IMPROVEMENTS IN THERMOMETERS
Year: 1879

page_text: LETTERS PATENT to Clara Milton, of South Audley Street, in the County of
Middlesex, for the Invention of "IMPROVEMENTS IN THERMOMETERS." A
communication from abroad by David Winstanley, of Paris, in the Republic of
France
Sealed the 26th September 1879, and dated the 28th March 1879.
PROVISIONAL SPECIFICATION left by the said Clara Milton at the Office of
the Commissioners of Patents on the 28th March 1879.
CLARA MILTON, of South Audley Street, in the County of Middlesex. ." IMPROVE.
MENTS IN THERMOMETERS." (A communication from abroad by David Winstanley,
of Paris, in the Republic of France.)
This Invention, which relates to improvements in thermometers, has especial
reference to what is called the "air thermometer," and to various applications of
the same.
The "air thermometer” is an instrument which indicates changes of temperature
by means of the dilation and contraction of a volume of enclosed gas, and it is
known to be more sensitive (that is to say, more rapid in effecting its indications)
than those thermometers by which changes of temperature are manifested through
the volumetric variations of liquid substances.
"
With the exceptions of the "differential thermometer" of Leslie, and the
thermoscope" of Rumford, the "air thermometers" hitherto in use have been
furnished with cisterns open to the external air, and have in consequence given
indications in which the effects of temperature were confused with those resulting
from the barometric variations of the atmosphere, whence the air thermometer
has thus far proved of very limited use and application.
"
"
One improvement consists essentially of a means of rendering the enclosed gas
of the "air thermometer" independent of the barometric variations of the external
or atmospheric air without preventing its dilation and contration under the influence
of thermal changes.
In order to accomplish this the enclosed gas of the improved thermometer is
subjected to the influence of an insulated barometric column, and the whole is

page_text: hermetically sealed up, thus effectually getting rid of the barometric influence of the
external air. One modification of this improvement consists in the use of a U-shaped
tube, having limbs some thirty odd inches in length closed at their extremities, and
containing in the one metallic mercury, and in the other common air or other gas
at the ordinary tension of the atmosphere at sea level. If this tube is placed in a
vertical position, with the ends up, it will be found that the mercury sinks in the
first limb, and indicates by its columnar height the tension of the gas enclosed in
the other or second limb.
Variations in the pressure of the external or atmospheric air can obviously
produce no effect on this insulated barometric column, but as the tension of the gas
enclosed in the second limb varies with its temperature, it follows that the height of
the mercurial column enclosed in the first limb will vary with the temperature as
well, and the whole instrument is therefore a true "air thermometer," uninfluenced
by the barometric variations of the external air, and giving its "readings" in the
varying columnar elevations of the mercury in the first limb.
Of course the "readings" may be effected in either limb as the mercurial column
descends in one whilst rising in the other.
A second modification of this improvement consists in making the first limb
terminate in a bulb having a much greater sectional area than the limb itself, and
further, in adjusting the instrument so as to leave the upper surface of the mercury
at or about the middle of that bulb; the result of this is that the vertical movement
of the mercurial surface will be substantially confined to the air column or second
limb, and accordingly increased in its extent therein.
A third modification of this improvement consists in terminating both limbs in
bulbs, so as to increase the mercurial movement still more as the proportional
expansion of the gas is lessened, and with it the diminution of tension which results
therefrom, the mercury being adjusted in the first limb, as described with reference
to the second modification.
A fourth modification of this improvement consists in placing the second limb in
a horizontal instead of in a vertical position. When this is done (and each limb
terminated in a bulb and the mercury being adjusted in the first limb, as described
with reference to the third modification), the movement of the index attains its
maximum, as there is then practically a constant pressure on the gas enclosed, and
no column to be upraised at all.
