Iv | NATURE OF THE RADIATIONS 121 
is opposite in sense to the deviation observed for the @ or cathodic 
rays from the same material. 
M. Becquerel’, by the same method, found that the a rays from 
polonium were deviated in the same direction as the @ rays from 
radium ; and thus that they also consist of projected positive bodies. 
In both cases, the photographic impressions were sharply marked 
and did not show the same diffusion which always appears in 
photographs of the 6 rays. 
83. Electrostatic deviation of the a rays. If the rays 
are charged bodies, they should be deflected in passing through a 
strong electric field. This was found by the writer to be the case, 
but the electric deviation is still more difficult to detect than the 
magnetic deviation, as the intensity of the electric field must of 
necessity be less than that required to produce a spark in the 
presence of radium. The apparatus was similar to that employed 
for the magnetic deviation (Fig. 25) with this exception, that the 
brass sides which held the plates in position, were replaced by 
ebonite. Alternate plates were connected together and charged 
to a high potential by means of a battery of small accumulators. 
The discharge in the electroscope, due to the a rays, was found to 
be diminished by application of the electric field. With plates 
‘055 cm. apart and 45 cms. high, the diminution was only 7 °/, 
with a P. D. of 600 volts between the slits. With a special arrange- 
ment of plates, with slits only ‘01 cm. apart, the discharge was 
diminished about 45 °/, with an electric field corresponding to 
10,000 volts per cm. 
84. Determination of the constants of the rays. If the 
deviation of the rays in both an electric and magnetic field is 
known, the values of the velocity of the rays, and the ratio e/m of 
the charge of the particle to its mass can be determined by the 
method first used by J. J. Thomson for the cathode rays. From 
the equations of a moving charged body, the radius p of curva- 
ture of the path of the rays in a magnetic field of strength H 
perpendicular to the path of the rays is given by 
m 
1 @. R. 136, p. 431, 1903. 
