412 Intelligence and Miscellaneous Articles. 



1. If a steel bar be put in contact with the pole of a magnet, and, 

 for a point M of the bar, the value of the current of demagnetiza- 

 tion at the ordinary temperature be determined, and the bar be 

 afterwards slightly heated with a spirit-lamp, the value of the de- 

 magnetizing current corresponding to the point M is found to be 

 very notably augmented. 



2. AVhen the bar is allowed to cool in contact with the magnet, 

 the magnetization does not retrograde, but receives a slight incre- 

 ment. 



3. When the bar has returned to the ordinary temperature, 

 removing it from the magnet for a few moments is sufficient to 

 cause a portion of the increment resulting from the heating to dis- 

 appear : when contact between the magnet and bar is reestablished, 

 we do not find the same total magnetism as before contact was broken. 



The new facts which I have ascertained are as follows : — 



4. When the steel bar put in contact with the magnet, instead of 

 being very moderately heated, has its temperature gradually raised 

 until it assumes the blue tint, the magnetism at first rises, reaches 

 a maximum, and then retrogrades. In a series of experiments upon 

 a bar of 24 centims. length and 10 millims. diameter I ascertained 

 that, when one end of the bar was put in contact with the pole of 

 a magnet, the total magnetism of the middle point was represented, 

 at the surrounding temperature, by the number 41-6 ; on gradually 

 heating the bar, I found that the magnetism took in succession the 

 values 44, 51, 55-2, 52, 52-8, 52-1, 50, 48-5, 48, 48. 



5. When, after being strongly heated, the bar is left in contact 

 with the magnet during the whole time of cooling, the total mag- 

 netism is augmented in proportion as the bar cools ; and on its 

 arrival at the surrounding temperature, the magnetism retains a 

 value much superior to that which it had before the heating. In 

 the series of experiments just now mentioned the value of the total 

 magnetization was 63*2 after the heating, while before it was only 

 41-6. 



6. We have seen above (4) that when the temperature of the bar 

 exceeds a certain limit, its total magnetism diminishes, instead of 

 continuing to increase. One might infer from this that the mag- 

 netization of the bar brought back to the ordinary temperature would 

 likewise be less, if the temperature to which it was raised exceeded 

 the limit of which I have just spoken. I have proved that it is not 

 so. The total magnetization of the bar, restored to the ordinary tem- 

 perature, is the greater the more the bar has been heated, at least 

 provided its highest temperature was below that which gives to steel 

 the blue tint. 



7. When the bar has returned to the ordinary temperature, it 

 suffices, as I have said (3), to suppress contact between the magnet 

 and the bar for a few seconds in order to cause the loss of a part 

 of the increment of magnetism resulting from the heating — but only 

 a part ; even after breaking contact the total magnetization remains 

 greater than before the heating ; and I have verified, in a great 

 number of experiments, that the increase of magnetism is, at least 

 approximately, equal to the increment of the permanent magnetism. 



