Images(5)

De la Rive's egg

Datecirca 1920

Inventory NumberDW0538

ClassificationDischarge Tube

Subject

Maker L. E. Knott Apparatus Company 1896 - early 1930s

Cultural Region

Place of Origin

Dimensions31.5 x 11 x 10 cm (12 3/8 x 4 5/16 x 3 15/16 in.)

Material

DescriptionAn egg-shaped glass bulb with a long inward side tube along its long axis and two electrodes. One of the electrodes is at the top end of the egg, while the other has the shape of a ring around the inward tube and is attached to a short side tube. The whole tube rests atop an electromagnet whose core extends into the bulb via the long inward side tube. The electromagnet is attached to a wooden stand. There are two binding posts on the base so the instrument could be linked to a battery.

This instrument was sold $9.50 in 1921 by the L. E. Knott Apparatus Co. For the trade catalogue, see the online version here.

Signedon base: Knott

FunctionThis is an evacuated tube designed to explore the effects of magnetic fields on cathode rays. When the electrodes are connected to a large voltage, cathode rays would be produced by the cathode and travel in the general direction of the anode. The glass would glow as some of the electrons hit it and with enough gas in the tube, the path of the cathode rays would become visible. One could observe the difference in the glowing patterns due to magnetic fields by altering the current flowing through the electromagnet as its core extends to the center of the tube using the inward tube. In general the cathode rays would take a helical trajectory from cathode to anode in the presence of the magnetic field.

On Auguste-Arthur de la Rive, and to view a short movie of this instrument in action, see the following website.

A video recording of an example of De La Rive's egg in use, recorded by Dominique Bernard at the University of Rennes (France), is available on Youtube here.

ProvenanceDavid Wheatland acquired in Shirley, Massachusetts, 1970.