CHAPTER IV. 



THE STANDARDIZATION OF THE FOG CHAMBER BY THE AID OF 



THOMSON'S ELECTRON. 



THE CONSTANT e, EXPRESSED IN TERMS OF VELOCITIES OF THE IONS. 



42. Advantages. Of all the methods which I have tried to evaluate 

 the coronas in terms of the number of nuclei which they represent under 

 given conditions of exhaustion, the above method is the most expeditious 

 and promising. A single experiment need take but a few minutes. Inci- 

 dentally the observer learns whether negative and positive ions have 

 been captured, for on using the table of coronas which I developed here- 

 tofore, the value of e may be computed and the result must coincide with 

 Thomson's datum. 



a 



a 



FIG. 17. Fog chamber with plate electrical condenser. 



43. Plate. These experiments were of a tentative character and the 

 condenser used was a plate of brass P, of area .4 = 5X15 sc l- cm - sus ' 

 pended at a distance of i cm. above the water W, and parallel to it. It 

 was supposed under these circumstances the discharge current in the 

 presence of radium in sealed aluminum tubes placed at R in fig. 17 

 would be largely confined to the narrow space between plate P and 

 water W, which was earthed, but this proved not at all to be the case, 

 as will be seen presently. In the absence of radium, the leakage was 

 throughout negligible, the conductor a being sheathed by the hard rubber 

 tube b, kept dry except during use. The fall of potential was measured 

 by a graduated galvanoscope, whose capacity was in parallel with P. 

 The number of ions n was found from the aperture of the coronas on 

 condensation. We may therefore write for the charge per ion, if i is the 

 distance of P above the water-surface W, and V the potential difference 

 in volts 



Cl V 



300 A Un V 



54 



