Improvements in Apparatus for Measuring the Velocity of Sound and the Speed of Projectiles.
Year: 1898

page_text: Date of Application, 15th Nov., 1898
Complete Specification Left, 18th July, 1899-Accepted, 23rd Sept.,
1899
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Measuring the Velocity of Sound and
the Speed of Projectiles.
I, Professor Dr. WALTHER WOLFF, of No. 188 Uhlandstrasse, Charlottenburg,
near Berlin, in the Empire of Germany, Physician, do hereby declare the nature
of this invention to bo as follows:-
-
This invention relates to an instrument for measuring the velocity of a sound
wave more especially the velocity of travel of a single shock or concussion of air
such as is caused by the report of a firearm or other explosions.
The invention consists in a hollow box or receptacle closed on all sides and
provided with a hole in its cover or in one of its sides which is closed by a rigid
lid held down by a spring and causing the interruption of an electrical current,
when it is slightly raised by the action of the sound wave.
The box is preferably made of wood and closed at the top by a cover, which for
the sake of investigating the interior can be hinged to the edge of said box and
secured by a lock. In the middle of said lid or cover a hole is cut by which the
interior of the box communicates with the atmosphere. This opening however is
closed from below by a lid, provided with an arm rigidly fixed to it. By means
of this arm the lid is hinged loosely to a metal block which in its turn is screwed
or otherwise secured to the underside of the cover.
Thus the lid would have a tendency to open merely in consequence of the effect
of gravity and in order to prevent this, a spring is secured to the block and
presses with its free end onto the inner extremity of the arm thus holding the lid
closed under ordinary circumstances.
The said lid is so constructed as to slightly overlap the opening on all sides.
Opposite the arm a second arm is firmly secured to the lid which carries a
contact-screw provided with a platina tip and opposite said arm a second metal
block 18 secured to the cover of the box and is provided with a corresponding
platina contact plate.
Two binding posts are electrically connected with the two metal blocks and also
connected with any suitable source of electricity.
At the bottom, the box is provided with a partition which encloses a condenser
of any suitable type the ferminals of which are likewise connected to the
blocks.
The operation of my apparatus when used for measuring the velocity of sound
produced for example by the report of a fire arm is as follows:
Two instruments of the kind herein described are arranged and connected to an
electric battery and an electrically controlled chronograph of any suitable known
kind, preferably of the kind known under the name of le Boulangé chronograph.
The pair of my hereindescribed indicators are placed as nearly as possible in
the direction in which the sound wave or the concussion of air caused by the
explosion travels and the distance between them is measured.
The binding posts are connected by wires with the source of electricity and

page_text: with the chronograph which is arranged to mark any interruption of the current
and to measure the time that elapses between two interruptions.
The contact screw is then adjusted so as to ensure a good contact without lifting
the lid appreciably off the surface of the cover.
When the explosion takes place a wave of compressed air travels over the
two instruments and as it passes them, slightly lifts the lid and with it the contact
screw off its seat and thereby causes a short interruption of the current. The
two interruptions caused thus by the wave passing over the two instruments
give a measure of the velocity of the wave because the distance between the two
instruments is known and likewise the time which has elapsed between the two
interruptions.
If means are provided for causing the interruption of the current simultaneously
with the firing of the explosion, such as for instance if the projectile were made
to cut a wire conducting a current or the like, it will be sufficient to provide
only one of my instruments and this way of proceeding is even preferred because
it is thus easier to make sure that the line connecting the point at which the first
interruption is formed with the point at which the second interruption is formed
coincides with the direction in which the sound wave travels.
Since the projectiles of modern firearms travel faster than sound and produce
a local wave of compressed air this apparatus is also adapted to measure the speed
of projectiles and it is also adapted to investigate, certain qualities of explosives
because I have found that the speed at which a sound wave caused by an
explosion travels will vary appreciably with certain industrially important
qualities of the explosive employed.
The use of the condenser is not absolutely essential but it is well known that
the application of a condenser will greatly diminish sparking at the point of
interruption and the consequence will be that the interruptions become much
shorter and thereby the measurements more exact.
11
1
זו.
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
Improvements in Apparatus for Measuring the Velocity of Sound and
the Speed of Projectiles.
I, Professor Dr. WALTHER WOLFF, of No. 188 Uhlandstrasse, Charlottenburg,
near Berlin, in the Empire of Germany, Physician, 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:-
This invention relates to an instrument for measuring the velocity of a sound
wave more especially the velocity of travel of a single shock or concussion of air
such as is caused by the report of a firearm or by other explosions.
The invention consists in a hollow box or receptacle closed on all sides and
provided with a hole in its cover or in one of its sides which is closed by a rigid
lid held down by a spring and causing the interruption of an electrical current,
when it is slightly raised by the action of the sound wave.
Of the accompanying drawings:
Figure 1 is a vertical section through my improved apparatus taken on
line -d of Figure 2.

