ON STANDARDS OF ELECTRICAL RESISTANCE. 127 
Ov er .. 99°744 20:2 99-766 20-2 
eas... cet 99-793 20-2 99-762 20-2 
Mee LT... AG 99:955 20-0 99:926 20-2 
From the above numbers it will be seen that the conducting power has not 
changed, the differences in the values being in all probability due, as above 
stated, to temperature. 
If the passage of a current really altered the conducting power of a wire, 
then of what use would resistance-coils be? The above experiments prove 
that a much stronger current than is used for testing the resistance of a wire 
has no effect on it. 
Apprnvix B.—On the Variation of the Electric Resistance of Alloys due to 
Change of Temperature. By A. Marruressen, F.R.S. 
Iy the Appendix to the Report of your Committee read at the Meeting 
held last year, I gave a Table containing the results of experiments with 
some alloys, made with a view to find out the alloy whose conducting power 
decreases with an increase of temperature in the smallest degree. With the 
same apparatus, &c., I haye, in conjunction with Dr. C. Vogt, experimented 
with the following alloys. 
(With each series the formula deduced from the observations for the cor- 
rection of the conducting power for temperature is given, where is equal 
to the conducting power at the temperature ¢° C. Silver (hard-drawn) is 
taken at 0°=100. ) 
Composition of alloy by weight. Length den mm.; diameter 0-470 mm. 
(1) LS 95:3 ’ Conducting power. 
BREE adie iss bk 4:7 12 0 2°3573 
Made from pure metals. 56:0 2:3138 
Hard-drawn. 100-0 2-2798 
A=2-3708—0-0011555¢+ 0:0000024542. 
Length 4 mm,; diameter 1:217 mm. 
(2) Cote 95:0 . ’ Conducting power, 
ee 5:0 5 0 2-0819 
Hard-drawn. 57:5 2-0424. 
100-0 2-0067 
A=2-0967—0-0010057¢ + 0:00000105227. 
This and the two following alloys were made by Messrs. Johnson and 
Matthey. No. 2 was made to check the results obtained with No. 1; for 
those given with Nos. 3 and 4 appeared to show that some mistake had been 
made with No.1. That this was not the case is proved by No.2. It is, how- 
ever, a very curious fact that the percentage decrement increases in this 
manner, for in no other series of alloys has this behaviour been noticed. Its 
cause may be attributed to the existence of chemical combinations in the 
solid alloys of gold and iron. 
Nos. 3 and 4 are very brittle, and therefore difficult to draw. 
Length 184 mm.; diameter 0-943 mm. 
(3) Gold $3. 23548 90:0 T. Conducting power. 
meee 55 PTY 10-0 14:0 1:9822 
Hard-drawn. 57:0 1:7951 
100-0 1:7010 
A=2:0632 —0:0061367¢+ 0:000025137. 
