IMPROVEMENTS IN BAROMETERS OR INSTRUMENTS FOR MEASURING ALTITUDES OR THE PRESSURE OF THE ATMOSPHERE OR ELASTIC FLUIDS
Year: 1862

page_text: LETTERS PATENT to Thomas Evans Blackwell, of Orsett Terrace, Hyde
Park, in the County of Middlesex, Civil Engineer, for the Invention
of "IMPROVEMENTS IN BAROMETERS OR INSTRUMENTS FOR MEASURING
ALTITUDES OR THE PRESSURE OF THE ATMOSPHERE OR ELASTIC FLUIDS."
Sealed the 17th April 1863, and dated the 5th December 1862.
PROVISIONAL SPECIFICATION left by the said Thomas Evans Blackwell
at the Office of the Commissioners of Patents, with his Petition, on the
5th December 1862.
I, THOMAS EVANS BLACKWELL, of Orsett Terrace, Hyde Park, in the County
of Middlesex, Civil Engineer, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN BAROMETERS OR INSTRUMENTS FOR MEASURING
ALTITUDES OR THE PRESSURE OF THE ATMOSPHERE OR ELASTIC FLUIDS," to be
as follows:-
My Invention for improvements in barometers or instruments for measuring
altitudes or the pressure of the atmosphere or elastic fluids, relates to a novel
mode of constructing these instruments, so as to make them portable, and yet
at the same time exceedingly sensitive and accurate. The desired object is
effected in some of my improved instruments by a combination of several
separate improvements, but in other instruments some only of the improve-
ments are comprised. In all my improved instruments, however, the
variations in pressure are ascertained by means of elastic vacuum chambers,
as in the ordinary aneroid barometer, and I find it convenient to employ four
or more elastic chambers arranged in groups or sets, so that the inequalities of
pressure or inaccuracies of action in any of the several chambers shall be com-
pensated by the others. In all my instruments these vacuum chambers are
directly attached to helical or other springs, the power of which has been pre-

page_text: viously. ascertained with great care, and which reciprocate the expansion or
compression of the chambers accordingly as they are acted upon by diminished
or increased pressure.
In some of my instruments which correspond in general form to the
ordinary aneroid barometer, the resultant motion of these vacuum chambers
and springs is communicated to the index by bars, levers, or other suitable
mechanical contrivances. The effect of such arrangements is to give a large
amount of range or angular motion to the index, so as to render the instru-
ment specially applicable to the measurement of moderate differences of
heights and pressure; but inasmuch as the giving this enlarged amount of
angular motion or range to the index would limit the range of pressures to be
observed by any one instrument, I adapt a means of adjusting the tension of
the springs to any greater or less range of pressure which may be exerted in
the vacuum chambers. This is done by means of a screw attached to the
rear end of the springs, by means of which their tension or pressure on the
vacuum chambers can be varied to the extent required.
In other of my instruments which usually take the form of an elongated
cylinder of portable size, there is fixed on the axis connecting the vacuum
chambers with the helical spring a gauge point, which moves either way with
the axis according as the vacuum chambers are compressed or expanded by
an increase or diminution of external or atmospheric pressure. There is also
fixed to the inside of the cylinder or case of the instrument a small bracket
or frame carrying a kind of bell-crank lever, the shorter arm of which is,
when the instrument is set for commencing observations, brought into imme-
diate contact with and just touched by the gauge point, the larger arm coming
at the same time into exact contact with the curved face of a block or surface
at the lower end of the instrument. The gauge point when raised or
depressed by a greater or less pressure exerted on the vacuum chambers can,
for the purpose of ascertaining the amount of motion gone through, be brought
back to its normal condition by means of a screw attached to the opposite end
of the spring. The ratio between the tension of the spring and the movement
of the vacuum chambers under 'known pressures having been experimentally
determined, the value of the amount of motion gone through by the gauge
point is read off on a scale attached to a micrometer screw, and working upon
or through the lower end of the instrument into a corresponding female screw
attached to a cross head at the lower end of the spring. At this part of the
spring the movement in a rectilinear direction is greater than the movement
of that end attached to the gauge point of the vacuum chambers.
Having experimentally determined the ratio of these movements and known

