316 A M. Mayer on measuring Electrical Conductivities. 
has found that an alloy of 1 part of silver and 2 of gold pre- 
sents almost as much resistance as German silver. 
Iron.—The three following determinations were made of the 
conductivity of the best quality of iron wire relatively to the 
standard copper wire. 
1) The resistance of 240 in. of copper wire 36° y in. of i iron wire. 
2) ‘i ““c a“ 111°6 “ a be 1 
3) “ “6 “ 60 ses “ sé 8: rs ed s“ “ 
Giving for the relative conductivity of iron, 
(1) 240 : 3647 = 100: 15-29 
(2) 1116: 1616 == 100: 14-48 
67 0: 14-45 
° 1474 = Mean. 
E. Becquerel (Ann. de Ch. et Phys., IIT, xvii, 266) gives 13°6 
for the Seaacany of iron, copper being ‘100; and both wires 
hard-drawn ; while Matthiessen (Phil. Trans. 1858, 1862) deter- 
mines 16°81 as the conductivity of iron, copper being 100, and 
both hard-drawn. 
The mean of Becquerel and Matthiessen = 15-20 
My determination = 14°74 
ban = 46 
copper and iron wires in (8) were gu. of from the 
laut used in (2); but the wires used in (1) w ae a from 
parts of the coils removed from the lengths (2) an d (8). This 
accounts for the close agreement of (2) and (8) and the higher 
number obtained in (1 
My d etermination therefore appears to compare favorably 
with those made with different methods by these experimental: 
: ‘‘appears,” because although the copper was of ex- 
cellent aaliee and the iron the best procurable, yet Vey were 
not chemically examined as to their purit 
Another series of determinations was Snel by comparing 
the lengths of co oapne: and of iron wires which would equal 1p 
resistance one and the same length of German silver wire, used 
as a term of comparison. The result agreed with the above 
determinations. 
6. Ona gem ce of the method. 
mg “to the line of the a ; ane expen whose atic 
into'a coil of 8 ft. in a containing 4 turns. The termi- 
nals of this coil were connected by binding bo Re wan the 
