322 LENZ ON THK VARIOUS CONDUCTING POWERS 



that thick conductors conduct electricity better than thin ones. How 

 far the conductibility of metals is altered by even a very slight mixture 

 of foreign substances, is proved by the experiments of Pouillet with 

 wires made of different alloys of silver with copper, and gold with siher. 

 These prove that their conductibility is far below that of pure unalloyed 

 metals. Thus, for instance, the conductibility of fine gold = 84'4'1, 

 that of the 18-carat gold = 14*77, whilst the silver with which the gold 

 is alloyed is a much better conductor than fine gold itself. 



In order to avoid the inequality of the purity of the copper, I pro- 

 cured the wires myself by cutting a thick piece of copper into smaller 

 pieces, and drawing it afterwards to different thicknesses: but the thinner 

 wires become thus by drawing somewhat more dense than the thicker 

 ones, which produces always a difference in the substance. I endea- 

 voured to remedy this evil by making the wires red hot before covering 

 them with silk ; but the greater or less degree of heat may perhaps have 

 some influence. 



From tliese observation it follows, that so close an agreement cannot 

 be expected from the following experiments as from those made for 

 the purpose of ascertaining the influence of the length of wires on their 

 conductibility ; this agreement will, however, be sufficiently close to 

 remove every doubt with respect to the correctness of the law to be 

 established. 



The wires employed were, as has already been said, wrought all 

 out of the same piece of thick wire, and drawn through the holes 

 1, 6, 11, 18, 24, 30, with which numbers they are also marked in the 

 table ; they were all heated to redness and overspun with silk, and were 

 successively inserted between the electromotive spiral and the wdre of 

 the multiplier, and the deviation determined in the same manner as in 

 the previous experiments. In order to obtain the proportion of the 

 sections of the wires, I took 2 feet of each and weighed them before 

 they were covered with silk. The weight is proportional to the section, 

 and is as follows : 



Weight of 2 feet of wire No. 1 7*7370 grammes. 



No. 6 5-0250 



No. II 3-2408 



No. 18 1-4783 



No. 24 0-7750 



No. 30 0-3616. 



It is not of much importance to know the absolute thickness of the 

 wires, but it may be easily deduced from this, that the diameter of the 

 wire No. 1 was nearly 0-046 Engl. line. 



The experimeiits were thus performed : I observed first the deviation 

 without any wire being interposed, then with the interposition of No.l, 2, 



