242 



Mr. F. E. Smith. On the Construction of [Mar. 10, 



ments when the mode of erection introduced the " end correction/' 

 but the fittings were not adapted for the measurement of resistance on 

 the Carey Foster bridge. 



Each horizontal line indicates a separate filling. 



The unit of resistance employed in the evaluation of the standards 

 is that derived from the coils belonging to the British Association, and 

 assumed as equal to 10 9 C.G.S. units. 



The difference between the observed resistance, employing this unit, 

 and the calculated resistance in international ohms, is shown in the 

 following table : — 



Standard. 



Mode of Erection I. 



Observed 

 resistance 

 in ohms. 



Theoretical 

 resistance in 

 international ohms. 



Observed — 

 theoretical 

 value. 



Difference 

 from mean. 



M 

 P 

 T 

 U 

 Y 

 W 

 X 

 Y 

 Z 



Gr 



S 



1 -00005, 

 0-99938 4 

 -99912! 



-99912 9 



1 -00043 3 



-99915o 



1 -00006 3 



-99926, 



1 -00032 5 

 1 -00034., 

 1 00025 4 



-99994,; 

 -99930 4 

 -999046 



-99904 6 



1 -00036! 



-99905 5 

 0-99998 



0- 99915 5 



1- 0('024 s 



1 -00027 

 1 -00016 



-00010 6 

 -00008 

 -O0007 5 

 -00008 3 

 -00007- 

 -O0009 7 

 -00008 3 

 -00010 8 

 -00007 7 

 -00007 

 -00009 

 -00008 5 



+ -00002! 



o 5 



lo 



- 0, 



+ lo 



o 2 



+ 2, 

 Os 

 1 



+ 1 





Another series of observations shows that the resistance of the unit 

 employed as 1 international ohm at the Eeichsanstalt is greater than 

 the resistance of the international unit derived from the eleven mercury 

 standards constructed at the National Physical Laboratory by 



0-00002 ohm. 



A comparison with the results obtained by Dr. Glazebrook in 1888 

 for the specific resistance of mercury indicates that the unit of 

 resistance, as used at the Cavendish Laboratory, Cambridge, in 1888, 

 may still be recovered. 



From this it follows that — 



Eesistance of 1 international"! fEes. of unit employed and~j 

 ohm (as derived at the > - < assumed as equal to 10 9 > 

 N.P.L.) J L C.G.S. units " J 



= 0-00008 5 ohm. 



