The Cathode Ray Tube site
History and Physics Instruments
Fuel for tubes
Heinrich Daniel Ruhmkorff (1803-1877)
A German engineer working in Paris opened his own workshop in Paris in 1837 producing
scientific instruments. He gave his name to the high tension coil around 1855 which was able
to generate tensions up to 200KV. It was a further development of techniques used before.
The instrument consist of a small primary coil and a large secondary coil where the high
tension is formed by a mechanical breaker system. In the wooden base there is room for an
capacitor made of paper and metal foil.
Ruhmkorff coils were used to activate the Crookes, Geissler and X-ray tubes.
Most of the coils come from the last quarter of the 19th and beginning of 20th Century, the
dimensions vary from small to huge ones, depending on the amount tension that was needed
which was expressed in centimeters.
The coils are real often beauties with nice lacquered mahogany base and brass connections or
Heinrich Daniel Ruhmkorff
Early advertisement of Ruhmkorff coils and Geissler tubes.
This is a German Ruhmkorff small coil ca 1900. It measures 8x15cm.
French Radiguet Ruhmkorff coil
early 20th Century. 22x12cm
Close-up of the breaker system.
In the wooden bottom (box) of the old Ruhmkorff or spark
coil you will find a capacitor witch consists of paper
and metal foil. In one of my coils the paper sheets were
old book pages with photographs of pre WW I soldiers!
The early power source, the Grenet Cell
The Grenet Cell or pile invented by the German
Johann Christian Poggendorff (1796-1877)
It is a galvanic battery filled with an acid solution
potassium dichromate. The electrodes are made
of zinc and carbon and generates 1,96 Volts, in
practice many cells were coupled to make a
workable power source.
The voltage rapidly dropped when the cells were
used. The zinc element which is positioned in the
middle can be shifted upwards or lowered by the
middle connection on top.
Two small French Ruhmkorff coils early 20th century.
Sizes 15x9 and 7x12cm. These two coils are from the same manufacturer and were mainly used for activating small Geissler tubes and other physics experiments. Often sold as a complete kit including Geissler rotator for education.
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A Pericaud toy experiment box ca1920
Containing a Grenet cell with a bottle of potassium dichromate, Ruhmkorff coil, and a small Geissler tube.
A large Ruhmkorff coil ca1890
French Pericaud Ruhmkorrf coil
Pericaud from Paris made scientific toys like Ruhmkorff coils, rotators and Geissler tubes.
Collection of French toy instruments ca1900