IMPROVEMENTS IN COMPENSATION BALANCES FOR WATCHES AND CHRONO- METERS
Year: 1878

page_text: LETTERS PATENT to Charles Vander Woerd, of Waltham, County of Middlesex,
and State of Massachusetts, United States of America, for the Invention of
"IMPROVEMENTS IN COMPENSATION BALANCES FOR WATCHES AND CHRONO-
METERS."
Sealed the 28th June 1878, and dated the 24th April 1878.
COMPLETE SPECIFICATION filed by the said Charles Vander Woerd at the
Office of the Commissioners of Patents on the 24th April 1878.
CHARLES VANDER WOERD, of Waltham, in the County of Middlesex, and State
of Massachusetts, United States of America. "IMPROVEMENTS IN COMPENSATION
BALANCES FOR WATCHES AND CHRONOMETERS."
The form of compensation hitherto employed in the balances of watches and
chronometers can be made perfect only for two critical temperatures; and for inter-
mediate or extreme temperatures the compensation is more or less imperfect.
Devices called secondary or auxiliary compensation have been applied to remedy
this defect in a partial degree.
The effect of the temperature is to modify the elastic force of the spring as well
as to change its length, and to change the form of the balance, and perfect compen-
sation requires that the time of vibration of the balance shall be constant under all
the vicissitudes of temperature to which the instrument may be subjected. This
requires that an arrangement of the parts shall be made, such that the moment of
inertia of the balance shall inaintain a constant ratio to the moment of the elastic
force of the balance spring.
The law of the change of the effective elastic force of the spring is not certainly
known, but sufficient is known in regard to it to make it certain that the compen-
sation cannot be made perfect except at two temperatures. The expressions for the
variations of these moments in respect to the temperature, give, when graphically
represented, two curved lines, and the adjustment can be made only for the two
points where these curves intersect.

page_text: My Invention consists in the employment of an entirely different arrangement of
bimetallic laminae from that hitherto used in compensation balances, said improved
arrangement being such that the ratio of the moments of the balance and of the
spring shall remain constant during all the temperatures to which the watch or
chronometer may be subjected while in use.
To enable others skilled in the art to make and use my Invention, I will proceed
to describe the same with reference to the accompanying Drawings forming a part of
this Specification, in which,-
Figure 1 is a diagram representing on an enlarged scale the motion of one of the
segments of the rim of a compensation balance under a decrease of temperature,
when the laminae are arranged in parallel connected strips as hitherto.
Figure 2 is a diagram representing the motion of one of the segments when the
laminae are arranged according to my Invention.
Figure 3 represents an enlarged view of the balance complete, constructed in
accordance with my Invention.
In said Drawing, A, A, represent the segments of the rim of a compensation
balance. These segments, instead of being bimetallic throughout their entire length,
that is to say, composed throughout of parallel strips of steel and brass as heretofore,
are bimetallic only a portion of their length, and these bimetallic portions are located
as close as possible to the inner or fixed ends of the segments; i and o represent
said bimetallic portions or laminae, i being the inner portions, which are of steel and
are integral with the segments A, and o being the outer portions, which are of a
composition of higher expansibility than ordinary brass. (I prefer to employ for
said composition equal parts of copper and zinc.)
The parts o and i are arranged in the form of intermeshing teeth, as shown in
Figure 3, the steel segments being grooved or serrated along the portions i to
receive the parts o which are fused solidly to the steel, and the parts o are turned
down or cut away on the perimeter of the balance, so that the fine edges of the
steel teeth separate the parts o into successions of prisms.
The number of teeth in the bimetallic portions will depend upon the thickness of
the segments A, and the length of the bimetallic portions should in general be equal
to about one-sixth of the circumference of the balance.
By this arrangement of bimetallic laminae, the following advantages are
obtained-
:-
First. The action is different from that of continuous or parallel bimetallic
laminae, in that the difficulties arising from the constrained and irregular action of
the parallel laminae are avoided, and that freedom of movement of the compensating
weights, which is necessary to fulfill the actual requirements of the adjustment for
temperature, is provided for.
Secondly. It is always possible to find the number of teeth in the bimetallic part
of the rim, and thus the proper relative proportions between the parts o, i, which,
in connection with the proper compensating weights, will make the motion of these
weights correspond with the requirements of the balance spring for tantochronous
vibrations at different temperatures.
In order to lighten the steel rim and keep the effective weight of the balance as
near the extremities of the segments A as possible, I drill one or more holes / in the
segments, between the bimetallic parts and the compensating weights, so that the
desired effect may be produced by a limited are of two metals. This provides also
for a delicate adjustment of the poise of the balance.
The movement of the compound laminae under a decrease of temperature in the
form of bimetallic compensation hitherto used is shown in Figure 1. The inner
curve represents the rim of the balance at a middle or normal temperature. The
outer curves represent its successive positions at diminished temperatures, and the
oblique lines a, a, b, b, etc., show the motion of the compensating weights placed at
different positions on the rim. The curves described by these weights do not in
any case change the moment of inertia of the balance in the required ratio, and the
compensation is therefore imperfect.

page_text: The motion of the rim of the balance, when constructed in accordance with my
Invention, is shown in Figure 2. The inner curve shows the normal position at a
middle temperature, and the other curves show its motion under successively
diminished temperatures. The curved lines a¹, a', shows the path of the extremity
of the bimetallic arc or portion o, i, and 6', 6', shows the curve described by the
compensating weight at the outer extremity of the segment.
The proper number of teeth in the bimetallic parts to correspond with the
thickness of the continuous steel rim, to be easily found by actual adjustment,
will give to this curve the form which is required in order that the rate of change
of the moment of inertia of the balance shall be always sensibly the same as that of
the moment of the elastic force of the balance spring, so that the compensation may
be made practically perfect. The forms and relation of the curves in the two cases
will be similar when the temperature is increased from the normal temperature
considered.
The rim of the balance is cut very close to the extremities of the arms B to form
the outer ends of the segments A, and the compensating weights W are placed near
the outer ends of the segments.
The holes h are made in order to keep the resultant action as far as possible from
the bimetallic parts of the rim.
I claim as my Invention,―
1st. A compensation balance, in which a highly expansive metal is combined
with steel for the regulation of the compensation, according to the methods herein
stated, and in the form and manner shown and described.
2nd. In a compensation balance, the bimetallic portions or laminae o, i, arranged
in the form of intermeshing teeth at or near the inner ends of the segments A,
substantially as and for the purpose specified.
3rd. In a compensation balance, the segments A, composed of a single metal
excepting at their inner ends, where they are provided with the more highly expan-
sible portions o, arranged as shown and described.
4th. A compensation balance. having steel segments A which are serrated at
their inner ends, and provided between the serrations with a more highly ex-
pansive metal fused to the steel and arranged in a series of prisms, as set forth.
In witness whereof, I, the said Charles Vander Woerd, have hereunto set my
hand and seal, at Boston, Massachusetts, United States of America, this 12th
day of April, A.D. 1878.
Witnesses,
GEORGE WILLIS PIERCE.
CHARLES FREEMAN BROWN.
CHARLES VANDER WOERD. (LS.)