IMPROVEMENTS IN MERCURIAL THERMOMETERS
Year: 1861

page_text: LETTERS PATENT to Louis Marino Casella, of Hatton Garden, in the
County of Middlesex, Optician, for the Invention of "IMPROVEMENTS IN
MERCURIAL THERMOMETERS."
Sealed the 18th February 1862, and dated the 22nd August 1861.
PROVISIONAL SPECIFICATION left by the said Louis Marino Casella
at the Office of the Commissioners of Patents, with his Petition, on the
22nd August 1861.
I, LOUIS MARINO CASELLA, of Hatton Garden, in the County of Middlesex,
Optician, do hereby declare the nature of the said Invention for "IMPROVE-
MENTS IN MERCURIAL THERMOMETERS," to be as follows:-
My Invention refers particularly to minimum temperature thermometers,
and consists in providing an additional chamber communicating with the
mercury, in which the mercury is free to rise and fall with variation of
temperature, and in forming the chamber in such manner that on the mercury
being caused to flow out of such chamber as hereafter explained the flow will
be arrested, and the mercury in the ordinary thermometer tube will indicate
the actual temperature at the time of making the observation, the lowest
degree to which the temperature may have fallen having been indicated by
the ordinary tube up to that moment.
The most convenient means of carrying my Invention into effect is as here-
after described. I attach at or near the lower end of an ordinary thermo-

page_text: meter indicating tube another shorter and bent tube of larger bore, into which
the mercury is free to flow. I obtain my stop in the short tube by forming
the bore of two different diameters. As the temperature falls so does the
mercury in the indicating tube; but no matter how high the temperature
may rise, the mercury in the indicating tube does not show such rise (except
as hereafter explained), but indicates the minimum degree to which the tem-
perature may have fallen, the bent tube being sufficiently capacious to receive
any mercury which may be expanded consequent upon any increase in tem-
perature. Thus the thermometer will always indicate the lowest degree
to which the temperature may have fallen since it was last set or moved.
Now, to ascertain the actual temperature, carefully raise the bulb end of the
thermometer to allow the mercury to flow down the indicating tube, when the
mercury will flow out of the bent tube, and on reaching the stop occasioned
by the difference of diameter of bore in the bent tube, the mercury will
suddenly-stop-in the indicating tube, and show the actual temperature.
There are other means of causing a stop in and of forming the expansion
chamber, which I will set forth in my Complete Specification; but those I
have described I have found to answer well.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Louis Marino Casella in the Great Seal Patent Office on
the 22nd February 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, LOUIS
MARINO CASELLA, of Hatton Garden, in the County of Middlesex, Optician,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-second day of August, in the year of our
Lord One thousand eight hundred and sixty-one, in the twenty-fifth year of
Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said Louis Marino Casella, Her special licence that I, the
said Louis Marino Casella, my executors, administrators, and assigns, or
such others as I, the said Louis Marino Casella, my executors, adminis-
trators, and assigns, should at any time agree with, and no others, from time
to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the United
Kingdom of Great Britain and Ireland, the Channel Islands, and Isle of
Man, an Invention for "IMPROVEMENTS IN MERCURIAL THERMOMETERS," upon

page_text: the condition (amongst others) that I, the said Louis Marino Casella,
my executors or administrators, by an instrument in writing under my, or
their, or one of their hands and seals, should particularly describe and
ascertain the nature of the said Invention, and in what manner the same
was to be performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the date of the
said Letters Patent.
NOW KNOW YE, that I, the said Louis Marino Casella, do hereby
declare the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by the
following statement thereof, reference being had to the Drawings hereunto
annexed, that is to say :-
My Invention has reference to the construction of minimum temperature
mercurial thermometers, and consists in providing such a thermometer with
an additional chamber communicating with the mercury in the thermometer,
and in forming the outlet of the additional chamber in such a manner that
the end of it shall form a flat surface or stop, herein-after called a diaphragm,
so that on the mercury being caused to flow out of such chamber into the
thermometer, as hereafter explained, the flow of the mercury along the indi-
cating tube will cease at the point at which it indicates the actual temperaturo
at the time. If the thermometer be then placed in a horizontal position,
and exposed to lower temperatures varying from time to time, the mercury in
the indicating tube will, notwithstanding any intermediate elevations of the
temperature, indicate the lowest temperature to which the instrument may be
exposed until the time when the mercury which, upon the elevation of the
temperature has flowed into the additional chamber, shall be caused again to
flow out of the additional chamber, and indicate a higher temperature in the
manner herein-before mentioned.
The manner in which I prefer to carry my Invention into effect is as
follows:-I attach at or near the lower end of an ordinary thermometer
indicating tube, and communicating with it another shorter tube of larger
bore, which I prefer to make bent in order that the weight of the mercury in
it may not interfere with the proper action of the instrument when placed in
the position herein-after mentioned. At the outer end of this short tube is a
flat surface (which I call a diaphragm) formed by attaching to it the flat
surface at the end of the outlet from the additional chamber, and the orifice
or bore of the outlet from the additional chamber must be larger than the
bore of the indicating tube.
Figure 1 in the accompanying Drawings is a front elevation of one of my

