THE X-RAYS. 153 



With a tube thus become very hard I took a very flue photograph of 

 a double-barreled gun Avith inserted cartridges, which showed all the 

 details of the cartridges, the inner faults of the Damascus barrels, etc., 

 very sharply and distinctly. The distance from the platinum plate of 

 the discharge tube to the photographic plate was 15 centimetelrs and 

 the exposure twelve minutes — comparatively long iu consequence of 

 the small photographic action of the very slightly absorbable rays (see 

 below). The Duprez interrupter had to be replaced by the Foucault 

 form. It would be of interest to construct tubes which would make it 

 possible to use still higher potentials than before. 



Self-evacuation has been above assigned as the cause of the growing 

 hardness of sealed tubes, but this is not the only cause. There are 

 changes in the electrodes which produce this effect. I do not know the 

 nature of these changes. * * * 



The observations recorded in these paragraphs and others not given 

 have led me to the view that the composition of the rays proceeding 

 from a platinum anode of a discharge tube depends upon the frequency 

 and form of the discharge current. The degree of tenuity, the hard- 

 ness, is important only because the form of the discharge is thereby 

 influenced. If it were possible to produce the proper form of discharge 

 for the generation of X-rays in any other way, the X-rays might be 

 obtained with relatively high pressures. 



0. The results appearing in theflve preceding paragraphs have been 

 those most evidently to be derived from the accompanying exxjeriments. 

 Summing up these separate results, and being guided in part by the 

 analogy which holds between the behavior of the visible radiations and 

 X-rays, one arrives at the following conclnsions: 



(a) The radiations emitted by a discharge tube consist of a mixture 

 of rays of different absorbability and intensity. 



(h) Tlie composition of this mixture is in a marked degree dependent 

 on the frequency aiid form of the discharge current. 



(c) The rays receiving preference in absorption vary with different 

 bodies. 



(d) Since the X-rays are generated by the cathode rays and have in 

 common with them various characteristics — as the exciting of fluores- 

 cence, photographic and electrical actions, an absorbability depending 

 in a marked degree on the density of the medium traversed, etc. — the 

 conjecture is prompted that both plienomena are processes of the same 

 nature. Without committing myself unconditionally to this view, I 

 may remark that the results of the last paragraphs are calculated to 

 raise a difficulty in the way of this hypothesis. This difficulty consists 

 in the great difference between the absorption of the cathode rays 

 investigated by Lenard and the X-rays, and second that the transmissi- 

 bility of bodies for the cathode rays is related to their density by other 

 laws than those which govern their transmissibility for X-rays. 



With regard to the first point, considerations present themselves 

 under two heads: (1) As we have seen in section 7, there are X-rays of 



