Bulle Electric Clockswere developed by two Frenchman in @1918. During this time there was a trend of developing clocks operating on battery. In 1920 a patent was taken out by Favre-Bulle for electric clocks. Between 1920 to 1952 @300,000 clocks were made using same contact system housed in 100 types of different design cases.
The clock works on the reaction between a permanent bar magnet and an electric coil, and so it is also known as an Electromagnetic clock.The Bulle Magnet is a different type of magnet made of cobalt steel in either an arc or U shape having 3 poles South-North-South. When the coil is activated at the centre point of it's swing, the coil’s field cuts the magnetic field to create the opposing reaction driving the pendulum away. Usually the resistance of the coil is 1100-1200 ohms. Bulle clocks operates on 1.5V DC Battery.
Original Bulle Clock fully in working order, keeping good time. Housed in a heavy brass case with four side glass.
When the pendulum is in motion, it makes and breaks electric contact at the pin and the fork. Current flows for the split second of contact, activates the coil and produces a magnetic field around the coil. The magnetic field opposes the field in the bar magnet, which pushes (impulses) the coil - hence pendulum swings away from the central magnetic pole.
It runs on 1.5V DC at very low current. The Circuit is very simple with a battery, a switch and a coil all in series. The coil is of @1100 ohms made from 0.71 mm enamelled copper wire.