Electric Field of the oc, ft, and Secondary Rays. 731 
potential of whichever sign, the amount o£ primary ft and 7 
rays falling on the plates will also be the same for all 
Fig. 3. 
RA. 
TO W/MSHURST T 
substances used as radiators. Thus we have a thoroughly 
satisfactory comparative test of the secondary radiations from 
the various materials employed. 
The results obtained are shown in fig. 4 (p. 732), and it will 
be seen that the curves for each substance are unexpectedly 
symmetrical *. The abscissae denote potentials and the ordi- 
nates the percentage ionization effects observed. The upper 
curves were obtained when the radiators were negatively 
charged, and the lower curves for the reverse charge. 
It will be noted that the lighter substances emit rays 
which, regarded as a group, have a relatively low velocity. 
These slow electrons are readily retarded and made to 
diverge when the radiator has a positive charge, and easily 
accelerated and concentrated by a repulsion towards the 
electroscope. The numerical values are given in Table III., 
p. 732. 
* The details of these curves (fig. 4) would repay further investigation. 
They diverge near the origin somewhat more rapidly than is shown in 
the figure, and there are some indications of points of inflexion on the 
upper curves. The details will necessarily depend on the angles and 
distances between the principal parts of the apparatus. 
