420 Drs. Beattie and De Smolan on the Conductance 



lamp*. The rays from the lamp were allowed to pass from a 

 lead cylinder surrounding it and connected to the case of the 

 electrometer by a small hole about *3 square centim. in area. 

 They fell on the aluminium sheath transparent to them and 

 rendered the air between it and the insulated aluminium 

 within conductive. 



To get a definite difference of potential, the two pairs of 

 quadrants of the electrometer were placed in metallic con- 

 nexion. Then one terminal of a battery or of an electrostatic 

 induction machine was connected to the internal coatings of 

 the two quasi leyden-jars, and the other terminal to the 

 case of the electrometer. The difference of potential pro- 

 duced was measured by a multicellular voltmeter in the case 

 of voltages under 500 volts, and on a vertical single-vane 

 voltmeter for higher differences. 



When the desired difference of potential had been estab- 

 lished, the metallic connexion of the battery, or of the electric 

 machine, with the internal coatings of A and B was broken, 

 and this charged body left to itself. To find the loss due to 

 imperfect insulation the pair of quadrants in metallic connexion 

 with the outside coating of B was insulated in the ordinary 

 way, and the deviation of the electrometer reading from the 

 reading obtained when the quadrants were metallically con- 

 nected — which we shall call the metallic zero — per minute 

 was observed. To find the loss when the rays were acting, 

 the two pairs of quadrants were again placed in metallic 

 connexion and the Rontgen lamp set going ; then the pair 

 of quadrants connected to the outside coating of B was 

 insulated from the other pair, and the deviation from the 

 metallic zero again observed per minute. 



We tried various differences of potential, ranging from a 

 few volts to 2200 volts. The results we obtained showed that 

 the rate of leak did not appreciably increase from a voltage 

 of about 6 volts to 2200 volts. 



Positive and negative charges leaked away at the same 

 rate. These results confirm and extend through a very wide 

 range of voltage the result announced by Thomson and 

 McClelland in a paper communicated to the Cambridge 

 Philosophical Society March 1896. 



To test the conductivity induced in air by uranium, we first 

 used the two-leyden method described at the beginning of 

 this section. The leyden A was a cylinder of aluminium 

 with one end covered with aluminium. This cylinder formed 



* Tlie Rontgen lamp was a focus tube of the Jackson pattern. 



