292 proceedings: philosophical society 



PHILOSOPHICAL SOCIETY OF WASHINGTON 



The 802d meeting was held at the Cosmos Club, March 2, 1918. 

 Vice-President Humphreys in the chair; 40 persons present. The 

 minutes of the 801st meeting were read in abstract and approved. 



Lieut. D. L. Webster presented a paper on Emission quanta phe- 

 nomena in X-rays, illustrated by lantern slides. The paper was- a brief 

 account of the work on this subject that has appeared in the past three 

 3^ears in the Physical Review and the Proceedings of the National Academy 

 of Sciences. 



In the general radiation spectrum, the frequency whose quantum 

 is the energy of one cathode electron was found by Duane and Hunt, 

 and by Hull, to have an upper limit, at which the spectrum ends. It was 

 shown by Webster that the existence of such a limit to the spectrum is 

 direct evidence that the rays are trains of periodic waves rather than 

 pulses; and with further experimental work, that if atoms in the anti- 

 cathode could be struck only by electrons of a definite velocity, any 

 atom's chance of emitting rays of a given f requeue}^ jumps from zero 

 discontinuously to a finite value as the energy of the cathode electron is 

 raised continuously past the quantum value of that frequency. A 

 further continuous increase of energy of the cathode electron would 

 produce a continuous decrease of intensity of rays of that frequency. 



For the characteristic rays of the K series, it was found by Webster 

 that no such rays are produced until the cathode electron's energy 

 reaches the quantum value of the highest frequency of the series, at 

 which point all the lines of the series appear together. Their intensities 

 increase by the same law for all lines, but this law is very different from 

 that holding for any given frequency in the general radiation. These 

 phenomena are all consistent with the hypothesis that the primary 

 characteristic rays produced by cathode rays come from the same 

 atomic mechanism as the secondary characteristic rays occurring in 

 fluorescence. This statement holds, whatever that mechanism may be. 



For the L series it was found by Webster and Clark that the laws are 

 similar to those of the K series except that the lines must be considered 

 as belonging to at least two, and probably three, separate series, each 

 of which behaves like the K series. 



Discussion: This, paper was discussed by Messrs. Swann, White, 

 and FooTE. 



The second paper, on Determination of the constant Co of Plan.k's law, 

 was presented by Major C. E. Mendenhall. It was illustrated by 

 lantern slides. No abstract furnished. A paper of the same title was 

 published in the Physical Review, 15 : 515. November, 1917. 



Discussion: This paper was discussed by Messrs. Crittenden, 

 Abbott, Coblentz, Foote, Sosman, WhiteI^ Swann, and Webster. 



H. L. Curtis, Recordiyvj Secretary. 



