1904.] at the Temperature of Boiling Hydrogen. 



247 



are algebraically higher than in Centigrade degrees, a peculiarity which 

 is shared with them by gold. It is also remarkable that in the cases of 

 all the purest metals examined, their resistances calculated by either 

 method of reduction vanish at temperatures above - 273° C. (Au 33 

 was not so pure as Au 40 , which was electrolytic gold.) 



As measurers of temperature gold and silver seem to be the best. 

 One prominent characteristic associated with them is, that their S's 

 are the smallest. Clearly those metals (if there are any) are accurate 

 temperature measurers for which S vanishes, so that we expect those 

 to be best in which this constant is least. There is a further 

 characteristic displayed by the best metals as shown in Table I, 

 which may be explained thus : both methods of reduction rely on 

 the parabola, and the farther away the representative arc of the 

 parabola is from the vertex of the curve, the more nearly straight does 

 this arc become and the smaller will 8 be. Now in both metals 

 referred to, especially in the purer specimens, this characteristic is 

 most marked compared with the other metals employed.* 



It is worthy of note that for these pure platinums the average value 

 of 8 is very nearly 2*5, while Callendar's platinums, also pure, gave 

 1*5 — 1'6. Is the parabola determined by the resistance at 444 0, 53 C, 

 100° C. and 0° C, different from that determined by the resistances at 

 100° C, 0° C, and - 182° -5 C. ? In the sequel I shall show that these 

 must be different, and, in fact, that we must look for an entirely 

 different hypothesis to correlate resistance and temperature. 



As a matter of interest, in the last line of Table I, I have noted the 

 ratio in which the resistance of each metal at 0° C. is reduced on 

 cooling it to the boiling point of hydrogen. This seems to be a 

 quantity showing no connection with other properties of metals. 



So far we have looked at the results rather from the point of view of 

 metals as thermometers. But a much more important question is, 

 What is the relation between resistance and temperature in metals 



We are entitled to consider the temperatures at which liquid oxygen 

 and hydrogen boil under atmospheric pressure as being known to 

 within one- or two-tenths of a degree, namely, - 182 0, 5 C. and 



- 252°'5 C. Further observations made with the constant-volume 

 hydrogen gas thermometer lead to the conclusion that hydrogen 



# In the Callendar parabola (A — T) 2 = P(B — R), the values of A for Au 40 and 

 .Ag 43 are —27,053° and 14,520° (the only other one greater than 10,000° being 



— 18,087° for Au 33 ), and the corresponding values of B are —598° and 177° (the 

 only other one greater than 100 being 135° for P 2 r). Similarly in the Dickson 

 parabola (a + R) 2 = p (b + T) the values of a for Au 40 and Ag 43 are —1080° and 

 339° (the only other two greater than 100 being 251° for P 27 and -129° for Au 33 ), 

 and the corresponding values of b are —11,841° and 7319° (the only others greater 

 than 2000° being —8100° for Au 33 and 2881 for Ag 34 ). This characteristic conies 

 out equally strongly when the curves are reduced to a common resistance of (say) 

 1000 ohms at 0° C. 



