A Thermometric Circuit Closer.
Year: 1894

page_text: Date of Application, 17th Mar., 1894
Complete Specification Left, 17th Dec., 1894-Accepted, 9th Mar., 1895
PROVISIONAL SPECIFICATION.
A Thermometric Circuit Closer.
I, RICHARD PEARSON, of 154, Gresham House, Old Broad Street, London, E.C.,
Mining Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to an improved device consisting of a thermometer balanced'
free to oscillate by the expansion or contraction of the fluid contained in it so as to
automatically complete or break an electrical circuit used for any purpose, such as
fire alarm, or a water sprinkler, or for indicating the rise or fall of temperature by
an alarm, or applied to other purposes.
Dated thie 17th dow of March 1884
I, RICHARD PEARSON, of 154, Gresham House, Old Broad Street, London, E.C.
Mining Engineer, 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 :-
My invention relates to a thermometric electric circuit closing device, and consists
of a thermometer mounted on a horizontal axis and so balanced as to be caused to.
oscillate under the displacement of the centre of gravity by the expansion and
contraction of the thermometric fluid, and by such oscillation to automatically
complete or break an electrical circuit used for any purpose, such as for sounding
an alarm of fire; actuating a water-sprinkler; or for merely indicating, by an
audible or other signal, the attainment of a predetermined limit of temperature.
The thermometer used is of the kind in which mercury is used not as the
thermometric agent but only to indicate the expansion and contraction of a
lighter fluid, such as an acid or alcohol, under variations of temperature, the form
of thermometer adopted being that known as a maximum and minimum thermo-
meter, the bore of the tube being, however, of considerably greater diameter
than usual in order that the volume and weight of the mercury contained may
be sufficient for the purpose. This kind of thermometer is especially suited for
the purpose I have in view, not by reason of the two-fold indications which it
affords but because the motion of the mercury column under expansion aud
contraction of the motive fluid has the effect of shortening the length of the
mercurial column in one leg and of lengthening it to a corresponding extent in
the other, the two variations conducing towards the same mechanical result, so
that the balance is disturbed twice as powerfully as would be the case by an
equal variation of the length of the column in one leg alone. Moreover this
kind of thermometer admits of the use of a mercurial column of relatively large

page_text: section without the large bulb which would be required for an ordinary ther-
mometer wherein the mercury itself is the thermometric fluid, and I am thus
enabled to obtain sufficient motive force to overcome friction and ensure efficient
action and perfect electrical contact, within a small compass and with short
- leverage.
The invention is illustrated in the accompanying drawings, forming part of
this Specification, wherein
Figure 1 is a side elevation and Figure 2 a plan of the thermometric portion of
the alarm.
The same letters of reference denote like parts in both figures.
A is an ordinary maximum and minimum thermometer fixed on a wooden scale B
and mounted to oscillate on a pair of horizontal pivots C. D, E, are binding posts
for connection of the wires in the circuit of which is the battery and the alarm or
other device to be operated by the passage of the current. The post D is connected
with a spring contact d placed beneath the bulb end of the thermometer and the
post E is connected with one or both the centres C which are of brass and are in
electrical contact with the pivot-bearing plates c which rest on them and are
connected by a wire with a contact lip e fixed to the end of the scale B and pro-
jecting down in position to come down upon the spring contact d when the equipoise
of the instrument is disturbed by a rise of temperature, and so complete the
electrical circuit.
The instrument is mounted on its centres so as, at the normal temperature of an
apartment, to be in a condition of or approaching stable equilibrium, the length of
the mercurial column in both legs extending to about the axis of oscillation or
nearly so. Thus arranged a very slight increase of temperature will cause the fluid
in the bulb a to expand and drive the mercury down the one leg and up the other,
the shortening of the mercury column in the "minimum" leg lightening the
instrument at one side of the axis at the same time as the lengthening of the column
in the "maximum" leg.beyond the axis increases the weight at the opposite side
of the centre of oscillation and causes the bulb end to quickly and powerfully
preponderate so as to bring the instrument to the position shewn in dotted lines and
close the circuit at e, d. Should a fall of temperature then occur, the motion of the
mercury in the opposite direction will cause the instrument to resume its original
position and break the circuit. The action will be similar when by a fall of
temperature much below the normal, the mercury column in the minimum leg
extends past the axis of oscillation whilst that in the other leg recedes from the
axis, so that the instrument may be used in greonhouses and other places where the
temperature is required to be kept within certain limits of heat and cold.
In order that the balance of the instrument may be readily adjusted so as that it
will oscillate at any given temperature, receptacles r, r', covered by pivoted shutters
are provided in the scale for small shot or other convenient form of removable
weight by means of which a rough adjustment suitable for general purposes may be
obtained whilst a means of finer adjustment, such as is requisite for sick wards, is
provided in the form of a jockey-weight w fitted to slide along the scale and adjusted
directly or by means of a traversing screw T.
In order to avoid breaking of the mercurial column by a sudden oscillation,
which breakage is liable to occur by reason of the comparatively large bore of the
tube, I prefer to employ a thermometric fluid of higher specific gravity than alcohol.
For this purpose
find that dilute sulphuric acid of a specific gravity of 1-222
is suitable.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I would observe that I
am aware that it has heretofore been proposed to balance an ordinary mercurial
thermometer for similar purposes, but without practical result, I do not, therefore
claim the adaptation of any but the kind of thermometer herein specified, viz. :-
one in which mercury serves only to render visible the expausion and contraction of

page_text: a lighter fluid and also as the means of producing the oscillation of the instrument,
and I declare that what I claim is :-
A thermometric electric circuit closing device consisting of a thermometer of the
kind specified mounted to oscillate upon a horizontal axis and combined with
6 electric circuit closing contacts, substantially as specified.
Dated this 17th day of December 1894.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.