page_text: pressures, I graduate a scale for the linear movements on the body of the
instrument; such scale, although much larger than the range of the gauge
point itself will admit of, is in this instrument further subdivided in effect
by the addition of a micrometer to the head of the screw; the divisions on this
micrometer are proportioned to the rectilinear movements of the nut upon the
screw while being adjusted.
In order to measure differences of pressure with this instrument it will be
necessary to compare any two or more observations as read off by the coarser
and finer adjustment. In each instance the difference in the reading subject
to correction for temperature will represent the difference in pressure, and
therefore the difference in altitude.
Instruments constructed on the principle above set forth may be em-
ployed for any purpose in which it may be desired to ascertain or register.
the surface or other pressure of the atmosphere as in anemometers, or for
instruments, such as steam or pressure gauges, for ascertaining the pressure:
of other aeriform fluids or of liquids.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Thomas Evans Blackwell in the Great Seal Patent Office
on the 5th June 1863.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS.
EVANS BLACKWELL, of Orsett Terrace, Hyde Park, in the County of Middlesex,,
Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters.
Patent, bearing date the Fifth day of December, in the year of our Lord
One thousand eight hundred and sixty-two, in the twenty-sixth year of;
Her reign, did, for Herself, Her heirs and successors, give and grant unto
me, the said Thomas Evans Blackwell, Her special license, that I, the
said Thomas Evans Blackwell, my executors, administrators, and assigns,
or such others as I, the said Thomas Evans Blackwell, 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 Invention of "IMPROVEMENTS IN BAROMETERS. OR INSTRU-
MENTS FOR MEASURING ALTITUDES OR THE PRESSURE OF THE ATMOSPHERE OR ELASTIC
FLUIDS," upon the condition (amongst others) that I, the said Thomas Evans
Blackwell, by an instrument in writing, under my hand and seal, should

page_text: 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 Evans Blackwell, 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, reference being had to the Drawings hereunto annexed;
and to the letters and figures marked thereon (that is to say):-
My Invention of "Improvements in Barometers or Instruments for Measuring
Altitudes or the Pressure of the Atmosphere or Elastic Fluids relates to a novel
mode of constructing these instruments, so as to make them portable, and yet
at the same time exceedingly sensitive and accurate. The desired object is
effected, in some of my improved instruments by a combination of several
separate improvements, but in other instruments some only of the improvements
are comprised. In all my improved instruments, however, the variations in
pressure are ascertained by means of elastic vacuum chambers, as in the ordi-
nary aneroid barometer, and I find it convenient to employ four or more elastic
chambers arranged in groups or sets, so that the inequalities of pressure, or
inaccuracies of action in any of the several chambers, shall be compensated by
the others. In all my instruments these vacuum chambers are directly attached
to or connected with helical or other springs, the power or elastic force of
which has been previously ascertained with great care, and which reciprocate
the expansion or compression of the chambers accordingly as they are acted
upon by diminished or increased pressure.
Some of my instruments correspond in general form to the aneroid barometer,
and are shewn in the accompanying Drawing at Figures 1, 2, and 3. The
resultant motion of the combined vacuum chambers and springs is commu-
nicated to the index by bars, levers, or other suitable mechanical contrivances,
as will be seen in the Drawing, in which Fig. 1 is a front or face view of
the instrument; Fig. 2 is a back view of the inside, the back plate having
been removed so as to expose the internal parts; Fig. 3 is a horizontal section
of the same.
a, a, is a metal framework for supporting the principal working parts; b, b
are two sets of vacuum chambers, one set of which is shewn detached and in
section at Fig. 4. These vacuum chambers on the lower bar of the frame
a are attached at their upper ends to the extremities of a bar or crosshead c
which is connected by means of a link d, to one end of a vibrating lever e, the
opposite end of which is connected by another link to the adjustable vibrating

page_text: lever which is mounted on the spindle f¹, which carries the rack lever g.
The lever f is adjustable on the spindle f¹, by means of a slot and screw, as
shewn in Figs. 2 and 3, so that the length of the leverage may be regulated
and adjusted with nicety. The lever g is provided at one end with a counter-
balance weight g', and at the other with a sector rack 92, which gears into
and drives a pinion on the spindle h of the index arm i. To the upper end
of the sets of vacuum boxes b, b, are connected the helical springs j, j, which are
suspended by their opposite ends from the arms of a crosshead k. This cros=-
head is secured to the inner end of a rod shewn by dots in Fig. 2, and which
is screwed at the opposite end and passes through a nut l, shewn detached in
plan at Fig. 5. The effect of this arrangement of parts is to give a large
amount of range or angular motion to the index i, so as to render the instru-
ment specially applicable to the measurement of moderate differences of heights
and pressure. The extent of this motion may be indicated and made more
easily apparent by the employment of the brass index haud i*, which is mounted
on a centre in any convenient manner so that it may be moved by hand to
any point, at which it will remain until moved again by hand to some other
point. Inasmuch as the giving an enlarged amount of angular motion or
range to the index as above mentioned would limit the range of pressures to be
observed by any one instrument, I adapt a means of adjusting the tension of
the springs to any greater or less range of pressures which may be exerted in
the vacuum chambers. This is done by means of the adjusting or regulating
screw and nut 1, attached to or connected with the rear end of the springs j, j,
as above mentioned. By screwing up or unscrewing this regulating screw and
nut, the tension or pressure of the springs j, j, on the vacuum chambers b, b,
can be varied to the extent required, and consequently the instrument can be
adjusted to any pressure with facility.
'
In the accompanying Drawings Figs. 6, 7, 8, and 9 represent various views
of another form of my improved instrument, which in this instance is made in
the form of an elongated cylinder of portable size. Fig. 6 is an elevation of
one side of the tube, and Fig. 8 is a similar view of the tube as seen at a point
at right angles to Fig. 6; Fig. 7 is a longitudinal vertical section, and Fig. 9
is an end view of the instrument, shewing a micrometer arrangement for reading
off observations with additional accuracy.
a, is the case of the instrument; b, the set of vacuum boxes or chambers pro-
vided with a rod c, which passes through a bracket fixed to the side of the case.
The end of this rod c is pointed, and is called the gauge point. It bears against
one arm of a bell-crank lever e, which turns in bearings in a bracket f; the
larger arm of this lever extends back to a cylindrical block n, for the purpose
C

