668 Dr. A. S. Eve on the Effect of 



effect of dust, an old coat was struck smarily with the hand, 

 and the cloud of dust was found to be strongly electrified 

 with large ions giving 30 to 60 Div./min. at B, corresponding 

 to 500,000 ions per cm 3 . The charge observed was, doubtless, 

 due to friction, as with the dust in Lichtenberg's figures. 

 Some experiments were made with various fine dusts, but 

 these soon affected the insulation, and after recleaning the 

 instrument these tests were for the time abandoned. 



Again, a positively charged wire from a Wimshurst 

 machine was suspended at the mouth of a funnel which 

 replaced the cylinder V. No negative ions were detected at 

 B because they were drawn to the positive wire, but the 

 number of positive ions was very large and the ionization 

 current at B was great, giving about 50 Div./min. 



Smoke and Ionization Current. 



To investigate the effect of smoke on ionization, on the 

 recommendation of Professor H. A. Wilson, arrangements 

 were made to work at a much higher potential. The single 

 leaf on electroscope B was replaced with a leaf of paper w ith 

 Dutch-metal foil pasted on each side ; this was suspended 

 freely by a short strip of single Dutch-metal foil. The 

 cylinder and leaf were first connected to a leyden-jar and 

 Kelvin electrostatic voltmeter, and were charged to poten- 

 tials from 1000 to 2000 volts by an electrophorus. The 

 central system was then disconnected from the leyden-jar 

 and the air current was started through the tubes in the 

 usual way. 



As the inner and outer radii of the testing vessel B were 

 1*55 and 1*1 cm. with a clearance of 4*5 mm., the electric 

 force was large, and, with a potential on the central cylinder 

 of 1000 volts, the electric force varied uniformly from 4U00 

 to 2500 volts/cm. across the air-gap. 



As a contrast, with A at 300 volts, the electric force varied 

 from 1100 volt/cm. near the surface of the central wire to 

 73 volt/cm. at the boundary of the surrounding cylinder. 

 That is, the average field in B was 3000 volt/cm. and in A 

 600 volt/cm. 



The results obtained with this new arrangement were very 

 striking. When the radium was in place under V and the 

 air current started, the effect of introducing tobacco-smoke 

 was to decrease the current in A (low potential) and to 

 increase the current in B (high potential), and this was the 

 case whether A and B were used separately or together. It 

 is probable that the current even in B was far from being 

 " saturated." 





