museum items
Crookes railway tube or Paddle wheel
Oven magnetron
Geissler tube with 4kV AC supply
Geissler tube with liquid outer jacket
Lighting Gallery

Interesting Items

Interesting old items are shown on this page. Most should be in a museum.

Giessler Tubes: This is a very simple old 'Geissler' tube used for demonstrating electrical discharge through low pressure gas. In this instance, I think the gas is Argon. The tube is about 26 cm long and the evacuating seal is visible on the top right. A supply voltage of 4kV is required to run the tube.

A more typical ornate Geissler tube is shown hereThis example also contains a fluorescing liquid, in a second jacket, around part of the discharge tube. The liquid glows due to the UV content in the light from the discharge. 'Mouse over' the two images to see them running. The tube is shown running with an AC HF supply.

Crookes railway Tube: Invented by Sir William Crookes, this evacuated tube has a paddle wheel which can move along the internal glass rails. The paddles are made from mica with fluorescent paint on the tips. A potential difference across the two electrodes can cause electrons to travel from the negative electrode (Cathode) to the positive electrode (Anode). Since the paddles turn, Crookes suggested that the cathode rays (electrons) must be particles with mass. It was later ascertained that it was not the direct action of electron bombardment that lead to the movement, but the fact that the vacuum is not perfect. The remaining molecules of air act on the paddles either thermally or by their electrical charge.

Magnetron: This device produces microwave energy. The complete device is shown on the left and the working parts are shown on the right. Essentially, the device is a diode valve, or vacuum tube. The anode has compartments like spokes which form resonant cavities. Current flows around these compartments are caused by the magnets which can be seen removed on the right and in place on the left image. The fins on the left image are to help remove the heat from the anode. The heater and cathode connections can be seen on the box below. The box contains filters to prevent the microwave radiation being brought out via the wires. The radiation is emitted from the top antenna. 'Mouse-over' the image for a close-up cross-section

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