on the Magnetic Properties of Iron. 11 



depending upon the temperature; with very weak fields the 

 second stage is not reached until the temperature is between 

 600° C. and 700° C, and then the permeability increases with 

 great rapidity. Under a magnetizing force of such a strength 

 that the second stage is just entered upon while the metal is 

 cold, the rate of increase in permeability as the temperature 

 is raised is comparatively slow. From this it appears that 

 the effect of heat in hastening the transition from stage to 

 stage is greater at high than at low temperatures. 



Curves showing the relation between permeability and 

 magnetic force, at different temperatures. Avere drawn with a 

 view to ascertain the rate of transition as the temperature is 

 raised. 



Table I. (p. 12) gives the results obtained while the 

 temperature was kept as nearly constant as was practicable 

 during each set of readings. 



These results are shown graphically in fig. 6; the scale of 

 magnetic force is different for each curve, being regulated so 

 that the maximum permeability occurs at the same distance 

 along the horizontal axis in each case. The ordinates for the 

 curves are drawn to the same scale except for a temperature 

 of 735° C. : in this case the scale is reduced to ■§■ for con- 

 venience in plotting, it will be seen from the figure that 

 the curves are very similar to one another, and it will be 

 found on reducing the ordinates in a suitable ratio for each 

 temperature that the curves practically coincide. 



The experiments were repeated several times, it being found 

 that the kicks in the galvanometer with extremely small forces 

 giving the first stage of the magnetizing process for the 

 higher temperatures were in some experiments slightly larger 

 than those from which the permeabilities given were calculated. 

 This was attributed to the demagnetizing process not entirely 

 wiping out all the effects of previous magnetism, the residual 

 effect being noticeable only at high temperatures. In each 

 case, however, as the second stage was entered upon, the 

 corresponding kicks in each series of readings for the same 

 temperature were practically identical. 



Representing the results of experiment as in the figure, we 

 see clearly that the effect of heating is to bring on the suc- 

 cessive stages of the magnetizing process with values of the 

 magnetic force depending upon the temperature. 



The relation between temperature and magnetizing force 

 in hastening the transition from stage to stage may be ascer- 

 tained by observing the force necessary to bring on any 

 definite point in the process of magnetization for different 

 temperatures. For this purpose the point at which the 



