( B47 ) 



perceptible ciiiTent while its resistance, owing to the variations 

 which it undergoes, must always be determined separately. The 

 connections which instead of this are added to that ofComm. N".27 

 are in principle the potentiometer-arrangement and have been drawn 

 diagrammatically in the annexed figure ^). 



ell 



^7 5> c.\ 







ace. 



ii- 



In the circuit of an accumulator (with a negligible resistance) 

 three resistance-boxes Ra, H^c, l^c aiid a fixed resistance R' are 

 introduced, of which the first serves to regulate the resistance in 

 the whole circuit, the second and third serve as shunts for two 

 circuits A and B in which the observation-element and the battery 

 of comparison-elements are insei-ted, while the third, a resistance 

 of 8000 f2 tested at the Phys. Techn. Reichsanstalt serves as a 

 shunt for the circuit C, in wliich is inserted a battery of Weston- 

 elements. These side circuits may be connected to the galvanometer, 

 each by means of its own commutator wdth mercury contacts (as 

 described in Comm. X". 27 see pi. V) and be commutated in order to 

 read in how tar we have attained tlie desired zero-adjustment by 

 regulation of the different resistances and to apply a correction for 

 the deflection which might have remained. 



The principal resistance-boxes are adjusted by means of plugs like 

 the auxiliary boxes arranged in parallel for tlie finei* adjustment. 

 Tills is preferable to an adjustment with a slide-wire where also 

 small diilerences remain ^). As the Ra, Rw ^"d Re are known aitproxi- 

 mately beforehand, (with an adjustment at — 116° C. about 7290 ii, 

 40 52 and 40 i2 respectively) the current given by the Weston- 

 elements will always be very small. In order to make it still less 



1) Gf. for instance Jaeger, Die Normale) emente, p. 100. 



Dewar and Fleming, Phil. Mag. (5), 40, 95. 1895. 

 -) Cf. Lehfeldt, Phil. Mag. Ser. G Vol. 5. p. 668 1903. 



Proceedings Royal Acad. Amsterdam. Vol. VI. 



43 



