690 Mr. Alan A. Campbell Sicinton [Feb. 4, 



fixed an electromagnet, producing straight magnetic lines across the 

 path of the rays. As soon as the magnets are excited the cathode 

 beam is deflected and split up, and instead of having a single narrow 

 line of luminescence, we now have many lines with dark intervening 

 spaces, all in constant movement. An experiment like tiiis cannot be 

 shown to an audience, but I have prepared photographs which will 

 make the effect produced clear. Fig. 9 is a photograph taken without 

 camera or lens, and produced simply by binding a strip of sensitive 

 photographic film round the bulb of the tube and making a single 

 discharge by a single break of the contact-breaker of tlie induction 

 coil. The film being in close contact with the glass is impressed by 

 tlie luminous bands that the unequally deflected c.ithode rays pro- 

 duce on the latter, and we have a photographic image of the bands 

 for a single electrical discharge. Nor is this all. By inserting 

 between the glass and the photographic film a piece of very thin 

 black j)aper, so placed as to cover only one-half of tlie spectrum, it is 

 possible to obtain a photograph of the bands, one half of which is due 

 to the visible fluorescent luminosity of the glass, and the other half 

 to the invisible Eontgen rays produced by the impact of the cathode 

 rays on the glass. 



Fig. 10 is such a photogra[)h, and it will be seen that the Uontgen 

 rays are also given off in bands, which are co-terininons with the 

 fluorescent bands though photographically fainter tlian the latter. 

 In the photographs shown, this difference in density between the two 

 images is lessened by the interposition between the glass and the 

 film in the case of the luminous portion of a thin sheet of slightly 

 yellow celluloid. Without this the difference would be so great that 

 it would not be possible to show both images upon a single film. Of 

 course, this faintness of the l\ontgen ray bands is only to be expected, 

 as in tlie photograph of the luminous bands the Eontgen rays are also 

 present, so that in the one case the photographic image is the result 

 of both descripti<»ns of radiations, and in the other is caused by only 

 one. It is worthy of note that in the spectrum image produced by 

 the Eontgen rays, the greatest photographic effect is always produced 

 by the least deflected of the cathode ray streams, that is to say, by that 

 stream which presumably was travelling at the greatest velocity. It 

 is obvious that the cathode ray atoms which are travelling most 

 rapidly will be the ones least deflected, just as the faster is the flight 

 of a bullet the flatter is its trajectory. Hc;re we have a probable 

 explanation of the existence of the bands which most likely are due 

 to the atoms of the cathode rays having either from the first different 

 velocities imparted to them, due to tlie oscillatory character of the 

 induction coil discharge, or from tlieir gathering into gronps travelling 

 at different velocities on the well-known principle that occasions the 

 traflic in the street to form knots of maxima and minima, owing to the 

 faster vehicles catching up the slower and being impeded by them. 



The axial stream in the centre of the hollow cathode ray cones 

 juay possibly also be due to the same cause. 



