A CERTAIN IMPROVEMENT OR IMPROVEMENTS IN THE BAROMETER
Year: 1842

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
READMAN, of Islington, in the County of Middlesex, Gentleman, send
greeting.
!
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Seventh day of March, in .the fifth year of Her reign, did, for
Herself, Her heirs and successors, givo and grant unto me, the said James
Readman, my. exors, adññiors, and assigns, and such others as I, the said
James Readman, my exors, adiñiors, or assigns, should at any time agree with,
and no others, from time to time and at all times thereafter during the term
of years therein expressed, should.and lawfully might make, use, exercise, and
vend, within that part of Her Majesty's United Kingdom of Great Britain and
Ireland called England, Her Dominion of Wales, and the Town of Berwick-
upon-Tweed, my. Invention of "A CERTAIN IMPROVEMENT OR IMPROVEMENTS IN
THE BAROMETER;" in which said Letters Patent there, is contained a proviso,.
that I, the said James Readman, shall cause a particular description of the.
nature of my said Invention, and the manner in which the same is to be:
performed, to be enrolled in Her said Majesty's High Court of Chancery
within six calendar months next and immediately after the date of the said
in part recited Letters Patent, 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
James Readman, do hereby declare that the nature of my said Invention, and

page_text: the manner in which tho same is to be performed, are fully described and
ascertained in and by the following Specification thereof, reference being had
10 the Drawings hereunto annexed, that is to say:-
Whereas, the pressure of the barometric column of mercury added to the
atmospheric pressure on the surface of the mercury in the cistern being equal
to the atmospheric pressure on the exterior bottom of the cistern, it follows
that if we place the cistern with its contents upon the top of a spring or other
exacily adjusted balance, the depression caused in the balance will be no more
than what is due to the weight at the moment of the cistern and its contents,
independently of the barometric column, on account of the weight of that column
being counterbalanced by the atmospheric pressure on the exterior bottom of
the cistern, but as the mercury in the cistern is the source whence the baro-
metric column is derived, and as the quantity in the cistern is increased or
diminished according to the height of that column, it follows also that as the
barometric column is caused to rise or fall by variations in the weight of the
atmosphere, so the weight of the cistern will be proportionably increased
or diminished, and the spring or other balance on which it presses be to the
same extent raised or lowered. And whereas it is further obvious, that if we
ascertain how many inches or parts of inches are included within the extreme
range of the barometric column, and what the weight of so many inches or
parts of inches of mercury is, and to what extent the addition of such weight
to the cistern will cause the spring or other balance to be depressed, we may
from these data construct an index which, being attached to the balance, shall
shew, on inspection, the smallest changes in the height of the barometric
column.
Now, therefore, my said Invention consists in employing an index acted
upon by the rising and falling of a balance in manner aforesaid, and also in
employing a steelyard balance, hereafter to be described, to indicate the
changes in atmospheric pressure, whereby I get rid of three defects in the baro-
meter as commonly constructed, namely:-First, the difficulty of ascertaining
the proper allowance to be made for the expansive effects of changes of tempe-
rature on the barometric column; second, the smallness of the range; and
third, the disturbing influence of alterations in the lovel of the mercury in the
cistern.
In Figure 1 of the Drawings hereunto annexed I have shewn the manner
of constructing a wheel barometer on this principle; a, b, c, is a cylinder
containing mercury; d, e, a second cylinder, which floats in the mercury
within the other, forming the cistern of the barometer, (the mercury in the
cylinder a, b, c, serving the same purpose as the spring balance before spoken

page_text: of); a, the barometrical tube; f, a brass rim which runs round the top of
the cistern d, e, and to the bottom of which is soldered the projecting.
circular plate g; h, i, are two uprights which are screwed into the plate g..
and are united at top by a cross piece k; is a toothed rack, which rises
from the centre of the cross piece k; m, a toothed wheel, into which the rack
works, and to the axis of which wheel is attached the pointer of a properly
graduated dial plate; n, o, antifriction wheels, attached on each side to the
projecting rim g, and which work in grooves in the frame pieces r, s; p, a
third antifriction wheel, against which the rack 7 works as it rises and falls. To
keep the rack in a direct line with the centre of the cistern, the tube of the baro-
metric column is bent aside a little at t, as shewn in the Drawing. The mode of
action is as follows:-As the quantity of mercury in the cistern d, e, is increased
or diminished, the cistern rises or falls in the mercury contained in the outer
cylinder a, b, c, and through the medium of the uprights h, i, and rack and wheel
l, m, the exact amount of the rise or fall is communicated to and indicated by the
pointer of the index. When it is desired to render this instrument portable,
the plate g is brought close down upon the cylinder a, b, c, so as to serve as a
lid to it. The instrument is then held in an inclined position till the tube a³
is completely filled; the tube a³ is next enclosed from its fastenings, and pressed
against the bottom of the cistern (which is protected by a piece of soft leather),
after which the stopper u is slid down the tube a' and closes the mouth of the
cistern. By applying a fixed scale to the side of the tube a* of an instrument.
of the preceding description, very minute changes in atmospheric pressure
might be rendered perceptible; for besides the actual lengthening or shorten-
ing of the barometrical column by changes of pressure, such a scale would.
indicate the rise and fall of the cistern, the amount of which could be added to.
the range of the column. Thus, suppose the column to fall from 31 to 28
inches, if the cistern were fixed, the scale would indicate a fall of only 3 inches.;
but if the cistern is made to float in mercury, in manner before described, so
that it rises and falls in proportion to any increase or diminution in the quan-
tity of mercury in it, or if it is placed on a spring or other balance which is
effected in the same way, then, the barometric column will have a further fall.
proportionate to the depression caused by the addition of the three inches of
mercury to the cistern. In graduating the instrument the following direc-
tions should be attended to:-Assuming the extreme range of the barometric
column to be three inches, the weight of these three inches should be ascer-
tained, and an equivalent amount of mercury taken from the cistern, marking
exactly the position of the index pointer both before and after the operation.
A quantity equivalent to the excess of the column above twenty-eight inches

