produced by the Splashing of Mercury. 



467 



Taking 85 volts as saturation voltage this gives with this 

 apparatus a mobility for the slowest ions of '013 cm. per 

 volt-cm. for the positive ion. 



A similar examination of the negative ionization gave the 

 saturation voltage of the negative as about 300 volts, 

 corresponding to a mobility of *004 cm. per volt-cm. The 

 fact of the negative ion having the least mobility appeared 

 so remarkable that the positive current was again examined 

 to see if it had really been saturated. 200 volts were placed 

 on the first electrode and 200 on the second. A considerable 

 current was found on the second electrode. The curve 

 giving the relation between the current and the voltage was 

 therefore investigated over larger ranges of voltages and had 

 the appearance shown in fig. 2, curve A. A distinct flat 



Fig. 2. 



500 GOO 



part exists between voltages of about 100 to 150 volts and a 

 further flat part from 300 volts onward. The upper part of 

 the curve may be due to ions of small mobility or it may be 

 due to neutral doublets, similar to those observed by Thomson 

 in canal rays, which break up under the action of a field or 

 from other causes. If ions of small mobility were present 

 we should expect the curve to rise gradually, never snowing 

 a flat part until all the ions are removed, and, as is seen, this 

 is not the form the curve takes. It cannot be due to the 

 formation of ions by collision as generally understood, as 

 this would require a field of 30,000 volts per cm. ; the field 



212 



