Improvements in Apparatus for Measuring Short Intervals of Time, Especially Applicable for Timing the Exposure of Sensitive Surfaces used in Photography.
Year: 1890

page_text: Date of Application, 29th July, 1890
Complete Specification Left, 29th Apr., 1391-Accepted, 18th July, 1891
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Measuring Short Intervals of Time,
Especially Applicable for Timing the Exposure of Sensitive
Surfaces used in Photography.
I, WILLIAM EDWARD GIBB, of Pyrgo Park, in the County of Essex, Gentleman,
do hereby declare the nature of this invention to be as follows:-
My invention has for its object a device by which short intervals of time can be
easily and accurately measured, as for instance where a photographic plate has to
be exposed for a very few seconds.
The improved apparatus consists of a small case of any suitable shape, but
preferably circular so as to somewhat resemble that of a watch. Upon one side of
this case in a suitable position I arrange a dial, the rim of which is divided into
spaces representing a certain number of seconds, each of which is further subdivided
into fifths or other desired fractions of a second. The dial is provided with a hand
or needle carried upon a central spindle, which is made to make a sufficient part of
a revolution when required by means of a spring contained in the case.
At the
other end of the spindle at the back of the case is a knob or handle by which
it can be turned round so as to wind up the spring and adjust the index hand to
any desired point.
I also provide an external knob or button by pushing which the spindle is
released and the spring then brings the index hand back to its original position.
In order that the hand may so return to its position at exactly the requisite speed,
so that its point passes between each two divisions of the dial in exactly one second,
I connect a train of toothed wheels and pinions to the main index spindle described
and upon the spindle of the last of such pinions I fix a toothed escapement wheel
the teeth of which act upon an escapement of the usual form which accordingly is
made to oscillate rapidly backward and forward as the wheel revolves. The axis
of the escapement also carries an arm provided at its outer end with a small hammer
which as it oscillates strikes a small bell or device so that when the apparatus is in
motion it is audible.
By carefully adjusting the escapement and the oscillating hammer, the speed of
the index hand can be readily so adjusted that it passes over each division on the
dial in exactly one second. A toothed wheel or pinion is fixed upon a spindle which
is made to revolve rapidly, when the spring is in action and an arm presses
against the teeth of the pinion or wheel so as to act as a brake against it and
prevent the index hand and the train of wheels from revolving by the action of the
spring until the arm is withdrawn.
In order to ensure the continuance of the movement of the index hand if the
pressure upon the knob should be removed, I use the following arrangement.
I make the knob press upon the end of a lever the other end of which carries the
bar which acting as a brake upon the toothed pinion or wheel already described,
prevents the train of wheels from revolving until the knob is pressed. I also
arrange a spring hook which when the lever is pressed as just described engages
with its end and prevents it from returning when the pressure of the knob is with-
drawn, and so stopping the wheels.
Upon the axle of the index hand I arrange a projecting piece or cam which raises
the hook and releases the lever, such releaše taking place at the instant when the
hand has reached the point marked zero.
The action of the apparatus is as follows:-The index hand is first turned, round
until it points to the number of seconds and fractions of seconds for, which the
exposure of a photographic plate is desired. At the moment when the exposure

page_text: commences the small knob is pressed, and the spring hook is released withdrawing
the brake arm, and the wheels and index are set in motion the bell or other device
sounding and the index hand moving until the zero point is reached, when the cam
upon the index spindle has released the spring hook, and allowed the brake arm
again to come into contact with and stop the wheels and index hand, the lens of the
camera being at the same moment closed. A fixed stop is also arranged which
prevents the index hand being moved back beyond the zero point.
It is evident that the device by which the train of wheels is released and the
index hand is allowed to travel back at the proper speed to the zero point may be
varied more or less as may be found convenient.
Any desired number of smaller dials may be provided upon the face of the
instrument each dial having an index or pointer which can be moved round by hand.
These dials are numbered separately and their edges are graduated to represent
seconds and fractions of seconds. Each dial corresponds with one of the photo-
graphic plates which has been exposed, and its index is turned round to the point
shewing the exact time of such exposure.
The face of the instrument with the dials may be closed by a glass in a hinged
frame.
My improved apparatus may be used for other purposes where it is desired to
measure accurately pre-determined short intervals of tiine.
.
Dated this 29th day of July 1890.
EDWARDS & Co.,
35, Southampton Buildings, Chancery Lane, London,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Apparatus for Measuring Short Intervals of Time,
Especially Applicable for Timing the Exposure of Sensitive
Surfaces used in Photography.
I, WILLIAM EDWARD GIBB, of Pyrgo Park, in the County of Essex, Gentleman,
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, and accompanying drawing, that is to say:-
My invention relates to improvements in devices for measuring short intervals
of time, as for instance where a photographic sensitive surface has to be exposed to
light for a very few seconds, and the objects of my improvements are first, to
provide means whereby an index hand can be readily set to the required period of
time which is to be measured, second, to enable the measuring device to be set in
motion at the instant required, third, to produce an audible sound during the period
of time which is to be measured, and fourth, to cause the index hand to stop directly
the desired period of time which is to be measured has elapsed.
I effect these objects by the mechanism illustrated in the accompanying drawing,
in which
Figure 1 is a view from the back with the back plate removed,
Figure 2 is a view from the back with the back plate in place,
Figure 3 is a front view and
Figure 4 is a view from the left hand, and Figure 5 a view from the right hand.
Similar letters refer to similar parts in the several figures.
a is a cylindrical case, of metal or other suitable material, and having at its
front a dial divided into spaces representing a certain number of seconds, which
again are further subdivided into fifths or other fractions of a second. The dial b
is provided with a hand or index c, carried upon a spindle d which turns in holes in
the parallel plates e, f, which form a frame and are held together by stays g. 9. g.
The spindle d is made to make a sufficient part of a single revolution when required,
by means of the coiled spring h. At the other end of the spindle d, at the back

