548 PROFESSOR C. G. KNOTT ON MAGNETIZATION 



in an anti-induction wound coil of asbestos-covered wire which could be kept at any- 

 desired temperature by means of a suitable current passed through it. The resistance 

 of the nickel wire itself served as thermometer. 



The nickel wire formed one arm of a Wheatstone bridge ; and the change of 

 resistance, when any given field was applied, was measured by deflection on a delicate 

 galvanometer, the constant of which was determined from time to time by the deflection 

 produced when a known change of resistance was made in one of the other arms of the 

 bridge. The method was in fact identical with that already described in my earlier 

 papers. 



The electromagnet was standardised by means of a bismuth coil placed in various 

 positions within the air-gap, and an estimate made of the average fields across the area 

 occupied by the nickel coil for certain definite values of magnetizing current. The 

 fields for the currents used in the experiment were then determined graphically by 

 interpolation. 



Each separate experiment was carried out in the following manner : — A suitable 

 current was passed through the heating coil surrounding the nickel wire ; and when 

 the temperature became steady, as indicated by the steadiness of the resistance of the 

 nickel, the real measurements began to be made. For every such temperature reached, 

 the nickel coil was subjected to various magnetizing fields and the corresponding 

 changes of resistance measured. A curve was then constructed on section paper in the 

 usual way, showing the relation between magnetizing force and resistance change. 

 This was done for each temperature ; and from the graphs so obtained a new set was 

 formed giving the relation between temperature and resistance change due to the 

 application of given chosen fields. 



The individual measurements in the order in which they were obtained are given 

 in the appendix ; and in the table given here, the results are arranged in a form which 

 shows at a glance the peculiarity already referred to. The most striking results are 

 also indicated graphically in the diagram. 



The experiments on which this table is based were all performed between 25th May 

 and 14th June 1904, and the date is given in the first column. The second column 

 contains the resistances of the wire at the various temperatures, which were indeed 

 measured by means of the corresponding resistances, and are entered in the third 

 column. The remaining six columns contain the resistance changes, estimated per 

 100,000, produced by the six fields the values of which are entered along the tops of 

 the columns. The total change of resistance of the wire in any particular case can be 

 found by dividing by 100,000 and multiplying by the resistance as given in the second 

 column. 



Running our eye down the column headed by field 3800, we see that the percentage 

 change of resistance due to the application of this field steadily falls off as the temperature 

 rises until the temperature of 260° C. is reached. Did the rate of fall continue constant, 

 the change of resistance due to magnetization would vanish about 360°. Instead of so 