page_text: Figure 3 is a diagram showing my improved apparatus in connection.
The same letters of reference are used to indicate the same parts in the several
figures:
K is a box preferably made of wood and closed at the top by a cover D, which
for the sake of investigating the interior can be hinged to the edge of said box
and secured by a lock. In the middle of said lid or cover D a hole L is cut by
which the interior of the box k communicates with the atmosphere. This
opening L however is closed from below by a lid P, provided with an arm B
rigidly fixed to it. By means of this arm B the lid P is hinged loosely to the metal
block A which in its turn is screwed or otherwise secured to the underside of
the cover D.
Thus the lid would have a tendency to open merely in consequence of the effect
of gravity and in order to prevent this a spring F is secured to the block A and
presses with its free end on to the inner extremity of the arm B thus holding the
lid P closed under ordinary circumstances.
The said lid P is so constructed as to slightly overlap the opening L on all
sides.
-
Opposite the arm B a second arm Ę is firmly secured to the lid P which carries
a contact-screw S provided with a platina tip and opposite said arm a second
metal block C is secured to the cover of the box D and is provided with a
corresponding platina contact plate.
Two binding posts Kl + and Kl are electrically connected with the two metal
blocks A and C as indicated by dotted lines and also are supposed to be con-
nected with any suitable source of electricity such as the battery I, Figure 3.
At the bottom the box K is provided with a partition which encloses a con-
denser G of any suitable type the terminals of which are likewise connected to
the blocks A and C.
The operation of my apparatus is illustrated by the diagram Figure 3.
H (Figure 3) is a gun or firearm of any kind, or any other arrangement for
causing explosions; K, and K, are two instruments of the kind herein described I is
an electric battery and M is an electrically controlled chronograph of any
suitable known kind, preferably of the kind known under the name of le Boulengé
chronograph.
The pair of my herein described indicators are placed as nearly as possible
in the direction in which the sound wave or the concussion of air caused by the
explosion travels and the distance between them is measured.
The binding posts are connected by wires with the source of electricity I
and with the chronograph M, which is arranged to mark any interruption of the
current and to measure the time that elapses between two interruptions.
The contact screw S is then adjusted so as to ensure a good contact without
lifting the lid P appreciably off the surface of the cover D.
When the explosion takes place a wave of compressed air travels over the two
instruments and as it passes them, slightly lifts the lid P and with it the contact
screw S off its seat and thereby causes a short interruption of the current. The two
interruptions caused thus by the wave passing over the two instruments give a
measure of velocity of the wave because the distance between the two instru-
ments is known and likewise the time which has elapsed between the two
interruptions.
If means are provided for causing the interruption of the current simultaneously
with the firing of the explosion, such as for instance if the projectile were made
to cut a wire conducting a current or the like, it will be sufficient to provide only
one of my instruments and this way of proceeding is even preferred because it is
thus easier to make sure that the line connecting the point at which the first
interruption is formed with the point at which the second interruption is formed
coincides with the direction in which the sound wave travols.
Since the projectiles of modern firearms travel faster than sound and produce
a local wave of compressed air this apparatus is also adapted to measure the

page_text: speed of projectiles and it is also adapted to investigate certain qualities of
explosives because I have found that the speed at which a sound wave caused
by an explosion travels will vary appreciably with certain industrially important
qualtities of the explosive employed.
The use of the condenser G shown on the drawing is not absolutely essential
but it is well known that the application of a condenser will greatly diminish
sparking at the point of interruption, and the cousequence will be that the
interruptions become much shorter and thereby the measurements more exact
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:-
1. The combination with a suitable source of electricity, and an electrically
controlled chronograph of any suitable type, of two boxes placed 'at a measured
distance in the direction in which a sound wave travels, said boxes being provided
with openings closed by a rigid lid hinged at one side and forming an electrical
contact at the opposite side and being held down on to said opening by means of
a spring, and of suitable electrical connections substantially as and for the purpose
set forth.
2. The combination with a suitable source of electric current, means for breaking
said current at the moment of an explosion, and a suitable electrically controlled
chronograph; of a box placed at a measured distance from the source of said
explosion and being provided with an opening closed by a rigid lid hinged to
the wall of said box at one side and forming an electrical contact at the opposite
side, said lid being held down upon said opening by means of a spring, sub-
stantially as and for the purpose set forth.
3. The combination with a box having an opening communicating with the
atmosphere, said opening being closed by a rigid lid hinged to the wall of said
box al one side and forming an electrical contact at the opposite side, of a
condenser connected electrically in parallel with said lid, substantially as and for
the purpose set forth.
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IN A TO
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.