Prof. Thomson on the Conductivity of Commercial Coppei'. 473 



appeared now certain that these differences were owing to different 

 qualities of the copper wire itself, and it became important to find 

 how wire of the best quality could be procured. Accordingly, 

 samples of simple No. 22 wire, and of strand spun from it, distin- 

 guished according to the manufactories from which they were sup- 

 plied, were next tested, and the following results were obtained : — 



Table of relative conducting qualities of single No. 22 Copper wire, 

 supplied from manufactories A, B, C, D. 



The strands spun from wire of the same manufactories showed 

 nearly the same relative qualities, with the excejition of an inversion 

 as regards the manufactories B and D, which I have been led to 

 believe must have arisen from an accidental change of labels before 

 the specimens came into my hands. 



Two other samples chosen at random about ten days later, out of 

 large stocks of wire supplied from each of the same four manufactories, 

 were tested with different instruments, and exhibited, as nearly as 

 could be estimated, the same relative qualities. It seems, therefore, 

 that there is some degree of constancy in the quality of wire supplied 

 from the same manufactory, while there is vast superiority in the 

 produce of some manufactories over that of others. It has only 

 to be remarked, that a submarine telegraph constructed ivith 

 copper wire of the quality of the manufactory A of only i^j ^f 

 an inchin diameter, covered with gutta-percha to a diameter of a 

 quarter of an inch, would, with the same electrical power, and the 

 same instruments, do more telegraphic work than one constructed 

 with copper tvire of the quality D, of ^ of [an inch diameter, 

 covered with gutta-percha to a diameter of a third of an inch, to 

 show how imjjortant it is to shareholders in submarine telegraph 

 companies that only the best copper wire should be admitted for 

 their use. AVhcn the importance of the object is recognized, there 

 can be little difficulty in finding how tlie best, or nearly the best, 

 wire is to be uniformly obtained, seeing that all the specimens of two 

 of the manufactories which have as yet been examined have proved 

 to be of the best, or little short of the best quality, while those of 

 the others have been found inferior in nearly constant proportion. 



What is the cause of these differences in electrical qunlity is a 

 question not oidy of much practical importance, but of high scientific 

 interest. If cliemical composition is to be looked to for the explana- 

 tion, very slight deviations from perfect purity must be suflicient to 



FMl. Mar/. S. 4. Vol. 15. No. 103. June 1858. 2 I 



