IMPROVE- MENTS APPLICABLE TO SELF-REGISTERING GAUGES, THERMOMETERS, BAROMETERS, AND OTHER MERCURIAL METEOROLOGICAL INSTRUMENTS
Year: 1855

page_text: LETTERS PATENT to Enrico Angelo Ludovico Negretti and Joseph
Warren Zambra, both of Hatton Garden, in the City of London,
Meteorological Instrument Makers, for the Invention of "IMPROVE-
MENTS APPLICABLE TO SELF-REGISTERING GAUGES, THERMOMETERS, BAROMETERS,
AND OTHER MERCURIAL METEOROLOGICAL INSTRUMENTS."
Sealed the 8th April 1856, and dated the 15th October 1855.
PROVISIONAL SPECIFICATION left by the said Enrico Angelo Ludovico,
Negretti and Joseph Warren Zambra at the Office of the Commissioners
of Patents, with their Petition, on the 15th October 1855.
We, ENRICO ANGELO LUDOVICO NEGRETTI and JOSEPH WARREN ZAMBRA,
both of Hatton Garden, in the City of London, Meteorological Instrument
Makers, do hereby declare the nature of the said Invention for "IMPROVEMENTS
APPLICABLE TO SELF-REGISTERING GAUGES, THERMOMETERS, BAROMETERS, AND OTHER
MERCURIAL METEOROLOGICAL INSTRUMENTS," to be as follows:-
Our Invention of improvements applicable to self-registering gauges, thermo-
meters, barometers, and other mercurial meteorological instruments, relates
to the means of causing such instruments to indicate or register the minimum
or lowest point to which the column of mercury has fallen since a prior
observation was made. In order to effect this object, I employ a small conical

page_text: plug or plunger, with a pointed end, like a needle, and insert the same in
the tube above the column of mercury. This conical plug will be capable
of moving freely in the bore of the tube, and as the mercury. descends
therein will of course fall with it; but when the mercury ascends in the tube,
it will pass the pointed end of the plunger, and rise above the same without
acting thereon.
thereon. The plunger will therefore remain stationary, and conse-
quently indicate the lowest point to which it has descended. These plungers
may be made of steel or other suitable substance, and when used in thermo-
meters, or instruments of small bore, solid steel pins of the proper form will
be found most suitable; but in instruments of large bore, such as large
barometers or mercurial gauges, we sometimes propose to employ hollow
plungers of the proper form. These may be made either of glass, platinum,
or some substance not liable to be acted on by mercury, and may be filled
with mercury, in order that the plungers may be made as near as practicable
to the specific gravity of the mercury in the column.
We also propose to adapt two tubes to one bulb, and by partially choking
one of the tubes at or near the neck, the mercury in rising will have a
tendency to rise in the unchoked tube, which may be made to indicate the
maximum temperature, while the mercury in the choked tube when falling
will run into the bulb, and indicate the minimum temperature.
A minimum thermometer may also be made by employing a supple-
mentary reservoir, into which the mercury shall run when it descends, instead
of finding its way through the bulb into another tube.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Enrico Angelo Ludovico Negretti and Joseph Warren
Zambra in the Great Seal Patent Office on the 15th April 1856.
TO ALL TO WHOM THESE PRESENTS SHALL COME, we, ENRICO
ANGELO LUDOVICO NEGRETTI and JOSEPH WARREN ZAMBRA, both of Hatton
Garden, in the City of London, Meteorological Instrument Makers, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Fifteenth day of October, in the year of our Lord
One thousand eight hundred and fifty-five, in the nineteenth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto us, the
said. Enrico Angelo Ludovico Negretti and Joseph Warren Zambra, Her

