2 Stokes, on the Nature of the Rout gen Rays. 



observing the positions of the shadows cast by bodies 

 subjected to the discharge of the Rontgen rays — to 

 investigate, I say, the place within the tube from which 

 the rays appeared to come. Now, when the shadows 

 were received on a photographic plate, and the shadow 

 was joined to the substance casting the shadow, and 

 the joining lines were produced backwards, as a rule 

 they tended more or less nearly to meet somewhere 

 within the tube — Crookes' tube, I will now call it — 

 and some people seem to have had the idea that at 

 that point of meeting or approximate meeting there 

 was something going on which was the source of these 

 rays. I have in my hands a paper published in St. 

 Petersburg by Prince B. Galitzin and A. v. Karnojitzky, 

 which contains some very elaborate photographs obtained 

 in this way. A board was taken and ruled with cross 

 lines at equal intervals, and at the points of intersection 

 nails were struck in in an upright position. The board 

 was placed on top of the photographic plate, with an 

 opaque substance between — a substance which these 

 strange Rontgen rays are capable of passing through, 

 though it is impervious to light. The shadows cast by 

 the nails were obtained on the photograph, and this 

 paper contains a number of the photographs. It is 

 remarkable, considering the somewhat large space in the 

 tube over which the discharge from the cathode is 

 spread, that the shadows are as sharp as they actually 

 are ; and the same thing may be affirmed of the ordi- 

 nary shadows of the bones of the hand, for instance, 

 which one so frequently sees now. Another remarkable 

 point in these photographs is that in some cases it 

 appears as if there were two shadows of the same nail, 

 as though there were two different sources from which 

 these strange rays come, both situated within the 

 Crookes' tube. Now, have we a right to suppose that 



