Improvements in Barometers.
Year: 1899

page_text: Improvements in Barometers.
I, CHARLES MURRAY PLAYFAIR, care of Messrs. Cox & Co., 16, Charing Cross,
London, Lieutenant in the Royal Artillery,, do hereby declare the nature of
this invention to be as follows:-
My invention relates to improvements in barometers and the chief object of
my improvements is to increase the sensitiveness of such instruments.
In carrying my improvements into effect I employ a cylindrical or other
suitably shaped vessel with an open mouth capable of being closed by the glass
or other tube of the barometer. Into this vessel I pour any suitable liquid
until the vessel is say half full. The liquid I prefer to employ is glycerine,
with a trace of water added, on account of its low specific gravity and its
non-liability to freeze or evaporate. The glass tube which is open at both ends
is inserted into the mouth of the vessel and after the joint has been made
airtight I pour a sufficient quantity of glycerine down the tube until the column
in the tube has risen to a convenient height and the air in the vessel has been
sufficiently compressed but any other method of compressing the air or other
gaseous contents of the vessel might be adopted.
To adjust the glycerine column for height I alter the capacity of the vessel
so as to increase or diminish the compression of the air therein and this may
be effected in various ways as for example,-I make the vessel with a spring
metal side or bottom preferably convex on the exterior, and alter the capacity
of the interior of the vessel by means of an adjusting screw or any equivalent
appliance.
All the foregoing parts are mounted in a slide on a suitable frame, the slide
being regulated by an adjusting screw or the like. The frame also carries a
scale by which the instrument is read and may also carry various other scales
used for adjusting it or for other purposes, as for example, determining the
height above sea level.
or.
To correct the glycerine column for temperature I adjust a pointer fixed to
move with the slide to a figure corresponding to the temperature at the time
of observation on a suitably graduated scale on the stationary frame;
alternatively, instead of regulating the movement of the slide by hand I might
employ any suitable form of mechanical device for effecting the adjustment.
automatically.
Dated this 2nd day of February 1899
H. B. BARLOW & GILLETT,
Agents for Applicant.

page_text: I, CHARLES MURRAY PLAYFAIR, care of Messrs. Cox & Co., 16, Charing Cross,
London, Lieutenant, Royal Garrison Artillery, do hereby declare the nature of
this invention and in what inanner the same is to be performed, to be parti-
cularly described and ascertained in and by the following statement:-
My invention relates to improvements in barometers, and the chief object of
my improvements is to increase the sensitiveness of such instruments.
In the accompanying sheet of drawings-
Figure 1 is an elevation of a barometer made according to my improvements
and Figure 2 is a detail view of the same on a larger scale.
In carrying my improvements into effect I employ a cylindrical or other
suitably shaped vessel or reservoir. C of any material with an open mouth,
capable of being closed by the glass or other tube D of the barometer: I fit
the tube D which is open at both ends into the mouth of the reservoir Cand
make an airtight joint between the two.
I pour a suitable liquid E down the tube until it rises to a convenient height
in the tube but any other mode of filling the tube and reservoir might be
adopted. The liquid I prefer to use is glycerine (pure or with a trace of water
added and colouring matter if necessary) on account of its low specific gravity
and its non-liability to freeze or evaporate.
It might be advantageous to put any gas other than air into the reservoir
in addition to the liquid.
The reservoir C and tube D are mounted on a suitable frame F and are
either fixed or adjustable relatively to one another.
To adjust the glycerine column for height above the sea level I alter the
capacity of the reservoir C so as to increase or decrease the internal pressure
by means of a screw G or some equivalent device.
This may be effected in various ways, e.g., I make the reservoir with a spring
metal side or bottom preferably convex on the exterior and alter the capacity
of the interior of the reservoir by means of the adjusting screw G. The
relative sizes of the reservoir and bore of the tube depend upon the amount
of sensitiveness required.
The tube is open at both ends and a loose plug H of some porous material
as cotton wool is inserted at the top to keep out dust, or a cap could be fitted
to shade the top.
The frame F slides in another frame J which carries various scales K, L, M,
and there is a thermometer N attached to some part of the instrument.
These need not all be used.
A. B are the two verniers moved by the mill headed screws P, P. The
scale K can be graduated to correspond with the scale of the ordinary mercury
barometer, by direct comparison, or could have a scale of natural inches or
other divisions marked on it.
The scale L is graduated in feet to measure altitudes; this scale can be
made to work in a slide Q so as to get actual instead of relative readings.
The scale M is used to correct the instrument for temperature, and is
constructed as follows:-
A datum mark R is made on the slide F and a mark is made opposite to
it on the blank scale M; one of the verniers is then set to the height of the
column, the temperature of the attached thermometer is noted.
The whole instrument is then placed in a different temperature, say 10 degrees
different.

page_text: The screw S which moves the slide F up or down in the frame J is now
turned until the top of the column is in its original position, i.e., is level with
the vernier that was first set.
Another mark is made on the scale M opposite to the new position of the
datum mark R.
The space between the two marks on the blank scale is divided into as many
equal divisions as there were degrees of difference of temperature, in the above
case 10 degrees.
The scale is completed by marking off these equal divisions until it is
conveniently full. The temperatures corresponding to these divisions are noted
opposite to them.
When reading the instrument the attached thermometer is first read and the
datum mark made to correspond to this temperature on the scale M, by
turning the screw S.
One of the verniers is then set to the top of the column and the reading
is taken in the ordinary way.
Instead of using the screw S I might employ any suitable form of mechanical
device for regulating the movement of the slide automatically and so com-
pensating the column for temperature.
It will be obvious that the instrument can be made of any convenient size.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is―
1. The herein described improvements in barometers which improvements
consist essentially in fixing the barometer tube in the open mouth of an adjust-
able reservoir the gaseous contents of which are sealed by the liquid column
in the tube and the height of the column is adjusted by altering the internal
capacity of the reservoir all substantially as herein set forth.
2. In combination with the matter set forth in Claim 1, means for compen-
sating the liquid column for temperature substantially as specified.
3. The general construction combination and arrangement of parts consti-
tuting an improved barometer substantially as and for the purposes herein
described with reference to the accompanying drawings.
Dated this 2nd day of November 1899.
H. B. BARLOW & GILLETT,
Agents for Applicant, 17, St. Ann's Square, Manchester.