ON STANDARDS. OF ELECTRICAL RESISTANCE. 139 
TABLE. 
Conducting power | Percentage variation in 
at 0°. conducting power be- 
tween 0° and 100°. 
reer I ee are 38-2 
Other pure metals in a solid state eae 29°3 
DRIMOREP EN oe clases see 44:5 15:5 
REET Ris alii Pate tele ee s cots 31:6 11:3 
PR aE. ete On 18-0 Fat 
ae iGold=silver® 2260 22. 2s 15-0 6-5 
PM ce cfate oie eh sys! «5 irdaysiage sf < 4:5 a9 
oo 2h MORRIE SRR IGrrip ry Sires 10°6 o:2 
, lo Hie cae See ae 12:0 4:8 
» German silver}.......... 7:8 4-4 
ere tn ic aur asld > wen 6-7 31 
The method and apparatus employed for the above determinations, together 
with the precautions taken to ensure correct results, have already been 
describedt. We have made only three observations between 0° and 100°, 
for it was found that they gave almost exactly the same formule for the 
correction of the conducting power for temperature as if we had taken seven 
or more observations between 0° and 100°. Each of the above values for the 
conducting power, at those temperatures, is the mean of three or more 
observations. It was easy to obtain the desired temperatures as a mean of 
several observations, after very little practice. I have no doubt that, in the 
course of our experiments, we shall be able to find-an alloy, the conducting 
power of which will decrease between 0° and 100° even less than that of silver- 
platinum. The experiments are being continued, and I hope, before the next 
meeting of the Association, to be able to lay before you results which will 
throw more light on the subject, as well as to propose an alloy with a 
minimum variation in its conducting power due to change of temperature, 
which may be made commercially in a cheap manner of the common com- 
mercial metals, and possessing those properties which are essential that it 
should have. 
Apprnpix B.—On the Electrical Permanency of Metals and Alloys, 
By Dr. Marrmessen, F.2.S, 
Having, in conjunction with Prof. Thomson, been requested by your Com- 
mittee to make some experiments on this subject, we thought it advisable for 
one of us to undertake some preliminary experiments in which all possible 
disturbing causes were isolated. The chief of these are, oxidation by the 
oxygen of the air, as well as by acids produced by the oxidation of the oil 
or grease with which a wire is almost always covered when drawn, as the 
holes in the draw-plates are generally oiled or greased; stretching during the 
process of covering and winding ; and after being wound on the bobbin, elon- 
gation by expansion or contraction, owing to variations of temperature, &c. 
These, I think, have been obviated in the following manner :—The wires were 
carefully wound round a glass tube in order to bring them into a smaller 
compass, and after taking them off, they were placed inside wide glass tubes, 
and soldered to two thick copper wires, these having been previously passed 
through corks which fitted into the ends of the glass tube ;. through each of 
the corks a small glass tube passed, drawn out in the middle to enable it to be 
* Phil: Mag. Feb. 1861. + Phil. Trans. 1862, pt. 1. t Ibid. 
