1887.] On the Magnetisation of Iron in Strong Fields. 205 



greatest induced magnetism in samples of the form A (fig. 1), is 

 probably not very different from this. 



In the following experiment a bobbin of annealed Swedish iron, of 

 the size and shape shown in fig. 2, was tested by withdrawing it from 

 the field. The columns of the table have the same meaning as before, 

 except that the quantity in column VIII, now headed J) — |jj r , is not 

 the whole induction per sq. cm., but that part of the induction which 

 disappeared when the test-piece was withdrawn from the field. In 

 this case the section of the iron was the same as before, but the space 

 between the inner and outer induction coils (S 3 ) was 0*308 sq. cm. 

 There were fourteen turns in the inner coil and twelve in the outer. 



Swedish Wrought Iron : Sample B. 



I. 



Pi. 



II. 



in. 



IY. 



x 2 . 



y. 



VI. 



Field 

 round 

 iron 

 neck per 

 sq. cm. 



VII. 



Correc- 

 tion to 

 be sub- 

 tracted 

 from Xj. 



VIII. 



S-Sr. 



IX. 



Current 

 in field 

 magnets, 

 amperes. 



125 



5 



9,290 



131 



•5 



11,350 



2060 



6,690 



180 



27,460 



4'08 



134 



5 



9,950 



147 







12,690 



2740 



8,900 



250 



29,230 



7-77 



139 



5 



10,320 



153 



5 



13,250 



2930 



9,510 



260 



30,320 



10-9 



141 



•5 



10,470 



157 







13,550 



3080 



10,000 



280 



30,710 



14-2 



143 



5 



10,620 



160 







13,810 



3190 



10,360 



290 



31,130 



16-5 



144 







10,660 



162 



•o 



13,990 



3330 



10,810 



300 



31,220 



18 -9 



145 



5 



10,770 



163 



5 



14,120 



3350 



10,880 



300 



31,560 



22-9 



147 







10,880 



166 







14,330 



3450 



11,200 



310 



31,860 



26-5 



The residual magnetism may be corrected for by adding 500 as 

 the value of §) r to each of the numbers in column VIII. We then 

 obtain for the highest induction ^ the value 32,360. 



The following results relate to test-pieces of the form and size 

 shown in fig. 1 : — 



Swedish wrought iron. Form of Sample A. Section of iron neck 

 = 0*669 sq. cm. Section to middle of induction coil = 0*708 sq. cm. 

 Loss of induction per sq. cm. tested on withdrawing the bobbin 



(8~8r). 



Current in field magnets, 

 amperes. 



3-92 



7-48 

 11*3 

 14-0 

 17-9 

 20-1 

 20 4 



27,550 

 29,420 

 30,240 

 30,460 

 30,960 

 31,180 

 31,290 



