﻿318 Geological Society : — 



If the potential at Z equalled that at W, the formula 



■n _ (a+R).(A+R) 



3 G+R+A+r 

 would of course he sufficient. 



" Measurement of the Internal Resistance of a Multiple Battery 

 by adjusting the Galvanometer to Zero." By Henry Mance. 



The following method of taking the internal resistance of a battery 

 will be found to give excellent results when several cells are to be 

 tested. 



Take one element from the rest of the cells, and arrange the circuit 

 as in the annexed figure. Connect the poles of the battery under 

 observation by a shunt S, and adjust the resistance of the latter till 

 zero is obtained on the galvanometer. 



E 



Let E be the number of cells tested, 40i l ^1'/f/t/ 



Then 



e number of cells opposed, 



$ = resistance of shunt, / ^^ — r 



R= internal resistance of E. / 



In practice I usually returned the detached cell to the battery 

 when S x E gave the internal resistance of the whole within a frac- 

 tion of a unit. 



It is assumed that the electromotive force in e equals that of the 



Q 



whole battery multiplied by -p ; the chance of error on account of 



this not being exactly the case would be lessened by detaching a 

 larger number of cells than one, when the internal resistance of the 

 remaining portion would be given by the first formula. 



GEOLOGICAL SOCIETY. 



[Continued from p. 155.] 



Nov. 9, 1870.— Joseph Prestwich, Esq., E.R.S., President, 

 in the Chair. 



The following communications were read : — 



1. " On the Carboniferous Flora of Bear Island (lat. 74° 30' N.). 

 By Professor Oswald Heer, P.M.G.S. 



The author described the sequence of the strata supposed to 

 belong to the Carboniferous and Devonian series in Bear Island, and 

 indicated that the plant-bearing beds occurred immediately below 

 those which, from their fossil contents, were to be referred to the 

 Mountain-limestone. He enumerated eighteen species of plants, 

 and stated that these indicated a close approximation of the flora to 



