A Physical Measurement of X-Rays.— liv Howaud L. 

 Bronson, Ph. D., Projcssor oj Physics in Dalhousis 

 University. 



(Road 15 March 1915) 



Introduction. 

 The use of Roentgen rays by the medical profession has 

 increased very rapidly during the past few years, but, as yet, 

 no method of measurement has been generally accepted. 

 At present a large variety of instruments, methods, and units 

 are used. For adding another method to the number already 

 too large, the writer finds his justification in the fact that he 

 not only employs a physical measurement of some accuracy, 

 but also that is it not too complicated for practical use. All 

 the physical principles used are old and have bsen used 

 before. 



The problem was suggested to the writer several years 

 ago by Dr. G. P. Girdwood of Montreal, but a satisfactory 

 galvanometer was not available at that time. The galvano- 

 meter needed for this work should be of the D'Arsonval 

 type with a sensitiveness of at least 5 x 10"^" amperes per 

 scale division, but should not be delicate mechanically. 

 The resistance of the galvanometer is unimportant, but it 

 should have as short a period as possible and at the same time 

 be critically damped on open circuit. Dr. Edward Westoii 

 has recently developed an instrument which just meets these 

 requirements. One of these he very kindly loaned for this 

 work. The other things essential for satisfactorily carrying 

 out this work were supplied by Dr. W. H. Eagar of Halifax, 

 who was kind enough to place his office and most excellent 

 X-Ray equipment at my disposal. In addition to this, 

 experiments were carried on at Dalhousie University and at 

 the Nova Scotia Technical College with the apparatus belong- 

 ing to these institutions. 



Froc & Trans. N. S. Inst. Sci., Vol. XIV. Tra.vs. 2. 



(17) 



