66 Modern Cannon Powder. | January, 
1. The determination of the time taken by a projectile in 
traversing various intervals within the bore of the gun, 
which was effected by means of a chronoscope invented by 
Capt. A. Noble, a member of the Committee, and made at 
the Elswick Ordnance Company’s Works. ‘This will be 
described hereafter. 
2. The determination of the pressure direCtly, by means 
of Rodman’s pressure-gauge fitting on the exterior of the 
gun, and communicating with the interior of the bore by 
means of a hollow screw-plug. 
3. The determination of the pressure directly, by means 
of an inner gauge termed a “ crusher,’”’ which was designed 
by the Committee to overcome certain defects inherent in 
the Rodman gauge. 
4. The determination of the velocity of the projectile 
after leaving the gun, by means of Navez-Leur’s or Le Bou- 
leugé’s electro-ballistic apparatus, commonly used for this 
purpose. 
The chronoscope and the method of connecting it with 
the interior of the gun are shown in Plate II. The prin- 
ciple of action consists in registering, by means of electric 
currents, upon a recording surface travelling at a uniform 
and very high. speed, the precise instant at which a shot 
passes certain defined points in the bore. The instrument 
may be divided into two portions; the one consisting of the 
mechanical arrangement for obtaining the necessary speed, 
and keeping that speed uniform; the other forming the 
electrical recording arrangement. 
The first consists of a series of thin metal discs, AA, each 
36 inches in circumference, fixed at intervals upon a hori- 
zontal shaft, s Ss, which is driven at a high speed bya heavy 
weight, B, arranged according to a plan originally proposed 
by Huyghens, through a train of gearing multiplying 625 
times. The driving weight is continually wound up during 
the experiment by means of the handle u, and the requisite 
speed is obtained by accelerating the motion by the handle c. 
The precise rate at which the discs are moving is ascer- 
tained by the stop-clock, D, which can, at pleasure, be 
connected, or disconnected, with the revolving shaft, BE, and 
the time of making any number of revolutions of this shaft 
can be recorded with accuracy to the 1-1oth part of a 
second. 
The speed attained is generally about 1000 inches per 
second linear velocity at the circumference of the revolving 
discs, so that each inch represents the: 1-10o0oth part of a 
second, and, as the inch is subdivided by the vernier, v, into 