page_text: special license that we, the said Enrico Angelo Ludovico Negretti and Joseph
Warren Zambra, our executors, administrators, and assigns, or such others
as we, the said Enrico Angelo. Ludovico Negretti and Joseph Warren
Zambra, our executors, administrators, 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 APPLICABLE TO
SELF-REGISTERING GAUGES, THERMOMETERS, BAROMETERS, AND OTHER MERCURIAL
METEOROLOGICAL INSTRUMENTS," upon the condition (amongst others) that we,
the said Enrico Angelo Ludovico Negretti and Joseph Warren Zambra, by an
instrument in writing under our hands and seals, or under the hand and seal
of one of us, 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 we, the said Enrico Angelo Ludovico Negretti and
Joseph Warren Zambra, do hereby declare the nature of our said Invention,
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement, reference being had to the
Drawing hereunto annexed, and to the letters and figures marked thereon
(that is to say):
Our Invention of "Improvements applicable to Self-registering Gauges,
Thermometers, Barometers, and other Mercurial Meteorological Instruments,"
relates to the means of causing such instruments to indicate and register tho
minimum or lowest point to which the column of mercury has fallen since a
prior observation was made. In order to effect this object, we employ a small
conical plug or plunger, made by preference of steel or other metal; and having
pointed ends, and this plug or plunger is inserted in the tube above the column
of mercury. This conical plug will be capable of moving freely in the bore of
the tube, and as the mercury descends therein will of course fall with it;, but
when the mercury ascends in the tube, it will pass the lower pointed end of the
plunger, and rise above the same without raising or moving the plunger. This
latter will therefore remain stationary, and consequently indicate the lowest
point to which it has descended, and will not be affected. by any subsequent
rise in the temperature. These plungers may be made of steel or other
suitable substance, and when used in thermometers, or. instruments of small
bore, solid steel pins of the proper form will be found most suitable; but in

page_text: instruments of large bore; such as large barometers or mercurial gauges, we
sometimes propose to employ hollow plungers, of the proper form. These may
be made either of glass, platinum; or some substance not liable to be acted on
by mercury, and. may be filled with mercury, in order that the plungers may
be made as near as practicable to the same specific gravity as the mercury in
the column.
We would here remark that we prefer to read the temperature from the
upper end of the steel plunger or plug that is enclosed in the glass tube, but if
desired, the temperature.may be read. from the lower end of the plunger, or
from the mercury itself.
.
Another improvement consists in constructing thermometers which will
indicate both the minimum and maximum temperatures. For this purpose
two tubes are adapted to one. bulb, and one of the tubes must be partially
choked at or near the neck, or both tubes may be partially obstructed in the
bore; but when such is the case, the tube which is intended to indicate the
minimum temperature must be choked to a greater extent than the other, as
this compound thermometer is based. upon the principle that the mercury will
have a greater tendency to rise in the one tube than the other, owing to the
greater obstruction that is opposed in the obstructed tube to its passage.
The mercury in falling, in consequence of any reduction in temperature, will
do so equally in both tubes; but in rising, in consequence of a rise in tem-
perature, the mercury will have a tendency to rise in that tube which is least
obstructed in preference to the other tube. The least obstructed tube, which
is intended. to indicate the maximum temperature, must also be placed at such
an inclination, that the mercury upon a fall in temperature will not have a
tendency to run back into the bulb, but, on the contrary, to remain in statu
quo in the tube, which will therefore indicate the maximum temperature to
which the instrument has been submitted, while the mercury in the other
tube when falling will run into the bulb, and by means of the pointed plug
or plunger will indicate the minimum température.
In the accompanying Drawing we have shewn views of various forms of
thermometers constructed according to our improvements.
Fig. 1 represents a minimum thermometer, with a vertical bulb or reservoir;
and Fig. 2 is a similar view of another form of instrument, in which the bulb is
placed horizontally. The advantage of the latter form is that a greater length
of tube for registering the temperature may be obtained without lengthening
the instrument. Fig. 3 is a view of the steel plug or plunger, which we
propose to place in the bore of the thermometer tube. It will be seen that

