April 10, 1896.] 



SGIENGE. 



543 



path of the X-rays the fiuoroscope will 

 light up. While making this particular 

 observation I noticed that when the tube 

 was operating especially well a faint fluor- 

 escence was still present even if no re- 

 flecting body was in front of the slit. Pre- 

 cautions were observed to exclude any radi- 

 ance that might reach the fiuoroscope di- 

 rectly by a sort of diffraction around the 

 edges of the slit, but still the fluorescence 

 in the fiuoroscope persisted. There was 

 evidently a difiuse scattering of the Eontgen 

 radiance in the air itself. This, however, 

 is so small that it is distinctly noticeable 

 only when the tube operates so powerfully 

 that a strong image' of the hand on the 

 fluorescent screen can be obtained by the 

 radiance reflected from a pine board two 

 inches thick and 16 inches square, placed 

 at a distance of six inches from slit. With 

 a good sized tube of proper vacuum and 

 working at the temperature of highest effi- 

 ciency this intensity is not at all difficult to 

 obtain, provided, of course, that one has 

 sufficient electric power to excite the tube. 

 These experiments prove beyond all 

 reasonable doubt that the Eontgen radi- 

 ance is diffusely scattered through bodies, 

 gases not excepted. We may call it diffuse 

 reflection, if we choose, provided that we 

 do not imply, thereby, that we must neces- 

 sarily assume an internal inter-molecular 

 regular reflection, in order to explain the 

 phenomenon. For if a pufi" of smoke be 

 forced through a pile of wood some of it 

 will come out pretty well scattered, al- 

 though we cannot speak here of a reflection 

 in the ordinary sense, but rather of deflec- 

 tion, reserving the term ' reflection ' for 

 those particular cases in- which the angle 

 of incidence is equal to the angle of deflec- 

 tion. It might turn out, for instance, that 

 the X-rays are due to a circulating motion 

 of ether and that the stream lines are de- 

 flected and diffusely scattered within the 

 molecular interstices of ponderable sub- 



stances. Appearances seem to speak more 

 in favor of this %'iew than in favor of a wave 

 motion of ether. 



The diffuse scattering of the Eontgen 

 radiance by bodies placed in its path maj"- 

 be also described by saying that every sub- 

 stance ivhen subjected to the action of the X-rays 

 becomes a radiator of these rays. This state- 

 ment will be more complete than the state- 

 ment that a diflrise reflection takes place, if 

 my observation should prove correct that 

 the maximum effect in the fluoroscope is 

 obtained when the largest surface of the 

 body, acted upon by the Eontgen radiance, 

 is placed -parallel to the fluorescent screen. 

 For in that case there is actually secondary 

 radiation due to the diffuse scattering which 

 proceeds normally to the surface of the in- 

 tercepting body. 



The fact that opaque bodies like metals 

 are less effective in producing this secondary 

 radiation leads to the conclusion that there 

 is in these bodies an internal dissipation of 

 the E5ntgen radiance much greater than in 

 the case of transparent dielectric substances. 

 A properly constructed bolometer should 

 give us much information on this point, and 

 it is my intention to take up this subject as 

 soon as time and facilities will permit. 



These diffusion effects, which are present 

 even in air, bring the Eontgen radiance into 

 still closer resemblance to the principal 

 features of the cathode rays which were 

 studied by Professor Lenard. The differ- 

 ence in their behavior towards magnetic 

 force is still to be explained. Is it not pos- 

 sible that this magnetic effect in air is 

 masked by the diffuse scattering of the X- 

 rays ? 



In conclusion I wish to observe that 

 among the several theories proposed to ac- 

 count for the properties of the X-rays we 

 may insert one which can be easily inferred 

 from the somewhat neglected essay which 

 the late Prof. v. Helmholtz wrote toward 

 the closing days of his life. It is the essay, 



