54 



Prof. J. A. Fleming. 



at the same time by means of a platinum thermometer (Pi) used in 

 previous researches. 



The conversion of the platinum temperatures into centigrade tem- 

 peratures was effected by means of a table drawn up Mr. J. Hamilton 

 Dickson* for this thermometer. 



The measurements of the resistance at low temperatures ( - 78"2° 

 and - 182*5°) was obtained by measuring the coil in liquid air and 

 melting CO2 at the Royal Institution Laboratories, by kind permission 

 of Professor Dewar. 



The total resistance of the nickel calculated from the above observa- 

 tions is set out in the form of a curve (fig. 1), having resistance as 

 ordinates and temperature as abscissse. 



The curves are given both for temperature in centigrade degrees and 

 temperature in platinum degrees. The curve shows that the resist- 

 ance is falling steadily downwards to a zero value as the absolute zero 

 of temperature is approached. 



. In fig. 2 the portion of the curve between 0° C. and 100' C. is shown 

 in an enlarged scale. In fig. 3 the volume-resistivity is set out in terms 

 of temperature. 



The results show that the vOlume-resistivity or resistance per centi- 

 metre-cube of this electrolytic nickel at 0° C. is 6935 C.G.S. units. 

 The average temperature coefficient between 0° C. and 100° C. is 

 0-00618. 



The above observations indicate that this electrolytic nickel, as pre- 

 pared by Mr. Swan, has an exceedingly difi'erent and much lower 

 resistivity than that employed for test by Matthiessen thirty-five 

 years ago. 



The value of the mean temperature-coefficient of the nickel used in 

 the experiments of Fleming and Dewar in 1893, and prepared by 

 Dr. Ludwig Mond, was 0-00622t between 0° C. and 100° C. It is 

 clear therefore that some extraordinary electrical difference exists 

 between nickel as it can now be produced electrolytically and nickel 

 as it was produced by Matthiessen for his experiments. 



It would be interesting to ascertain if any specimen of nickel known 

 ±0 have been used by Matthiessen for his experiments still exists, and 

 if so, to discover the nature of the impurity (if impurity was present), 

 or at least the physical difference, which caused his nickel to have 

 nearly double the electrical resistivity of that which can now be pro- 

 duced. 



I desire to record my thanks to Mr. J. E. Petavel and to Mr. A. 

 Blok for assistance in these experiments. 



* ' Phil. Mag.,' June, 1898. 



t ' Phil. Mag.,' September, 1893. 



