Duration of luminosity of electric discharge in gases and vapours: further studies

In several previous papers, I have described experiments showing that the luminosity of the spark or arc discharge through gases and metallic vapours lasts for an appreciable length of time after the discharge has ceased to pass, and that the luminous vapour can be removed from the region where the electric current is passing, and still remain luminous, showing the same spectrum as before, though in certain cases some lines of this spectrum fade out sooner than others. The present paper is a continuation of these studies. 1. The Luminous Jet at Very Low Pressures. Effect of a Transverse Electric Field . The first experiments to be described were designed to observe the effects at very low gaseous pressures, and with small currents. The advantage of this is that the luminous particles in the jet are then comparatively free to move under the action of an external force, and their motion in an electrostatic field can be conveniently examined. Moreover, since the ions are few, they do not disturb the uniformity of the electric field applied for this purpose.

Luminous vapours distilled from the arc, with applications to the study of spectum series and their origin.-I

In a paper entitled "Duration of Luminosity of Electric Discharge in Gases and Vapours," reference was made to a known phenomenon shown by the mercury arc in vacuo : when mercury is allowed to distil away from a mercury lamp into a lateral tube sealed on to it, the rapidly moving vapour carries its luminosity for a long distance out of the electric field. It was shown how effects not essentially different might be obtained with mercury, and other metals also, using not the arc, but the leyden jar spark between poles of the metal; but this method, owing to the intermittence of the sparks and the small scale of the effects, is far less satisfactory than the use of the arc. At the time of writing the paper cited, I thought that it would be very difficult to extend the use of the arc to metals less volatile than mercury, but the problem has proved more tractable than was expected 2. Method of Experimenting-Apparatus used . The vessel in which the arc is confined will be called, for convenience, a lamp, though it is not used directly as a source of light.

Duration of luminosity of electric discharge in gases and vapours

The electric discharge produces luminosity in any gas or vapour through which it passes. The question presents itself, Does the luminosity persist after the current has ceased, or does its top immediately ? A full answer is likely to be of great importance in unravelling the cause and mechanism of the luminosity. There are exiting observations bearing on the subject, but these are somewhat scattered in the literature, and, so far as I am aware, their mutual relations have not been pointed out. It is hoped in this paper to do something towards systematising and extending them. The most conspicuous phenomena in this connection are the various forms of afterglow which have been discussed in previous papers. But these are not really relevant to tire present subject, for they are due to secondary causes of a chemical nature. Some of them, produced in gaseous mixtures containing oxygen, are due to the interaction of ozone with other substances present. Others, again, are connected with the formation of an active modification of nitrogen. In none of these cases can the after-luminosity be considered continuous with the luminosity of tire discharge which produced it. For it is always much less brilliant, even at first, and always has a quite different spectrum.

Bakerian lecture.—The discharge of electricity through gases. (Preliminary communication.)

The phenomena of the electric discharge in gases excite a wide­ spread interest at the present time. It could hardly be otherwise ; for although our knowledge of electric manifestations is increasing in all directions, we cannot be assured of the correctness of our ex­planations while the mysterious appearance of the gas discharge remains unexplained.