Improvements in Electric Contact Mechanism.
Year: 1889

page_text: COMPLETE SPECIFICATION.
Improvements in Electric Contact Mechanism.
of
I, HENRY SMITH PRENTISS, of 1264 Waverly Place, Elizabeth in the County
Union and State of New Jersey in the United States of America Mechanical Engineer,
do hereby declare the nature of this invention and in what manner the same is to
be employed to be particularly described and ascertained in and by the following
statement:-
The object of this invention is to provide a device having the nature of a cam which
shall close an electric circuit but once in two revolutions of the shaft upon which the
device is fixed.
The invention is illustrated in the accompanying drawing, in which Figure 1. is a
side view of a disc in which the invention is embodied, with a portion of the cover cut
away, and Figure 2. is a section through the line 2, 2, of Figure 1.
In
The device may be fixed upon a shaft S, by means of the set screw s. Within the
disc A is formed a continuous groove a baving its lowest portion, or portion nearest
the periphery of A, at a'. This groove contains a small portion of mercury m.
the position shown in Figure 1. the device has just operated or performed the function
required, and is ready to be carried forward for another operation. The groove a
can be traced by the dotted lines in Figure 1 throughout two complete turns or
revolutions within the disc. If we suppose the shaft S is turning so as to carry the
disc in the direction indicated by the arrow, it is evident that the mercury m will be
carried, or will run within the groove a in the direction shown by the small arrows.
When the disc A has made one revolution the mercury will stand in the groove a at
the point a. The groove at this point is at the back side of the disc as shown in
Figure 2, and it passes therefore behind that portion of the groove which is shown
at a. The continued revolution of the disc carries the mercury through that part of
the groove shown at at and as, and finally at the end of the second revolution will
reach the portion warked a. A very slight additional motion allows the mercury to
drop into the place a', that is at the point from which it started.
In falling down the perpendicular part of the groove just beyond a, the mercury
envelops the two ends of a small wire wo which may be conveniently attached to the
shaft as shown, and this operation will close an electric circuit of which the shaft may
form a part, and the other terminal may be a spring pressing against the edge of the
disc. The circuit may include any device which is required to be operated. Hence it
will be seen that the cam has been obliged to make two complete revolutions in order
to close the circuit once.
The device is useful in many places, but is especially useful in a clock where some
device, as a calendar, is desired to be set in operation once in 24 hours, and this device
saves the necessity of adding a 24 hour wheel to the clock.
It will of course be plainly seen that three or more turns or convolutions of the
duct may be made in the same manner, in which case the operation of the device
takes place but once in the number of turns of the shaft corresponding to the number
of such convolutions.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. A disc or wheel having a closed duct or groove, which makes two complete turns
or convolutions within said disc, a conducting fluid within said duct, and means, as
the wires w whereby an electric circuit is closed by the passage of said fluid at a certain

page_text: 2. The combination of the shaft S, the disc A having the duct formed within it, in
two complete convolutions and closing upon itself as shown, the mercury or conducting
fluid and the conducting wires through which a circuit is closed by the passage of said
mercury.
3. The combination of a shaft, a disc or wheel carrying a duct which makes two
complete convolutions, and closing upon itself, a moving body within said duct, and
means whereby an electric circuit is closed by the passage of said body through a
certain predetermined part of said duct.
Dated December 24th 1880
HENRY SMITH PRENTISS.
By Harris & Mills,
23, Southampton Buildings, London, Agents.