its general adoption for the proof 
of powder, for which purpose it is peculiarly adapted, as, by means of the 
velocity scale, it can be very readily and rapidly worked, and its construction 
is so simple that it appears little liable to get out of order. 
Since the date of the above comparative trial, the Le Boulenge chrono¬ 
graph has been adopted for general use in ballistic experiments, and more 
especially for the proof of gunpowder, both at home and in India. These 
instruments have also been set up by all the leading manufacturers of 
powder, as, without some such means of testing their powder during manu¬ 
facture, they find it difficult to produce the high quality now required for 
our accurately-shooting rifled guns. 
In proof of powder, and other experiments at the E.G.F. Proof Butts, 
it is customary to use two instruments for measuring the velocity of 
each shot. They are set up side by side, and by using a double set of 
screens and currents two perfectly distinct records of the velocity of each 
shot are obtained. This arrangement is most useful in furnishing con¬ 
firmatory evidence of the accuracy of the results given by each instrument. A 
table is subjoined—taken at random from some of the Committee's experiments 
with field gunpowders—wdiich exhibits the accordance of the two instruments 
used at the Proof Butt, when in good order and on a favourable day. 
Date of firing, 24th April, 1875. 25-pr. E.M.L. gun, Expl. No. 398. 
Object of experiment, to test the result of firing different charges from a 
rear and from a forward vent. 
