348 Dr Searle, The comparison of nearly 
§ 8. Practical example. The following results were obtained 
by G. F. C. Searle and A. L. Hughes, using four sub-standards 
each nominally of one ohm resistance. 
The six direct determinations of differences gave the values, 
A, =A — B= — 282 x 10-8, A,>=A-—C= 512x106 ohms, 
A;=A-D= 458x10-§, A,=B-C= 843x10-5 ohms, 
A;=B-D= 732x10-§, Ag=C-— D=-— 65x10-6 ohms. 
Hence =A, — A,— A5;= — 1857 x 10-6 ohms, 
na=Ag+Ay—Ag= 1420x 10-6 ohms, 
ny=Azt+tAs;+Ag= 1125x10-6 ohms. 
Then A=4(2m+ 2+ y3)= —292x 10-6 ohms, 
VY=4( m+2n2+ 3)= 527x10~-6 ohms, 
Z=4( m+ yo+2n3)= 453x10-6 ohms. 
We can now find A, B, C, D in terms of M, the mean value of the four 
resistances. Thus 
A=M+4 (ny +n2+n3)=M+4+172 x 10-6 ohms, 
B=A—X=M+464~x 10-6 ohms, 
C=A - Y=M—355x 10-6 ohms, 
D=A-Z=M—281x 10-6 ohms. 
If we assume that Mis accurately one ohm, we have the values 
A=1:000172, B=1:000464, C=0°999645, D=0'999719 ohms. 
The discrepancies between the observed and the calculated differences are — 
shown in the table. The differences are given in millionths of an ohm. 
AaB A=€6 | A=D | “B22 ¢9)| Se Spe een 
Observed — 989 512 458 843 732 — 65 
Calculated — 299 527 453 819 745, aA | 
The greatest discrepancy only amounts to 24 millionths of an ohm. 
§9. Lffect of finite resistance of connectors. If we treat the — 
copper connectors as linear conductors, we can easily modify the 
equations so as to take account of the resistances of the various 
parts of the connectors*. When the connectors are treated as 
* Methods of dealing with non-linear conductors are given in my paper ‘‘ On 
resistances with current and potential terminals,” The Electrician, March 31, 
April 7, 14, 21,1911. The paper is also published separately by The Electrician. 