page_text: this plug or plunger is provided at the upper end with an acute point, and at
the lower end with an obtuse point. The latter part rests on the column
of mercury in the tube, and descends with it, but does not sink therein. It
will also allow the mercury to pass by and over the plug, which will not be
moved or raised thereby. The minimum temperature to which the instrument
has been exposed may therefore be read off from the upper end of the plug or
plunger; and in order to set the instrument for a second observation, the plug
and any mercury that, may be above it must be brought into the upper reser-
voir at the top of the tube, which may be done by simply turning up the
instrument, and then as the instrument is free from air above, the mercury may
the better be run back again into the tube, and the plunger or plug allowed to
resume its place on the surface of mercury.
Fig. 4 is a view of our improved instrument for indicating and registering
both the maximum and minimum temperature in the same instrument. a is
the minimum tube, and 6 the maximum tube, which are connected together
at their lower ends, and communicate by means of one common tube with the
bulb or reservoir of mercury at c. These tubes with their common bulb are
mounted upon a board d, which is provided with a hole and clamp screwe
whereby the board with the tubes may be placed and held in any position that
may be required. A small standard thermometer f of the ordinary kind is
secured to the board d in any convenient manner for indicating the present tem-
perature. Both the tubes a and b are partially choked or obstructed either by
partially closing the bore, by twisting or bending the tube, or by placing therein
a small piece of enamel or glass, as in our improved maximum theremometer
previously patented by us; but the tube a is obstructed to a greater extent than
the other one b. Upon the instrument being exposed to a low temperature, the
mercury in the tube a will fall, and upon the temperature rising, the mercury
instead of rising again in the tube a will rise in the tube b, where it will meet
with less obstruction than in a. Upon the temperature falling again, the
mercury will not descend again in the tube 6 from the degree that it has
indicated, but owing to the partial obstruction that has been made in the tube,
as at g, the column of mercury will be cut in half, and only the lower portion,
viz, that below the point g, will pass into the bulb, as in the improved maximum
thermometer previously patented by us, and now well known to scientific men.
Should; however, the temperature continue to descend even below that already
indicated in the tube a, .the mercury will descend in the latter to a still lower
point, and will not ascend again until the instrument is re-set. In order to set
the instrument for a second observation, the present temperature must be read;

page_text: off from the thermometer f, and (the board d having been previously unclamped)
the two tubes a and b must be made to indicate the present temperature. This
they may easily be made to do, by moving the board on its centre or supporting
pin until the mercury in both tubes is brought to a level, in which there will
be no difficulty in doing, as a vacuum is made in both tubes, and the mercury
will flow from one to the other with facility.
The instruments shewn in Figures 1 and 2 may be made to indicate either
maximum or minimum temperatures, as may be desired. When intended to
indicate the minimum temperature, they must be suspended vertically, as
shewn in the Drawing; but when required to indicate the maximum tempera-
ture, they may be suspended horizontally, and the plug or plunger must be
brought into the reservoir above, and the glass tube partially choked or
obstructed at any convenient point; and as the minimum temperature has been
read from the upper end of the plug or plunger, a separate scale must be
provided for indicating maximum temperatures, and may be applied in any
manner well known to thermometer makers.
In applying our Invention to barometers or mercurial gauges where the
bore is much greater than in thermometers, a steel plug would be liable to be
lifted by the mercury in rising, owing to the steel plug being of less specific
gravity than the mercury; on the other hand, if platinum or other heavy metal
were employed, errors might arise from the superior specific gravity of the
plunger. To obviate this, we propose for these purposes to make the plug of
thin platinum and fill it with mercury, as already mentioned. We have not,
however, shewn any Drawings of barometers or gauges with our improvements
adapted thereto, as, with the exception of the addition of the plug or plunger,
they will not materially differ in construction from those now used for similar
purposes.
Having now described our improvements applicable to self-registering
gauges, thermometers, barometers, and other mercurial meteorological instru-
ments, and explained the manner of carrying the same into effect, we claim
as the Invention secured to us by Letters Patent as aforesaid,-
First, constructing thermometers and other mercurial instruments, as above
mentioned, in the manner shewn in Figures 1, 2, and 3, for the purpose of
causing such instruments to indicate the minimum temperature or pressure
to which they have been exposed since a previous observation. We claim
particularly the use of the plug or plunger shewn in Fig. 3 for the purpose
above set forth. We also claim to use these instruments for indicating either
minimum or maximum temperatures, as above described..

page_text: Second, we claim the mode of constructing thermometers as shewn in Fig. 4,
or any mere modification thereof, for indicating both minimum and maximum
temperatures, as above explained.
In witness whereof, we, the said Enrico Angelo Ludovico Negretti and
Joseph Warren Zambra, have hereunto set our hands and seals, the
Fifteenth day of April, in the year of our Lord One thousand eight
hundred and fifty-six.
Witness,
J. W. MOFFATT,
66, Chancery Lane.
E. A. L. NEGRETTI. (L.S.)
J. W. ZAMBRA.
(L.S.)