312 



Mr. J. Brown. 



[Nov. 18, 



within about 0*01 inch. IY, the point where index came to rest 

 with the plates so closed. V, the swing on separating the plates. 

 VI, the final deflection with plates apart. The prefix L signifies a 

 left-hand deflection towards the copper quadrant; E. a right-hand 

 one towards the zinc quadrant. 



I. 



II. 



III. 



IY. 



Y. 



VI. 



+ 



L44 



L29 



L38-5 



L55 



L435 





E55 



R39-5 



E48-5 



E66 



E54 





E54 



R38 



E48 



E635 



E53-5 



+ 



L44 



L33 



L39 



L515 



L435 



It is evident there were electrical charges present, although there 

 was no actual metallic contact at which any " Scheidungskraf t " 

 could exist to produce them. (See Appendix.) 



36. In conclusion, the following diagrams represent the distribution 

 of potential according to the theory here adopted. 



Fig. 5 gives the state of things in a closed zinc-water-copper cell of 

 uniform resistance throughout its circuit; N" and P understood as 

 joined in closed circuit. 



Fig. 6 shows the same cell with the metals apart ; the two metals 

 being covered with moisture films, which are practically a portion of 

 the electrolyte and (in so far) at the same potential. This shows 

 also graphically the explanation of Sir William Thomson's " water- 

 drop " experiment, referred to before (§ 28). 



Fig. 7 is a cell divided in the copper part of the circuit, where 

 instead of the potential of a film on the zinc, as in fig. 6, we have the 

 lower potential of that on the copper piece connected to the zinc. 

 The terminals of like metal in this way permit the electromotive 

 force of the cell itself to be measured in the usual electrometric way. 



Fig. 8 represents either a zinc- water-copper cell divided in its 

 electrolyte, or the ordinary static experiment where the difference of 

 potential of the films on two metals in contact is measured. 



It is to be borne in mind that these diagrams are only of a qualita- 

 tive nature, as the difference of potential between the dry metals and 

 water, &c, in contact with them has not yet been experimentally 

 determined. 



Appendix. 



The experiment described, § 35, leads to the following theoretical 

 considerations which have been in part suggested and put into form 

 by Mr. J. Larmor, of St. John's College, Cambridge. 