"
There is of course no especial reason why mercury should be employed as the
material of the barometric column, as any other liquid of high boiling point (sul-
phuric acid, for example) may be used. The desired condition being that a
"Torricellian vacuum "
shall exist in the space above the regulating column. It is
not however essential that a "Torricellian vacuum shall be there formed, for if
there should be gas or vapour in both bulbs, the instrument is a true "air ther-
mometer," indicating actual as well as differential temperature so long as there is a
difference of level in the two surfaces of the liquid material enclosed, for as any
difference in the height of the fluid contained in the limbs of the differential
thermometer depends on the different tensions to which its surfaces are respectively
exposed, it follows that actual differences of temperature, even though experienced
in both limbs alike, will cause a movement of the indices as long as there is any
actual difference of tension to begin with, for as the tension of a gas (whatever that
tension may chance to be), varies proportionately with its temperature, any actual
differences in tension experienced in the different limbs must vary also, and with it
the difference in height of the two liquid columns.
In the differential thermometer of Leslie however, as now constructed, the differ-
ence in tension of the gases enclosed in the bulbs of the different limbs is so
extremely slight that actual changes of temperature experienced in both bulbs
alike produce a movement in the liquid columns so very trivial as to be practically
invisible, and (so far as the present inventor has found) as to have escaped
detection.

page_text: Though therefore a vacuum is not essential at the summit of the compressing
column it is any rate desirable, as that difference which is essential obviously attains
its maximum when a given something is compared with nothing instead of with
another given something which is merely or a very little less. Hence the desirability
of a perfect vacuum in the space above the regulating column, and the present
inventor's preference for the "Torricellian vacuum," which is the nearest approach
to it of which we know.
Neither is it absolutely necessary that the limbs of the said U-shaped tube shall
be thirty odd inches long, for all that is needed is that the one containing the
compressing column shall be suited to the tension of the gas enclosed within the
other and within its bulb, that is, so adjusted as to give the "Torricellian vacuum"
preferred. As the tension of the gas enclosed may in the construction of the instru-
inent be fixed at what is required, the length of the limb containing the controlling
column may likewise be what is chosen or required.
It is not however absolutely necessary to have a controlling column at all, as the
controlling pressure, which is all that is wanted or required, may be obtained,
according to a second improvement, by enclosing an elastic box (essentially similar
in properties and construction to those now employed in aneroid barometers) in
such a manner that the fluid of the index column is made to surround it, and so to
press and operate thereon.
In the ordinary construction of the above described improved "air thermometer,"
the inventor prefers to employ an arrangement (such as the following), in which the
first limb or tube (which is intended to contain the controlling column or insulated
barometer) is terminated at its superior extremity by a cylinder of much greater
sectional area than either of the tubes or limbs, and at its base is curved round and
joined to a second cylinder of the same dimensions and capacity as the first, and
from which springs the second limb or tube (supporting the bulb of air), the mercury
or other fluid intended to afford the pressing column being adjusted, so that each of
the cylindrical receptacles is half filled thereby, and the tube connecting them of
course wholly so. In the other tube, and filling the other half of the cylinder
beneath, the inventor employs another and lighter fluid to afford the indications of
the atmospheric thermal changes. Ordinarily, the inventor employs sulphuric acid
as the lighter fluid and mercury as the heavier, but where extreme ranges are
required, that is to say, where the spaces indicating thermal degrees are intended
or required to be large, the inventor employs ether or some other highly volatile
liquid as the lighter one, for the vapour tension of such a liquid adds considerably
to the magnitude of the results desired or attainable otherwise.
$6
In order to apply the above described improved "air thermometer" to the
thermograph," it is simply necessary, according to a third improvement, to balance
the former in such a manner as to cause mechanical motion, when the centre of
gravity of the system to which it is attached is moved under the influence of varying
temperatures, or when the centre of gravity of the system is maintained, and the
expansive and contractile power of the gas employed by abutment against a
stationary controlling column, gives motion to the apparatus by which that column
is sustained.
