544 Mr. F. E. Smith on Bridge Methods for Resistance 



Table IT. 

 Leads A from the Gamb. Scientific Inst. Co. 



Resistance of C Ieads = about 0*112 ohm. 



0-112 



Ratio O/P :■ 



1-0014 



] 0006 



0-9997 



0-9997 



J 0003 



09999 



10005 



10006 



0-9999 



9999 



0-9999 



1-0006 



1-0000 



0-9999 



0-9999 



0-9999 



9995 



0-9986 



0-9997 



9992 



0-9995 



Maximum variation = 0*23 per cent. 



Table III. 

 Leads B. from the Camb. Scientific Inst. Co. 



Resistance of C leads = about 0'112 ohm. 



55 }? ■ -t 5 j = ,, U'llO ,, 



Ratio O/P :— 



0-9865 

 0-9867 

 0-9S57 



0-9853 

 0-9846 



0-9857 



0-9859 

 09870 

 0-9848 



Maximum variation = 0*24 per cent. 



The changes which we have recorded might conceivably 

 hive taken place during measurements of temperature. It' 

 the leads obtained from Dr. Harker were used with a 

 platinum thermometer of 26 ohms resistance at 0° C, a 

 change of 1 per cent, in the ratio C/P would introduce an 

 error of o, 06 in measurements of temperature. During our 

 observations the ratio changed by 0*57 per cent., which is 

 equivalent to about 0°'034 0. The change of 0*28 per cent, 

 recorded for the A leads (Table II.) corresponds to about 

 0°*031 C. These errors are very considerable, although not 

 so large as those recorded by Dr. Chree. For measurements 

 accurate to 0°*001 C. the ratio of (J to P must keep constant 

 within 1 part in 10,000 if the C leads have a resistance of 

 0*1 ohm. 



The changes in the ratios are, we think, easy to explain. 



