Leonard.] dUU ^^oy_ oq, 



tended from cathode to cathode outside the tube. The x-raj-s and 

 fluorescence were seemingly destroyed in this manner in all forms of 

 double cathode tubes used with the alternating current. 



The form of interference which was first observed was therefore the 

 establishment of a path for the conduction of the electricity from 

 cathode to cathode outside the x-ray tube, or in other words the com- 

 pletion of a short circuit between the cathodes in the induced electric 

 field outside the tube. 



But why was it possible to complete this short circuit, in one tube, bj- 

 introducing the aqueous vapor at a single point opposite the reflector 

 and midway between the cathodes, and impossible to do it in any other 

 tube of the same type? Is there any reasonable theory which will logi- 

 cally explain this difference '? 



A critical examination of two tubes of this type shows that in tube A 

 the cathodes are in such relation to the planes of the reflector that light, 

 obeying the law of reflection, and emanating from the cathodes, would 

 be reflected at such an angle as to leave a wedge-shaped area beneath 

 the reflectors and between tlie two bundles of rays, free from their in- 

 terference. 



An examination of tube B shows that no such area would be formed, 

 and that the two bundles of rays Avould be united in the median line. 



The fluoroscope shows that this median area is the area of most in- 

 tense fluorescence, as x-rays enter it from both reflectors. 



Suppose the rays obeying the law of reflection within the tube are the 

 cathode rays, which become the Lenard rays outside the tube. 



In tube A they would be reflected from the median line and leave a 

 field of x-rays free from their interference. We have then here a 

 purer field of x-rays, which w^ould easily account for the greater 

 rapidity and sharpness of definition which this tube has exhibited, as 

 illustrated by the unintensified half-minute exposure negatives of the 

 hand and other objects, and the six-minutes exposure of the normal 

 trunk of a five-year-old boy. 



Would this supposition account for the absence of a conductive area 

 midway between the two cathodes, which, when supplied by the aqueous 

 vapor, results in the extinguishing of the x-ray and fluorescence '? It 

 would, if we consider the Lenard rays to be capable of conducting 

 electricity while the x-raj^s are not. Under these conditions the 

 aqueous vapor between the bundles of Lenard rays, in the case of tube 

 A, would form the connecting link in the short circuit between the 

 cathodes. But how about tube B — if this theory is correct, how can avc 

 explain the difference in the phenomenon observed in it '! 



In this tube we saw, that the bundles of reflected Lenard rays occupied 

 the median field beneath tlie reflectors and were continuous, while llic 

 areas of non-conduction lay between the cathodes and the bundles of 

 Lenard rays. 



By placing two small ]>i('ces of moistened ])aper in these two non- 