In one modification or arrangement in which this is practically the case, the stem
of the thermometer is circularly curved and mounted concentrically upon a wheel
delicately poised upon its central point, and a terminating bulb thereof is balanced
by the counterpoise on the wheel, the regulating column in the opposite end or other
portion of the tube being also balanced by a weight suspended by a cord passing
round the grooved periphery of the wheel.
In this improved arrangement changes of temperature cause partial revolutions of
the wheel the one way when the change is for the greater, and the other way when
for the less. Thus this instrument may be employed either as a thermometer in
itself or as a means of giving motion to the pencil of the thermograph, through one
or other of the ordinary appliances now in use in divers instruments constructed to
that end.

page_text: When used as a thermometer merely the temperature is read off on a scale
attached to the movable wheel, and pointed to by a finger fastened to the stationary
stand, or on a scale in which these conditions are reversed, and when applied to give
motion to the pencil of the thermograph, the movement of the wheel is communi-
cated by a cord or equivalent device to the mechanism by which the pencil is moved.
When a maximum of motion or mechanical pressure is required, the inventor
employs in this arrangement also a more or less volatile liquid, as well as that
forming the controlling column, in order to obtain the additional effects of its vapour
tension:

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Clara Milton in the Great Seal Patent Office on the 27th September
1879.
CLARA MILTON, of South Audley Street, in the County of Middlesex. " IMPROVE-
MENTS IN THERMOMETERS." (A communication from abroad by David Winstanley;
of Paris, in the Republic of France.)
This Invention bas especial reference to what is generally called the "air-
thermometer," and to various applications of the same.
The "air-thermometer" is an instrument which indicates changes of temperature
by means of the dilation and contraction of a volume of enclosed gas, and it is
known to be more sensitive (that is to say, more rapid in effecting its indications),
than those thermometers by or in which changes of temperature are manifested
through the volumetric variations of liquid substances.
With the exceptions of the "differential-thermometer" of Leslie, and the
thermoscope" of Rumford, the "air-thermometers" hitherto in use have been
furnished with cisterns open to the external or atmospheric-air, and have in
consequence given indications in which the effects of temperature were confused
with those resulting from the barometric variations of the atmosphere, whence the
"air-thermometer" has hitherto proved to be of a very limited use and application.
Now one of the improvements constituting the present Invention consist
essentially of a means of rendering the enclosed gas of the "air-thermometer"
independent of the barometric variations of the external or atmospheric-air, without
preventing its dilation and contraction under the influence of thermal changes.
In order to accomplish this, the inventor of the present improvements subjects
the enclosed gas of the thermometer to the influence of an insulated barometric
column and hermetically seals up the whole, so as effectually to get rid of the
barometric influence of the external air.
One of the means by which this result is attained is illustrated on the accom-
panying Sheet of Drawings, in Figure 1, wherein it is shown as consisting in the
use of a U-shaped tube 1, having limbs 2, 3, some thirty odd inches in length, and
closed at each extremity; one limb (2) containing metallic mercury, and the other
common air or other gas at the ordinary tension of the atmosphere at sea-level.
Upon this tube being placed in a vertical position with the ends up (as shown) the
mercury sinks in the limb 2, and indicates by its columnar height the tension of
the gas enclosed in the limb 3.
Variations in the pressure of the external or atmospheric-air can obviously
produce no effect on this insulated barometric column, but as the tension of the
gas enclosed in the limb 3 varies with its temperature it follows that the height
of the mercurial column enclosed in the limb 2 will vary with the temperature as
well, and the whole instrument is therefore a true air thermometer, uninfluenced
by the barometric variations of the external air, and giving its "readings" in the
varying columnar elevations of the mercury. Of course the "readings" may be
effected in either limb, as the mercurial column descends in one whilst rising in the
other.
Another modification of this improvement, and according to which the same
result is attained, is illustrated in Figure 2, where the limb 2 is shown as
terminating in a bulb 4, having a much greater sectional area than the limb
itself; the instrument being adjusted so as to leave the upper surface of the
mercury at or about the middle of the bulb; the result of this arrangement is that
the vertical movement of the mercurial surface will be substantially confined to the
limb 3, and accordingly increased in its extent therein.
