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[Feb. 21, 



on which they impinge ; they both traverse opaque films of metal ; 

 they both produce actinic effects on photographic plates. That the 

 Rontgen rays are something different from the Lenard rays is proved, 

 I think, by the fact that they are not by any means so absorbable bj' air. 



It may be interesting to know how Rontgen's original eii'ects were 

 obtained. He took an ordinary Crookes tube, or at least a tube con- 

 taining the proper vacuum, and completely covered it with blackened 

 pasteboard so as to render it light tight to ordinary light. He took a 

 paper screen which he painted with a substance capable of being ex- 

 cited by fluorescence, a solution of barium-platino-cyanide. He then 

 found that wherever this screen was impinged on by the Rontgen rays, 

 it fluoresced. 



Rontgen found, that his rays, like the Lenard rays, possess the strange 

 power 9f passing through many substances opaque to ordinary light. 

 It is generally believed that the source of the Rontgen rays is the por- 

 tion of the glass tube which receives the bombardment of the molecules 

 shot off from the negative electrode. In other words, the Rontgen 

 rays are caused by the cathode rays. That they are not the cathode 

 rays themselves is evident from a brief review of some of their charac- 

 teristics. 



1. The Rontgen rays are invisible to the eye. 



2. They excite fluorescence. (In this respect, however, they agree 

 with the cathode rays and the Lenard raj^s.) 



3. They produce actinic effects. In this respect they agree with the 

 Lenard rays, but are entirely differentiated from the cathode rays. A 

 photographic plate has been placed inside a Crookes tube and the 

 cathode rays have been caused to impinge on it. They failed to pro- 

 duce any actinic effects. There are clearly then these differences ; the 

 Rontgen rays produce actinic effects ; i. e., they possess the power of de- 

 composing a photographic salt placed on a sensitive plate, and are not 

 deflected by a magnet. This latter point has been confirmed recently 

 by some very careful experiments made by Dr. Oliver Lodge. The 

 apparatus would have detected any deflection had it existed. 



There is, however, a marked similarity between the Lenard and the 

 Rontgen rays. The source of both is believed to be the cathode rays. 

 Thej" each produce fluorescence ; each possess the power of passing 

 through substances ordinarily opaque, the opacity increasing appa- 

 rently with the density, thou^gh not in direct proportion with the den- 

 sity. The Rontgen rays, however, difler in the valuable property of 

 not being so readily absorbed. The Lenard rays, though not deflected 

 by a magnet, in free air, are deflected by a magnet when they are 

 caused to enter a highly exhausted chamber — at least, so Lenard states. 

 It is said that Prof. Wright, of Yale, a careful student and one whose 

 opinion is to be regarded, does not think that the Rontgen rays difler 

 from the cathode rays. He rather looks on the Rontgen rays as 

 strained cathode rays. 