page_text: hereafter explained. A helical spring j, is attached by one end to the rod o
the vacuum boxes b, and by the other end to the cross head k, in which is made
a female screw to receive an adjusting screw d, which turns freely in the block n
at the head of the instrument. This screw d is provided with a milled head n
so that it may be turned with facility by the finger and thumb, and it also carries
an index plate n², which also works on an accurately divided micrometer plate g
fixed on the end of the tube a. The cross head k is worked up and down in a
vertical direction by turning the milled head n', of the screw d, in the required
direction. One end of this cross-head works in a guide (Fig. 8), and the
other end projects through and works in a slot k³ (Figs. 8 and 9) in the side
of the instrument. This end of the cross head acts as an index, whereby when
the instrument is in adjustment, an observation as to the pressure on the vacuum
boxes may be read off on a divided scale made at the side of the slot. On the
rod connecting the vacuum boxes or chambers 6 with the helical spring j there
is a gauge point, which moves either way, that is up or down, with the rod,
according as the vacuum chambers are compressed or expanded by an increase
or diminution of atmospheric or other external pressure. In order to test and
ascertain that the vacuum boxes 6 and spring j are in perfect equilibrium, the
bell-crank lever e, e', is employed; it is mounted on the inside of the cylinder
or case of the instrument on the small bracket or frame f. The shorter arm
of this lever, when the instrument is set for commencing observations, is
brought into immediate contact with and just touched by the gauge point of
the rod c; the longer arm e¹ of the bell-crank lever comes at the same time
into exact contact with the curved face of a block or other surface n, placed at
the other end of the instrument, near the termination of the longer arm e of
the bell-crank lever. The gauge point of the rod c, when raised or depressed
by a greater or less pressure exerted on the vacuum chambers b, can, for the
purpose of ascertaining the amount of motion gone through, be brought back
to its normal position by means of the screw d. The ratio between the tension
of the spring j and the movement of the vacuum chambers b under known
pressures having been experimentally determined, the value of the amount of
motion gone through by the gauge point of the rod c is read off on the scale
attached to the side of the instrument, increased accuracy of observation being
attainable by means of the micrometer at the lower end of the instrument.
The screw d extends through the end of the instrument, and works into a
corresponding female screw attached to the cross head k at the other end of
the spring. At this part of the spring the movement in a rectilinear direction
is greater than the movement of that end attached to the gauge point of the
vacuum chambers b. Having experimentally determined the ratio of these

page_text: movements and known pressures, I graduate a scale for the linear movements
on the body of the instrument, such scale, although much larger than the
range of the gauge point itself will admit of, is in this instrument further
subdivided in effect by the addition of the micrometer index to the head of the
screw. The divisions on this micrometer are proportioned to the rectilinear
movements of the nut of the cross head k upon the screw while being adjusted.
In order to measure differences of pressure with this instrument, it will be
necessary to compare any two or more observations as read off by the coarser
and finer adjustment. In each instance the difference in the reading subject
to correction for temperature will represent the difference in pressure, and
therefore the difference in altitude, and the altitude may be calculated
therefrom.
Instruments constructed on the principle above set forth may be employed
for any purpose in which it may be desired to ascertain or register the pressure
of the atmosphere, as in anemometers, or for instruments, such as steam or
pressure gauges for ascertaining the pressure of other aeriform fluids or of
liquids.
Having now described my Invention of "Improvements in Barometers or
Instruments for Measuring the Altitudes or the Pressure of the Atmosphere
or Elastic Fluids, and having explained the manner of carrying the same
into effect, I claim as the Invention secured to me by Letters Patent as
aforesaid, the mode herein set forth of constructing instruments for measuring
or ascertaining altitudes or pressures of the air or fluids.
I claim particularly the combination of the vacuum chambers or boxes and
springs, with a screw or other suitable adjustmeut, whereby the tension of the
springs and the pressure on the vacuum chambers or boxes may be brought
into equilibrio for the purpose herein set forth.
I further claim the mode shewn of ascertaining when the vacuum boxes
and spring are in equilibrio, and also the use or application to the instrument
of the micrometer arrangement, whereby variations in pressure may be
ascertained with great accuracy.
In witness whereof, I, the said Thomas Evans Blackwell, have hereunto
set my hand and seal, the Thirteenth day of February, in the
year of
our Lord One thousand eight hundred and sixty-three.
THO8. E. BLACKWELL. (L.S.)