326 C. G. KNOTT 



and myself* tliiit at a dull red heat, which is just the temperature at 

 which the thermoelectric change occurs, a sudden change in the rate 

 of increase of resistance of iron as compared with the corresponding 

 quantity for platinum seems to take place. Von Waltenhofen has 

 also shown that for steel wires the rate of change of resistance above 

 a red heat tends to fall otf. If, then, there should be any connection 

 between the two phenomena, something similar ought to exist in the 

 case of nickel. Also, since the thermoelectric peculiarity for nickel 

 occurs at a considerably lower temperature, somewhere between 200' 

 and 320° C, the comparison obviously may be more easily effected. 

 A preliminary experiment in which the wire was heated up in oil to a 

 temperature of 300" C. gave a promising result. The method of ex- 

 periment finally adopted was as follows. The wires to be tested were 

 raised to a red heat inside a porcelain vessel set in a charcoal furnace. 

 Two wires Avere tested simultaneously, or rather in rapid succession, 

 as the furnace slowly cooled. One of the wires was always a certain 

 piece of platinum wire which served as a thermometer. The other 

 wire was nickel, palladium, or iron, the last two being studied so as to 

 make sure that the peculiarity shown by the nickel was a real property 

 of the metal. In the graphical representation of the results, giving 

 the resistances of the various metals at different temperatures in terms 

 of the corresponding platinum resistance, palladium showed as a 

 straight line, iron as a curve of constantly increasing steepness, that is 

 concave upwards, and nickel as a curve with a point of inflexion, 

 concave upwards at temperatures below 300° C. and concave down- 

 wards at higher tem})eratures. At 320° a very sudden decrease 

 occurred in the rate of increase of temperature. The following table, 

 abstracted from the complete paper, brings out the differences between 



* Procccdiugs lloyal Society of Ediubuvgli (1875). 



