731 Dr. Tycho E:son Auren on Scattering and 



The tension, applied at the bulb from a high-tension trans- 

 former, could be read off on a kilowattmeter attached to the 

 primary circuit o£ the transformer, and could also be 

 accurately regulated. In the course of my experiments 

 tension has been continuously observed, and a continuous 

 regulation has been made. The variations in the tension 

 have only exceptionally reached - 5 k'v. The composition 

 of radiation has been varied not only by variation of tension, 

 but also by aluminium filters of the thicknesses of 0*5-3*6 cm. 

 For each determination, as a rule, five different measure- 

 ments have been made, which have very nearly agreed with 

 one another, and have seldom diverged more than 0*5 per 

 cent, from the mean. Repeated determinations of the 

 absorption of the same substance have shown that the agree- 

 ment of the values found is always remarkably close. 



In Table I. there are noted down the tensions used in the 

 different compositions of radiation, the thickness of the 

 respective aluminium filters, the values observed in these 

 radiations for the atomic absorption coefficient of Cu relative 

 to water (/ecu/H 2 o), the corresponding values of the mass 



absorption coefficient of Cu ( -Cu J and the effective wave- 

 length (X e ) in Angstrom units, calculated by the aid of the 

 table of Barkla and White*. 



Table I. 



Notation. 



Approximate 



tension in 



kv. 



The 



of a 



filt 



thickness 

 u minium 

 3r in cm. 



*Cu/H 2 0- 



P 



X e . 108 

 cm. 



I. .. 



.... 70 





0-5 



654 



6-30 



0-359 



II. .. 



75 





10 



49-4 



3-64 



0-302 



III. .. 



.... 80 





1:5 



403 



2-62 



0-264 



IV. .. 



.... 85 





20 



33-8 



202 



0-237 



V. .. 



.... 95 





2-5 



28-6 



1-60 



0-215 



VI. . 



.... 100 





3-6 



23-4 



1-28 



0-194 



In the determination of the atomic absorption coefficient 

 of H relative to water in my experiments published pre- 

 viously, I have started from the point of view that the law of 

 additivity is strictly valid, and, consequently, that this 



* Barkla and White, Phil. Mag. xxxiv. p. 272 (1917). 



