82 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



71. Aluminum core charged with radium tubelets I=V. Data. The 



air in the condenser C is now highly ionized and its voltage becomes 

 appreciable. The data obtained are given in table 24 and fig. 28. The 

 needle is positively charged thus (virtually) impelling positive ions to- 

 ward the quadrants of the condenser. In the four series of data observed 

 the aluminum core of the condenser is twice joined to the electrometer, 

 the brass shell being put to earth (series i and 4) and twice commutated 

 (aluminum to earth series 2 and 3). The results are identical, except that 

 in series 3 the insulation was perhaps better. The accelerated march of 

 the needle from rest is obvious in both curves and is thus independent of 

 the sign of the limiting voltage V '^. It may be mere inertia, but it is of 

 less consequence here because the initial data are not needed in the 

 computation of table 25. 



72. Results. lonization N. Voltaic contact potential difference V c .- 

 The equations 



may now be used to compute N and V c . The constants are numerically 

 (all in scale parts, i cm. equivalent to 0.0595 volt) 



* = 3 6.iXio 6 1^ =-3-45 ^=0.142 K' = 39 . 7X io 6 V", = + 9-3 



Hence 



JV= 1,750,000 ions, either positive or negative. 

 1/^=6.37 cm., or 0.38 volt. 



73. Voltaic contacts: aluminum=zinc, aluminum=copper, aluminum- 

 aluminum. The results obtained for aluminum-brass made it desirable 

 to investigate similar cases for other metals and zinc; copper and alumi- 

 num suggested themselves. These were used in form of thin sheets of 

 the metal, bent into cylindrical shells about as large as the above brass 

 shell. No special care was here taken to secure accurate diameters, 

 nor to prepare the metal surfaces. The aluminum core with the radium 

 tubelets (I to V) within, was the same as heretofore. The data are shown 

 in table 25 and in fig. 29. All potentials are given in scale parts where 

 i cm. is equivalent to 0.092 volt. The charging current for the electro- 

 meter, found in the absence of radium before and after these experiments, 

 was V a = 0.0454 cm. 



Since we may write algebraically 



and 



