378 
ME. F. A. ABEL’S CONTRIBUTIONS TO 
are covered with white paper coated with lamp-black, are fixed upon one. common shaft, 
which is driven at high speed by means of a falling weight, continually wound up, and 
a series of very accurately constructed multiplying-wheels. The speed usually attained 
by these disks (the precise rate of which is ascertained by means of a stop-clock) is about 
1000 inches per second linear velocity at their circumference; so that 1 inch of the 
latter, travelling at that rate, represents the one-thousandth part of a second ; and as, 
in reading off the records obtained, 1 inch is divided into a thousand parts by the vernier 
used, a linear representation is thus obtained of intervals of time as minute as the one- 
millionth part of a second. The uniformity of rotation of the disks during the duration 
of an experiment is ascertained by a series of observations of the speed, by means of 
the stop-clock. Each revolving disk is brought into connexion with one of the secondary 
wires of an induction-coil, and the other wire is attached to an insulated discharger, fixed 
opposite the edge of its corresponding disk, and adjusted so that its point is just clear 
of the latter. If, therefore, the primary circuit of any one of the induction-coils is 
interrupted (e. g. by suddenly severing the conducting-wire) the induced current must 
leap across, at that instant, from the discharger to the circumference of the disk, and 
will produce a small but distinct white spot on the blackened paper. As all the disks 
revolve with the same velocity, it is obvious that if the primary circuits of their 
respective coils be simultaneously interrupted, the spots produced by the discharge of 
the secondary currents on all the disks will be in a straight line, but that, if they be 
successively interrupted, the spots on the several disks will form a curve, varying in 
character with the intervals of time which have elapsed between the successive develop- 
ment of the respective secondary currents. In using this chronoscope to measure the 
rate of progression of a projectile in a gun’s bore, the shot is made to sever the primary 
wires of the coils which it passes in succession, by ineans of cutters which slightly project 
in the bore, and which it therefore brings to bear upon the wires as it passes over them. 
In applying the instrument to the measurement of the speed of detonation in open air, 
or of the rate of its transmission through tubes, the only difference in the modus ojpe- 
rcmdi consisted in the manner of effecting the rupture of the primary wires. * 
The disks of gun-cotton used in the experiments for determining the rate at which 
detonation is propagated in open air were ranged in a row or train upon the ground 
(or, rather, upon the level surface presented by a support of very thin narrow deal board) ; 
they consisted generally of disks 3 inches in diameter, varying somewhat in thickness 
in different experiments ; they were either ranged in a continuous row, each disk 
touching the one on either side, or with equal spaces intervening between them. At 
the commencement of the row, or train, the wire forming the primary circuit of the 
coil connected with the first chronoscope-disk was tightly stretched across the part 
where detonation was to be first established. To facilitate the sudden severance of the 
circuit by the explosion, this part was composed of a fine copper wire, insulated by 
means of a silk covering, which was held in close contact with the gun-cotton surface, 
across which it was stretched by being fastened round the insulated heads of two hook- 