A third modification of this improvement is illustrated in Figure 3, and consists
in terminating both limbs 2, 3, in bulbs 4, 5, respectively, so as to increase the

page_text: mercurial movement still more as the proportional expansion of the gas is thereby
lessened, and with it the diminution of tension which results therefrom, the
mercury in this instance also being adjusted in the bulb 4 of the limb 2, as
described with reference to the next preceding modification.
A fourth modification of this improvement is illustrated in Figure 4, and consists
in placing the limb 3 in a horizontal instead of in a vertical position. When this
is done and each limb terminated in a bulb (the mercury being adjusted in the
bulb 4 of the limb 2, as in the two next preceding modifications) the movement of
the "index" attaius its maximum, as there is then practically a constant pressure
on the gas enclosed, and no column to be upraised at all.
"
"
There is of course no especial reason why mercury should be employed as the
material of the barometric column, as any other liquid of high boiling point
(sulphuric acid for example) may be used; the desired condition being that a
Torricellian vacuum shall exist in the space above the regulating column. It is
not however essential that a "Torricellian vacuum shall be there formed, for if
there should be gas or vapor in both bulbs the instrument is a true "air thermo-
meter," indicating actual as well as differential temperatures so long as there is a
difference of level in the two surfaces of the liquid material enclosed, for as any
difference in the height of the fluid contained in the limbs of the differential
thermometer depends on the different tensions to which its surfaces are respectively
exposed, it follows that actual differences of temperature even though experienced
in both limbs alike will cause a movement of the indices as long as there is any
actual difference of tension to begin with; for as the tension of a gas (whatever
that tension may chance to be) varies proportionately with its temperature, any
actual differences in tension experienced in the different limbs must vary also, and
with it the difference in height of the two liquid columns.
68
In the differential thermometer" of Leslie, however, as now constructed, the
differences in tension of the gases enclosed in the bulbs of the different limbs is so
extremely slight, that actual changes of temperature experienced in both bulbs
alike produce a movement in the liquid columns so very trivial as to be practically
invisible, and (so far as the inventor of the present improvements has found) as to
have escaped detection.
Though therefore a vacuum is not essential at the summit of the compressing
column, it is at any rate desirable, as that difference which is essential obviously
attains its maximum when a given something is compared with nothing instead
of with another given something which is merely or a very little less. Hence the
desirability of a perfect vacuum in the bulb 4, and the present inventor's preference
for the "Torricellian vacuum," which is the nearest approach to it that is known.
Neither is it absolutely necessary that the limbs of the said U-shaped tube shall
be thirty odd inches long, for all that is needed is that the one containing the
compressing column shall be suited to the tension of the gas enclosed within the
other and within its bulb, that is, so adjusted as to give the "Torricellian vacuum"
preferred.
As the tension of the gas enclosed may, in the construction of the instrument, be
fixed at what is required, the length of the bulb containing the controlling column
may likewise be what is chosen or required.
It is not however absolutely necessary to have a controlling column at all, as the
controlling pressure, which is all that is wanted or required, may be obtained,
according to a second improvement, and which is illustrated in Figure 5, by
enclosing an elastic box 6 (essentially similar in properties and construction to
those now employed in aneroid-barometers) in such a manner that the fluid of the
index-column is made to surround it and so to press and operate thereon.
In the ordinary construction of the above described improved "air-thermometer,"
the inventor prefers to employ an arrangement (such as is illustrated in Figure 6)
in which the limb 2, which contains the controlling column or insulated barometer,
is terminated at its superior extremity by a cylinder 4 of much greater sectional
area than either of the limbs 2, 3, and at its base is curved round and connected to

page_text: a second cylinder 7 of the same dimensions and capacity as the cylinder 4, and
from which springs the limb 3 supporting the air-bulb 5, the mercury or other fluid
intended to afford the pressing column being adjusted so that each of the cylindrical
receptacles 4, 7, is half filled thereby, and the limb 2 connecting them of course
wholly so.
