DowLiNG & Haughey — Electrification, Phosphorus Smoke Nuclei. 55 



back to the origin. Before considering the observations, we will describe 

 this final apparatus. 



X. — A small bell- jar (/, fig. 6) was cemented to a disc {A) of Acheson 

 graphite, which rested on a ring of hard paraffin. Beneath this wax ring a 

 disc of sheet metal (B), furnished with a hole, about 2 cms. diameter, 

 rather to one side, was sealed. Below this was another wax ring, which in 

 turn rested on a second metal plate (C), furnished with a large excentric 

 hole. The joints were made air-tight. The holes in the discs being on 

 opposite sides, the phosphorus rested on the lower plate on the inner side 

 of the hole. Air was drawn through by suction applied to the bell-jar, and 

 the smoke yielded up its charge to the graphite plate, while the ions were 

 withdrawn by the electric field between B and C. A was connected to the 

 electroscope, B to earth, and C to a potential divider. It was found that 



c-l_ 



/^ump 



^^eiecCroscope.. 



ecu-th 

 poren.ao.L 



cU victor. 



Ftg.6 



the greater part of the ions were removed, except with the lowest field 

 strengths. To investigate the effect of the ions, a piece of metal foil was 

 placed over the phosphorus, so as to permit the air-stream to pass while 

 protecting it from the electric field. The curves, fig. 7 and fig. 8, show some 

 of the results obtained : the former refer to the smoke-charging experiments, 

 while the latter represent the effect of the ions alone. 



XI. — We now proceed to the consideration of the results obtained. 

 In the first place, it may be pointed out that all the four methods are in 

 agreement in one important respect. The same average increment in field 

 strength (2'9 volts per cm.) corresponds to a " step," whether the field is, on 

 the whole, large or small, or whether the phosphorus is smoking vigorously 

 or only feebly. This is in keeping with our assumption of the uniformity of 

 size of the particles, for we may well suppose that the step in field strength 

 is determined by the extra work required to attach an additional electron. 

 This would require equal increments of field in a given case ; but if the field 

 increment is found to be always the same, the particles must always be of 

 the same size. 



