Abstract
THE discharge tubes used for advertising are a development of the old Geissler and Crookes tubes in which various beautiful effects were produced when evacuated tubes filled with certain gases were excited by an induction coil. In the January Engineering Supplement to the Siemens Magazine, there is an interesting article on the construction and the physical theory of commercial discharge tubes by E. A. Beavis. Forty years ago, the gases used were mostly nitrogen and carbon dioxide, and these required continual replenishing. It was only when the rare gases, argon, neon, helium, etc., were experimented with that it was found possible to obtain a reasonably permanent luminous discharge. These gases are not subject to absorption to anything like the same extent as the commoner gases. Neon at a suitable pressure gives more visible light and has a lower electrical resistance than the other permanent gases and hence a greater length of tubing can be operated for a given voltage. Neon has a cheerful red glow, argon gives a faint lavender colour and has little luminosity, and helium has a whitish glow. Combinations of various gases and vapours with neon and the use of coloured glass tubes have enabled many striking and pleasing coloured effects to be obtained. The positive column extending to the anode forms the main region of luminosity in the tube. By mixing traces of impurity in the gas, it is possible to obtain narrow cords of light which move within the tube and give rise to the type of discharge known as the ‘ripple neon’. Sometimes also the column of light splits up into rows of coloured discs which often rotate round the axis of the tube. These effects are known as ‘striations’. Alternating current is used for operating commercial tubes. As the voltage absorbed under running conditions is about 200 volts per foot of tube, it is usually divided up into a number of sections each supplied by a separate transformer.
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Neon Signs. Nature 133, 206 (1934). https://doi.org/10.1038/133206a0
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DOI: https://doi.org/10.1038/133206a0