﻿1164 Balance Method of measuring X-Bays. 



of steadiness of the balance is mainly due to the instrumental 

 side of the high tension apparatus. 



How far the ionization produced by X-rays in the air of a 

 vessel may serve as a reliable indicator of the intensity of the 

 former is for experiment to decide. With any change of 

 wave-length the issue becomes complicated by the selective 

 production of characteristic and scattered radiation at any 

 surface struck by the incident rays. The effect can hardly 

 completely begot rid of because of the necessity for windows 

 to the vessel. The apparatus shown in fig. 2 was constructed 

 so as to reduce the above effect to a minimum. 



Necessity for an International Unit of X-ray intensity. 



The need h;is long been felt for a unit of X-ray intensity 

 which shall receive International sanction. Investigators who 

 wish to compare their results have of necessity recourse to 

 various indicators, over the performance of which there is, 

 however, not too much confidence. Attempts have from 

 time to time been made to express the output of X-ray tubes 

 in terms of the gamma rays from radium ; more, however, 

 with a view to comparing their relative output of energy 

 than to standardize X-ray intensity in terms of the constant 

 source of radiation which a sealed preparation of radium 

 affords. 



The need mentioned above is also an urgent one in the 

 practice of medical radiology at the present time. The 

 radiologist who is dispensing X-rays wields a highly compli- 

 cated collection of apparatus ; he is provided with X-ray 

 tubes, the dimensions and output of which increase almost 

 yearly, but so far he has not been given the security he needs, 

 namely, a unit of intensity of the rays he is using. It seems 

 that this can hardly be done without action of some sort by 

 physicists, and the suggestion is made here, as it has been 

 made elsewhere as well ns by others, that steps be taken to 

 fix upon some International Unit of X-ray intensity which 

 will serve at one and the same time the interests and 

 requirements of physical and medical investigators. 



