254 Intelligence and Miscellaneous Articles. 



We thus observed that the quantity of residual magnetism slowly 

 diminishes as the temperature of magnetization is increased ; it is 

 still considerable at incipient redness, but becomes insensible at a 

 cherry-red heat. 



The magnetism, which is rapidly lost if the bar is allowed to 

 cool, is preserved at any temperature if the same calorific state is 

 maintained— if not indefinitely, at least during a time so long that 

 the very slow enf eeblement observed can be attributed to oscillations 

 of temperature resulting from the difficulty of keeping a very high 

 temperature perfectly constant. An augmentation or a diminu- 

 tion of temperature is accompanied by a loss of magnetism, which 

 therefore does not depend on the temperature at which the bar was 

 magnetized, but is a correlative phenomenon of the thermal state. 

 The quantity of magnetism at a determinate temperature depends 

 on the nature of the steel, the temperature of magnetization, and 

 changes of state subsequently undergone. 



"When the bar is heating, the magnetism diminishes according 

 to a law which depends on the composition of the steel, but in a 

 pretty regular fashion ; when it is cooling, the law of the loss of 

 magnetism is very different from that of the loss of heat. The 

 temperature diminishes, as we know, at first rapidly, then less and 

 less quickly, and can be represented approximately by Newton's 

 formula, 



6=e ai . 



The magnetic loss is, on the contrary, very slow at the com- 

 mencement, then augments very rapidly, to resume afterwards a 

 decreasing value. The annexed Table gives the quantity of mag- 

 netism, measured from minute to minute, in a bar magnetized at 

 about 350° G. :— 



Times 012 3 456 7 89 10 60 



Quantities of 1 29 2 9 28-8 28«7 27 19 12 8 6-5 5 4 1-5 



magnetism/ 

 Temperatures 350° 200° 100° 12° 



We see that it remains nearly constant during three minutes, 

 then loses in four minutes two thirds of its value, lastly diminishes 

 less and less quickly, and when the bar has arrived at the ordinary 

 temperature has only fa of its initial value. 



When we vary the temperature of magnetization, the time during 

 which the loss remains very slight goes on increasing as the initial 

 temperature is raised, although the cooling is more and more 

 rapid. Besides, the time is independent of that during which 

 the magnetism has been kept constant by maintaining the tempe- 

 rature. 



When a bar which was magnetized when hot has been allowed 

 to cool and is again heated, we observe that the quantity of magne- 

 tism increases and may attain to three times the value which it had 

 preserved, remaining nevertheless below that possessed by it at the 

 time of its magnetization. This is similar to M. Wiedmann's 

 observation concerning the magnetic moment of bars magnetized 

 at 100°. 



But in following the quantity of magnetism during the heating 



