Improvements in Chronographic Apparatus for Determining the Velocity of Projectiles or for similar purposes.
Year: 1897

page_text: Date of Application, 3rd Nov., 1897
Complete Specification Left, 13th Jan., 1898--Accepted, 19th Feb.,
1898
Improvements in Chronographic Apparatus for Determining the
Velocity of Projectiles or for similar purposes.
I, FREDERICK JOHN JERVIS-SMITH, of 28, Norham Gardens, Oxford, Clerk in
Holy Orders and Millard Lecturer in Mechanics, Trinity College, Oxford,
M.A., F.R.S., do hereby declare the nature of this invention to be as follows:
In the well known methods of determining the velocity of projectiles by firing
through wire screens, when the projectile cuts the first wire screen, its path may
be affected by contact with the wire, and when the projectile is light its path
may be considerably changed in direction as is the case in shot used in sporting
guns. To obviate this source of error, I use screens of paper, ordinary brown
paper stretched on frames, answers well. To this paper, usually on the side
furthest from the gun 1 attach a Branly detector furnished with conducting wires,
which are connected to the chronograph. The Branly detector consists of a
small tube, such as a piece of goose quill, furnished with conducting plugs at
either end, the space between the plugs being partly filled with metalic filings.
The detector becomes a good conductor of electricity when acted on by an electrical
discharge from an induction coil, or electrophorus, but when the detector is shaken,
as it is by the paper screen it ceases to act as a conductor, and the current is
broken, if the detector be attached to the sheet of paper so as to be out of the line
of fire of the gun, it may be easily reset, that is again made to conduct, by electri-
fying it, through the wire by which it is connected to the chronograph. The screen
is then ready for another experiment. I do not tie myself down to use screens only
made of paper, I also for the same purpose, use a flexible disc or tympan made
of paper or parchment or mica or suitable substance attached to the end of a
short cylinder or frustrum of a cone, to the centre of the disc or tympan I attach
a Branly detector with wires leading from it to the chronograph. I place the
axis of the cylinder or frustum of the cone at right angles to the line of fire of the
gun, the cylinder or frustum of the cone being placed near the line of flight of
the shot. As soon as the wave of air due to the moving shot impinges on the
disc or tympan the circuit is broken and the usual record is made by the chrono-
graph. The detector is reset in the same manner as when attached to the screens
and disc apparatus
before mentioned. In the manipulation of the
mentioned, on a gun range, and also in those circumstances in which a gun is
fired by electricity, or by compressed air, a certain amount of danger arises, due
to the fact that the gun may be accidentally fired from the chronograph room, or
In order
by the person in charge of firing guns by electricity or compressed air.
to guard against this source of danger, I place in the circuit of the firing wire
a safety lock and key, constructed thus. In a small box, similar to a door lock,
I fix two flat insulated springs, about one inch apart, each spring is attached to
the firing wire of the gun, the springs can only be connected together by the
introduction, through the key hole, and rotation of the key, furnished with a trans-
verse conducting end. The key is attached to the person in charge of the gun and
screens

page_text: screens on the gun range, by means of a chain or cord, the safety lock is placed
behind the gun. In order that the gun may be fired from the chronograph, the
man in charge of the gun, must be standing close to the safety lock with the key
inserted in it and rotated, it is thus impossible for the man at the gun range to be
in front of the gun when fired by the chronograph. When compressed air is used
to fire the gun, the key acts upon a valve or stop-cock enclosed in a box, so that
air can only pass to the gun when the key is inserted and rotated as in the case of
electric firing.
Instead of a rotated key, a suitable plug may be used, attached to the man who
has charge of the gun and the screens, the box in which the springs are fixed
(or in case of pneumatic firing, the valve,) is locked or sealed to prevent the springs
or valve being tampered with. The wire from the chronograph leading to the
safety lock is lead in through casing or a tube to ensure its protection.
Dated this 2nd day of November 1897.
. Improvements in Chronographic Apparatus for Determining the
Velocity of Projectiles or for similar purposes.
I, FREDERICK JOHN JERVIS-SMITH, of 28, Norham Gardens, Oxford, Clerk in
Holy Orders and Millard Lecturer in Mechanics, Trinity College, Oxford,
M.A., F.R.S., do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement: -
I will describe my invention with the aid of the accompanying drawings.
In the well known methods of finding the velocity of projectiles and shot from
sporting guns by firing through wire screens, when the shot or projectile cuts
through the first wire screen, if the shot be light its path may be considerably
changed in direction, this is especially the case in shot from sporting guns. To
obviate this source of error, I use a screen a of paper as represented at Fig. 1, thin
brown paper answers well stretched from its four corners a', a', a', a' by means of
cords attached to a frame a² a² a² a² the lower ends of which are driven into the
ground of the range. To this stretched sheet I attach by cement, a Branly
detector a furnished with conducting wires at, at which go to the electromagnetic
styli of a chronograph.
The Branly detector consists of a small tube, such as a goose quill, furnished
with conducting plugs at either end, the space between the plugs being partly
filled with metal filings such as filings of copper. The detector becomes an
excellent conductor of electricity when acted on by an electrical discharge from
an induction coil or an ordinary electrophorus, but when the detector is shaken as
it is by the impact of the shot on the paper screen, it ceases to conduct and the
circuit is broken, and a mark made by a chronograph stylus on a suitable moving
surface, it is preferable to attach the detector a³ to one side of the sheet of stretched
paper so that it is out of the line of fire of the gun, after being shaken it is restored
to its state of conductivity by being electrified through the wire which connects it
to the chronograph, it is then ready for another experiment. I find that an
ordinary electrical gas lighter produces sufficient electricity to reset the detector
with.
I also use another form of apparatus for the same purpose, and in this case I
cause the compressed air wave which accompanies a projectile to affect a Branly
or bad contact detector 6¹ attached to a flexible disc or tympan b, b (see Figures 2

