236 REPORTS ON INVESTIGATIONS AND PROJECTS. 



( 5 ) Kathodo-luminescence : 



Preliminary work on kathodo-luminescence, an account of which was pub- 

 lished in 1909,* is being followed up by Mr. J. A. Veazey. The greater part 

 of the year was employed in the construction, assembling, and calibration of 

 the apparatus, which consists of a Fluess mechanical air-pump and a rotary 

 mercury air-pump, in tandem for the production and maintenance of high 

 vacua; a large four-plate, motor-driven, electrostatic machine; electrostatic 

 voltmeters for the measurement of potentials ; galvanometers for determin- 

 ing the flow of current through the vacuum-tube and of the leakage current 

 due to the kathodic discharge ; a photometer and spectro-photometer for the 

 optical observations. This portion of the work is now completed, and it is 

 confidently expected that within the next few months data will be obtained 

 which will greatly add to our definite knowledge of the laws of kathodo- 

 luminescence. 



(6) X-ray Luminescence : 



In the course of our studies of fluorescence and phosphorescence we have 

 from time to time used X-rays as an exciting agency and have compared the 

 efl^ects with those obtained by means of light. A systematic quantitative 

 study of X-ray luminescence is now proposed and apparatus for the produc- 

 tion of rays of the highest intensity has been ordered, on trial. This work 

 will probably be placed in the hands of Mr. A. H. Forman, who has for two 

 years been engaged in researches involving the use of X-rays. 



(7) The Effect of Temperature on Fluorescence and Phosphorescence : 



Quantitative studies of low temperature, down to — 190° C, upon the loca- 

 tion and intensity of the bands of fluorescence spectra, which were begun in 

 the spring of 1909, have been continued during the past year. The measure- 

 ments show that what all writers have hitherto considered as single bands 

 and treated as units are in many cases complex in structure, consisting of an 

 aggregation of overlapping bands, which can not be separated by spectro- 

 photometric or photographic methods. These overlapping components are, 

 however, frequently differently affected by change of temperature, so that 

 the comparison of the curves giving the distribution of intensities in a flu- 

 orescence spectrum affords definite indication of the number and location of 

 the bands of which the spectrum is composed. Numerous determinations of 

 the eft"ect of low temperatures upon the intensity and rate of decay of phos- 

 phorescence have also been made. Some of the results of these investiga- 

 tions were given in a paper read before the April (1910) meeting of the 

 American Philosophical Society, and a further report will shortly appear in 

 the Physical Review. 



Two years ago Dr. R. C. Gibbs began the spectrophotometric study of the 

 effect of temperature upon the absorption and fluorescence of various glasses. 



* Nichols and Merritt, Physical Review, xxviii, p. 349. 



