630 Mr. J. Wilson Swan [May 20, 



trolytic copper, and are representative of the present state of things. 

 The three old pieces are taken from three well known old submarine 

 telegraph cables, and they show how very bad the copper was when 

 it was first employed for telegraphic purposes, and how great has 

 been the improvement. I will take No. 1 wire as the standard of 

 comparison. It is a piece of the wire about to be supplied to the 

 Post Office Telegraph Department for trunk telephone lines. It will 

 show the very high standard of conductivity that has been reached in 

 the copper of commerce. I am indebted for it, and for two out of 

 three of the old cable wdres, to Mr. Preece. No. 2 wire is made from 

 electrolytic copper, deposited in my own laboratory. No. 3 is also 

 electrolytic copper, but such as is commercially produced in electro- 

 lytic copper refining, it has been supplied to me by Mr. Bolton, to 

 whom I am also indebted for wire No. 6 — a particularly interesting 

 specimen : it is from the first Trans- Atlantic cable — the cable of '58. 

 No. 4 wire is from the Ostend cable of 1860, and No. 5 wire is from 

 the old Dutch cable. These wires are so arranged that I can send a 

 small and constant current partly through any one of them, and 

 partly through a galvanometer. When this is done the result will be 

 a deflection of the spot of light on the scale from the zero point to an 

 extent corresponding to the resistance of the particular wire in the 

 circuit. The worse the wire is, the greater will be the deflection. 

 We will begin with the Post Office sample first. I connect the 

 galvanometer terminals to wire No. 1, you see there is a deflection of 

 ten degrees. I will now shift the contacts to wire No. 2 — exactly 

 the same length of wire is included — but now you see there is a 

 deflection of slightly less than ten degrees, showing that this wire 

 has a little lower resistance than No. 1. The difi"erence is very small 



it may be 2 per cent. — and 2 per cent, less of it would be required 



to conduct as well as the No. 1 wire. The next is No. 3. This is 

 Mr. Bolton's wire, and shows a resistance almost equal to the last. 



Nos. 1,2, and 3 are, therefore, nearly alike, and have a degree of 

 conductivity almost as high as it can possibly be. 



Now we come to the three old wires. 



We will take No. 4 (the Ostend cable). There, you see, is a 

 great difference. Instead of spot of light being on the tenth degree, it 

 is upon the eleventh. 



We will now try No. 5 (the Dutch cable). That drives the index 



to 17. 



Now I change to No. 6 (the old Atlantic cable), and we have a 

 deflection of no less than 25 degrees. I suppose we may assume that 

 this wire fairly represents the commercial conductivity of copper in 

 1858, for it is highly probable that for a work so important as the 

 first Atlantic cable every care would be taken in the selection of 

 the copper. 



The result of this experiment shows that the copper of that cable 

 was extremely bad as a conductor, that in fact it is 150 per cent, 

 worse than the best commercial copper of to-day. In other words, it 



