L'Arc électrique

R., A.

doi:10.1038/111805a0

Books Received
Published: 16 June 1923

L'Arc électrique

A. R.

Nature volume 111, page 805 (1923)Cite this article

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Abstract

THE first chapter of the work under notice contains the more important formulae obtained by modern physicists in connexion with the electric arc. A drawback to the use of these formulas is that it is difficult to find out where theory ends and empiricism begins. If we accept the formulae we have to abandon the theory of dimensions as applied to equations. In the second chapter Mrs. Ayrton's work is well described.—It is stated that Blondel was the first to prove that there was no appreciable counter electromotive force in the arc. If E denotes the potential difference across the arc and I the current through it, then dE/dl is called the resistance of the arc, and it is pointed out that it is a negative quantity. A good description is given of magnetic and mercury vapour lamps. The phenomena shown by the so-called “non-arcing” ffletals, such as phosphor-bronze, aluminium-bronze, aluminium and zinc, are attributed to a metallic oxide covering the electrodes with an insulating layer or to the vapour being difficult to ionise. It is pointed out that although the current and voltage vanish instantaneously in alternating current arcs, yet their power factor is not unity. This is stated to be due to the fact that they do not both follow the sine law. As a matter of fact, provided that the ordinate of the current wave is always proportional to the ordinate of the voltage wave, and they vanish instantaneously, the power factor would be unity whatever the shape of the voltage wave. The third chapter gives the technical applications of the electric arc to searchlights, furnaces, electric welding, for producing high-frequency waves, and in electric “safety valves “for protection against lightning.

L'Arc électrique.

Par Maurice Leblanc fils. (Recueil des Conférences-Rapports de Documentation sur la Physique. Vol. 3, 1^re Série, Conférences 7, 8. Édité par la Société Journal de Physique.) Pp. 131. (Paris: Les Presses Universitaires de France, 1922.) 10 francs.