Theory of Galvanic Polarization. 427 



to a limit of considerable magnitude the capacity of the con- 

 densing arrangement remains constant. 



As Sp is measured from a minimum value, it follows that in 

 the immediate neighbourhood of that value ($e) 2 must vary as 

 Sp ; so that the discrepancies for small values of Sp in the third 

 column are merely to be attributed to the special difficulty of 

 the observations in that part of the series. 



Taking the second line of the table to give the average 

 value of this constant, we may calculate the thickness of ihe 

 dielectric, supposed to have the properties of vacuum, and 

 therefore to have unit specific inductive capacity, on the sup- 

 position that the arrangement acts as an ordinary condenser. 

 When e=0, Lippmann found by direct measurement that the 

 surface-tension was '304x981 C.G.S. units, which there- 

 fore corresponds to p = 750 millim, When e = *024 D, we 

 have o>= — --88, Sp = 337 ; therefore the change of the surface- 

 tension corresponding to Se is 



ST=||^x -304x981. 



This, as we have seen, is equal to the energy of the polariza- 

 tion charge per unit area. Now, taking a Daniell to be l'l 

 volts, i. e. 1*1 x 10 8 C.G.S. electromagnetic units, which is the 

 same as l'l x 10 8 -r-(2'98 x 10 10 ) C.G.S. electrostatic units of 

 potential, we have, 



87r. thickness ' 

 therefore thickness of dielectric 

 _ (Be? 

 8tt.BT 



= C00325) 2 

 3370 ' 

 = •313 x 10- 10 metre. 

 This calculation has already been made by Lippmann 

 (Comptes Rendus, 1882, quoted in Thomson and Tait's 

 4 Natural Philosophy,' 2nd edit., Appendix, " On Size of 

 Atoms "). It gives an estimate of a molecular distance, viz. 

 that at which the two electrified layers are held by molecular 

 chemical forces, which, notwithstanding the very rough sup- 

 positions on which it is founded, ought to be of the true order 

 of magnitude ; and Lippmann has pointed out that it agrees 

 sufficiently with the estimates assigned by Sir W. Thomson 

 and others from different considerations. 



It is a satisfactory verification of the general notions in- 



