IMPROVEMENTS IN THERMOMETERS
Year: 1881

page_text: LETTERS PATENT to William Bentley Fowle, of the City of Newton, County
of Middlesex, State of Massachusetts, United States of America, for an
Invention of "IMPROVEMENTS IN THERMOMETERS."
PROVISIONAL SPECIFICATION left by the said William Bentley Fowle at
the Office of the Commissioners of Patents on the 29th March 1881.
WILLIAM BENTLEY FOWLE, of the City of Newton, County of Middlesex,
State of Massachusetts, United States of America. "IMPROVEMENTS IN THERMO-
METERS."
"
This Invention relates to that class of instruments known as mechanical thermo-
meters, the manner of construction and operation of which renders practicable,
accurate, and convenient a class of instruments which has hitherto been inaccurate
and unsatisfactory.
To facilitate the description of my Invention, and to show more lucidly and
briefly wherein it attains greater accuracy, durability, and simplicity, I would state
that the important points to be secured in its practical operation are,-
First. A correctly graduated scale or movement of the index hand by which a
change of any stated number of degrees of temperature may be correctly recorded
by the index hand, whether the test be applied in high, low, or mean temperature,
at the same time being correct in its indications in a test from a very high to a
very low temperature, or vice versa.
Second. These instruments being made of various dimensions, the dial plate
being from the size of the tiny watch charm to that of the turret clock, it is
essential that the position of the index hand should point at a given temperature
to precisely the same place on the index dial showing no deflection from the
operation of gravitation on any of its internal parts.
Third. The means of obtaining a perfectly steady action of the index hand, and
at the same time a free action of all the working parts without compromising the
accuracy of the instrument in extreme temperatures, as, for instance, where a hair
spring is used.

page_text: Fourth. In the larger sizes of the instruments by its peculiar construction a
heavy hand may be carried with equal accuracy, while the sensitiveness of its
operation in rapid changes is not materially disturbed.
My Invention is described as follows:-To a metal plate is secured at one end
a strip composed of two metals, brass and steel fused together, which by their
unequal expansion and contraction in changes of temperature are deflected from
their normal position. At the other end of this bi-metallic strip is attached a pin
which plays freely in a groove or slot. This groove or slot is in a part of a rack
which gears with a pinion which is a part of the pivot or shaft that carries the
index hand over the dial plate.
It being found however that when using a single strip or lamina of a bi-metallic
nature a deflection of several degrees of the index hand was produced by the action
of gravitation on the bi-metallic strip in certain positions it became necessary in a
portable instrument to devise some means of correcting this error; this object I
attain by introducing an auxiliary strip precisely like the first suspended at the
opposite end of the metal plate or frame, and connecting it by means of a pin
working in a groove or slot cut in the rack, and at a point opposite and equi
distant from the shaft or pivot of the rack. By this means any tendency of one
bi-metallic strip to become depressed by the action of gravitation is counterpoised
by the weight of its auxiliary strip drawing in an opposite direction. The part of
the rack having thereon the grooves or slots is turned aside from the line of the
brass plate so that the direct action of the metal strip shall be at a right angle
with the grooves. The metallic strips are so placed when adjusting the instrument
that there shall be a slight side draw or tension upon the pivots of the segment,
thus producing an even tension through its action in a wide range of temperature,
and securing in the pivots and connections, by which means there is no uncertainty
in the position of the hand at any given temperature. The outer ends of the
bi-metallic strips are fastened to the metal plate by means of a piece of metal bent
at right angles, and having in its base a slot in which two set screws are placed, so
that by raising them slightly the metal piece bearing the ends of the bi-metallic
strips may be moved back or forth, thus moving the pins playing in grooves or
slots at the other ends of the strips from the centre pivot of the rack, by which
means the instrument can be accurately adjusted. The operation of my.I
Invention
is as follows:-
Any change of temperature causes the bi-metallic strips to deflect by the unequal
action of their component metals. This action is communicated to the rack or
segment through the pins and slot connection, and changed from the reciprocating
to the rotary motion. From the rack or segment the motion is communicated to
the pinion, thence to the index hand, the direct action in its transit to the index
hand being largely multiplied, so that a single turn of the hand will indicate a
change of 120 degrees.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Bentley Fowle in the Great Seal Patent Office on the
22nd September 1881.
