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X. On the Electric Conducting Power of Alloys. By A. Matthiessen, Ph.D. 
Communicated hy Professor Wheatstone. 
Eeceiyed NoTember 17, — Bead December 22, 1859. 
The method employed for the following determinations is described in the Philosophical 
Magazine (February 1857). The precautions taken were the following: — 
1. Almost all the wmes were determined in naphtha (rock-oil), and the temperature 
observed. 
2. They were all soldered to two thick copper wires, whose resistances were known 
and brought into the calculations. 
3. Two separate wires of each alloy, of different diameters, were generally pressed or 
drawn (as it was thought possible that in pressing out the wires they might contain 
alloys of different compositions, as, for instance, when the amalgams are pressed, we find 
that at first almost pure mercury comes out of the small hole), and two determinations 
were made with wires cut from the first, and a third from the second wire. 
4. The higher bismuth alloys were pressed in very fine wires, about 0'2 millim. 
diameter, in order to obtain concordant results*. 
5. The diameters of the wires were measured at each end, and generally also in the 
middle ; pieces of the wire, after the resistance had been determined, being bent at the 
ends, so that they were at right angles to each other, and to the intermediate portion of 
the wire, in order that the diameter might be measured in two directions, which are 
also at right angles with each other, by laying the wire with its two ends vertical in 
succession. The brittle wares were broken in short lengths, a number of them measured, 
and the mean taken of the values so found. 
6. A number of normal wires of different lengths were used, so that when the resist- 
ances were great, equally accurate results could be obtained. 
7. Those bismuth-alloys which expand on cooling, so much that the liquid metals 
break through the crust and form globules on the surface, were recast in small pieces, 
so that one whole piece was used for pressing the wire ; for it is very possible that the 
globules which form on the surface have a different composition from the part which 
first solidifies. 
All the wires which were not pressed were hard drawn, and they were compared with 
a hard drawn pure silver wire, whose conducting power, taken at 0°f, =100. 
To save space only the mean of the three determinations will be given ; the bismuth-tin 
series, however, is given in full, and serves as a fair specimen of the accuracy of the 
experiments ; and when no concordant results could be obtained, a mark ( ff- ) will be 
* Philosoptieal Transactions, 1858. t All the temperatures are in the Centigrade scale. 
MDCCCLX. Z 
