IMPROVEMENTS IN AUTOMATIC CONTACT-BREAKERS FOR ELECTRIC BELL AND OTHER ELECTRIC OR GALVANIC CIRCUITS
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by Thomas Wilkins at the Office of the
Commissioners of Patents on the 22nd October 1879.
THOMAS WILKINS, of 96, Lyndhurst Road, Camberwell, in the County of Surrey,
Engineer, and Patent Agent. "IMPROVEMENTS IN AUTOMATIC CONTACT-BREAKERS
FOR ELECTRIC BELL AND OTHER ELECTRIC OR GALVANIC CIRCUITS."
An electric bell or other electric or galvanic circuit having been completed,
it is frequently advantageous that the said circuit should be broken and the
current stopped automatically after a period of time more or less long, so that the
contact having been made no attention be required or further means taken to
break contact. In order to perform this prepare the surfaces where contact is
made and broken in such way that the one will slide into or upon the other, and
I mount one or both of them upon a nonconducting material in such way that in
their normal position they are not electrically in contact. I next construct an air-
chamber or vacuum-bellows in such way that a valve opens outwards to allow air
to pass freely out of the said air-chamber or vacuum-bellows, and the said valve or
valves, as more than one may be used, then closes and prevents air readily
entering the said air-chamber or vacuum-bellows, although a spring or springs of
india rubber or other suitable material, or the action of gravity upon the bellows
or chamber, or a suitable weight be caused to act upon the said chamber or bellows
to bring it back to its normal position. A slight leakage is however permitted,
either by not allowing the valve aforesaid to fit accurately, or by leaving the
material of which the said chamber or bellows is wholly or partly made slightly
porous, or by making one or more small air-holes in the said chamber or bellows. I
connect the said air-chamber or vacuum-bellows with the aforesaid contact surfaces
in such way that when the said bellows or chamber has the air expelled from it
the said surfaces are brought into contact or vice versd; when the said surfaces are
brought into contact the said bellows or chamber has the air expelled from it, and
as the said bellows or chamber is more or less slowly refilled with air the said
surfaces slide for a time in or upon one another, and after a time contact ceases and
the electric or galvanic circuit is broken. I form and arrange the springs so that
their force upon the said bellows or chamber can be varied; by this means the time
during which the surfaces are allowed to remain in contact can be varied.
In lieu of the said air-chamber or vacuum-bellows I sometimes use a" clockwork"
arrangement, having either a spring or weight as motive power, and a "fly," such

page_text: as is used in a musical-box, or a suitable "escapement" movement to regulate the
speed, and I connect the aforesaid surfaces of contact with this said mechanism in
such way that when the surfaces aforesaid are brought in contact the said
mechanism is wound up, and as its spring or weight runs down at the speed
determined by the said fly or escapement, the mechanism causes the said surfaces
to slide in or upon one another for a time, they then part contact and the electric
circuit is broken.
Sometimes I place two or more contact surfaces in a suitable container, into
which a conducting liquid, such as mercury, or a metallic or other powder of good
conducting power can be injected and act as conductor between those insulated
contact surfaces; the container being provided with a means by which the said
liquid or powder can escape, a current passes until contact is broken in con-
quence of that escape. A simple form of apparatus for this purpose would be a
container similar in form to an hour glass. One or more of the surfaces of contact
would be at the narrow neck, and the other surface or surfaces of contact would be
at a short distance from that neck, the latter surface or surfaces being insulated
from the surface or surfaces at the neck. So long as the liquid or powder in the
container is below the surfaces of contact the circuit will remain broken and no
current will pass, but on inverting the container the liquid or powder will come in
contact with the surfaces of contact and be a conductor between them, allowing a
current to pass, but the liquid or powder gradually escapes into the lower half of
the compartment and contact is at length broken.
Sometimes I cause the current to be broken automatically after a given time by
hanging a chamber similar to an hour-glass in form upon pivots in such way that
when that part of the chamber containing the liquid or powder is placed uppermost
the surfaces of contact shall be in contact, but when after a time the liquid or
powder has escaped from that part of the chamber into the part below the neck
the centre of gravity of the whole chamber and material in it, taken as a whole, is
so altered that the position of the chamber is automatically reversed and the
surfaces of contact are parted. The surfaces of contact are of course suitably
insulated.