142 REPORT—1862. 
as a means for the reproduction of standards of electric resistance. From 
the experience which one of us has had on this subject, it is more than pro- 
bable that if pure metals be-prepared by different chemists in the ordinary 
way of business, variations in their conducting power would be found equal 
to several per cent. Thus, copper supplied as pure by a well-known assayer 
had a conducting power equal to 92, whereas pure copper conducts at the 
same temperature 100*, Again, the pure gold of the assayer conducts only 
65-5, whereas pure gold at the same temperature would have a conducting 
power equal to 737. In order to show that the conducting power of com- 
mercial metals varies to a great extent, we give in the following Table (X.) 
the values found for that of the different coppers of commerce ; and it will be 
evident from it,.that to take a given length and weight or section of a com- 
mercial metal as unit, as has often been done, is very wrong, and can only 
lead to great discrepancies between the results of different observers. 
Taste X.t 
(All the wires were annealed.) 
Conducting power. 
BUTE COP POLY Pela: -hssras Sig oi0.a8~ so8. aye ois 100-0 at 15:5 
Lake Superior native, not fused ........ 98°8 at 15°5 
Ditto, fused, as it comes in commerce.... 92°6 at 15-0 
MVOC ES LUA < evens ite iss aoekec ste Riagals ob, 20muate 88-7 at 14-0 
IBesiselected ss Seth Br acca aes tinea 81-3 at 14:2 
Bright copper wire. lw jwene iledle 72-2 at 15°7 
Toush Coppers: . «cepa eo beware Hey 71:0 at 17°3 
Dem 5 FAS 5. a nicne ali ated dutin tae 59-3 at 12:7 
iO WN 5 a sa derahaats, a2 NS his Dame me 14-2 at 14:8 
Similar variations will be found with most other metals, and we shall give 
examples of these further on. 
2. On its homogeneity and its molecular condition.—It is well known that 
the wires of some metals require much more care in drawing than in others: 
thus, copper and silver, if not annealed often enough during the process of 
drawing, will often become quite brittle, and break off short when bent. 
Now, if the fracture be closely observed, it will be seen that the wire is hol- 
low; in fact, wherever it is broken, cavities will be found, and sometimes of 
a millimetre or two in length; so that such a wire may almost be regarded 
as a tube with a very fine bore. The reason of this is simply that in not an- 
nealing the wire often enough, the internal part of it becomes hard and brit- 
tle, whilst the outside remains annealed, from the heat evolved by its passage 
through the holes of the draw-plates ; after a time, however, the inside, being 
very brittle, will give way, whilst the outside is still strong enough to bear 
the force used in drawing it through the draw-plates. These places in the 
wires are easily discovered on drawing the wire finer; for then at these points 
the wire slightly collapses, owing to the quicker elongation of the weak points 
by the force used in drawing. Silver and copper are the only metals which 
have been experimented with in this manner ; we are therefore unable to say 
whether it may occur with the other metals. However, although no such wires 
could be used for experiments, yet what has been shown possible to occur to 
such a marked extent when purposely trying to obtain such results, may occur 
* Proceedings of the Royal Society, vol. xi. p. 126. 
+ Phil. Trans. 1860, p. 176. 
t Report of the Government Submarine Cable Committee, p. 335. 
