772 POPULAR SCIENCE MONTHLY. 



sought in the papers of Crookes, Hertz, Leiiard, and Rontgen ; 

 and the interest in the mysterious manifestations of these invisi- 

 ble rays is twofold : first, in regard to the possible application of 

 the phenomena to surgery, since the rays show a specific absorp- 

 tion, passing more easily through the flesh than through bones or 

 glass or metallic particles ; and, secondly, in relation to the ques- 

 tions whether we are dealing here with radiant matter shot forth 

 from the negative pole or cathode or with longitudinal waves of 

 electricity. 



Let us first examine the possibility of the practical application 

 of the cathode photography to surgery. The term cathode is ap- 

 plied to the zinc pole or negative pole of an ordinary battery. It 

 is that terminal of an electrical machine which glows least in the 

 dark when the machine is excited. It is the shortest carbon in 

 the ordinary street electric lamp. The positive carbon or anode 

 burns away twice as fast as the negative carbon or cathode. If 

 the electric light is formed in a high vacuum by means of a great 

 electro-motive force, we no longer have a voltaic arc or a spark ; 

 instead of this the exhausted vessel is filled with a feeble lumi- 

 nosity, and a beam of bluish rays is seen to stream from the nega- 

 tive terminal or cathode. When these rays strike the glass walls 

 of the vessel they excite a strong fluorescence. If the glass con- 

 tains an oxide of uranium this fluorescence is yellow ; if it contains 

 an oxide of copper it is green. Rontgen supposes that this fluo- 

 rescence excited by the cathode rays is connected in some way with 

 the formation of what he terms the X rays. Now, a photograph 

 of the bones in the hand, for instance, can be obtained by placing 

 a sensitive plate in an ordinary photographic plate-holder. Rest- 

 ing the hand on the undrawn slide in the daylight, with the palm 

 of the hand outward and toward the cathode, and about six inches 

 away from it, the bones of the hand are thus brought in the 

 nearest possible position to the sensitive plate. At the time of the 

 present writing, the breast and the abdomen of the human body 

 present too great thickness for successful photographs, and the 

 attempts to obtain representations of the cavity in which the brain 

 is situated have been failures, since the rays do not show any 

 marked difference in fleshy tissues. Nothing can be obtained in 

 these attempts to photograph, the brain but a contour of the cav- 

 ity in which it is situated, and possibly a shadowy representation 

 of a bullet which might be imbedded in the head. The method 

 of obtaining a successful photograph of the hand shows the pres- 

 ent limitations of the method. In order to obtain a fairly sharp 

 shadow of a bone or of a shot, it should not be more than an inch 

 away from the sensitive plate. The term shadow, however, is 

 somewhat misleading. The photograph of the hand by the X 

 rays is entirely different from one produced by resting the hand 



