178 



BARUS— METHOD OF STANDARDIZING 



[April 24, 



In the following experiments I have returned to the measure- 

 ments of A'' in terms of e and the velocities of the ions, modifying 

 the method by using the cylindrical fog chamber both as an electrical 

 condenser for the measurement of current, as well as for the speci- 

 fication of the number of ions in action by aid of the coronas of 

 cloudy condensation. 



1 



\^ 



f.^ 



FiQ. 1 





fTrl 



F 



JL!S Tl Tl 1 



i T — J 1 



e *c e e 



2. Apparatus. — This consists of a cylinder of glass C, F, about 

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

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

 in the usual way. There is a layer of water zv 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, as 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 .64 cm. external diameter. 

 Sealed tubelets of radium r, r, . . . may be placed at intervals within 

 this tube to ionize the surrounding wet air. The walls being about 

 .1 cm. thick, ft and y rays are wholly in question. Neither emanation 

 nor a rays escaped the double thickness of aluminum. The tube tt' is 

 grasped at f by a sheath of hard rubber with an annular air space 

 and fixed in place by a rubber cork. If care be taken to keep the 

 tube in dry air except when in use, there is no conduction leakage 

 of consequence. 



The end t, m.oreover, is placed in connection with a Dolezalek 

 electrometer, by aid of a thin wire (not shown) running axially 



