PHYSICS — NICHOLS. ^ ■■*' 235 



Nichols, Edward L., Cornell University, Ithaca, New York. Grant No. 

 575. Continuation of researches on fluorescence and phosphorescence. 

 (For previous reports see Year Books Nos. 4, 5, 6, and 7.) $3,000. 



During the past twelve months the work on fluorescence and phosphores- 

 cence carried on by or under the direction of Prof. Ernest Merritt and myself 

 in the Physics Laboratory of Cornell University has consisted of the follow- 

 ing researches. 



The Experimental Determination of the Actual Distribution of Energy in 

 Various Fluorescence Spectra: 



In this investigation the visible spectrum of our acetylene standard flame 

 was compared with spectrum of an ideal black body of known temperature, 

 and from these measurements the distribution of energy in the spectrum of 

 the standard flame was computed by the application of Wien's law. From 

 these data the distribution of energy of any source of light that has been 

 properly compared with the standard can be computed. Careful spectro- 

 photometric studies of the fluorescence spectra of solutions of fluorescein, 

 eosin, and resorufin have been made; corrections for absorption and slit- 

 width have been applied and the energy curves for these fluorescent sub- 

 stances determined. The relation of these curves to the energy curves of the 

 spectra of incandescent black bodies is of great interest and the development 

 from entirely independent considerations of equations describing this impor- 

 tant type of luminous emission is in progress. 



The Determination of the Influence of Wave-length upon the Effectiveness of 

 Monochromatic Radiation in Exciting Fluorescence: 



In these experiments we dispersed the light from a Nernst filament by 

 means of a large spectrometer and used successively various wave-lengths of 

 the continuous spectrum of this source in the excitation of the fluorescence 

 of a number of liquids. The brightness of the exciting light was measured 

 and the brightness of the fluorescence produced was determined. The absorp- 

 tion coefficient of the fluorescent liquid for each wave-length was likewise 

 determined. We were thus enabled, by means of the data established in the 

 course of the work already described, to compute the relative effects of equal 

 amounts of energy of absorbed light of the various wave-lengths in produc- 

 ing fluorescence. The experimental data of this research are complete and 

 the results are now being prepared for publication. 



The Quantitative Study of the Effects of Low Temperature upon Fluores- 

 cence Spectra: 



Some years ago Dewar and other writers published observations upon the 

 effect of low temperatures on the brightness and color of phosphorescent sub- 

 stances, and the first of our present series of papers (Physical Review, vol. 