page_text: mercurial minimum thermometers; Figure 2 is an enlarged view, showing those
parts to which my Invention particularly refers; and Figure 3 is a vertical
section through the line a, a, of Figure 2.
A is the mercury bulb; B is the indicating tube; C is a bent tube, the
bore of which is larger than that of the indicating tube, and bent (with the
additional chamber at the end of it) in the direction shown. At a, a, the bent
tube is terminated by a diaphragm or flat surface, in which is an orifice
(larger than the bore of the indicating tube) forming the outlet from the
chamber or reservoir b, as clearly shewn in the enlarged view, Figure 2.
By means of a diaphragm formed, as herein-before mentioned, when the whole
of the mercury has been caused to run out of the additional chamber in
setting the thermometer, as herein-after mentioned, the further flow of the
mercury will be stopped, and, as I believe, by the adhesion of the mercury to
the diaphragm formed at the outlet of the additional chamber, and the use of
a-stop-or-diaphragm-for-arresting-the-flow-of-the-mercury-is,-I-believe,-novel-
in the construction of minimum thermometers.
As the temperature falls so
does the mercury in the indicating tube, but when the temperature rises, the
mercury in the indicating tube does not shew such rise (except upon setting
the instrument, as hereafter explained), 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 temperature passing into the additional
chamber, which is made sufficiently capacious to receive any mercury which
may be expanded consequent upon any increase in temperature within the
desired range.
A thermometer made in this manner, after being set as
herein-after directed, should be kept in a horizontal or nearly horizontal
position, as shewn in Figure 1, with the additional chamber upwards, and it
will, until again set, continue to indicate the lowest degree to which the tem-
perature may have fallen. I prefer to suspend such an instrument by a back
plate at one end, and to support it at the other end, as shewn in Figure 1.
In order to set the thermometer or ascertain the actual temperature of the
place when the mercury in the indicating tube indicates a lower temperature,
raise the bulb end of the thermometer, so as to allow the mercury to flow
gently down the indicating tube, when the inercury will flow out of the
additional chamber, but as soon as it is empty the flow of the mercury will
cease, and the mercury in the indicating tube will indicate the actual tem-
perature. And if the mercury should, by placing the instrument in an
unusual position or otherwise, occupy an improper place in the indicating
tube, the instrument should be held upright with the bulb downwards until the
mercury runs down and fills the additional chamber, after which it may be set

page_text: in manner above described. The glass bulb and indicating tube, with the
bent tube and additional chamber having been made in the manner above
described, are filled with mercury, and deprived of air in the ordinary way in
which thermometer tubes are treated.
The glass instrument having been filled with mercury, the surplus mercury
warmed out, and the end of the indicating tube closed in the usual way, it is to
be pointed for graduation in a horizontal position with the additional chamber
empty, and the mercury adhering to the diaphragm.
And having now described the nature of my said Invention, and in what
manner the same is to be performed, I declare that I claim as my improve-
ments in mercurial thermometers,-
First, constructing a mercurial thermometer of an ordinary thermometer
bulb and indicating tube combined, with an additional mercurial chamber tube
and stop or diaphragm, for the purpose of indicating minimum temperature, as
herein-before described.
And, second, the employment in minimum mercurial thermometers of a
diaphragm to arrest the flow of mercury by the mercury adhering thereto, as
herein-before described.
In witness whereof, I, the said Louis Marino Casella, have hereunto
set my hand and seal, this Twenty-second day of February, One
thousand eight hundred and sixty-two.