482 Messrs. G. C. Foster and O.J. Lodge on the Flow of 



the equipotential lines were replaced by the following arrange- 

 ment. A thin cylindrical rod of brass, to which two wires could 

 be attached, slid vertically in a V-groove down the side of a rect- 

 angular wooden block. The lower end of the rod was filed accu- 

 rately flat and perpendicular to its length, so as to touch the 

 tinfoil with its entire surface. Constant pressure against the 

 tinfoil was maintained by placing a weight on a cap fixed to its 

 upper end. Two such rods constituted the electrodes A and B ; 

 and tolerably constant contacts could be made with them after a 

 little practice. Nevertheless individual readings are apt to vary 

 a good deal, and it is necessary to take the mean of several di- 

 stinct experiments in order to get a single trustworthy result. 



The numbers given in the annexed Table will serve to illustrate 

 the variations occurring among single readings. They refer to a 

 set of experiments in which the electrodes were placed approxi- 

 mately at the ends of a diameter of a circular disk. 





2a. 



s. 





26-30 



69-4 





26-22 



69-7 





26-30 



68-3 





26-30 



68-3 





26-00 



67'5 





26-31 



68-7 





25-95 



690 





26-25 



68-6 





26-30 



69-8 





26-00 



69-4 





26-25 



67'9 





26-31 



68-7 





2605 



69-2 



Means 



26-20 



68-80 



52. The principal results of the measurements of resistance 

 made by the method explained above are given in the Tables 

 which follow, in such a way as to show how far they agree with 

 the values indicated by theory. Every entry in the Tables is a 

 mean value deduced from the number of experiments stated in 

 the first column ; the last column in each Table contains a quo- 

 tient which theoretically should be constant. Common loga- 

 rithms are employed, except when it is otherwise stated. The 

 symbols used in the headings of the columns have the following 

 significations : — 



R, resistance in terms of an arbitrary unit ( = '00155 ohm; 

 being the resistance of one centimetre of the wire E F). 



oc, resistance of the contacts between the electrodes and the 

 sheet (found by special experiments). 



€, ratio of the resistancesEDFandEABF(figs. lor3),ory (§50). 



