Mr. E. H. M. Bosanquet on Electromagnets. 

 Permeabilities or Susceptibilities. 



319 





Small 

 inductions. 



Maximum 

 permeability. 



Permeability for 



33=10,000. 



For 



33=14,000*. 



Oast iron 



f 50 



1 80 



J 160 



1240 



T200 

 1450 



J 450 



1470 



170 

 250 



700 



800 



1800 

 2500 



29001 

 3000 J 



30 



80 



400 

 500 



1200 

 2000 



2000 



20 

 100 



500 

 1000 



600 



860 



Malleable cast iron . . . 

 Wrought iron 



Charcoal iron 





Cast tool steel (hard).. 



„ (soft) ... 



f 40 

 1 50 



f 90 

 1120 



145 

 155 



420 

 460 



100 

 130 



3501 



450/ 



70 

 86 



200 



Saturation-points. 



n= 



Cast iron 9,000—14,000. 



Malleable cast iron 14,000—16,000. 



Wrought iron | _ 17,000-19,000. 



Charcoal iron j *f,vw *«/,vw 



Cast tool steel, both hard and soft 20,000. 



The malleable cast-iron rings were supplied to me by 

 Messrs. Crowley, of Sheffield. The material cuts exactly like 

 charcoal iron ; and it seemed probable that its magnetic qua- 

 lities might be similar to those of charcoal iron. In this case 

 the possibility of casting the material would have been of the 

 highest importance with reference to dynamo machines. 



The results for ordinary cast iron show that it is wholly 

 unfit for use in dynamo machines ; the low saturation-point 

 being particularly objectionable. The malleable cast iron 

 would undoubtedly be a great improvement on ordinary cast 

 iron ; but still inferior to wrought iron. 



It may be noted that the variations of temper in the differ- 

 ent rings of malleable cast iron did not appear to correspond 

 to any recognizable differences, either mechanical or magnetic. 

 About the time these experiments were drawing to a close 

 I became aware, by a notice in ' Nature/ that Dr. Hopkinson 

 had communicated to the Royal Society a series of investi- 

 gations apparently similar to my own. I have not yet been 

 able to learn any thing about the contents of the paper in 

 question ; but considering the diversity of the properties of 

 different specimens, as well as of the methods in use, I still 

 hope that my results may not be without usefulness. 



* As before, IS stands for the magnetic induction, or number of lines of 

 force across unit area ; /x for permeability or susceptibility. 



