[mclennax-kets] 



ELECTRICAL CONDUCTIVITY 



51 



with the complete absorption of the same radiation by air at 101 atmos- 

 pheres and consequently about 576 times greater than the greatest 

 copper ionisation chamber about 10 cm. in diameter and about 12 cm. 

 in length. The air in this cylinder was kept at atmospheric pressure 

 and as the range of the alpha rays from polonium is about 3*8 cm. 

 in air at this pressure, it is clear that the dimensions of the receive:- were 

 such as to insure the complete absorption of all the alpha radiation 

 emitted by the plate. The electrode was connected as before to the 

 quadrants of the electrometer, and the currents were measured with 

 different fields applied to the region traversed by the rays. Here 

 again it was found necessary to attach a sulphur condenser of high 

 capacity to the quadrant system in order to take the readings con- 

 veniently. The total capacity of the measuring system used in this 

 case was 8142'e.s.u. 



A set of readings taken with this arrangement both witli positive 

 and negative potentials applied to the cylindrical receiver is given in 

 Table V, and the curves corresponding to these are shown in Fig. 6. 



TABLE V. 



Ionisation produced in air at Atmospheric Pressure by the Alpha Rays from the. 



Polonium. 



Here it will be seen the readings obtained with negative fields 

 were considerably higher than those obtained under corresponding 

 voltages with positive fields. This no doubt arose from the mobility 

 of the positive ion being less than that of the negative. With both 

 fields it will be seen saturation currents were obtained with potentials 

 of approximately 400 volts applied to the cjdinder. 



As the capacity of the measuring system was 8142 e.s.u. it will be 

 seen from the readings given in the table that the maximum conductivity 

 in this case was about 16 times greater than the maximum obtained 



