W772 PROPERTIES OF THE RADIATIONS [CH. 
is attached rapidly takes up the potential of the air surrounding 
the active substance. In this respect it is more convenient and 
rapid in its action than the ordinary taper or water dropper, but on 
account of the disturbance of the electric field by the strong 
ionization produced, it is probably not so accurate a method as 
the water dropper. 
113. Effect on liquid and solid dielectrics. P. Curie! 
made the very important observation that liquid dielectrics became 
partial conductors under the influence of radium rays. In these 
experiments the radium, contained in a glass tube, was placed in 
an inner thin cylinder of copper. This was surrounded by a con- 
centric copper cylinder, and the liquid to be examined filled the 
space between. A strong electric field was applied, and the current 
through the liquid measured by means of an electrometer. 
The following numbers illustrate the results obtained : 
| 

Conductivity in 
substan 
SUSE ES megohms per 1 cm. 

Carbon bisulphide | 20 ealO meee 
Petroleum ether oe NE 5 
Amyline hed “he LA as 
Carbon chloride | Sauare 
Benzene as pedal Lib Moko 
Liquid air | coy ee 
Vaseline oil 16 


= : | 

Liquid air, vaseline oil, petroleum ether, amyline, are normally 
nearly perfect insulators. The conductivity of amyline and petro- 
leum ether due to the rays at —17°C. was only 1/10 of its 
value at 0°C. There is thus a marked action of temperature on 
the conductivity. For very active material the current was pro- 
portional to the voltage. With material of only 1/500 of the 
activity, it was found that Ohm’s law was not obeyed. 
The following numbers were obtained : 
Volts Current 
50 109 
100 185 
200 255 
400 335 
1 CG. R. 134, p. 420, 1902. 
