1904.] at the Temperature of Boiling Hydrogen. 



249 



Next, the curves for P 7 , Au 40 , the two silver, and Pd^,, are very 

 approximately parallel. Of the two palladiums, Pd 35 would appear to 

 have contained so much impurity as to have behaved almost like an alloy. 

 The two alloys take up quite independent positions compared either 

 with the purer metals, or with themselves, tending more to parallelism 

 with the axis of temperature. In this connection I may mention that 

 I constructed and used once or twice a carbon thermometer ; in its case 

 the resistance diminished as the temperature rose (a result already 

 known), and its " plot " departed still farther from the pure metals 

 than the alloys do, its a being - '08048. 



The magnetic metals present the most striking curves, being at first 

 sight quite unlike any of the others. But on closer inspection we shall 

 find that this is not so, and in fact they give the clue to the general 

 connection between resistance and temperature in metals. The 

 magnetic metals and gold were found to have negative values of 8. 

 Now, if we examine the curves of the other metals, they will all be 

 found concave towards the axis of temperature, for the arcs extending 

 from the boiling point of water, through the freezing point, down to 

 the boiling point of oxygen ; while below the boiling point of oxygen 

 these carves are convex to this axis. On the other hand, gold and the 

 magnetic metals are already convex to this axis from the boiling point 

 of water to the lowest temperature reached. 



This leads me back to the research made by Professor Fleming and 

 myself in 1896* on the electric resistance of mercury, in which we 

 were able to observe the resistance of the metal from far below its 

 melting point, and considerably aboye it when in the molten state. 

 The curve connecting the resistance of mercury with temperature, 

 throughout this range, including the change of state, was somewhat 

 like the disused old English f, the temperature being measured hori- 

 zontally to the right, and the resistance vertically upwards. In the 

 present instance, though in different circumstances, this same curve 

 reappears. 



For platinum, silver, copper, palladium, and the alloys these 

 experiments include a part of the curve (fig. 1) starting from (say) P, 

 passing through I, the point of inflexion, and through Q down towards 

 the absolute zero ; whereas, in the case of gold and the magnetic 

 metals, the corresponding part of the curve begins below I, (say) at Q, 

 and proceeds thence towards the absolute zero. Professor Callendar, 

 from former experiments of Professor Fleming and myself, had noticed 

 this behaviour in the case of platinum, f 



The eight observations below the boiling point of hydrogen are 

 shown in Plate 10. 



# " On the Electric Resistivity of Pure Mercury at the Temperature of Liquid 

 Air," ' Roy. Soc. Proc.,' vol. 60, p. 76. 

 f ' Phil. Mag.,' vol. 47, pp. 218, 222. 



VOL. LXXIII. T 



