L890.] Magnetic Properties of Alloys of Nickel and Iron. 9 



force 67 ; whilst Curve 10 shows the induction in terms of the 

 iperature to a different scale for a force of 64. These curves show 



mt, through a range of temperature from somewhat below freezing 

 to 580 C., this material exists in two states, either being quite stable, 

 the one being non-magnetisable, the other magnetisable. It changes 

 from non-magnetisable to magnetisable if the temperature be reduced 

 a little below freezing ; the magnetisable state of the material does 

 not change from magnetisable to non-magnetisable until the tempera- 

 ture is raised to 580 C. 



The same kind of thing can be seen in a much less degree with 

 ordinary steel. Over a small range this can exist in two states ; but 

 in changing its state from non-magnetisable to niagnetisable a con- 

 siderable amount of heat is liberated, which causes rise of tempera- 

 ture in the steel. It is observed in samples B and C of nickel steel, 

 as we have just seen, but at a higher temperature. 



As might be expected, the other physical properties of this mate- 

 rial change with its magnetic properties. Mr. Riley has kindly sup- 

 plied me with wire. 



The wire as sent to me was magnetisable as tested by means of a 

 magnet in the ordinary way. On heating it to a dull redness it 

 became non-magnetisable, whether it was cooled slowly or exceedingly 

 rapidly, by plunging it into cold water. A quantity of the wire was 

 brought into the non-magnetisable state by heating it and allowing it 

 to cool. The electric resistance of a portion of this wire, about 5 

 metres in length, was ascertained in terms of the temperature ; it was 

 first of all tried at the ordinary temperature, and then at tempera- 

 tures up to 340 C. The specific resistances at these temperatures 

 are indicated in Curve 11 by the numbers 1, 2, 3. The wire was then 

 cooled by means of solid carbonic acid. The supposed course of change 

 of resistance is indicated by the dotted line on the curve ; the actual 



CURVE 11. 



