188 DR CARGILL G. KNOTT ON THE 



general qualitative result was obtained. The method adopted was not one 

 which lent itself to accurate quantitative determinations, and to obtain such 

 is in itself an important quest. Moreover, the ultimate nature of the pecu- 

 liarity can only be seen in its true light by a direct comparison of the individual 

 characteristics as shown by iron and nickel. The great difficulty in making 

 such a comparison arises from the high temperature at which the phenomenon 

 shows itself in iron ; and a further complication springs from the change in the 

 metal, due to oxidation and tempering. In the case of nickel, however, the 

 critical temperature is within reach of a mercurial thermometer, and the 

 oxidation is insignificant. It is highly probable, then, that the results for 

 nickel will be more definite and unmistakable than those for iron.* 



In the experiments to be described, the resistances were measured by the 

 simple form of Wheatstone bridge. The wires were generally tested in pairs, 

 necessarily so in the measurements at very high temperatures. Four stout 

 copper rods, 60 cm. long, 7 square cm. cross-section, furnished with strong 

 shoulder binding screws at the extremities, were fixed in a vertical position 

 some little distance apart. Their lower extremities were joined in pairs by two 

 wires, one of which was a specimen of nearly pure platinum, and the other the 

 nickel, iron, or palladium wire which was being tested. The upper extremities 

 of the rods were joined by stout copper wires to a commutator, which was in 

 connection with a Wheatstone bridge resistance box of ordinary construc- 

 tion. The current was obtained from a gravity Daniell of high resistance ; 

 and the measurements were made by means of a dead-beat mirror astatic 

 galvanometer constructed by Elliott Brothers. 



The earlier experiments and some of the later ones were carried out by 

 Messrs Hirayama and Saneyoshi, two science students in the Imperial 

 University, Tokay o, and were originally intended simply as an exercise in 

 laboratory work. Two wires, one of nickel and the other of platinum, were 

 coiled in long spirals, and fixed to the lower extremities in the manner already 

 described. A vessel containing olive oil was then brought into position, so that 

 the wires were wholly immersed. The temperature was gradually raised by 

 means of a spirit-lamp, and the resistances measured at convenient intervals. 

 The temperatures were given by a centigrade thermometer, whose bulb hung 

 in the centre between the terminals of the wires. The oil was briskly stirred 

 the whole time, so as to secure a practically uniform temperature throughout 

 the mass. The thermometer itself was tested directly at freezing and boiling 

 points, and the necessary corrections applied. The error being the same at 

 both points, it was assumed to apply throughout the whole range of readings. 

 Two specimens of nickel wire were studied, which we shall distinguish as the 

 thick nickel and the thin nickel. Tables A and B give the observations for 

 * See also Proc. Soy. Sac. Edin., ix. 120, 1875-76. [P. G. T.] 



