Ionisation and Anomalous Dispersion

Abstract

THE experiment recently described in a letter in NATURE by Dr. Schott (January 17, p. 271) does not appear to me to have any very direct bearing upon ionisation. There appears to be no question but that the changes observed in the dispersion curve were due to an alteration in the optical density gradient of the sodium vapour, resulting from local heating by the wire. The experiment is very similar to one which I made two years or more ago, during an examination of the physical properties of the vapour. A wire was stretched through the tube, along its axis, and heated by a current. The vapour was observed to be much less dense around the heated wire. The observations were made by looking through the tube either at a sodium flame, or a lamp behind bluish-green glass (for which light the vapour was very opaque). On heating the wire a clear space appeared around it. If I remember rightly, I never published this result, as the experiment was one of a series which has not, even yet, been completed.