page_text: of the case, is fixed a knob or handle by which the spindle can be turned so as to
wind up the spring and adjust the index hand c to any desired point, the spring
being prevented from uncoiling by a ratchet-wheel and pawl in the usual way.
I also provide a knob or button by pressing which the spindle d is released,
in the manner hereinafter described, and the index hand allowed to return to its
normal position.
In order that the hand e may so return at exactly the requisite speed, so that its
point passes between two of the principal divisions on the dial in exactly one
second, I connect a train of toothed wheels m, m³, m², and pinions n, n¹, n², to
the main index spindle d, and upon the spindle of the last pinion n², 1 fix a
toothed escapement wheel the teeth of which act upon an escapement of the
usual form, which is accordingly made to oscillate rapidly backward and forward
as the wheel o revolves. The spindle of the escapement also carries an arm
provided at its end with a small haminer s, which as it oscillates strikes a
bell or other sounding device so that when the apparatus is in action the sound
is audible.
By carefully adjusting the escapement p and the oscillating hammer s, the speed
of the index hand c can be readily adjusted so that it passes over each principal
division of the dial in exactly one second.
n3, is a pinion which is also driven by the toothed wheel m2, and its spindle
carries the toothed wheel m³ which drives the spindle or cylinder nt, and u is a
wire which when pressed lightly against the teeth of the pinion n', instantly stops
the revolution of the whole train of wheels, but when removed allows them to
revolve freely.
In order to ensure the continuance of the movement of the index hand c if the
pressure upon the knob should be removed, I use the following arrangement, as
shewn in Figure 2.
The inner end of the knob presses upon a lever w turning
upon a centre, the end of the lever at w' pressing upon the lever y which carries
at its other end the wire u, the pressure of which upon the pinion or cylinder n
prevents the index hand c from moving round, as already described, until the
knob is pressed.
is a lever turning upon the centre 1 and having an angular notch at 2 which
is pressed against the angular end of the levery by a spring 3, so as to hold it back
and prevent it from returning when the pressure upon the knob / ceases, and so
stopping the revolution of the index hand c.
с
Upon the spindle d of the index hand c is fixed a projecting pin or cam 4 which
raises the lever and allows the lever y to be forced out by the spring 5, and the
wire u to be pressed against the pinion n', and so stop the further movement of the
index hand c, such stoppage taking place at the moment when the index hand has
returned to the point marked zero (0) upon the dial.
6 is a spring by which the lever to and the knob are returned to their normal
position when pressure upon the latter is removed.
The action of the mechanism described is as follows:-
The index hand c is first turned round by the knob until it points to the
number of seconds and fractions of seconds which are to be measured, for the
exposure of a photographic sensitive surface.
At the moment when the exposure commences, the knob is pressed down, and
the lever presses back the lever y, one end of which removes the wire u from:: the
pinion n whilst its other end is caught and held in the notch 2 in the lever z. The
train of wheels and the index hand c are instantly set in motion by the spring h,
and at the same time the bell t is sounded by the hammers operated by the
escapement t and the escapement wheel o. At the moment when the zero point is
reached by the hand c and the exposure is completed, the projecting pin 4 has
raised the lever z and released the lever y, the wire u coming in contact with the
pinion n stopping the further movement of the index hand and the sound of
the bell t.
In Figure 3 additional dials numbered I to VI, are shewn, each of which is

page_text: provided with an index hand. These index hands have no connection with the
mechanism described, but may be turned round by hand to record the exact time
of exposures of different sensitive plates or surfaces having corresponding numbers
upon them. The case a is provided with a hinged glass front, and with a metallic
back through which the knob or handle i projects.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, 1 declare that what I
claim is :-
1. In a device for measuring short intervals of time the combination of the
dial b, index hand e, spindle d, spring h, knob i, toothed wheels m, m', m²,
pinions n, n', n², escapement wheel o, and escapement p, all substantially as set forth
and shewn.
2. The combination of the dial b, index hand c, spindle d, spring h, knob i,
toothed wheels m, m³, m², pinions n, n', n², escapement wheel, escapement p,
hammer and bell " all substantially as set forth and shewn.
3. In combination with the spring h, toothed wheels m, m³, m², pinions n, n', n²,
escapement wheel o, and escapement p, the toothed wheel m³, pinions n³, n, and
moveable wire u, substantially as set forth and shewn.
4. In combination with the pinion nt, driven by the spring and wheels and
pinions m, m³, m², m³, n, n², n², n³, the wire u, lever y, lever notch 2, lever w,
knob, and projecting pin 4, and springs 3, 5, and 6, all substantially as set forth
..and shewn.
Dated this 20th day of A 1001
EDWARDS & Co.,
35, Southampton Buildings, London, Agents for the Applicant.