78 



Intelligence and Miscellaneous Articles, 







M 





M. 



M . 



E. 



M. 



1_£-2E - 



E. 



l-k~' 2E 



10-9 



510 



61-11 



6-8 



400 



5857 



10-5 



49-5 



60-07 



6-2 



380 



5922 



()•!> 



49-22 



61-06 



5-7 



36 



58-99 



9-5 



48-1 



60-69 



5-2 



34*0 



58-66 



1)10 



46-0 



59-10 



4-9 



330 



59-39 



8-5 



45-5 



60-25 



41 



28-7 



58-24 



8-4 



44-6 



59-37 



4-4 



31-0 



59-61 



815 



441 



59-49 



37 



26-7 



58-49 



7-6 



430 



60-07 



2-95 



22-6 



58-61 



7-2 



40-5 



57-26 



250 



20-0 



5900 



On discussing that formula we see that if E increases, 7c~ 2E di- 

 minishes and M increases. Therefore the magnetism augments 

 with the thickness of the bar. From a sufficient thickness (the less 

 as Tc is greater) the magnetism no longer augments with E, but 

 takes a limiting value 



This limiting value is the less the greater 7c is or the steel less con- 

 ductive ; whence it follows that steels which are much cemented 

 and chilled will be magnetized very little, and equally under all 

 thicknesses. Those singular kinds of steel which are no longer 

 magnetic are thus accounted for. 

 Developing Jc~ E , we can write 



M=4AE=/l 



EZ.fc 

 T72 



+ 



••> 



Supposing that E increases from E to ?iE, 



M=4A?iE(l- 



nEl.h 

 1.2 



+ 



■)■ 



but if we superposed n plates of thickness E, we should have 



M,=4A 



The ratio 



>iEf: 



EZ . h 

 1.2 



+ 



•■> 



M 1 _ 2-EZ.fc+ . 

 M 2-iiEUc. 



increases with n ; whence we see that a bundle of n plates will 

 always be more powerful than a bar of the same steel having the 

 same dimensions ; and the ratio will increase indefinitely with the 

 number of the plates. This justifies the employment of thin plates 

 in the construction of magnets. — Coniptes Rmdus de VAcademie des 

 Sciences, vol. lxxxii. pp. 19-24. 



