e
wire leaves the conductor and almost immediately establishes the
circuit through the next screen, by engaging with a second contact,
the time of the rupture being recorded on the cylinder by the second
marker. The velocity with which the cylinder rotates is such that the
distance between successive clock marks indicating seconds is about 18
in.; hence the marks corresponding with the severance of a thread can
be allotted their value in fractions of seconds with great accuracy.
The times when the shot passes successive screens being thus recorded
on the spiral described by the second marker, and the distance between
each screen being known, the velocity of the shot can be calculated.

Noble.

The chronoscope invented by Sir Andrew Noble is so well adapted to the
measurement of very small intervals of time that it is usually
employed to ascertain the velocity acquired by a shot at different
parts of the bore in moving from a state of rest inside the gun. A
series of "cutting plugs" is screwed into the sides of the gun at
measured intervals, and in each is inserted a loop of wire which forms
part of the primary circuit of an induction coil. On the passage of a
shot this wire is severed by means of a small knife which projects
into the bore and is actuated by the shot as it passes; the circuit
being thus broken, a spark passes between the terminals of the
secondary of the coil. There is a separate coil and circuit for each
plug. The recording arrangement consists of a series of disks, one for
each plug, mounted on one axle and rotating at a high angular
velocity. The edges of these disks are covered with a coating of
lamp-black, and the secondaries of the coils are caused to discharge
against them, so that a minute spot burnt in the lamp-black of each
disk indicates the moment of the cutting of the wire in the
corresponding plug. Hence measurement of the distance between two
successive spots gives the time occupied by the shot in moving over
the portion of the bore between two successive plugs. By the aid of a
vernier, readings are made to thousandths of an inch, and the
peripheral velocity of the disks being 1100 in. a second, the machine
indicates portions of time rather less than one-millionth of a second;
it is, in fact, practically correct to hundred-thousandths of a second
(_Phil. Trans._, 1875, pt. i.).

Le Boulenge.

In the Le