An Improved Electric Condenser.
Year: 1892

page_text: Date of Application, 30th May, 1892-Accepted, 2nd July, 1892
COMPLETE SPECIFICATION.
An Improved Electric Condenser.
1, WILLIAM THOMSON, Baron Kelvin of Largs, Professor of Natural Philosophy
in the University of Glasgow, in the County of Lanark North Britain, 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 following
statement :-
The object of the invention is to provide a practical air condenser of sufficient
size to make it convenient for use with the multi-cellular volt-meter or other
suitable direct reading electrostatic instrument in the determination of small
electrostatic capacities.
In order that my invention may be properly understood and readily carried into
effect I have hereunto appended two explanatory sheets of drawings which I will
now proceed to describe.'
Figure 1 is a plan, and Figure 2 is an elevation partly in section.
The instrument consists of two insulated systems, A and B. Each system is
formed of square cut thin metal plates a, a, a, and b, b, b, situated one above the other
in parallel planes and held together by four metal bolts passing through holes in their
corners the distance from plate to plate being regulated by metal washers
through which the bolts pass. These washers are made very exactly the same in
all respects, and the bolts are made to exactly fit the holes through them and the
corners of the plates, so that when the system is firmly bolted together the plates
are accurately parallel and perfect rigidity is secured. The outside plates of
system A are made circular in form and of thicker metal than the other plates of
the system; and the number of plates in this system is greater by one than the
number in system B. The two systems are situated relatively to each other so
that each plate of system B is midway between and parallel to two plates of
system A; and every plate of system A is similarly midway between and parallel
to two plates of system B with exception of the two outside plates of the system A
which only present one surface to the plates of the opposite system.
The bottom plate of system B is made of thicker metal than the other plates
of the system, and has formed on its lower surface a hole e and a slot d. The
system B is supported on three glass pillars e, e¹, e² fixed into screwed metal
sockets, passing through the base plate of the system A. One of the pillars fits
into the hole c, while a second fits in the slot d on the under surface of the lower
plate of system B. The third pillar is in contact with a plane part of the same
surface. The sockets carrying the glass pillars can be screwed in or out so as to
adjust the height of the supporting pillars until the plates of system Bare
exactly midway between the plates of the system A. This can be done by testing
the distance between the plates of the two systems by a standard gauge, and
when it has been completed the sockets are securely fixed by jam-nuts.
The bolts fixing the corners of the plates of system B are made long enough to pass
through wide conical holes cut in the top and bottom plates of system A, and the
nuts at the top end of the bolts are also conical in form, while conical nuts are also
fixed to their lower ends below the base plate of system A. Thumb screw nuts f
are placed upon the upper ends of the bolts after they pass through the holes in the
top plate of system A.
When the instrument is set up ready for use these thumb screws are turned up
against fixed stops g so as to be well clear of the top plate of system A, but when
the instrument is packed for carriage they are screwed down against the plate
until the conical nuts mentioned above are drawn up into the conical holes in the
top and bottom plates of system A.; system B is thus raised off the glass pillars,

page_text: and the two systems are securely locked together so as to prevent damage to the
instrument.
A dust-tight cylindrical metal case h, which can be easily taken off for
inspection, covers the two systems and fits on to a flange on system A. The
whole instrument rests on three vulcanite legs attached to the base plate of
system A; and two terminals are provided, one on the base plate of system A,
and the other j on the end of one of the corner bolts of system B.
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 air condenser substantially as described.
2. The method of insulating so as to obtain mechanical strength with sufficiently
large capacity without other insulator than air between the successive plates of
the two systems.
3. Arrangement of fixing the movable system so as to prevent injury in
carriage.
Dated this 28th day of May 1892.
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicant's Agents.