486 



REPORT — 1867. 



The value of R^, in the formula given at the commencement, was found 

 by two methods, Avhich we will call the indirect and direct method. In 

 the indirect method three sets of resistauce-coil?, a, h, c, were arranged 

 as in fig. 1, with a battery B, and a galvanometer G, and a shunt Z, equal 



Fig. 1. 



Eig. 2. 



aud b was then altered to b 



galvanometer ; the resistance a was next 

 J, so as to give the same deflection 



in resistance to ^^tj- of the galvanometer-coils. The resistance c was made 



equal to 1000 units, aud the resistances a and b adjusted until a convenient 



deflection was obtained on the 



changed to 



as before on the galvanometer G. Then calling d the deflection observed, G 



the resistance of the galvanometer, we have 



I {b — bjc ) 



a formula for which the resistance of the battery need not be calculated 



The second or direct method of obtaining E,j was first to calculate the resis- 

 tance of the batteiy B by the following formula (fig. 2) : — h and/ are vaiiable 

 resistances; r/ the resistance of the shunted galvanometer =47 '2 in my ex- 

 periments ; break the circuit at /, and adjust h till a convenient reading 

 is obtained ; then join /, as shown in the sketch, and adjust/ and h untU the 

 same deflection is obtained as before ; then, calling h^ the last resistance at h, 

 we have 



B=/ 



7i-h, 



0+K 

 Secondly, a direct deflection d was obtained witli 



cuit; then Ilj = H(? (I- + B + r/). 



The following is a record of the 



order : — 



September 22. — Discharge. — Yalues 



with 20 cells :— 



1 o 0° ^'^ 



167 107 166 



Adding 2-5 to compensate for portion of aii* < = 1G8"5, and the angle 

 very small, sin | i'=84'2.5. 



Test for insulation ; discharge after one minute's insulation 154. 



a resistance Jc in cir 

 experiments made iu 

 of i after 



chronological 



charging 



for one minute 



4^ 

 16.5 



5°. 

 165 



Mean. 

 160 



being 



