Permanent Magnets. 



181 



M„ 



Ml 



M'o 



N 



N 100 



M -M 100 

 Mo 



Mo-M'o 

 Mo 



Mo-No 



No-N 100 





Mo 



N 



I. Hard steel bar. 



71-5 41-5 44-8 

 134-5 1 89-2 ! 96- 1 

 195- ! 134-3 146-2 



37- 



85-5 

 133-3 



33-2 



77-8 

 120- 



0-420 

 0-321 

 0-311 



0-373 



0-286 

 0-250 



0-483 

 0-364 

 0-316 



0-103 

 0-090 



o-ioo 









II 



Tempered steel 



bar. 







44- 



27- 



30- 



! 29- 



27- 



0-386 



0-318 



0-341 



0-0690 



1485 



107-2 



114-5 



110-3 



101- 



0-278 



0229 



0-257 



0-0814 



219-5 



165- 



179- 



' 172- 



156- 



0-249 



0-184 



0-216 



0-0930 



317- 



239- 



260-7 



251-2 



226- 



0-246 



0-178 



0-207 



0-1003 



Soft steel bar, No. 1. 



85- 



45- ! 



38- 



33-2 | 



0-471 





0553 



0-126 



141- 



73-5 



68-5 



57- 



0-479 





0-514 



0-168 



193- 



99- 



loi- 



78-5 



0-487 





0-478 



0-223 



209-5 



109-5 



ns- 



88-2 | 



0-477 





0-451 



0-233 









Soft steel bar, No 



. 2. 







95-5 

 136-5 

 174-8 



49-7 



73- 



92-5 



54-2 



81-5 

 108-3 



\ 45- 

 1 69- 

 | 93-4 



39- 

 59- 

 76- 



0-479 

 0-465 

 0-471 



0-432 

 0-403 

 0-378 



0-529 

 0-495 

 0-466 



0-133 

 0-145 

 0-186 



Very soft steel bar which had been heated and slowly cooled many times. 



51-5 



34-5 



37- 







0-330 



0-282 





80-5 



54-5 



58- 







0-323 



0-279 





113- 



76- 



82- 







0-328 



0-274 





159-5 



103-3 



116-5 







0-353 



0-270 





181- 



113-5 



131- 







0-373 



0-277 





Mo is the intensity of magnetization before any change in temperature has 

 taken place ; M 100 , when first heated to 100° C. ; M' , after being again 

 cooled to 0° C. N and N 10 o are the intensities of magnetization at the tem- 

 peratures indicated by the subscripts after the magnet has been heated and 

 cooled fifteen times. 



ness of the steel would naturally affect the magnetization. 

 According to their experiments, if a glass hard steel rod is 

 thoroughly annealed by being kept at the temperature of boil- 

 ing water for a day or two and then magnetized to saturation 

 at the temperature of the room, the loss in magnetization on 

 being heated to the boiling point is relatively small and is 

 nearly independent of the time it is kept there. Nearly the 

 whole change takes place during the first ten minutes. On 

 the other hand, if the bar is not first annealed, the change is 

 much larger and is not complete after twenty-two hours heating. 

 B. Investigations on the effect of change of temperature on 