WILLIAM BENTLEY FOWLE, of the City of Newton, County of Middlesex,.
State of Massachusetts, United States of America. "IMPROVEMENTS IN THERMO-
METERS."
This Invention relates to that class of instruments known as mechanical thermo-
meters, the manner of construction and operation of which renders practicable,
accurate, and convenient a class of instruments which has hitherto been inaccurate
and unsatisfactory.
To facilitate the description of my Invention, and to shew more lucidly and
briefly wherein it attains greater accuracy, durability, and simplicity, I would state
that the important points to be secured in its practical operation are, first, a
correctly graduated scale or movement of the index hand by which a change of
any stated number of degrees of temperature may be correctly recorded by the
index hand, whether the test be applied in high, low, or mean temperature, at the
same time being correct in its indications in a test from a very high to a very low
temperature, or vice versa; second, these instruments being made of various
dimensions (the dial plate being from the size of a tiny watch charm to that of
a turret clock) it is essential that the position of the index hand should point
at a given temperature to precisely the same place on the index dial, showing no
deflection from the operation of gravitation on any of its internal parts.
Third. The means of obtaining a perfectly steady action of the index hand, and
at the same time a free action of all the working parts without compromising
the accuracy of the instrument in extreme temperatures, as, for instance, where
a hair spring is used.
Fourth. In the larger sizes of the instruments ability to carry a heavy hand
with accuracy, while sensitiveness of operation in rapid changes is not materially
disturbed.
i
These objects I attain by the apparatus and mechanism illustrated in the
accompanying Drawings which form part of this Specification, and in which-
Figure 1 represents in perspective the external face of the device complete.
Figure 2 represents a view of the mechanism detached; and
Figures 3, 4, 5, represent modifications of my Invention.
The letters A, A, Figures 1 and 2, indicate a casing which may be constructed of
metal, hard rubber, or other suitable material; the said casing is preferably made
cylindrical in shape, and is constructed in two parts similar to a pocket compass
case, the parts being separable so as to place the works within convenient reach
for cleaning or repairs. The interior of the lower part of the case is provided with
lugs, pins, or other supports C for the dial D, which is secured by means of suitable
fastenings E. To the lower or rear face of the dial is secured a metallic frame F
which carries the working parts of the device. To the said frame at one end is.
secured a bridge G similar to the bridge forming one of the bearings of the journal
of a watch escapement wheel. The letter H indicates the index or pointer shaft;
this shaft is journaled in a central bearing in the frame, and in a bearing in the
bridge so as to be capable of rotating freely, and projects through the dial at its
centre H, and has an index or pointer Hattached to it. The said shaft is provided
with a pinion I with which two toothed segments K and L engage.
The segment K is mounted on a shaft M journaled in bearings N, which shaft
has attached to it one end a hair spring O which serves to turn the shaft in one
direction. The other segment L is journaled on an arbor P secured to the supporting
frame, and has a short extension Q provided with a series of apertures whereby may

page_text: be adjustably connected to it a small link R. The said link connects with one end
of a bi-metallic strip S, which is curved and fastened at its other end to the
supporting frame.
The casing is provided on one or both sides with crystals similar to the crystals
of a watch by which the interior can be observed.
In the modification shewn in Fig. 3 but one segment is employed, and the hair
spring is dispensed with, two bi-metallic strips S, S, being employed; each of these
strips is securely fastened at one end to the back of the dial plate, the other ends
being connected loosely by means of link R with a segment at opposite sides of its
fulcrum, and at equal distances therefrom so as to act in unison upon the said
segment as the strips expand or contract, and thus ensure the proper operation of
the pointer or index in a positive manner.
