( 30H ) 



wii-o iiftor o;ioli complete (letermiiiation of the ratio. It' iii the 

 arnuigciiient of IM. 1, lij:^. 3, the coiiiiniitator (\ is placed difVerently, 

 we eau, iiislead of cüiiiparing the gold with the |)Uitiiiniii resistance, 

 compare the latter af once with the resistance in the box Rr,. 



In determining the i-atio hetween the resistances of the j)latinnm 

 wire and the values in l)ox 11.^ we have not, however, repeated the 

 whole measni'ement as described above for the determination of the 

 latio i)etween the platinum and the gold resistances, but (me measure- 

 ment sufficed. 



For with /(*5 instead of yv i^^^ in § '^ ^^'^ tind : 



1 + /? r^,, ir, "^ ^? + 1 \\\ 



where \\\ and IT.^ are the resistances of the circuits where the 

 galvanometer turns and the resistances occur. 



If we know the i-esistance of the turns, — mav be derived trom 



r,,, 



one determijuition of a resistance in the boxes. 



The resistances of the turns can be derived fiom the two deter- 

 minations of the ratio between the platinum and the gold I'esistances. 



Let A and /> be the resistances of the tui-ns round the galvaiu)- 

 meter, and )\ and / ., the resistances in the boxes, then they give with 



1 Tjc A 4- r ^ ^ Tjc 



1 + ,i r,,t B-^r, 1 + ^ 5 + r, 

 1_ r^ ^ B^r\ ^ r, 



whence A and B may be derived and consequently IPj and If, may 

 be found. Inaccuracies occur, that is to say we neglect the resistance of 

 the coiinecting wii-es between the commutator holes ; but as the value 

 of .1 and li was alxuit 940 Ohms, aji inaccuracy of 1 Ohm was 

 allowed and this resistance certainly remained below this amount. 



1 ^-x 



For the calculation il is iuiportaul lo i-emark that is einial 



«1 1 Tx (t\ ((^ a\ 



to — and is equal to , . while and — mav l)o derived 



directlv trom observation. Besides is small, so that in the last 



term of the equations an approximate value for ..4 and j8 is sufïicient. 



§ 9. Siirvey of an ohserratioii. The way in which the observations 



were made will be seen best from an instance which at the same 



