IMPROVEMENTS IN ANEROID BAROMETERS
Year: 1865

page_text: LETTERS PATENT to Thomas Cooke, of Buckingham Works, in the City..
of York, and of 31, Southampton Street, Strand, in the County of
Middlesex, Astronomical Instrument Maker, for the Invention of
"IMPROVEMENTS IN ANEROID BAROMETERS."
Sealed the 17th April 1866, and dated the 20th October 1865.
PROVISIONAL SPECIFICATION left by the said Thomas Cooke at the
Office of the Commissioners of Patents, with his Petition, on the
20th October 1865.
I, THOMAS COOKE, of Buckingham Works, in the City of York, and of
31, Southampton Street, Strand, in the County of Middlesex, Astronomical
Instrument Maker, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN ANEROID BAROMETERS," to be as follows:-
The aneroid has during the last two or three years, through its reduced size
and increased convenience, become a most valuable scientific portable instru-
ment; any improvement in its construction rendering it more reliable and more
accurate as a differential instrument will increase its value for general use, but
more especially so for measuring altitudes as required by the scientific traveller
and the engineer.
The aneroid as generally constructed consists of a very short cylindrical
box or vacuum chamber, the ends of which are made of thin metal, corrugated

page_text: for greater elasticity. When this box is exhausted of air and hermetrically
sealed, the centres of the two ends collapse or are forced together by the
external pressure of the atmosphere. These are made to separate again
nearly to their natural distance through the action of an external powerful
spring attached to the centre of one of the corrugated plates, whilst the
centre of the other is secured to a stout foundation plate. The atmospheric
pressure and the form of the strong spring balance each other, and any
variation in the pressure of the former produces a corresponding change in
the tension of the spring. The motion thus produced is conveyed by a system
of levers, and a délicate chain partly wound round a small cylinder, to the axle
or spindle of which carries the hand for indicating the variations on a suitably
graduated dial. The said spring is by means of a set screw adjusted to the
atmospheric pressure, as shown by a mercurial barometer.
This instrument is necessarily a little complicated and, though the principle
on which it is constructed is scientifically correct, it is subject to certain slight
nechanical irregularities in its action and indications. The delicate chain
referred to is one of the principal sources of error and of inaccuracy of the
aneroid, the links and their connecting pins gave rise to comparatively
considerable friction, and any trifling want of freedom in the working action
of the links in winding on to the index cylinder, and which may be produced
by a little rust, by the oil applied to them becoming stiff or glutinous, or by
other causes, will prevent the chain, which is only held in tension by the very
small force of a slender spiral check spring, from taking its true and correct
position on the cylinder.
The present important improvement consists in substituting for the chain
above described a very thin tape-like band or fine wire of any of the most
ductile metals, such as gold, platina, steel, or others. The slender metallic
band is reduced to such a thickness as to make it wind freely round the index
cylinder and bring it into close contact with it by the force of the spiral check
spring usually used for the chain. This thin metallic band is free from all
the irregularities to which the chain is subject, and when made of gold or
platina will be very durable in climates subject to much wet and dampness,
where the ordinary chain soon becomes useless.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Thomas Cooke in the Great Seal Patent Office on the
20th April 1866.
*1*
14
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
COOKE, of Buckingham Works, in the City of York, and of 31, Southampton
Street, Strand, in the County of Middlesex, Astronomical Instrument Maker,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twentieth day of October, in the year of our Lord
One thousand eight hundred and sixty-five, in the twenty-ninth year of
Her reign, did, for Herself, Her heirs and successors, give and grant
unto me, the said Thomas Cooke, Her special licence that I, the said
Thomas Cooke, my executors, administrators, and assigns, or such
others as I, the said Thomas Cooke, my 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 In-
vention for "IMPROVEMENTS IN ANEROID BAROMETERS," upon the condition
(amongst others) that I, the said Thomas Cooke, my executors or adminis-
trators; 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 Thomas Cooke, 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 fol-
lowing statement :-
'
The aneroid has during the last two or three years, through its reduced
size and increased convenience, become a most valuable scientific portable
instrument; any improvement in its construction rendering it more reliable and
more accurate as a differential instrument will increase its value for general
use, but more especially so for measuring altitudes as required by the scientific
traveller and the engineer."
The aneroid as generally constructed consists of a very short cylindrical

page_text: box or vacuum chamber, the ends of which are made of thin metal plates,
which are corrugated for the purpose of giving greater elasticity. When
this box is exhausted of air and hermetically sealed the centres of the two ends
collapse or are forced together by the external pressure of the atmosphere.
These are made to separate again nearly to their natural distance from each
other through the action of an external powerful spring which is attached to
the centre of one of the corrugated plates, whilst the centre of the other is
secured to a stout foundation plate. The atmospheric pressure and the force
of the said spring balance each other, and any variation in the pressure of the
former produces a corresponding change in the tension of the spring. The
motion thus produced is conveyed by a system of levers, and a delicate chain
partly wound round a small cylinder, to the axle or spindle which carries the
hand for indicating the variations on a suitably graduated dial. The said
spring is by means of a set screw adjusted to the atmospheric pressure, as
indicated by a mercurial barometer.
This instrument, as described, is necessarily a little complicated, and although
the principle on which it is constructed is scientifically correct, it is subject to
certain slight mechanical irregularities in its action and indications. The
delicate chain referred to is one of the principal sources of the errors and
inaccuracies of the aneroid. The links and their connecting pins give rise to
comparatively considerable friction, and any trifling want of freedom in the
working action of the links in winding on the index cylinder, and which want
of freedom may be produced by corrosion, by the oil applied for lubrication
becoming stiff or glutinous, or by other causes, will prevent the chain, which
is only held in tension by the very small force of a slender spiral check spring,
from taking its true and correct position on the cylinder.
The present important improvement consists in substituting for the chain
above described a very thin tape-like band or fine wire of any of the most
ductile metals, such as gold, platina, steel, or others. This slender metallic
band is reduced to such a thickness as to make it wind freely round the
index cylinder and bring it into close contact with it by the force of the
spiral check spring usually used for the chain. This thin metallic band is
free from all the irregularities to which the chain is subject, and when
made of gold or platina will be very durable in climates subject to much
wet and dampness, where the ordinary chain soon becomes useless.
Having now described the nature of the said improvements, and the manner
in which the same are to be carried into effect, I wish it to be understood
that what I claim as the Invention to be secured to me by the herein-before

page_text: in part recited Letters Patent is, the application to aneroid barometers of a
metallic tape-like band or fine wire in lieu of the chain hitherto employed, in
the manner and for the purposes substantially as herein-before described.
In witness whereof, I, the said Thomas Cooke, have hereunto set my
hand and seal, this Twentieth day of April, in the year of our
Lord One thousand eight hundred and sixty-six.
THOMAS COOKE. (L.S.)