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electric clocks

 A history of the evolution of electric clocks

C. Independency of battery
One of the points Bain made in his early patents was that the impulse given to the pendulum could be made independent of the battery voltage by using an electro-magnet to store energy in a spring or weight and then using the constant amount of stored potential energy to impulse the pendulum.

Charles Shepherd (1830-1905)
Charles Shepherd of Hendon devised such an arrangement (patent no.12567) in 1849 and his clock was a great success at the exhibition at Hyde Park in 1851. As a result of this success he was asked to build a clock for the Greenwich Observatory to control time signals by telegraph and to control the time ball at Greenwich and Deal.
The time ball was used enable the crew of ships laying at bay to synchronize their chronometers. Each day the time ball was raised to drop exactly at 1 pm.
The Neuch
âtel Observatory in Switzerland also installed one of his clocks.

As  the pendulum swings to the left it engages a catch and releases its gravity arm. The impulse pin fitted to the pendulum now receives an impulse from the gravity arm. At the end of the pendulum's excursion to the right, contact is made with the suspension spring and the electro-magnet is energized.  The armature of the electro-magnet now resets the gravity arm.


The picture here shows proud owners synchronizing their precious watches with the time indicated by the slave dial placed at the gate of the Greenwich Observatory.

Shepherd’s clock meant a big step forward to precision but there was still a long way to go. The pendulum has every kind of work to do, it charges into fixed contact points at the ends of its swing and unlatches its gravity arm in the same way.

time ball of the Greenwich Observatory

Paul-Gustave Froment (1815-1865)
Meanwhile in France
Paul-Gustave Froment, an instrument maker who at the age of eighteen had already built his first electro-motor and in 1851 had built the pendulum arrangement for Foucault's famous experiment, in Froment 1854 devised a much simpler and improved version of Shepherd's clock.

An important difference with Shepherd’s clock was that the force stored in a leaf spring had replaced gravity force.


On its swing to the left, the pendulum picks up a spring by means of
a contact screw. The electro-magnet is now energized and pulls its armature out of the way. The pendulum, on its return to the right, does not part from the spring until the latter has reached a point below that at which the pendulum found it. When the contact is broken the armature resets the spring.

The difference between its lift and fall is the total impulse given.

F C de Jong (1826-1876)
In 1865 F C de Jong, a clockmaker from Amsterdam, used a count-wheel not only to propel the hands, like Hipp did, but also to induce contact. Like Froment, he used a leaf spring to store potential energy. de Jong

Contact  making and impulsing occur when the pendulum is passing through its zero position when its kinetic energy is at its maximum and the interference to the freedom of the pendulum is kept to a minimum.
Quite an improvement compared to Froment's design.

On each swing to the right, the pendulum will propel a count-wheel and in doing so close contacts placed under it and activating the electro-magnets. The armature is pulled down and a pin fixed to the armature deflects a spring fitted to the pendulum. So potential energy is stored in this spring and is released to the pendulum.

Unfortunately, De Jong’s invention did not attract the attention of the rest of the world.  A remarkable fact, as his clock was comprehensively described in a well-known French journal for chronometers.

De Jong’s clock is exhibited in the museum of Schoonhoven and is one of the oldest Dutch electric clocks to have survived time.

David Gill (1843-1914)
Way down in South Africa, David Gill, director of the Royal Cape Observatory from 1879
till 1907, adapted Froment's system. In 1879 he replaced Gillspring force used by Froment by the force of gravity. He ordered his clock to be built by The Cambridge Scientific Instrument Co Ltd to set-up experiments to control his telescopes. Unfortunately no part of his clock has survived time.         animation
On its swing to the left the pendulum picks-up a gravity arm by means of a contact screw. The electro-magnet is energized and moves its armature out of the way to release the gravity arm. The pendulum, on its return to the right does not part from the gravity arm until the latter has reached a point below at which the pendulum found it.

The difference between lift and fall determines the amount of impulse given.
When the contact is broken the armature resets the gravity arm.

One of the problems left with Gill's clock was the poor contact making. As always, the limited pressure available from the pendulum made the contact unreliable.

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D. Reliability of contact making



Electricity & Magnetism
Electricity & Horology
   A.Electrostatic clocks
   B.The first inventors
   C.Independency of battery
   D.Reliability of contact making
   F.Count-wheel and impulse
   G.The first free pendulum
   H.Shortt's free pendulum
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