In the limb 3 and filling the upper half of the cylinder 7 the inventor employs
another and lighter fluid to afford the indications of the atmospheric or other thermal
changes. Ordinarily the inventor employs colored alcohol as the lighter fluid and
mercury as the heavier, but where extreme ranges are required, that is to say,
where the spaces indicating thermal degrees are intended or required to be large,
the inventor employs ether or some other highly volatile liquid as the lighter one,
for the vapor-tension of such a liquid adds considerably to the magnitude of the
results desired or attainable otherwise.
In order to apply the above described improved "air thermometer" to the "ther-
mograph" it is simply necessary (according to a third improvement) to balance the
former in such a manner as to cause mechanical motion when the centre of gravity
of the system to which it is attached is moved under the influence of varying
temperatures, or when the centre of gravity of the system is maintained, and the
expansive and contractile power of the gas employed by abutment against a
stationary controlling column gives motion to the apparatus by which that column
is sustained.
In one modification or arrangement, illustrated in Figure 7, in which this is
practically the case, the stem or tube 1 of the thermometer is circularly curved and
mounted concentrically upon a wheel 8 delicately poised upon its central point 9,
and a terminating bulb 5 of the portion 3 thereof is balanced by a counterpoise 10
on the wheel, the regulating column in the opposite end or other portion 2 of the
tube being also balanced by a weight 11 suspended by a cord 12 passing round a
peripheral groove 13 of the wheel, and being fastened at a suitable point.
In this improved arrangement, changes of temperature cause partial revolutions
of the wheel, the one way when the change is for the greater, and the other way
when for the less. Thus this instrument may be employed either as a thermometer
in itself or as a means of giving motion to the pencil of the "thermograph" through
one or other of the ordinary appliances now in use in divers instruments constructed
to attained that end.
**
When used as a thermometer merely, the temperature is read off on a scale
attached to the movable wheel, and pointed by a finger fastened to the stationary
stand, or on a scale in which these conditions are reversed, and when applied to
give motion to the pencil of the thermograph" the movement of the wheel is
communicated by a cord or equivalent device to the mechanism by which the pencil
is moved. The inventor however prefers to connect a needle directly with the
rotating wheel and let its point mark on a sheet of smoked paper in the manner
adopted in connection with other instruments at the observatory at Montsouris in
France, and probably elsewhere. When a maximum of motion or mechanical
pressure is required the inventor employs in this arrangement also a more or less
volatile liquid as well as that forming the controlling column, in order to obtain the
additional effects of its vapor-tension.
Having thus particularly described and ascertained the nature and object of the
said Invention, and in what manner the same is to be performed, I would observe
in conclusion that what the said David Winstanley considers to be novel and
original, and I therefore claim as constituting the Invention secured by the herein-
before in part recited Letters Patent is,-
Firstly. An "air-thermometer" constructed substantially as herein before described,
and in such a way as to isolate the gas or vapor therein enclosed from the baro-
metric variations of the external or atmospheric air, and subject it instead to the
pressure of an enclosed barometric column.
Secondly. An "air-thermometer" in which the gas or vapour is isolated from the
barometric variations of the atmosphere and subjected instead to the pressure

page_text: exerted by an enclosed elastic box (constructed of metal or other material)
substantially as herein before described.
And, Thirdly. The application and employment of this improved air-thermo-
meter"
as a means of gaining mechanical motion by so balancing it that changes in
temperature shall cause the apparatus sustaining it to move, and substantially for
the reasons given.
In witness whereof, I, the said Clara Milton, have hereunto set my hand and
seal, this Twenty-third day of September, in the year of our Lord One
thousand eight hundred and seventy nine.
CLARA MILTON. (L.B.)
1