554 



solid wire, is nothing in comparison with the differences presented by 

 different samples chosen at random from various stocks of solid wire 

 and strand in the process of preparation for telegraphic purposes. 



No. 16 Solid Wire. Pairs of samples in different states of prepara- 

 tion, each 1000 inches long. 



No. 14 Gauge Strand (seven No. 22 wires twisted together). Pairs 

 of samples in different states of preparation, each 1 000 inches long. 



* These resistances were measured, by means of a Joule's tangent galvanometer 

 with a coil of 400 turns of fine wire, in terms of the resistance of a standard con- 

 ductor as unity. The resistance of this standard has been determined for me in 

 absolute measure through the kindness of Professor W. Weber, and has been 



found to be 20,055,000 German units ( metre Y or G.580,000 British units 

 Vseconds-' 



