178 HENRY A. EOWLAND 



Now the greatest source of error in making coils is in passing from 

 the unit to the higher numbers. As the reproduction of single units 

 is a very simple process the single ohm is without much doubt correct, 

 and as the above proportion is correct within one part in 8,000 of what 

 it should be, it seems to point to the great exactness of the standards 

 then used, seeing that the exactness of the proportion could hardly have 

 been accidental. It is also to be noted that Messrs. Warden, Muirhead 

 & Clark's 10-ohm standard agreed more exactly with a set of coils by 

 Messrs. Elliott Bros, than their own unit E (10). 



The resistance of my coil as derived from the different standards is 

 as follows : 



From Elliott Bros, resistance coils 34-979 ohms. 



From Elliott Bros. 10-ohm standard 35-083 ohms. 



From W., M. & C.'s 10-ohm standard 35-024 ohms. 



From W., M. & C.'s 100-ohm standard 35-035 ohms. 



These give for my determination the values of the ohm as follows : 



From Elliott Bros, resistance coils . . .-99257 earth q ^*' 



sec. 



From Elliott Bros. 10-ohm standard -98963 " 



From W., M. & C.'s 10-ohm standard -99129 



From W., M. & C/s 100-ohm standard -99098 



For the reasons given above I accept the mean of the last two results 

 as the value of the ohm. 



To preserve my standard I have made two extra copies of it, the one 

 in German silver and the other in platinum silver alloy. The com- 

 parisons are given below. No. 1 is in German silver and the other in 

 platinum silver alloy. The temperature is 17- C. 



No. 1 1-00034 June, 1877. 



No. 1 1-00029 Feb., 1878. 



No. II -99630 June, 1877. 



No. II -99932 Feb., 1878. 



These are the values of the copies in terms of the original standard 



whose resistance is 34-719 earth quad \ 



sec. 



From these results it would seem that the German silver of which 

 the standard and No. I were composed was perfectly constant in resist- 

 ance. The wire has been in my possession for several years and seems 

 to have reached its constant state. 



The final result of the experiment is 



1 ohm = -9911 earth 



sec. 



