638 PROCEEDINGS OF THE AMERICAN ACADEMY. 



When the vacuum was increased to so high a degree that the bulb could 

 not be excited by a coil giving a six-inch spark, the application of the 

 magnetic field immediately resulted in the production of the rays. 



At the X-ray stage, when the cathode formed the end of a powerful 

 electro-magnet and the lines of magnetic force were directed along the 

 line of discharge, a violet light in the form of a ring appeared on the 

 back of the cathode toward the magnet, while the X-rays were greatly 

 increased in brilliancy together with the general fluorescence of the 

 tube. 



The increase in the X-rays, however, only appeared in a tube highly 

 exhausted and with the employment of a coil giving a twenty-four inch 

 spark. The coil was also provided with large condensers. The increase 

 in brilliancy of the X-rays viewed on a fluorescent screen was fully one 

 hundred per cent, and this increase suggests the possibility of a practical 

 use of the magnetic field in connection with the production of X-rays. 

 One can modify the state of the tube by modifying the magnetic field. 

 It may be also that by studying the effect of the field we can identify 

 the particles which bombard the anticathode. 



It was difficult to measure the strength of the magnetic field inside 

 the exhausted bulbs. The size of the electro-magnet was as follows : 

 Diameter of core, 2.5 cm. ; 15 layers of no. 12 copper wire, 37 turns 

 to a layer ; length of electro-magnet, 9.5 cm. ; distance of end of hollow 

 iron core from anode or cathode, 2 cm. Exciting current in electro- 

 magnet, 15 to 25 amperes. 



When the cathode mirror of an ordinary X-ray bulb is made the 

 anode instead of the cathode, the current passing in the usually un- 

 favorable way for the production of the rays, and at the same time is 

 also the pole of a powerful electro-magnet, the bulb gives out X-rays in 

 great abundance. This is not the case when the magnet is not excited. 

 The magnetic field, therefore, causes the anode to produce X-rays, prob- 

 ably by an increased energy of bombardment of the platinum focal plane 

 by the positive ions. I believe that if one studies the effect of the mag- 

 netic field on the anode, in the case of the stratifications showing an 

 effect of increased pressure at their centres (Figure 2), the production 

 of ring stratifications, one must be convinced that the effect of the mag- 

 netic field is to increase the free path of the positive ion and to permit it 

 to produce the X-rays by a bombardment similar to that of the negative 

 ion. There is another supposition, namely, that the magnetic field pro- 

 duces rays similar to the cathode rays ; certainly one can separate the 

 anode discharge into two by means of the magnetic field. 