In Figures 4, 5, and 6, as in Figure 3, one segment and two bi-metallic strips are
shewn. Said strips are preferably composed of brass and steel fused together,
which by their unequal expansion and contraction in changes of temperature are
deflected from their normal position.
At one end these bi-metallic strips are secured to the plate F, and at the other
they are attached to the pins g, which play freely in the grooves or slots h. These
grooves are formed in part of the segments K which gear with pinion I mounted
upon or forming part of the shaft H which carries the index hand H¹. I have
found that when using but a single strip or lamina, as represented in Figure 2,
especially if the hair spring was not employed, that a deflection of several degrees.
of the index hand was produced by the action of gravitation on the bi-metallic
strip; in certain positions it therefore becomes necessary in a portable instrument
to devise some means of correcting this error; this object I attain by introducing
an auxiliary strip S¹ precisely like the first suspended at the opposite end of the
metal plate or frame F, and connecting it by means of a pin g working in a groove
or sloth cut in the rack K, with a point opposite and equi distant from the shaft
or pivot P of the rack. By this means any tendency of one bi-metallic strip to
become depressed by the action of gravitation is counterpoised by the weight of the
auxiliary strip drawing in an opposite direction.
In Figure 6 the part of the rack having thereon the grooves or slots h is
represented as turned aside from the line of the plate F, so that the direct action
of the metal strips S, S¹, shall be at right angles with the grooves. The metallic
strips are so placed when adjusting the instruments that there shall be a slight
side draw or tension upon the pivots of the segments, thus producing an even
tension throughout its action in a wide range of temperature, and securing the
pivots and connections. With this arrangement there is no uncertainty in the
position of the hand at any given temperature. The outer ends of the bi-metallic
strips are fastened to the metal plate F by means of pieces of metal f, Figures 4, 5,
and 6, bent at right angles, and having in their bases slots in which two set screws
1, 1, are placed, so that by raising them slightly the metal pieces bearing the ends
of the bi-metallic strips may be moved back or forth, thus moving the pins g
playing in the grooves or slots h at the other ends of the strips from the centre
pivot of the rack, by which means the instrument can be accurately adjusted. The
operation of my Invention is as follows:-
Any change of temperature causes the bi-metallic strips to deflect by the unequal
actions of their component metals. This action is communicated to the rack or
segment through the pins and connection, and changed from the reciprocating to
the rotary motion. From the rack or segment the motion is communicated to the
pinion, thence to the index hand, the direct action in its transit to the index hand
being largely multiplied, so that a single turn of the band will indicate a change
of one hundred and twenty degrees.
When the hair spring is employed it will move the parts in one direction, but
where the two bi-metallic strips are employed the movement of the index hand
will be effected in a positive manner in both directions, and for this reason

page_text: preference is given to the arrangements represented by Figures 3, 4, 5, and 6 of the
Drawings.
Having described the nature of the Invention, what I claim and desire to secure
by Letters Patent is,―
First. The combination in a thermometer of two bi-metallic strips so connected
on different sides of the point of rotation of a segment as to act together in
operating the indicating hand, and so adjusted as to have a slight tension in
respect to each other, substantially as shewn and described and for the purposes
set forth.
Second. In a thermometer the use of pin and groove connections between
bi-metallic strips, and the rack or segment, in combination with groove or slot
arrangements at the fixed ends of the bi-metallic strips for the purpose of adjusting
the instrument, substantially as shewn and described.
Third. In a thermometer the combination of a bi-metallic strip adjustably
connected with the segment, a pinion on the pointer shaft, and a governing
device, whether consisting of a second segment and spring, or of a second bi-
metallic strip, substantially as described as and for the purposes set forth.
In witness whereof, I, William Bentley Fowle, have hereunto set my hand
and seal, this Thirty first day of August, in the year of our Lord One
thousand eight hundred and eighty one.
WILLIAM BENTLEY FOWLE. (L.S.)