PHYSICS — NICHOI.S. 237 



Measurements of the relative intensities of the various fluorescence bands 

 in the case of a number of uranyl salts show that the maximum of bright- 

 ness does not lie in the middle of the group, but is always displaced toward 

 the violet. The diminution in intensity in passing from band to band 

 towards the violet is thus more rapid than the diminution towards the red on 

 the other side of the maximum. The curves expressing this distribution of 

 intensities are similar for the various salts and all are of a type exactly cor- 

 responding to the curve of the distribution of intensities in the broad fluo- 

 rescence bands of many other substances upon which measurements have 

 been made. It seems probable that all such broad bands are really complex 

 and are made up of a group of narrower overlapping bands, and that in the 

 uranyl salts we have a case in which it is possible to study these narrower 

 bands in detail for the reason that at ordinary temperatures they overlap 

 only to a small extent. The distribution of intensities as determined by 

 monochromatic excitation, using successively all the ultra-violet lines of 

 sufficient intensity in the spectrum of the mercury arc, appears (as in the 

 cases of fluorescence hitherto investigated) to be independent of the mode 

 of excitation. Studies of the effect of change of temperature and of dehy- 

 dration of such salts as contain water of crystallization upon the position and 

 character of the various bands of the fluorescence and absorption spectra 

 have likewise been begun and numerous interesting and significant results 

 have already been obtained. It is proposed in the near future to redetermine 

 with great care the frequency differences in the overlapping regions of 

 fluorescence and absorption, to determine the manner in which the bands 

 observed at ordinary temperatures go over into the forms which exist at the 

 temperature of liquid air, and to study in greater detail the effect of dehydra- 

 tion and the behavior of completely dehydrated salts through a wide range 

 of temperatures. 



In addition to the above experimental work, much time has been given to 

 the preparation of a memoir to be published by the Carnegie Institution of 

 Washington, which is to cover our investigations during the years 1903 to 

 1910. 



During the year, Mr. H. E. Howe has continued his experiments looking 

 to the development of a practicable and really accurate photographic method 

 to supplant the use of the eye in the study of weak spectra and in the 

 measurement of bands of shorter wave-lengths. In this work important 

 advances have already been accomplished. 



Dr. J. A. Veazey continued, up to the first of June, the study of kathodo- 

 luminescence which he has had in hand under our direction since 1908. 

 Arrangements had been made under which he was to devote his time exclu- 

 sively to this topic throughout the coming year. It is with great regret, 

 however, that we have to report the death of this earnest and successful 

 coworker. Mr. Brown, a student assistant of Dr. Veazey 's during the last 

 year, will take up and continue the work in the near future. 



