PHYSICS — XICH0LS. 235 



anthracene, and Messrs. Howe and Phelps Gage have made numerous photo- 

 graphic determinations of the value of various flaming arcs and other sources 

 of light for purposes of excitation. Many tests of photographic plates have 

 also been made. 



(2) Fluorescence Absorption: 



In the course of the year the consideration of this subject, which has for 

 some time been in dispute, has been resumed, and by a variety of independent 

 methods the conclusion has been reached, in conformity with the results of 

 Camichael, Houstoun, and Wood, that the effect is either too small to detect 

 or non-existent.* 



(3) The Conductivity of Anthracene Vapor: 



The work of Mr. H. E. Howe, begun in 1908, has been completed, and his 

 resultsf have been published in the Physical Review for April 1910. Mr. 

 Howe finds that whatever dissociation may be supposed to occur when the 

 vapor of anthracene is excited to fluorescence does not produce a measurable 

 effect on the conductivity of the vapor. 



(4) Studies of Phosphorescence of Short Duration: 



During 1908-09, Dr. C. W. Waggoner} undertook the determination of 

 the form of the curve of decay in the case of phosphorescence of very short 

 duration. By means of a new form of phosphoroscope especially designed 

 for this work he was able to make observations for the complete determina- 

 tion of the curves of decay for substances, the phosphorescence of which had 

 vanished or become immeasurably faint in a few hundredths of a second. 

 He found these curves, like those depicting the decay of slowly decreasing 

 phosphorescence, which were the only cases previously investigated, to con- 

 sist of two parts, indicating two successive processes of decay merging into 

 one another. He also found that all the general laws determined for phos- 

 phorescence of slow decay applied to the cases of phosphorescence of very 

 brief duration. 



These investigations have been continued during the past year by Mr. Carl 

 Zeller,§ who has confirmed the results obtained by Waggoner and has in ad- 

 dition, by the use of the same phosphoroscope, made a detailed study of the 

 first process in the decay of several of the phosphorescent combinations of 

 Lenard and Klatt. Lenard, in a recent paper, has questioned the form of 

 this portion of the curve as given by us in our earlier work, but Mr. Zeller's 

 observations, which are carried to within less than a thousandth of a second 

 from the close of excitation, are conclusive as to the linear relation between 

 the reciprocal of the square root of the intensity and the time. 



* Nichols and Merritt, Physical Review, xxxi, p. 241. 1910. 

 t H. E. Howe, Physical Review, xxx, p. 453. 1910. 

 t C. W. Waggoner, Physical Review, xxvn, p. 109. 1908. 

 § Zeller, Physical Review, xxi, p. 367. 1910. 



