Improvements in Aneroid Barometers.
Year: 1899

page_text: Improvements in Aneroid Barometers.
We, GEORGE FORBES, Engineer, of 34, Great George Street, Westminster, and
JOHN MARSHALL GORHAM, Engineer, of 66, Victoria Street, Westminster, do
hereby declare the nature of this invention to be as follows:
Our invention relates to improvements in aneroid barometers, and the object
of our invention is to obviate the errors well known to exist in these instru-
ments, especially when used for measuring altitudes with great accuracy.
The usual method of arranging the mechanism is to provide a cylindrical
metallic chamber one end of which expands and contracts with variations of the
atmospheric pressure, the air inside the chambers being removed. The more-
ment of the end plate is communicated by levers or by means of a chain and
pulley to a pointer, and this gearing up to obtain an open reading from so small
a movement is one cause of inaccuracies, the reading of the pointer being
dependent on the amount of movement of the end plate.
By our method instead of measuring the movement of the plate we balance
the atmospheric pressure on the end plate by means of a spring or springs or
dead weights and thus weigh the atmospheric pressure, no movement of the
end plate of the metallic chamber is required excepting what is necessary to
deflect a small mirror in order to indicate that the instrument is in a state of
balance, the amount of deflection of the mirror is therefore of no consequence,
as the mirror reading is at zero when balance is restored.
In order to obtain an accurate adjustment we use a strong spring or heavy
weight to nearly balance the atmospheric pressure. The final adjustment being
made by a light spring or weight moving over a fine scale with vernier attach-
ment and lens. In order to obtain an accurate reading of the zero line from
the mirror we prefer to use a system of compound lenses, such as a telescope
with fine thread inside the eye piece, into which the zero line is reflected,
Dated this the 14th day of June 1899.
GEORGE FORBES.
J. M. GORHAM.
COMPLETE SPECIFICATION.
Improvements in Aneroid Barometers.
We, GEORGE FORBES, Engineer, of 34, Great George Street, Westminster, and
JOHN MARSHALL GORHAM, Engineer, of 66, Victoria Street, Westminster, do
hereby declare the nature of this invention and in what manner the same is to
be performed, to be particularly described and ascertained in and by the follow-
ing statement:-
-
Our invention relates to improvements in aneroid barometers, and the object

page_text: '
of our invention is to obviate the errors well known to exist in these instru-
ments, especially when used for measuring altitudes with great accuracy.
The usual method of arranging the mechanism is to provide a cylindrical
metallic chamber one end of which expands and contracts with variations of the
atmospheric pressure, the air inside the chamber being removed. The move-
ment of the end plate is communicated by levers or by means of a chain and
pulley to a pointer, and this gearing up to obtain an open reading from so small
a movement is one cause of inaccuracies, the reading of the pointer being
dependent on the amount of movement of the end plate.
By our method instead of measuring the movement of the plate we balance
the atmospheric pressure on the end plate by means of a spring or springs or
dead weights and thus weigh the atmospheric pressure, no movement of the
end plate of the metallic chamber is required excepting what is necessary to
deflect a small mirror in order to indicate whether the instrument is in a state of
balance, the amount of deflection of the mirror is therefore of no consequence,
as the mirror reading is at zero when balance is restored.
Referring to Figure 1, A is the ordinary diaphragm of an aneroid barometer.
B the spring resisting the atmospheric pressure on the surface of diaphragm C.
At D instead of the gearing and pointer to magnify the movement at C, we
place a mirror to indicate when the position of the diaphragm C is at zero,
this is brought to zero by the small weights E E, and is held between stops F F,
which allow it to move only about one thousandth of an inch on each side of
zero, whereas in the ordinary instrument the amount of the movement is
registered by the pointer.
The method of reading therefore is to add or take off weights until the fine
line G in Figures 1 and 2 in the eye piece H is opposite the zero line on the
scale J, indicating that the diaphragm C is in its normal position, each weight
represents so many feet of altitude.
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that
what we claim is:-
A barometer of the aneroid class in which the air pressure on the diaphragm
is measured by a counteracting pressure which brings the diaphragm back
to its normal position.
רדי
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