THE ROYAL ARTILLERY INSTITUTION. 
13 
these machines proved successful. It was found almost impossible to 
give a uniform motion of rotation, and they were not able to measure 
with greater accuracy than to about the of a second. Thus we might 
possibly commit an error of a second, which, with a ball at a velocity 
of 1400 feet per second, would amount to almost 50 feet. Gregory 
professed to measure to the ijv part of a second, but even that admitted of 
too great an error. 
5. About 1760, General D’Antoni, of the Sardinian army, estimated 
the velocity of projectiles by firing them into a homogeneous butt of known 
consistency. Its consistence was determined by the use of a standard 
gun, whose velocity had been ascertained by other means, and whose 
penetrations into the butt with a given charge ought always to be the 
same. The gun was placed near the butt, and several shots were fired to 
obtain a mean, taking care to fire each shot into a fresh part of the butt. 
Thus, suppose the consistence of the butt to have been determined equal to 
96,000, then _ 
j 96000 x x 
in which 
V = velocity required. 
x — mean penetrations in feet, 
d — diameter of ball in feet. 
Experiments made by this method gave the following velocities. 
Table III. 
SHOWING THE VELOCITY OE SHOT DETERMINED BY EIRING INTO A. BUTT 
OE KNOWN CONSISTENCY. 
Nature of gun. 
Weight of 
projectile. 
Charge. 
Velocity. 
Remarks. 
lbs. 
lbs. 
32-pr... 
32 
12 
1349 
Common cannon powder used. 
16-pr, .................. 
16 
6 
1433 
Mean atmosphere. 
8-pr.... 
8 
4 
1530 
4-pr... 
4 
2 
1510 
6. In addition to those already mentioned, it appears that in 1764 
Lieut. De Butet, of the Italian service, invented the following machine 
for determining initial velocity. He applied a little plate of metal, pro¬ 
vided with a moveable index, to any wheel that turns with a regular 
constant motion and sufficient velocity. The index is held at some distance 
from the circumference of the wheel by a thread that is stretched across the 
mouth of the gun. When the gun is fired, the shot breaks the thread and 
sets a spring at liberty, which instantly presses the index against the wheel, 
upon which it describes an arc, until it is checked by the impact of the 
shot against a moveable butt, placed at the distance of a few feet. Eor this 
