﻿Electric Discharge in Liquid Oxygen, Air, §c. 235 



diameter, electrified to the same electric density, reckoned 

 according to the total electricity in any small volume (elec- 

 tricity of air and of spherules of water, if there are any in it), 

 would produce a difference of potential of 38 million volts 

 between its surface and centre. In a thunderstorm, flashes 

 of lightning show us differences of potential of millions of 

 volts, but not perhaps of many times 38 million volts, between 

 places of the atmosphere distant from one another by half a 

 kilometre. 



XXV. Preliminary Note on the Spectrum of the Electric 

 Discharge in Liquid Oxygen, Air, and Nitrogen. By 

 Professors Liveing and Dewar*. 



IN making the experiments here described we desired, if 

 possible, to observe the emission-spectra of the several 

 substances, stimulated by the electric discharge, while at 

 temperatures of 1 80° to 200° below zero. It seemed probable 

 that the characters of these spectra would give some indica- 

 tions of the physical state of the substances operated on. 



In order to prevent the rapid heating of the electrodes by 

 the discharge, they were made of considerable size. One was 

 a disk of platinum about one centimetre in diameter, convex 

 on one side, and having its convexity turned towards the 

 other electrode, which was made of a piece of platinum wire 

 about two millimetres thick. Even these electrodes were 

 much heated, became red-hot when they were not in the 

 liquid, but the spark passed through the gas immediately 

 above the liquid. When actually immersed in the liquid 

 they could hardly have been, except locally at the point of 

 discharge, at any temperature sensibly different from that of 

 the liquid. Experiments were made also with electrodes of 

 aluminium, but with no different results as regards the spec- 

 trum except the introduction of the shaded bands due to 

 alumina instead of the lines of platinum. 



The liquids experimented on were contained in double test- 

 tubes of large dimensions, having the space between the two 

 tubes highly exhausted. The electrodes, insulated, except at 

 the extremities, by glass tubing and wax or gutta-percha, 

 were passed through a rubber-stopper which closed the tube. 

 Through this stopper was also passed a glass tube, which was 

 left open while experiments were made at the atmospheric 

 pressure, but was connected with a powerful rotary air-pump 

 when it was desired to exhaust the gas in the tube. 

 * Communicated by the Authors. 



