542 
Dr. Hans Geiger on the Irregularities in 
aluminium foil in order to avoid possible disturbances from 
air-currents. By means of a screw S the distance of the 
radioactive matter U from the vessel B could be varied and 
a balance obtained between the ionization currents in A 
and B. When the balance was obtained as closely as possible.. 
S.[j— 
Fig. 3. 
-Xoov 
the needle of the electrometer showed small oscillations 
which were observed over a definite time, generally five 
minutes. 
With this arrangement, a comparison was made between 
the irregularities of the ionization currents produced by a par- 
ticles with those produced by a current of the same intensity 
due to (3 particles. 
Two wires which had been exposed to the radium emanation 
were placed at R and U quite close up to the vessels A 
and B (fig. 3). The ionization in this case is almost entirely 
due to a. particles. The oscillations of the needle over a 
space of five minutes are shown in the Curves I. and II. 
of fig. 4. The intensity of the radiation was for Curve I. 
340 and for Curve II. 1100 divisions per minute on the 
electrometer-scale, where one division corresponds to the 
calculated ionization produced b} about 22 a particles. The 
Curves III. and IV. of the same figure were obtained 
under the same conditions except that the ionization in 
the cylinders A and B was produced by ft particles. For this 
purpose a little glass tube containing about 5 ing. EaBr 2 
was brought near to the vessels and its distance adjusted 
till the ionization in both cylinders was equal and of the same 
