( 293 ) 



values ranging fVoni 0.00219 to 0.00214). As according lo § 3 

 Conmi. N". 77 the resistance of' tiie platinum wire It is e(|ual to 

 the diiierence between two measured resistances, one t (the resi- 

 stance of the leads), another II -\- t, and as the branches of the bridge 

 are so nearly enual, i\^^ is eliminated, and hence we iier(l not know 

 the value of r.^^. 



To the resistances read on the box //.,', the corrections found Iw 

 calibration must be applied. We may easily convince ourselves that 

 the arrangement of box //./' [)arallel to l)ox //.,' has no [)ercep(ii)le 

 influence on the value of the corrections at /i.,'. The corrections of 

 the errors in the nominal box values could be neglected for all 

 coils below 1 Ohm. 



For the measurements at low temperature a correction ha<l to be 

 applied, because during the regulation of the tempera! ii re the mean 

 deflection was not zero. 



In order to express that deflection in terms of the resistance, the 

 platinum thermometer in the bridge, after the measurements were 

 made, was replaced by an equally large box resistance and for a 

 known modification of this resistance the deflection was observed. The 

 regulation of the temperature was in most cases so successful that 

 it was hardly necessary to take the correction into consideration. 



The resistance, measured near 0'', was reduced to 0° (*. with the 

 approximate formula ]r= 1J0.041(J -)- 0.0038(^4^ — 0.00000 103 J r), 

 derived from preliminary observations. 



§ 8. Survey of a measurement. The course of a measurement is 

 described in § 5. 



The quantities which are derived directly from observation are given 

 in table I (p. 294). Under the head "Connection" I have recorded bet^veen 

 which blocks of' the commutator C^ a conducting connection existed. 



Therefore commutator C.^ was not used while the measurement 

 lasted. This had become possible because the platinum wire was 

 wound free from induction, so that no induced currciil was observed 

 when the [)rincii)al cui-reid was closed. 



From these data we now derixe foi- each conncclion I lie \alue of 

 U^, i.e. the resistance of the branch of the bridge in which the 

 resistance boxes are placed (apart IVoni /,, ). 



If the x'alue of /i*, which is found when w c measui-e llie plaliinim 

 wire with the leads, is (liuiiin>he(l l»y Ihe \alue of //., which is found 

 with Ihe leads alone, we oblain (he resistance of ihe plalinnni wire, 

 in the supposition I", that the arms of ihe bridge aree(|nal, 2". llial 

 dui'ing the measurement the mean delleclion was zei-o ami 3". thai ihe 

 resistance box requires no correction. l''(»r each of these sn[»positions 



