the Radiation from Radioactive Bodies. 541 
type. The vessels A and B were closed at E and F by alumi- 
nium foil and connected with the opposite poles of a battery o£ 
400 volts, the middle point o£ which was earthed. A narrow 
pencil of a. rays was sent through both vessels from the point 
R, and as in practice the vessel B was somewhat larger than 
A it was easy to balance the two opposite ionization currents. 
Now r in this case any effect of the irregularities of the 
radiation itself was eliminated, since each a particle con- 
tributed equally to the ionization currents both in A and B. 
The experiment, however, did not show an entire absence of 
the oscillations of the electrometer needle, but the effect was 
undoubtedly smaller than when the ionization currents of the 
same intensity were produced from two different sources at 
R and U, R producing ions only in A and U only in B. The 
two curves given in fig. 2 correspond to the movement 
Fiff. 2, 
Z 3 
Time in Minutes. 
of the needle of the electrometer over a time of 4*5 minutes. 
Curve I. shows the effect due to one source of rays, Curve II. 
the effect of two separate sources. The intensity of the 
radiation was the same for both curves. The small oscil- 
lating effect shown in Curve I. was probably due to the 
irregular thickness of the aluminium foil D. Some of the 
particles were stopped in the leaf and could not produce 
ionization in B, while other particles passed through the 
small holes, thus producing a stronger ionization in B than 
in A. 
The general arrangement used for the further experiments 
is shown in fig. 3. E is the electrometer of which one pair of 
quadrants was earthed and the other pair connected with two 
ionization vessels A and B. The outsides of the vessels were 
charged up to + 200 and —200 volts respectively. The radia- 
tion from suitable radioactive substances was allowed to pass 
into the vessels through two openings which w^ere covered with 
Phil Mag. S. 6. Vol. 15. l\ 7 o. 88. April 1908. 2 O 
