230 



SCIENCE. 



[N. S. Vol. III. No. 59. 



through all bodies. Concerniug the X-rays 

 the same may be said. 



In his latest work Lenard has investi- 

 gated the absorption coeifieients of various 

 bodies for the cathode rays, including air 

 at -atmospheric pressure, which gives 4.10, 

 3.40, 3.10 for 1 cm., according to the degree 

 of exhaustion of the gas in discharge tube. 

 To judge from nature of the discharge, I 

 have worked at about the same pressure, 

 but occasionally at greater or smaller pres- 

 sures. I find using a Weber's photometer 

 that the intensity of the fluorescent light 

 varies nearly as the inverse square of the 

 distance between screen and discharge tube. 

 This result is obtained from three very con- 

 sistent sets of observations at distances of 

 100 and 200 mm.; hence air absorbs the 

 X-rays much less than the cathode rays. 

 This result is in complete agreement with 

 the previously described result, that the 

 fluorescence of the screen can be still ob- 

 served at 2 metres from the vacuum tube. 

 In general other bodies behave like air; they 

 are more transparent for the X-rays than 

 for the cathode rays. 



11. A further distinction, and a note- 

 worthy one, results from the action of a 

 magnet. I have not succeeded in observing 

 any deviation of the X-rays oven in very 

 strong magnetic fields. 



The deviation of cathode rays by the 

 magnet is one of their peculiar character- 

 istics ; it has been observed by Hertz and 

 Lenard that several kinds of cathode i-ays 

 exist, which differ by their power of excit- 

 ing phosphorescence, their susceptibility of 

 absorption and their deviation by the mag- 

 net ; but a notable deviation has been ob- 

 served in all cases which have yet been in- 

 vestigated, and I think that such deviation 

 affords a characteristic not to be set aside 

 lightly. 



12. As the result of many researches, it 

 appears that the place of most brilliant 

 phosphorescence of the walls of the dis- 



charge tube is the chief seat whence the 

 X-rays originate and spread in all direc- 

 tions ; that is, the X-rays proceed from the 

 front where cathode rays strike the glass. 

 If one deviates the cathode rays within the 

 tube by means of a magnet, it is seen that 

 the X-rays proceed from a new point, i. e., 

 again from the end of the cathode rays. 



Also for this reason the X-rays which 

 are not deflected by a magnet cannot be 

 regarded as cathode rays which have passed 

 through the glass, for that passage cannot, 

 according to Lenard, be the cause of the 

 different deflection of the X-rays. Hence, 

 I concluded that the rays are not identical 

 with the cathode rays, but are produced 

 from the cathode rays at the glass surface 

 of the tube. 



13. The rays are generated not only in 

 glass. I have obtained them in an apparatus 

 closed by an aluminium plate 2 mm. thick. 

 I propose later to investigate the behavior 

 of other substances. 



14. The justification of the term ' raj^s,' 

 applied to the phenomena, lies partly in the 

 regular shadow pictures produced by the 

 interposition of a more or less permeable 

 body between the source and a photographic 

 plate or fluorescent screen. 



I have observed and photographed many 

 such shadow pictures. Thus, I have an 

 outline of part of a door covered with lead 

 paint ; the image was produced by placing 

 the discharge tube on one side of the door, 

 and the sensitive plate on the other. I 

 have also a shadow of the bones of the hand 

 (Fig. 1); of a wire wound upon a bobbin; of 

 a set of weights in a box of a compass card 

 and needle completely enclosed in a metal 

 case ; of a piece of metal where the X-rays 

 show the want of homogeneity, and of other 

 things. 



For the rectilinear propagation of the 

 rays I have a pin-hole photograph of the 

 discharge apparatus covered wdth black 

 paper. It is faint, but unmistakable. 



