1909.] SIMILAR TO ROWLAND'S METHOD. 193 



5. Results: loiiicatioii, N. Voltaic Contact Potential Difference^ 

 Vc- — The equations 



V, = KVa/N—V , 

 — Vc = KVa/N—VJ, 



may now be used to compute N and Vc- The constants are numer- 

 ically (all in scale parts, i cm. equivalent to .0595 volt), 



K = 36.IXIO^ F„= — 345. Va = M^ 



Hence 



A'^^ 876,000 ions, either positive or negative, 

 Fc = 6.37 cms., or .^y6 volts. 



^ [The drift, Va, which in the above experiments was eliminated by com- 

 mutation, was eventually traced to a defect in the electrometer. It vanishes 

 on replacing the given instrument by another. Data since obtained for 

 Aluminium-Copper and Aluminium-Zinc condensers showed 



AI-Cu, Fc = .58 volts, 



Al-Zn, Vc = .06 volts, 

 or 



Zn-Cu, .52 volts, 



a result, however, which varied much with the surfaces, etc.] June, 1909. 



Brown University, 

 Providence, R. L 



PROG. AMER. PHIL. SOC, XLVIII. I92 N, PRINTED SEPTEMBER 3, I909. 



