Improvements in Balances.
Year: 1893

page_text: Date of Application, 1st Feb, 1893
Complete Specification Left, 1st Nov., 1893-Accepted, 2nd Dec., 1893
PROVISIONAL SPECIFICATION.
Improvements in Balances.
I, WILLIAM THOмsos, Baron Kelvin of Largs, Professor of Natural Philosophy
in the University of Glasgow, North Britain, do hereby declare the naturo of this
invention to be as follows:-
In balances supported by knife edges on fixed planes whether for ordinary
weighing or for the measurement of magnetic or electro-magnetic or electric forces
the bearing part of the knife-edge surface is made as nearly cylindric as possible,
and the fixed surface as nearly a true plane as possible. Vory perfect fulfillment
of these conditions is required for good action.
The object of my present improvements is to diminish these constructional
difficulties and to give greator sensibility and constancy, by a simpler attainment of
the necessary dynamical conditions.
Instead of supporting the beam by a straight knife-edge I support it by a single
curved edge which for brovity I shall call an axe-edge. For ordinary gravitational
weighings I use inverted axe-edges fixed to the two ends of the beam and scale pans
hung by inverted stirrups with flat planes resting on these axe-edges.
I use a single hard plane for the central support, and as in the ordinary balance,
I use lifters and forks.
When moderate accuracy suffices I use a saddle-shaped surface instead of a plane
for the central support, and instead of an axe-edge a concave knife-edge, which for
brevity I shall call a sickle-edge, attached to the beam and resting on as nearly as
may be the level part of the saddlo surface. The curvature of the sickle-edge
ought to be less than that of the vertical section of the bearing surface on which it
rests. It is sometimes convenient to use for the sickle-edge a portion of the inner
edge of a ring of agate or hardened steel or other hard metal ground with its inner
edge sharp all round; and to use for the saddle surface the saddle-shaped bearing
portion of a well rounded and polished hook of hard material. "In such cases hooks
on sickle-edges attached to the ends of the beam as in the cheaper forms of ordinary
balances may be used for carrying the pans.
When greater hardiness against lateral motions of the beam is wanted, I support
it on two hooks by a straight knife-edge fixed to it on one side and a sickle-edge
fixed to it on the other. This plan is particularly convenient for electric and
magnetic measuring instruments.
•
Dated this 31st day of January 1893.
BOTTOMLEY & LIDDLE,
154, St. Vincent Stroet, Glasgow, Applicant's Agents.
COMPLETE SPECIFICATION.
Improvements in Balances.
I, WILLIAM THOMSON, Baron Kelvin of Largs, Professor of Natural Philosophy
in the University of Glasgow, North Britain, do hereby declare the nature of
this invention and in what manner tho samo is to be performed to be particularly
described and ascertained in and by the following statement :-
In balances supported by knife-edges on fixed planes, whether for ordinary
weighing, or for the measurement of magnetic, or electro-magnetic, or electrio
forces, the bearing part of the knife-edge surface is made as nearly cylindric as
possible, and the fixed surface as uearly a true plane as possible. Very perfect
fulfilment of these conditions is required for good action.

page_text: The object of my present improvements is to diminish these constructional
difficulties and to give greater sensibility and constancy by a simpler attainment of
the necessary dynamical conditions.
Instead of supporting the beam by a straight knife-edge, I support it by a single
curved edge, which for brevity I shall call an axe-edge. For ordinary gravita-
tional weighings I use inverted axe-edges fixed to the two ends of the beam and
seale pans hung by inverted stirrups with flat planes resting on these axe edges.
I use a single hard plane for the central support, and as in the ordinary balance,
I use lifters and forks..
When moderate accuracy suffices-I use a saddle-shaped surface instead of a plane
for the central support, and instead of an axe-edge, a concave knife-edge, which for
brevity I shall call a sickle-edge, attached to the beam, and resting on as nearly as
may be the level part of the saddle surface. The curvature of the sickle-edge
ought to be less than that of the vertical section of the bearing surface on which it
rests. It is sometimes convenient to use for the sickle-edge a portion of the inner
edge of a ring of agate or hardened steel or other hard metal ground with its inner
edge sharp all round; and to use for the saddle surface the saddle-shaped bearing
porzion of a well-rounded and polished hook of hard material. In such cases hooks
on sickle-edges attached to the ends of the beam, as in the cheaper forms of ordinary
balances, may be used for carrying the pans.
When greater hardiness against lateral motions of the beam is wanted, I support
it on two hooks by a straight knife-edge fixed to it on one side, and a sickle-edge
fixed to it on the other. This plan is particularly convenient for electric and
magnetic measuring instruments.
In order that my invention may be properly understood and readily carried into
effect I have hereunto appended an explanatory sheet of drawings in the several
figures of which corresponding parts are marked with the same lettera of reference.
Figure 1 represents a balance the beam ▲ of which is supported on a single
curved edge « shown in cross section at Figure 2, resting on a flat plane b of hard
material. Two guide pivots o, d are attached to the beam, and have their axes in
line with the tangent line of the axe-edge. Four vertical guide bars e, one on each
side of each guide pivot are attached to the central supporting column. These hars
may be round wires or rods or rounded edges of a slot. They prevent the beam
turning in azimuth. Two end plates attached to the central column prevent
lateral motion of the beam. The scale pans may be hung by a hook in rounded
hole in the beam as shown at Figure 3, or inverted axe-edges may be used fixed to
the two ends of the beam and scale pans hung by inverted stirrups with flat planes
resting on these axe-edges.
When greater bardiness against lateral mutions of the beam is wanted, it may be
supported on two hooks g and h, as shown at Figures 4 and 5, by a straight knife
edge i on one side and a sickle-edge on the other side. The sickle edge may be a
portion of the inner edge of a ring of agate, or hardened steel, or other hard metal,
ground with its inner edge sharp all round.
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 1
claim is :-
In balances, the use of curved bearing surfaces with guides to prevent horizontal
motion of the axis, for supporting the beam, substantially as described, by which the
frictional error is reduced to a minimum, and the difficulty of obtaining alignment
in long flat knife edges is obviated.
ted this 31st day of October 1893.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.