IMPROVE- MENTS IN BAROMETERS
Year: 1850

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ADOLPHUS
OLIVER HARRIS, of High Holborn, in the County of Middlesex, Philosophical
Instrument Maker, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of the United Kingdom of Great
Britain and Ireland, bearing date at Westminster, the Nineteenth day of
December, One thousand eight hundred and fifty, in the fourteenth year of
Her reign, did, for Herself, Her heirs and successors, give and grant unto me,
the said Adolphus Oliver Harris, my exors, adññiors, and assigns, Her especial
licence, full power, sole privilege and authority, that I, the said Adolphus
Oliver Harris, my exors, adññiors, and assigns, or such others as I, the said
Adolphus Oliver Harris, my exors, adiñors, or assigns, should at any time agree
with, and no others, from time to time and at all times during the term of years
therein expressed, should and lawfully might make, use, exercise, and vend,
within England, Wales, and the Town of Berwick-upon-Tweed, and in the
Islands of Guernsey, Jersey, Alderney, Sark, and Man, and also in all Her
said Majesty's Colonies and Plantations abroad, the Invention of "IMPROVE-
MENTS IN BAROMETERS," being a communication from abroad; in which said
Letters Patent is contained a proviso that I, the said Adolphus Oliver Harris,
shall cause a particular description of the nature of my said Invention, and
in what manner the same is to be performed, by an instrument in writing.
under my hand and seal, to be inrolled in Her said Majesty's High Court
of Chancery within six calendar months next and immediately after the

page_text: date of the sard in part recited Letters atent, as in and by the same,
reference being thereunto had, will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Adolphus Oliver Harris, do hereby declare that the nature of the said
Invention, and in what manner the same is to be performed, are fully described
in and by the present Specification thereof, reference being had to the Draw-
ings hereunto annexed, that is to say :-
The said Invention consists of an improved mode of constructing barometers,
whereby the instrument is rendered more portable, more sensitive, and less
liable to derangement than barometers of the ordinary construction.
Figure 1 of the annexed Drawings is a representation of a portable
barometer constructed according to the said Invention. Figure 2 is a
sectional elevation of the glass tube and bulbs detached from the other parts.
A, A, is the tube which is of about one sixteenth of an inch in the bore,
and bent so that its two limbs L and R may be parallel to each other.
At one end it terminates in a short necked bulb B, which is kept permanently
open (more or less) to the atmosphere, and at the other in a bulb C, which is,
only opened for a short time during the adjustment of the instrument, but
is ultimately permanently closed. D is a small branch tube which forms an
extension upwards of the main tube A, from the throat of the bulb B, and
terminates at about the centre of that bulb. Mercury of as much purity as
is conveniently procurable is first poured in through the neck a into the bulb B
(the other bulb C being at this time closed) until the surface of the mercury
rises just sufficiently above the mouth of D to exclude the atmospheric
air, without the film of mercury over the mouth being of weight enough to
descend into the tube. An aperture is then made at bin the bottom of the
bulb C; carbonic oxide gas is then forced in through the aperture b, into the
bulb C, till all the atmospheric air remaining therein, or in either of the limbs
Land R, is expelled through the short branch tube D. The aperture at bis then
hermetically sealed, and more mercury poured in through the neck a until the
compression of the gas in the upper portion of the limb R and bulb C (at the
ordinary temperature of the atmosphere) is such that the surface of the
mercury in that limb stands at G; should it be found that there is too much
gas contained in the limb R and bulb C, to admit of the mercury rising to the
point G by compression, then the bulb must be re-opened, and a portion
allowed to escape. A plug of cane wrapped round with leather is then
inserted into the neck a, the pores of the cane being left open at top, in order
to admit of the free access of the atmospheric air into and out of the bulb B.
The barometric tube A, A, with its bulbs, having been thus filled and adjusted,

page_text: is put along with a standard barometer K, underneath the receiver of an air
pump, which is so constructed that it can at pleasure either condense or
exhaust, then by subjecting the barometric tube to different degrees of
pressure, either
exhausting or condensing the air in the receiver, or by
both, a scale of pressure H is obtained, corresponding with the inches' scale
upon any standard barometer, only that the divisions on the former scale are
smaller because the barometric effect of the atmosphere on the surface of the
mercury in the bulb B is counteracted by the resistance of the gas in the
bulb C. In order to supply the scale so obtained another scale I must be
formed, which may be a measure (within certain limits) of the expansion or
contraction of the gas in the limb R and bulb C, due to any increase or
decrease of temperature. It will be seen by referring to the Drawing that
the range of temperature provided for in the present instance is about 80°.
To obtain this scale the barometric tube A, A, is submitted to a similar process
to that generally employed for marking off the scale of a common thermometer,
that is, it is subjected to several different degrees of temperature along with a
standard thermometer.. When the principal points or the two extremes
corresponding with those of the standard thermometer have been thus marked
off upon the tube, then the tube is fixed to the plate, and the space between
the points on the tube laid down upon the plate, which is then divided into the
proper number of degrees. The scale is now ready for use, as represented in
Figure 1. The barometric scale H is not permanently fixed to the frame, but
is made to slide up and down with its graduated edge against the side of the
tube, and it carries at top an index pointer N, the length of which is
determined in the following manner :-The instrument is placed alongside of a
standard barometer, and the division of the sliding scale H, corresponding to
that on the standard barometer, which indicates the true barometric state of
the atmosphere at that time, is put in a line with the surface of the mercury in
the limb R, and the index pointer, which is made to adjust, is put immediately
over that degree upon the fixed scale I corresponding to the degree of tempe-
rature indicated by the standard thermometer K, and fixed in that position.
The instrument is now complete and ready for use.
In all subsequent
observations to ascertain the weight of the atmosphere, the index pointer N is
put immediately over the graduation or degree upon the fixed scale I,
corresponding to that indicated by the standard thermometer K when the
graduation upon the sliding scale H opposite to the line of the surface of the
mercury in the tube will indicate the height of the column of mercury which
is sustained by the weight of the atmosphere in the common barometer for
the time being. I prefer employing carbonic oxide gas to displace the atmo-

page_text: spheric air from the limbs and bulbs of the barometric tube, but any other gas
which, like it, has no affinity for mercury, will answer the purpose; or even air
may be substituted, though not advantageously. The prolongation. D serves to
prevent any air in the bulb B from passing down the tube L when the instru-
ment is reversed.
And having now described the nature of the said Invention, and in what
manner the same is to be performed, I declare that what I claim is the
employment in barometers of a column of compressed gas in combination
with a column of mercury in manner before described.
In witness whereof, I, the said Adolphus Oliver Harris, have hereunto
set my hand and seal, this Nineteenth day of June, in the year of our
Lord One thousand eight hundred and fifty-one.