CHAPTER V. 



THE ELECTRON METHOD OF STANDARDIZING THE CORONAS OF CLOUDY 

 CONDENSATION, IN TERMS OF THE VELOCITIES OF THE IONS. 



54. Introductory. In the following experiments I have returned to 

 the measurements* of TV in terms of e and the velocities of the ions, 

 Chapter IV, modifying the method by using the cylindrical fog chamber 

 both as an electrical condenser for the measurement of current, as well 

 as for the specification of the number of ions in action by aid of the 

 coronas of cloudy condensation. It is to be assumed that negative ions 

 only are caught in the fog chamber. 



55. Apparatus (fig. 19.) This consists of a cylinder of glass CF, 

 about 45 cm. long, 13.4 cm. internal diameter, closed at one end F, and 

 provided with a brass cap C with exhaust E and influx attachments /, 

 in the usual way. There is a layer of water w at the bottom. The glass 

 must be scrupulously clean within, and this is best secured by scouring 

 with a probang of soft rubber under water, until the water adheres as an 

 even film on shaking. The fog chamber is put to earth. 



A 



FIG. 19. Electrical condenser and fog chamber combined, showing the dis- 

 positio"h of the auxiliary condensers C' and C", the Clarke cell 5, and the 

 electrometer K, diagrammatically. Earthed wires are shown at e. 



The end F is perforated at h to receive the aluminum tube tt', closed 

 at t' and open at t, 40 cm. long and 0.64 cm. external diameter. Sealed 

 tubelets of radium rr may be placed at intervals within this tube to ionize 

 the surrounding wet air. The walls being about o.i cm. thick, ft and y 



*Amer. Journ. Sci., xxvi, 1908, p. 87; idem., p. 324. 



