196 Scientific Intelligence. 



the image of the intensely white spot on the oxide globule, from 

 which the arc starts, focused exactly on the slit. The spectro- 

 gram shows that the members of the triplet in question extend 

 only a relatively short distance from the globule, whereas the 

 remaining iron lines recorded by Geiger extend across the entire 

 field of view and are most intense in the region corresponding to 

 the arc proper. No difference in the appearance of the triplet 

 was observed when the voltage was changed from 220 to 60. 

 These lines also were present near the anode when the arc was 

 burned in air at a pressure of l cm of mercury. On the other 

 hand, when a small piece of iron wire was laid on the positive 

 electrode of a carbon arc, in air at atmospheric pressure, the 

 triplet could not be found, notwithstanding the fact that all the 

 other lines recorded by Geiger were photographed. When the 

 processes of oxidation and reduction which occur in the arc 

 between iron electrodes are taken into account together with the 

 conditions which hinder oxidation in the carbon arc, little doubt 

 can remain as to the oxygen origin of the triplet. The wave- 

 lengths of the lines are given as 7772*01, 7774-21 and 7775*50 A. U. 



The proof seems to be made final and conclusive by the follow- 

 ing argument of the authors. The " frequencies " of the lines 

 are 12866-68, 12863-04, and 12860-91 so that the first differences 

 become 3*64 and 2-13. The mean frequency differences of the 

 remaining triplets of the oxygen spectrum are 3 - 70 and 2-08. 

 Corrections to the frequencies of the lines of the first triplet 

 would only have to be +0-02, —0-04, and -f 0-01 respectively in 

 order to give the mean values just quoted. The corresponding 

 corrections to the wave-lengths would be — 0-012, -f- 0-024, and 

 — 0-006 A. U., all of which lie within the limits of experimental 

 error. Therefore, it is clear that the triplet belongs to oxygen 

 and that the evidence for the presence of this element in the 

 solar atmosphere has been strengthened as a consequence of the 

 apparent mistake of Geiger. — Ptcysik. Zeitschr, No. 25, p. 1267, 

 Dec. 1913. h. s. u. 



7. Fluorescence of the Vapors of Sulphur, Selenium and 

 Tellurium. — Although the number of fluorescent compounds is 

 comparatively great, nevertheless the number of chemical ele- 

 ments which have been shown to possess this property, in the 

 vapor state, is relatively fmall. In fact, prior to the latest work 

 of W. Steubing, the following list was probably complete, 

 namely: Sodium, potassium, rubidium, mercury, thallium, oxygen, 

 bromine and iodine. In the case of oxygen it was found by 

 Steubing that the fluorescent light, as well as the exciting radia- 

 tion, had wave-lengths less than 2000 A. U., that is, they fell 

 within the Schumann region so-called. By analogy with the 

 behavior of the vapors of the elements of the first group of the 

 Mendelejeff table one would expect the heavier elements of the 

 sixth, or oxygen group, to exhibit fluorescence having wave- 

 lengths greater than 2000 A. IT., and hence to be susceptible of 

 investigation with ordinary spectroscopic apparatus. Further- 



