682 Mr. A. S. Eve on the Secondary Radiation 
the y secondary rays consist of negatively electrified particles 
in motion. ‘To discern between these rays, thin screens of 
lead were placed close in front of the thin aluminium foil 
(02 mm.) which formed that face of the zine electroscope 
nearest the radium. About ‘2 mm. of lead reduced the effect 
to half value, and 1 or 2 millimetres removed it. It is plain 
that the rays deflected were of the nature of secondary radiation 
with low velocity and small penetrating power. 
The results obtained from an increasing series of lead 
screens in front of the aluminium foil are shown in fig. 8. 
Fig. 8. 
Scale Divisions 
TArckness 1m mm. 
The screens were ‘13 mm. thick. Curve I. represents the 
scale-divisions per minute for various thicknesses when there 
is no magnetic field. The scale-divisions are due to natural 
leak, secondary radiations, and y rays passing through the 
electroscope. A few screens increased the ionization cur- 
rents: this was due to the secondary radiation from the lead 
screens caused by the primary rays. This result is similar to 
Beequerel’s increased photographic effect with y secondary 
rays. After the maximum was reached, more lead screens 
decreased the ionization in the electroscope in a manner 
already explained, and as in fig. 6. 
Curve LL. shows the results when the magnetic field bends 
the rays towards the electroscope. The initial high value is 
Se 