page_text: to 5). The flexible disc b, b is attached to the end of a frustum of a cone 62 62 see
Figures 2 and 3 or to a cylinder 63 63, see Figures 4 and 5, the wires 64, 6 lead from
the Branly or bad contact detector 61 to the chronograph. A battery usually of
two Daniel cells of large dimensions, known as the tray form of Lord Kelvin, is
used in each case in the circuit of which the detector forms a part. The axis 65 b¹
of the cone b² Figures 2 and 3 or cylinder 3 Figures 4 and 5 is placed at right
angles to the path of the shot, and as close to it as convenient. I find out its
correct position thus, I fire a shot from the rifle which is fixed in a rest, through
two sheets of paper fixed at two screen distances along the gun range, I then bring
the ends of the frustum of the cone to within about six inches of the hole, it is
then readily affected by the compressed air wave due to the bullet from the rifle.
It is not absolutely necessary that the Branly detector should be attached to
the tympan as described, since the air wave will shake it when used apart from the
tympan, but the exact position of the detector can be readily determined on the
range, when attached to a cylinder or part of a cone as set forth.
As soon as the wave of air due to the moving shot causes the Branly or bad
contact detector to be shaken, the circuit is broken and the usual record is made
by the chronograph. The detector is reset in the same manner as when attached to
the first mentioned screens.
In the manipulation of the screens and apparatus mentioned on a gun range,
and when a gun or guns are fired by electricity or by compressed air, a certain
risk arises, due to the fact that the gun may be accidentally fired by a person
in charge of the chronograph or firing key, whether it be electrical or pneumatic.
To guard against this source of danger I place in the firing cireuit à safety lock,
see Figures 6 and 7 in which d', d, d, d' is a box seen from behind in Fig. 6 so
as to shew the interior and fixed on wall see Fig. 7. d², d2 are two flat insulated
springs which are connected to the wires d³, 13. These wires are led in through
the casing or a tube to insure their protection. d is a keyhole through which the
metal key d can be passed, and rotated, when it is rotated it connects and de
so that the circuit is completed through it; the key is attached to the man in
charge of the gun on the gun range by means of a chain or cord d, thus the circuit
cannot be closed unless the man has the key in the lock and rotates
is retained
it. I place the safety lock behind the gun so
a place of safety when
the chronograph is closed
and ready to fire the gun. Instead of this form of key a plug may be used also
attached to the man in charge of the gun, but the form of key described is
preferable as it is more guarded against being tampered with.
in
the circuit to
that the
man
When compressed air is used for firing a gun I replace the springs by a valve
shown in section and elevation respectively at Figures 8 and 9. c is a valve such
as a stop-cock, enclosed in a box e², e², e², e².
This valve can only be rotated by the introduction of the key e³ into the hole e
and the rotation of said key in connection with the valve; as in the former case
the key is attached to the man in charge of the range by a chain e, the tubes e, e6
lead to the gun and to the compressed air firing valve: the box is fixed to the
wall e7.
In each instrument the key is rotated through 90° to complete the circuit.
I would here remark that other forms of safety lock or valve and methods of
operating same may be employed so long as the key or the like is attached to the
man in charge.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is:-
1. The application of a Branly detector to a screen used on a gun range for
finding the velocity of projectiles and shot, substantially as herein set forth.
2. A method of breaking an electrical circuit by using the impact of an air
wave from a moving shot, on a Branly detector in close vicinity to the path of the

page_text: shot and not attached to any tympan or material surface, substantially as herein
set forth.
3. A method of breaking an electrical circuit by using the impact of an air
wave from a moving shot, on a tympan or material surface to which a Branly
detector is attached and placed in the electrical circuit, substantially as herein
set forth.
4. A safety lock by which the circuit between a gun and the firing contact is
closed by a key or the like attached to the person in charge of a gun only when the
said person is in a place of safety, substantially as herein set forth.
5. A safety pneumatic valve placed in the circuit of an air tube, by means of
which the gun is fired, which can only be opened when operated on by a key or
the like attached to the person in charge of a gun when he is in a position of
safety, substantially as herein set forth.
6. The improvements in chronographic apparatus for determining the velocity
of projectiles or for similar purposes, substantially as herein set forth and as
illustrated in the accompanying drawings.
·
HARRIS & MILLS,
23, Southampton Buildings, London, W.C., Agents.
HARRIS & MILLS,
23, Southampton Buildings; London, W.C., Agents.