on the Magnetic Properties of Iron. 3 



primarily to investigate the effect of heat on the magnetic 

 properties of certain alloys of iron, which, at the ordinary 

 temperature, had been previously found to give very different 

 magnetic results when in different physical conditions. 



It appeared desirable to examine the effect of heat on the 

 magnetic properties of wrought iron in weak fields, to see 

 when, as the temperature is raised, the successive stages of 

 the magnetizing process are brought on, and to obtain some 

 idea as to the rate of transition from stage to stage. 



The specimens were obtained from Messrs. Brunton & Son, 

 of Musselburgh, and were in the form of rings turned out of 

 solid blocks and annealed. The magnetization was measured 

 ballistically by reversing the magnetizing force, the arrange- 

 ment of the apparatus being very similar to that used by 

 Ewing and Klaassen*. 



The copper wire was insulated with asbestos paper, and thin 

 asbestos tape laid between the primary and secondary coils. 



The temperatures were estimated by the resistances of the 

 secondary coil and a platinum wire ; it was found that after 

 successive heating and cooling the resistance of the secondary 

 coil increased, at first very slightly, but after a time the 

 increase was proportionately large. A platinum wire was 

 wound around the ring between the primary and secondary 

 coils and its resistance measured as well as the resistance of 

 the secondary at each temperature. 



The specimens were heated in a Fletcher's improved 

 muffle furnace, and the temperature regulated by the 

 supply of gas. Before each experiment sufficient time was 

 allowed to get the temperature steady, and it was found that 

 in each case the temperature remained constant within 3° C. 

 during each set of readings. 



Wrought Iron Ring, 

 The dimensions of the ring were as shown : — > 



2-495 



_4 



^ 6-4 »- 



* Phil. Trans, vol. clxxxiv. A. p. 987 (1893). 

 B2 