page_text: is then to be deducted and the remainder returned. For instance, supposing
the weight of the three inches of the barometric column is three ouncès, and
that the cistern stands at twenty-eight and half. inches, you should then (pro-
ceeding as above directed) return only two and a half instead of three ounces,
the half ounce being deducted to allow for the half inch which the barometric
column exceeds 28 inches, and upon the flowing of which. into the cistern the
index pointer will be carried to its original position. The space included
between the two points is to be divided in the usual manner.
In Figure 2 of the Drawings hereunto annexed, I have shown how a barometer
on my improved plan may have a balance on the steelyard principle applied
to it. a, b, is a metal cylinder fixed to the bottom of the frame or case which
holds the cistern c, d. (the diameter of the cylinder being a little larger than
that of the cistern), and which partly encloses that cistern; round. the top of
the cistern there is a metal rin, which projects a little beyond the sides of the
cylinder a, b, and is levilled on part of its under surface to keep the cistern
exactly in the middle of the cylinder a, b; e, f, is a lever or steelyard, with.a
sliding weight 9 resting on a fulcrum at h; the short arm of the lever has a
termination of a crescent form (as shewn in the separate view given in
Figure 8), the two branches or horns of which have conical points which enter
into corresponding holes in the rim of the cistern. To ascertain the height of
the column, the lever is brought to a horizontal position by causing the short
arm to press upwards against the guage point 7, simultaneously with which the
crescent end of the same arm catching hold of the rim of the cistern raises it
also, and by means of the conical points inserted in the holes of the rim keeps
the cistern always at the same distance from the fulcrum. The sliding weight
is then moved towards the fulcrum, and the height of the column thus ascer-
tained. The adoption of this plan will not interfere with the ordinary scale
which may be still retained in combination with it. When the steelyard
lever is not required to be in use, it may be placed out of the way in the
vertical recess i, k, to which there is an opening in the side of the framework.
To register the indications of a barometer constructed in manner first herein-
before described, I place at the back of the cistern or.spring balance a circular
plate of metal covered in front with photogenic paper of the same size as the dial
plate, and make the centres of the two plates to coincide exactly. Betwixt the
circumference of the dial plate and the graduated circle on the face of it there
is a margin or border left of about an inch and a half in breadth, and across this
margin make a narrow slit directly over or under the centre of the plate.
Behind the dial and before this slit I place a slip of metal, which is attached to
the cistern balance or spring balance, the bottom of which, when the mercurial

page_text: column is at its highest point, is on a level with the upper end of the slit.
Now, as the rising and falling of the cistern or spring balance encreases or
diminishes the length of the line of light admitted on to the photogenic paper,
then causing the registering plate to revolve. (by a weight or by any other
convenient means), a circular border is formed on the photogenic paper, the
outer edge of which represents exactly the fluctuations in the atmospheric pres-
sure. But as the preceding method answers only for the day-time, I adopt the
following plan when it is desired to continue the registration both during night
and day: To the cistern or spring balance I affix a pencil, the point of which
is made by means of a spring to press lightly on a surface of common paper
stretched over the registering plate, so that on the plate being caused to revolve
(by a weight or otherwise, as aforesaid), the pencil. registers, by corresponding
lines on the paper, the rise and fall of the barometic column. As it is essential
to the accurate performance of the instrument, care must be taken that the
interior of the barometric tube and the external surface of the balance cistern
be truly cylindrical at those parts with which the mercury comes 'in-contact
in rising and falling.
And having now described the nature of my said Invention, and the manner
in which the same is to be performed, I declare that I do not claim any one
of the parts of any of the instruments before described as in and by itself new;
but that what I claim is,-
First, the placing of the cistern of the barometer upon a spring or other
suitable balance, by the elevation or depression of which balance the height of
the barometric column is ascertained, as well as the range of the column
increased.
Second, the placing the cistern of the barometer on mercury contained in a
cylinder, which mercury serves the same purpose as the spring or other balance
last before mentioned.
Third, the application of the steelyard balance, as herein described, to ascer-
tain the height of the barometric column.
Fourth, the application of photography, in the manner and by the means
herein before described, to registering the indications of barometers.
And such my said Invention being, to the best of my knowledge and belief,
entirely new, and never before used within that part of Her Majesty's United
Kingdom of Great Britain and Ireland called England, Her Dominion of
Wales, or the Town of Berwick-upon-Tweed, I do hereby declare this to be
my Specification of the same, and that I do verily believe this my said Speci-
lication doth comply fully and in all respects without reserve or disguise with
the proviso in the said herein before in part recited Letters Patent contained;

page_text: wherefore I hereby claim to maintain exclusive right and privilego to my
said Invention.
In witness whereof, I have hereunto set my hand and seal, this Seventh
day of September, One thousand eight hundred and forty-two.
JAMES (L.S.) READMAN.
AND BE IT REMEMBERED, that on the Seventh day of September,
in the year of our Lord 1842, the aforesaid James Readman came before
our said Lady the Queen in Iler Chancery, and acknowledged the Speci-
fication aforesaid, and all and every thing therein contained and specified, in
form above written. And also the Specification aforesaid was stamped accord-
ing to the tenor of the Statute made for that purpose.
Inrolled the Seventh day of September, in the year of our Lord One
thousand eight hundred and forty-two.