IMPROVEMENTS IN THERMOMETERS
Year: 1874

page_text: PROVISIONAL SPECIFICATION left by Louis Paschal Casella and
Samuel George Denton at the Office of the Commissioners of
Patents, with their Petition, on the 26th August 1874.
We, LOUIS PASCHAL CASELLA, of Holborn Bars, in the City of.
London, Scientific Instrument Manufacturer, and SAMUEL GEORGE
DENTON, of the same Place, Instrument Maker, in the employment of
the said Louis Paschal Casella, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN THERMOMETERS," to be as follows:-
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Our Invention has reference to those mercurial minimum ther-
mometers which are provided with an additional chamber communicating
with the mercury in the thermometer, the outlet of this additional
chamber being such that the end of it forms a flat surface or stop, or
fixed point, usually termed a diaphragm, so that on the mercury being
caused to flow out of such chamber into the indicating tube of the
thermometer, the flow ceases on reaching the fixed point owing to the
adhesion of the mercury to the diaphragm, at which point the tube
indicates the actual temperature at the time. As the temperature falls
so does the mercury in the indicating tube; but when the temperature

page_text: rises the mercury in the tube does not show such rise, but continues to
indicate the minimum degree to which the temperature may have fallen;
the increased bulk of the mercury produced by any rise in the tempe-
rature passing into the additional chamber.
Thermometers as heretofore made upon this principle have been
uncertain in their action in the course of manufacture, chiefly we
believe because the additional chamber has been formed with a pear-
shaped or gradually increasing bore, the effect of which shape is that
this chamber has a tendency sometimes to draw and sometimes to repel
the mercury, so that the manufacture of the instrument cannot be
depended upon.
Now our Invention consists in constructing the additional chamber of
uniform bore, or approximately so, and we find that we can thus rely
upon the proper action of the instrument. The additional chamber is
by preference horizontal and may communicate with any suitable part of
the bulb or of the indicating tube. We prefer however to form it behind
or below the bulb, and to carry out a contracted portion of the bulb to
which we connect the additional chamber.
The diaphragm or stop may be formed by fitting the additional
chamber in or to a portion of larger bore, the flat end of the additional
chamber constituting the diaphragm or fixed point, or it may be formed
by a fixed or movable plug of glass or other suitable material placed
within the additional chamber, to which plug the mercury will adhere
in the same manner that it does to the diaphragm to arrest the flow.
In applying our, Invention to a mercurial maximum thermometer, we
employ a similar horizontal additional chamber having a uniform or
approximately uniform bore. In this case the instrument is set by
allowing the additional chamber to become full. Increase of tem-
perature causes the mercury to rise in the indicating tube; but upon
the temperature afterwards decreasing the mercury in the additional
chamber flows towards the bulb, while that in the indicating tube
remains at the maximum point.