— 
Or 
ie) 
<= 
—— 
XX.—On the Variation with Temperature of the Electrical Resistance of Wires 
of certain Alloys. By Professor J. G. MacGrecor, D.Sc., and C. G. 
Kwott, D.Sc. 
(Read 19th July 1880.) 
The alloys which we used in the following experiments were in the form of 
very thin hard-drawn wires,—the same as those whose thermo-electric proper- 
ties we described in a paper published in the Transactions of this Society 
in 1877.* They were prepared by Messrs. Jonnson and Matruey of Hatton 
Garden, London. In giving their constitution we rely upon the authority of 
the manufacturers, as the quantities we had were too small to admit of our 
having them analysed. 
The thin alloy wires were successively soldered to thick copper wires, by 
means of which they were placed in one of the arms of a Wheatstone’s 
Bridge. The other three arms were composed of resistance coils, made by 
Euiott Broruers, London, and arranged in the dial form. In the bridge itself 
Thomson’s “ dead beat” galvanometer was used as galvanoscope. The thick 
copper wires were so arranged that the alloy wire occupied the central part of 
“ copper vessel, which was full of oil. As the alloy wires were in all cases 
short, the vessel required to be only about 5 inches in diameter. A ther- 
mometer hung so that its bulb was in the oil at the same level as the alloy wire 
and very near it. The vessel contained also a stirrer, and was heated by a 
Bunsen burner. 
We found that by careful heating and stirring we could bring the oil to a 
very nearly permanent state as to temperature. When by these means 
the thermometer had been brought to give for a considerable time the same 
indication, the temperature was read off, and the resistance finally determined 
at the same moment. 
As, by the Wheatstone’s bridge method, resistance can be determined with 
very great accuracy, the chief sources of error in these experiments lay in the 
determination of temperature. To avoid these care must be taken to ensure 
equilibrium of temperature between the wire, oil, and thermometer, and 
accuracy in the thermometer. As our wires were exceedingly thin (one or two 
inches having in all cases a resistance of several ohms) they would undoubtedly 
in a very short time take the same temperature as the oil. As they were 
* Trans. Roy. Soc. Edin., vol. xxviii. (1877), p. 321. 
VOL. XXIX. PART II. (as 
