( 304 ) 



l'esistanoes of ihc hvo wires was determined wliile we stirred. Before 

 and after tliis deterniinatioii, we iiieasiired the ralio helweeii llie 

 [)iatiiiuni I'esislrtiice and one of llie i-esislances in A'.. As a rnle liiat 

 resistance in //,. was taicen of wliieli llie \alne corresponded best with 

 that of the plalinnni wire. Tiienee tiie temperature eould be derived. 

 In lalei' measurements a lherm(>element was sometimes |»hieed inside 

 the ('vlinder C\ of llie wire, and after the temperature had been 

 determined once i)v ihe measurement of the ratio to //j, an assistant 

 at the thermoelement tool< care that the temjiei-ature remained constant 

 in the way described in ('onim. N". <S.']. Consequent l_v llie measure- 

 ments could be made in a still sliorlei- lime. 



§ 7. Calmlation and corrections. The mounting is drawn schema- 

 licallv in V\. 1, liii'. 2, where r^,i and r., are the resistances to be 

 conijtared, IT, and IT.^ the resistances of (he galvanometer condncts 

 |)rovided wiili Ihe resistance boxes //", and A*„. Sup[)Ose that with 

 certain values in the boxes there is equilibrium and (hat we can then 

 represent Ihe ralio between the Iwo currents in llie Iwo galvanometei' 

 conducts by ] -|- j:?, where {i may be coiisidered as a small number; 

 then we liaxe llie relation 



]\\ and )!'.,, howc^ver, are as regards the gaivanometer coils 

 copi>er resistances, and if a ral her high degi-ee of accui-acy is required, 

 ITj and ir._, ninsi be delermined before each determinaliou of llie 

 ratio between /•, and /;,, . If the galvanometer could be placed in 

 a space of constanl lenijieralui-e llie greatest ditHiculty of this would 

 be removed and one adjustment would show us the ratio. 



Il'i and ir., being unknown, we can proceed as follows. We add 

 to \\\ and W.^, «1 and 'f., units of resistance so that again (M|uili- 

 brium is attained, then we also have: 



1 /,. 11', 4- «: , i^ ^..• 



Hence 



i + /3v ^v, + a, ' 1+1? ir, + «; 



«, 



1 + i^ f-pt «a 



«, 



or 



•' 1 1 -» 1 



How large we shall choose « depends on circumstances. The 

 variations in IT. and \]\_ with regard to the leads during the course 

 of one experiment, as apj^eared in the measurements Avith the Wheat- 

 stone's bridge m the previous paper, certainly never exceeded O.üi 



