Electric Deviation of Rays from Radium. 183 



Direction of the Deviation of the Rays. 



In order to determine the direction of the deviation, the 

 rays were passed through slits of 1 mm. width. Each slit 

 was about half covered by a brass plate in which air-spaces 

 were cut to correspond accurately with the system of parallel 

 plates. Fig. 4 represents an enlarged section of three of the 



Fig. 4. 



plates, with the metal plate C half covering the slit AB. If 

 a magnetic field is applied, not sufficiently great to deviate 

 all the rays, the rate of discharge in the testing vessel when 

 the rays are deviated in the direction from A to B should 

 be much greater than when the magnetic field is reversed, 

 i. e. when the rays are deviated from B to A. This was 

 found to be the case, for while the rate of discharge was not 

 much diminished by the application of the field in one 

 direction, it was reduced to about one quarter of its value by 

 reversal of the field. 



In this way it was found that the direction of deviation in 

 a magnetic field was opposite in sense to the cathode rays, 

 i.e., the rays consisted of positively charged particles. 



Electrostatic Deviation of the Rays. 



The apparatus was similar to that employed for the mag- 

 netic deviation of the rays with the exception that the brass 

 sides, which held the plates in position, were replaced by 

 ebonite. 



Twenty-five plates were used of length 4*50 cms., width 

 1*5 cm., and average air-space of *055 cm. The radium was 

 •85 cm. below the plates. Alternate plates were connected 

 together and charged by means of a battery of small accumu- 

 lators to a potential-difference of 600 volts. A current of 

 hydrogen was used as in the case of the magnetic experiment. 



