PHYSICS. , 359 



17. The stimulation of special lines by light frequencies other than those emitted. Stanislaw 



Loria. 



18. A search for an efTect of temperature upon photo-electric emission. J. Rudd Nielson. 



19. Photo-electric analysis of radiations between the X-ray region and the optical region. 



E. H. Kurth. 



20. Magnetostriction as a function of crystal-orientation. S. R. Williams. 



21. Magnetic properties of sputtered cathode films. G. H. Cameron. 



22. Development of a very high-voltage constant potential generator. J. W. M. DuMond. 



23. Direct observation of the paths of B-rays in passing through atoms. D. H. Loughridge. 



24. Penetrating radiations on mountain peaks and in high airplane flights. Russel M. Otis. 



25. Measurement of the radioactivity of ordinary materials. I. S. Bowen. 



26. A new magnetometer. S. R. Williams. 



27. A comparison of Barkhausen efTects with magneto-stictive effects. S. R. Williams and 



H. K. Dunn. 



28. The laws of reflection of molecules. Paul S. Epstein. 



29. Quantum relations in magnetism. Paul S. Epstein. 



30. The combined Zeeman and Stark effects. Sinclair Smith. 



31. New series relationships in spectra. J. A. Carroll. 



32. Seismological and earth-tide measurements in southern California. W. T. Whitney. 



33. Mobilities of ions in flames as a function of inserted salts. W. M. Zaikowsky. 



34. A quantum theory of dispersion. C. G. Darwin. 



35. Interference phenomena in white light when a thick glass plate is compensated by air. 



W. N. Birchby. 



Nichols, E. L., Cornell University, Ithaca, New York. Report on studies in 

 luminescence. (For previous reports see Year Books Nos. 4-21.) 



Among the topics under investigation during 1923 the constitution of 

 luminescence spectra should probably be given first place. Aside from the 

 line-like spectra exhibited by certain fluorites holding traces of the rare earths 

 in solid solution, it had been known for some time luminescence spectra in 

 general might be divided into two classes: 



(a) The broad-banded spectra of such phosphorescent substances as wille- 

 mite, sidot blende, and the Lenard and Klatt sulphides. 



(b) The narrow-banded spectra of the uranyl salts and of certain organic 

 compounds. 



In 1917 ^ a detailed spectro-photometric study of the fluorescence spectra 

 of three of the Lenard and Klatt sulphides, made by Professor H. L. Howes, 

 at the writer's suggestion, brought out the unsuspected fact that the very 

 broad bands which are characteristic of these spectra are made up of two or 

 more groups of equidistant components. 



In 1918 2 investigation of the phosphorescence spectrum of a calcite from 

 Franklin Furnace revealed a similar structure, and in the same year Howes 

 showed that the fluorescence bands of iodine vapor as measured by McLen- 

 nan ^ can also be arranged in several series having intervals of constant 

 frequency. 



The extended spectro-photometric investigation of kathodo-luminescence, 

 done by Mr. T. Tanaka in our laboratory (see Year Book No. 21, p. 389), is 

 now completed and four papers containing the results are ready for publication. 

 The principal points may be briefly summarized as follows: 



(1) The kathodo-luminescence spectra of 129 solid solutions with 42 metals 

 as active agents were studied. Of these, 27 were Lenard and Klatt sulphides; 



1 Nichols, Amer. Philos. Soc, lvi, p. 261 (1917). 



* Nichols, Howes, and Wilber, Phys. Rev. (2), vol. xii, 364 (1918). 



^ Howes, Science, n. s., vol. xlvi, 96 (1918). 



