IMPROVEMENTS IN CLOCKS AND APPARATUS FOR GIVING UNIFORM MOTION
Year: 1871

page_text: LETTERS PATENT to Sir William Thomson, Knight, of Glasgow
College, Doctor of Laws and Professor of Natural Philosophy in
the University and College of Glasgow, for the Invention of
"IMPROVEMENTS IN CLOCKS AND APPARATUS FOR GIVING UNIFORM
MOTION."
PROVISIONAL SPECIFICATION left by the said Sir William Thomson
at the Office of the Commissioners of Patents, with his Petition, on
the 25th March 1871.
I, Sir WILLIAM THOMSON, Knight, of Glasgow College, Doctor of
Laws and Professor of Natural Philosophy in the University and
College of Glasgow, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN CLOCKS AND APPARATUS FOR GIVING UNIFORM MOTION,"
to be as follows:-
My Invention is applicable to mechanism for the automatic trans-
mission of telegraphic signals or for drawing paper to receive the writing

page_text: of autographic instruments, or for moving equatorials or heliostats as
well as to clocks.
I use a pendulum or other vibrator, but independently of it I produce
an approximately uniform motion of the whole train of wheelwork at
approximately the proper rate. I arrange that when the instrument
is adjusted to any speed within certain limits and left to itself it will
of itself vary the adjustment so as to augment its speed to something
above the proper speed; lastly, by a movement geometrically com-
parable with Graham's dead beat escapement I arrange that a shaft
or wheel turned by the mechanism shall keep a pendulum vibrating,
and shall be prevented by the pendulum from going round on the
whole faster than to allow one tooth or arm to pass during each
period of the pendulum's motion. One such tooth or arm suffices.
The tooth or arm may be rigid and rigidly attached to the shaft or
wheel, which for brevity I shall call the escapement wheel; but I
prefer to make it elastic or to connect it elastically with the escape-
ment wheel. When not touched by the pallet the escapement wheel
is carried by a diferential motion at a rate somewhat exceeding that
of another shaft, which I shall call the chronometer shaft, and which I
generally find it convenient to make coaxial with the escapement wheel.
But this differential motion carries the escapement wheel only by force
of friction, and at any time the escapement wheel may be stopped by
the application to it of a sufficient resistance to overcome this friction.
The action of the pendulum ensures the correct rate for the escapement
wheel. The adjustment acts so that when the chronometer shaft runs
at a speed lower than the average speed of the escapement wheel the
resistance is diminished or the moving force is increased so as to
augment the speed of the chronometer shaft. But when, on the con-
trary, the chronometer shaft gains on the escapement wheel the
adjusting action adds resistance or diminishes the moving force, and
so diminishes the speed of the chronometer shaft. The chronometer
shaft is connected by toothed gearing with a train of wheelwork by
which motion is imparted to the hands, discs, or counters required for
marking time or for producing the desired uniform motion.
*For a clock driven by water power I diminish or augment the
water supply according as the chronometer shaft gains or loses on the

page_text: For a clock driven by electro-magnetism a friction governor may be
used; but I prefer employing the differential motion to diminish or
increase the driving power from one grade to another or to several others
successively; and among various plans for carrying out this method I
have found the following very simple one to answer well:-The escape-
ment wheel and the chronometer shaft carry one of them a ring and
the other a metallic spring touching the ring. The ring is partly of
insulating material and partly of metal insulated from the spring except
when touched by it. The spring and the metallic part of the ring are
connected with complete metallic rings which are by tangent springs
kept permanently in connection with two fixed conductors. These con-
ductors are connected with the wire of the driving electro-magnet, either
in such a manner that when the spring makes contact with the metallic
part of the first-mentioned ring a shunt is applied to the electro-magnet,
and its power is diminished or in such a manner that when the spring
touches the non-metallic part of the ring the circuit of the electro-
magnet is broken. I double upon itself the wire used for shunt in order
to diminish the quasi inertia of the electricity flowing through it.
.
For the same reason I sometimes apply to the electrodes of the
driving electro-magnet a constant shunt of wire doubled on itself.
When an electro-magnet with soft iron core with alternate reversals
or make and break is used for the driving power I construct the soft
iron core altogether or in great part of thin iron wires varnished and
pressed close together. I use a pendulum, consisting of a heavy
weight attached to a short stiff bar of steel or other suitable material
jointed at one end to a long stiff zinc rod or tube, and supported hori-
zontally by a platinum wire attached to it at a point between that end
and the weight. The zinc rod and platinum bearing wire are approxi-
mately equal in length, and are each firmly attached to a solid block
constituting the top of the pendulum, which is hung by one or more
short springs attached to this block and to a very massive fixed block
or very rigid and rigidly fixed frame; or knife edges may be used for
supporting the pendulum; but I prefer springs, and I prefer a large
number of fine round platinum or steel wires to flat springs, as being
less liable to flaws and to imperfect elastic action.
When I use more than two bearing wires or springs I distribute the
weight as nearly equally as may be among all by attaching their upper

page_text: ends to transverse springs, each of which yields considerably to its
proportion of weight fixed.. And to secure a very definitely fixed
vertical axis for the pendulum's motion I use a massive well fixed
horizontal bar pressing laterally with a cylindrical surface against the
bearing wires with sufficient force to deflect the upper free portions of a
them through a considerable angle from the vertical; or I bring each
bearing wire round the top of a strong horizontal bar and down on the
other side, and hang upon it a weight equal to its proportion of the
whole weight to be borne.
The main weight (or pendulum "bob") is adjustable through a
sufficient range along the horizontal bar to give the correct com-
pensation for changes of temperature. According to practical trial I
use a spring joint in preference to a mechanical joint of any ordinary
kind, connecting the horizontal bar with the zinc rod to avoid friction
of solid on solid; but knife edges might answer, and would have the
advantage of occupying less space.
When it is desired that the clock shall strike the hours if it is driven
by electro-magnetic power I add mechanism by which a weight or
spring is wound up by the wheelwork during the time the clock is not
striking to supply energy enough for the striking; or when water power
is available I employ a water-power engine to perform the striking.
One way in which I execute this is by a cylinder with a piston and
valves worked by the piston, so that the piston moves to and fro
regularly at the proper rate for the striking as long as the valve
mechanism is left in gear. The striking mechanism of the clock throws
the water mechanism into gear at the right time, and throws it out
again when the proper number of strokes has been made.