THE ELECTROMETRIC MEASUREMENT OF THE VOL- 

 TAIC POTENTIAL DIFFERENCE, BETWEEN THE 

 TWO CONDUCTORS OF A CONDENSER, CON- 

 TAINING A HIGHLY IONIZED MEDIUM. 



By carl BARUS. 



(Read April 24, 1909.) 



I. Introductory. — The difficulties encountered in the preceding 

 paper (§4), were made the subject of direct investigation by replac- 

 ing the fog chamber with a metallic cylindrical condenser, the core 

 of which was an aluminum tube, 50 cm. long and .63 cm. in diameter, 

 the shell a brass tube, 50 cm. long and 2.1 cm. in diameter, coaxial 

 with the former. Sealed radium tubelets could be placed within the 

 aluminum tube, or withdrawn from it. Moreover, either the outer 

 coat or the core of the condenser could be joined in turn with the 

 Dolezalek electrometer, the other being put to earth. The conduct- 

 ing system now appears as follows (Fig. i), C being the outer coat 

 or brass shell, A the aluminum core and r the radium tubes in the 

 cylindrical core. Conductors are earthed at e. BB show the 

 metallic connections with the auxiliary condensers C, C" . E is one 

 of the insulated quadrants of the electrometer with the highly 

 charged needle A^, E being virtually also a condenser. 



c>7y. / 



A Clark standard cell may be inserted for standardization, but 

 it is otherwise withdrawn. 



Direct experiment showed the self charging tendencies to come 

 apparantly from the highly charged needle N, as if positive ions were 

 loged into the conductor EBBA for a positive needle, negative ions 



189 



