on the Magnetic Properties of Iron. 7 



It will be seen that the permeability increases slightly as 

 the temperature is raised to about 500° C. ; beyond this tem- 

 perature the permeability falls, at first slowly, but with great 

 rapidity as the critical temperature is approached. 



The explanation given by Professor Ewing for the results 

 of experiment with a field-strength giving a permeability- 

 temperature curve similar to fig. 2 is that heating facilitates 

 the alignment of the molecular magnets by weakening their 

 mutual forces, but the permeability does not rise appreciably 

 owing to the influence of oscillations supposed to be set up as 

 the temperature rises which oppose the alignment of the 

 magnets. This latter effect increases very rapidly as the 

 critical point is approached and the permeability falls. 



With fairly strong fields, such that the third stage of the 

 magnetizing process is brought on before any heat is applied, 

 there is no appreciable increase in permeability as the tempe- 

 rature rises, and the change from the magnetic to the non- 

 magnetic state takes place comparatively gradually. 



The curves drawn for successively smaller magnetizing 

 forces show that as the force is reduced the temperature at 

 which the permeability begins to fall increases. This may be 

 accounted for by the molecular magnets being less deflected 

 under weaker forces, and consequently the temperature 

 necessary to bring them parallel with the field will be 

 higher. 



It is seen from fig. 1 that the permeability decreases very 

 rapidly as the field is increased beyond the second stage; 

 consequently, by reducing the magnetic force so that less of 

 the third stage is entered upon before the magnetic quality is 

 lost, heating is more favourable to magnetization. 



The following values for the permeability at the tempera- 

 tures given were obtained with a force of 1*075 C.G.S., and are 

 shown plotted in fig. 3. 



Fig. 3. 



7000 

 6000 

 5000 

 4000 



3000 

 2000 

 1000 





















H-- 



■ /-07, 



r c.g. 



s 







































































































i 



100° 200° 300° 400° 500° 600° 700° 800° 

 Temperature in Degrees Centigrade. 



