Improvements in Electrical and other Measuring Instruments and Apparatus.
Year: 1893

page_text: Date of Application, 16th May, 1893
Complete Specification Left, 16th Feb., 1894-Accepted, 23th Apr., 1894
PROVISIONAL SPECIFICATION.
Improvements in Electrical and other Measuring Instruments and
Apparatus.
We, WILLIAM EDWARD AYRTON of 41 Kensington Park Gardens in the
County of London Fellow of the Royal Society, Professor of Electrical Engineering,
and THOMAS MATHER of 19 Agamemnon Road West Hampstead in the same
County, Electrician do hereby declare the nature of this invention to be as
follows:-
Our invention relates to the screening of electrical instruments and other apparatus
from disturbances caused by electric forces.
The improvements consist in coating or preparing the glass front, shade, or
other transparent substance through which the position of the working parts,
pointer or other indicating or recording mechanism or device is seen so as to form
a transparent, or nearly transparent, conducting, or partially conducting, screen.
Many measuring instruments have their indications or records temporarily
altered when the glass which covers the pointer or working parts is cleaned, and
instruments used on high potential circuits are influenced when the hand or other.
conductor is brought near them. To prevent these alterations we use a conducting
screen, and in order that any portion of the working parts, pointer, or other indicating.
mechanism or recording device may be seen, we form the screen in such a way as to
be more or less transparent or translucent.
In some cases the screen is formed on the inside of the glass cover, whereas in
other instances the screen is separate therefrom.
Deposits of carbon, silver, platinum, mercury, copper, or other metal in attenuated
form may be used and the deposition effected by mechanical, electrical, or chemical
means. Coatings of gelatinous substances, moisture, gums, gelatines, starch, or
cements, rendered conducting are sometimes employed.
Such deposits or coatings may be protected by varnish, enamel, or glass cover
plates, or by other means.
In some cases thin cells containing conducting liquid or jelly may be used.
It will be readily understood that our invention is not limited to electrical
instruments, for it may be used to screen any instrument apparatus or thing whose
action might be affected by electric forces.
Dated this Fifteenth day of May 1893.
WILLIAM EDWARD AYRTON.
THOMAS MATHER.
COMPLETE
SPECIFICATION.
Improvements in Electrical and other Measuring Instruments and
Apparatus.
We, WILLIAM EDWARD AYRTON of 41 Kensington Park Gardens in the
County of London, Fellow of the Royal Society, Professor of Electrical Engineering,
and THOMAS MATHER of 1 Solent Crescent West Hampstead (late of 19 Agamemnon
Road West Hampstead) in the same County Electrician 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 :-
(1.) Our invention relates to the screening of electrical instruments and other
apparatus from disturbances caused by electric forces

page_text: (2.) The improvements consist in coating or preparing the glass front shade
or other transparent substance through which the position of the working parts
pointer or other indicating or recording mechanism or device is seen so as to form a
transparent or nearly transparent conducting or partially conducting screen.
(3.) Many measuring instruments have their indications or records temporarily
altered by the approach of an electrified body or even by the electrification of the
glass which covers the working parts or pointer when the glass is cleaned, and
instruments used on high potential circuits are influenced when the hand or other
conductor, whose potential differs considerably from that of the working parts or
pointer, is brought near. To prevent these alterations we use a conducting screen,
but instead of employing sheet metal, foil wire netting or gauze, which has hitherto
been customary, we form the screen in such a way as to be more or less transparent
or translucent in order that any portion of the working parts pointer or other
indicating mechanism or recording device may be seen.
(4.) In some cases the screen is formed on the inside of the glass or other
transparent cover, whereas in other instances the screen is outside the glass or is
separate therefrom.
(5.) One method of forming a screen on the cover is to smoke it lightly, and so
put on a thin deposit of carbon which acts as an efficient screen without seriously
impairing the transparency of the glass. Instead of a film of carbon, deposits of
silver, platinum, mercury, copper, zinc, or other metal in attenuated form may
be used, the deposition being effected by mechanical, electrical, chemical or thermal
means.
(6.) We also employ various methods of making the transparent screens of
gelatinous materials, such as gelatine, isinglass, starch, gums or other transparent
cements which we render conducting by the admixture of acids or other conducting
substances. As examples we may mention the following detailed methods which we
have found to be particularly good, but we would have it understood that we do not
limit ourselves to these particular ways of making the screens, for it will be evident
that considerable variation may be made without departing from the essential
nature of our invention.
(7.) Dissolve a quarter ounce of transparent gelatine in one ounce of glacial acetic
acid heated to 100° C., and whilst still hot add to it a quantity of dilute sulphuric
acid, (8 parts water and one part concentrated acid by volume) equal to half its
volume and mix thoroughly. Polish the glass to be coated and heat it as hot as it
can be comfortably held in the hands, then apply the mixture of gelatine and acids
with a soft brush and allow it to stand in a dry place say for about 24 hours until
the coating becomes nearly but not quite hard. As a protection for the conducting
film so formed, one or more coats of Griffith's Transparent Antisulphuric Enamel
are put on.
(8.) Another method is to thin the solution of gelatine in acetic and sulphuric
acids above mentioned by the addition of more acetic acid and float the thin
solution over the glass, the excess of acetic acid being expelled by heat. Two or
more coats may be given in this way before applying the enamel either by brush or
by floating over.
(9.) Before applying the enamel or other varnish over the conducting coatings
described in §§ (6), (7), (8), an intermediate coating consisting of gelatine dissolved
in acetic acid or in water may be given in order to form a harder surface,
& the varnish subsequently applied. In cases where there is no probability
of the surface being touched or rubbed we may dispense with the protecting coating
of varnish.
(10.) In some cases we use cells containing conducting and transparent liquid or
jelly as screens. One way of doing this is to fix two plates of glass or other
transparent solid at a small distance apart and put the liquid or jelly in the
intervening space. It will of course be evident that the ordinary glass cover may
be used as one of the two plates.
(11.) Our invention is particularly useful for electrostatic instruments where the

page_text: working forces are feeble, for it enables us to screen them from disturbing influences
without hiding the working parts behind opaque covers. Electroscopes may be
screened by having the glass cover coated as described instead of by tinfoil as is
usually done, & electrometer jars may have their outsides coated, thereby allowing
the working parts to be seen, and at the same time forming efficient screens.
(12.) It will be readily understood that our invention is useful, not only for
screening electrostatic instruments, but for screening electrical measuring instruments
of the electromagnetic or other types, or for any kind of instrument or appparatus,
whether electrical or otherwise, from disturbances due to electric forces, which
might otherwise interfere with their correct working.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. In the screening of electrical and other instruments and apparatus, the use of
transparent conducting screens as described.
2. In the screening of electrical and other instruments the methods of constructing
transparent screens as described in paragraph (5).
3. In the screening of electrical and other instruments the methods of applying
a conducting transparent film or layer as described in paragraphs (6), (7), (8), (9),
and (10).
Dated this 15th day of February 1894.
WILLIAM EDWARD AYRTON.
THOMAS MATHER.