98 REPORT—1890. 
APPENDIX I. 
On the Values of certain Standard Resistance Coils. 
By R. T. Guazesroox, F.R.S. 
Tue B.A. Unit STanparps. 
The Standard B.A. units of the Association have during the year 
been several times compared together both by the Secretary and by Mr. 
Fitzpatrick. Table I. gives the results of two sets of comparisons made 
in August 1890; the differences between the various coils and the 
platinum silver standard Flat are given in the third column in bridge- 
wire divisions. One bridge-wire division is very nearly ‘00005 B.A. 
unit. 
TABLE I.—Resistance of the B.A. Standards, August 1890. 
pierence between each coil 
an lat in bridge-wire , J Change of 
Coil Tapio divisions ree resistance 
calculated per 1° in 
Observed From chart b.w.d. 
Aug. 15, 1890 1888 
A 17:2 27°8 33°0 - 52 28°6 
B 17°4 30°5 30°5 0:0 28°8 
C 17°6 22°2 23°0 - 08 14:2 
D 17°25 61:2 63°5 — 213 61:7 
BE 17°3 79'°2 795 -— 03 60°7 
F 17:3 3:2 = © SAF 12°7 57 
G Liz(ehs} — 22:0 - 18:0 -— 40 5:5 
H 17:4 - 170 — 15:0 -— 2:0 5°6 
August 19 
A 18:8 67°5 69°5 — 2:0 28°6 
B 17°8 60°6 62:0 seed: 28°8 
Cc 19-2 316 36°0 44 14°2 
D 18°8 145:7 151 5:3 61:7 
E 19:0 170°6 17:3 2°4 60:7 
F 18°9 2°9 = Us 12°4 ‘shat ( 
G 19:0 - 21°8 - 18:0 - 38 55 
H 19:0 - 177 - 15:0 = 7 56 
In the fourth column are given the corresponding differences 
obtained from the chart made in 1888. In the next column will be found 
the differences between the observed values and those given by the chart, 
while the sixth column gives the change in resistance for 1° C. for the 
various coils. It wiil be seen that for the first five coils the differences 
between observation and the chart are such as would be readily 
accounted for by a small error in the temperature, and we may say that 
there is no evidence of a change in the resistance of these coils relative 
to Flat. This conclusion is borne out by the results of a series of obser- 
vations made in January and February by Mr. Fitzpatrick. But when 
we come to the three platinum silver standards, F, G, H, the results are 
at once seen to be quite different. Thus F would appear to have risen 
relatively to Flat by about 12°5 bridge-wire divisions, while G and H have 
fallen by 4 and 2°5 divisions respectively. 
Since these are the most important standards, their temperature 
coefficients being all very small, it was necessary to examine their history 
