326 C. Barus — Thomsons Constant. 



the large deflections obtainable after many successive charges 

 would, in the absence of conduction leakage in the condensers, 

 make this method very satisfactory. 



In the definite measurements, however, almost the whole 

 capacity may be placed in the auxiliary condenser, so that the 

 capacities of the electrometer and fog chamber are of small 

 importance. Ratios of C'/C= 86/17, 30/17, 20/17, and others, 

 were tried. 



4. Method. — In the preceding paper the value of e found 

 was ultimately dependent upon the velocity of the ions in the 

 unit electric field. In the present experiments a value will be 

 investigated, based on the decay constant &=l*lxl0~ 6 , of the 

 ions. This method has the advantage that large core poten- 

 tials are admissible in the electrical condenser, so that an 

 ordinary graduated Exner electroscope suffices for the meas- 

 urement of current. The small capacities of the instrument 

 make it necessary to insert an auxiliary condenser, as other- 

 wise the discharges are too rapid for trustworthiness. 



If a is the number of ions produced per second per cubic 

 centimeter by the radium placed within the condenser core, 

 and iTthe number of nuclei (ions) found when the core is free 

 from charge, dn/dt=a—hJS r2 =0. Again if n is the number 

 of nuclei found when the core is charged and i the corrected 

 current observed, e Thomson's constant and v the effective 

 volume of the fog-chamber-condenser, dn/dt=7j(JV' z —n 2 ) — i/ev 

 = 0. Hence if the capacity of the system is O and V the 

 corrected fall of potential per second 



e=CV/(bv(N*-n' i )) 

 Usually V is measured in volts, so that "P/300 replaces V in 

 the equation. It is obvious that V must be large enough to 

 keep the current V constant, and the observations always show 

 this at once. 



5. Data disregarding external gamma rays. — The alu- 

 minum foil electroscope made it convenient to use the high 

 potentials of the electric lighting circuit (about 250 volts) for 

 charging. 



The number of nuclei (ions) found in the exhausted fog 

 chamber free from charge, at its central core, was ^=474,000. 

 The number of nuclei found in the exhausted fog chamber 

 when the core was charged to 250 volts was n 1 — 82,500. Hence 

 about 391,000 vanished in the presence of the electrical cur- 

 rent, the original apertures of the coronas being reduced 

 from about 22 degrees to 13 degrees. The drop of pressure 

 Sp/p — 'S0 nearly, was taken high enough to catch all the ions, 

 but not so high as to catch the vapor nuclei of dust-free wet 

 air. 



