296 Profs. Dewar and Fleming on the Electrical 



metals at very low temperatures is different to their order at 

 ordinary temperatures. At the lowest temperature reached the 

 best metallic conductor is pure copper. It may be remarked 

 that generally the best conductors amongst the pure metals 

 are those that are most sonorous: silver, aluminium, gold, and 

 copper would make good bells, whilst lead, thallium, tin, and 

 palladium, which are the worst conductors, would be un- 

 suitable for this purpose. The metals platinum, palladium, 

 have resistance-curves which have a marked concavity down- 

 wards when plotted in terms of Centigrade temperatures; 

 whilst nickel and iron have a considerable curvature in the 

 opposite direction. An examination of this chart will show 

 that the conclusion reached in our former paper is confirmed 

 by these more careful experiments, viz., that the electrical 

 specific resistance of all pure metals will probably vanish at 

 the absolute zero of temperature. 



§ 22. An examination has also been made of a large 

 number of alloys of known composition, and as the details are 

 too numerous to tabulate in full, we append two Tables (I. 

 and II.) which will show the volume-specific resistance in 

 O.Gr.S. units of these various alloys at different temperatures 

 stated in terms of platinum temperatures. At the same time 

 the composition of the alloy is given. Also we add a 

 Table III., in which the volume-specific resistance of each 

 alloy is given at 0° C, and the temperature-coefficient at 

 15° C. The resistance-curves of these alloys are shown in 

 the chart. 



Concerning these curves we may draw attention to the fact 

 that the curve of Hadfield's manganese-steel has a remarkably 

 sudden change of curvature at about —40° C. It will be im- 

 portant to investigate the magnetic qualities of manganese- 

 steel at a temperature of from — 30° C. to — 80°, and see if 

 possible what other physical changes take place at the time 

 when the temperature-coefficient undergoes a rapid change. 

 It will also be seen that the alloy manganin has a curve which 

 has a maximum at 16° C. Hence manganin has a zero tem- 

 perature-coefficient at 16° C, but a positive coefficient below 

 that temperature, and a negative one above. It is very in- 

 teresting to note the effects of the various constituent elements 

 in the alloys. An admixture of 6 per cent, of silver with 

 aluminium has a much greater effect in changing the specific 

 resistance than 6 per cent, of copper, whilst 3 per cent, of 

 aluminium has a greater effect still in changing the character 

 of copper. We have collected together into Table IV. the 

 volume- specific resistances of the pure metals, and also their 

 mean temperature-coefficients between 0° C. and 100° C. 



