ON PRACTICAL STANDARDS FOR ELECTRICAL MEASUREMENTS. 111 
motive force and of current may be conveniently made by means of the 
Weston normal cell. 
During the past two years comparisons of resistance coils and of 
standard cells, and comparative experiments with the silver voltameter, 
have been made by representatives of the National Physical Laboratory 
and the standardising laboratories of America, France, and Germany. 
The results obtained show better than any formal statement the remark- 
able agreement which now exists between the electrical standards of 
the four countries named. 
Table I. gives the results of measurements made at the Bureau of 
Standards, the Reichsanstalt, and the National Physical Laboratory, 
on four hermetically sealed resistance coils of manganin. The values 
given are in international ohms at 25° C. 
TABLE I. 
No. of ioe iebaNebeks P.T.R. PACKS i) ONE: <] B.S. B.S. Maximum 
Resist- March April June | Dec. Dec. Jan. June Differ- 
anceCoil 1911 | 1911 1911 1911 1911 | 1912 1912 ence 
eee 00005, 100005, 1-00004,' 1:00003,' 1-00005, 1-00005,) 1-00004,| 0-00001, 
12 /|1 00005, 1 00005, 1-00004,, 1- 00003, 1-00005,| 1-00005,) 1-00005,| 0-00001, 
3939 | 1: 00009, 1 00010, 1-00008, 1-00008, 1-00010,' 1-00009,) 1- 00010, 0-00001,) 
3940 | 1 00009, 1 00010, 1.00008, 1 00008, 1- 00010, 1: Bega 1: 00010;) 8 0- 00001, 
Table II. gives tae results of reesuvenn ete of the E.M.F. of the 
Weston normal cell. The measurements were made at Washington by 
representatives of the Bureau of Standards, the Reichsanstalt, the 
Laboratoire Central d’Electricité, and the National Physical Laboratory. 
The current was measured by means of silver voltameters of various 
types and capacities, and the electrolytes were from various sources. 
In the opinion of some of the experimenters certain forms of the volta- 
meters were untrustworthy and some of the electrolytes were known 
to be impure. The agreement of the various means, while being very 
Taste II. 
Number of Calculated ¥.m.F. | : 
Date, 1910 Voltameters |of Weston Normal Difference from 
in Circuit Cell at 20°C. | Mean. 1X10 
April 14 4 1-01825 | =. 
a 18 4 27 | 2A; 
» 20 8 31 0 
| ” 22 4 29 at 
” 26 8 37 +6 
» 28 4 32 aah 
” 3 5 36 |. 5 
” 5 8 35: +4 
” 7 8 28 2S: 
» 12 6 30 == 
| » 19 4 26 aaa 
Mean=1-01831. 
