204 



Prof. J. A. Ewing and Mr. W. Low. 



[Mar. 24, 



sponding total inductions in C.G.S. units. The difference of these, 

 given in the fifth column, when divided by S 3 , is the intensity of field 

 or magnetic force per sq. cm., in the space immediately surrounding 

 the iron. This is given in column VI. Multiplying it by S 3 , we have 

 the correction to be subtracted from X lt which is given in column VII. 

 Finally, by dividing the corrected value of X x by the section of the 

 iron S 1} we find j}, the magnetic induction in the iron per sq. cm. 

 Column IX gives the current in the field magnet coils in amperes. 



Lowmoor Wrought Iron : Sample B. 



I. 



II. 



X x . 



III. 



IY. 



x 2 . 



Y. 



X 2 — X], 



YI. 



Field 

 round 

 iron neck 

 per sq. 

 cm. 



YTI. 



Correc- 

 tion to 

 be sub- 

 tracted 

 from Xj. 



Till. 



IX. 



Current 

 in field 

 magnets, 

 amperes. 



127 



8,295 



109 



9,490 



1195 



3,630 



100 



24,700 



1-98 



143 



9,340 



1321 



11,540 



2200 



6,680 



180 



27,610 



4-04 



150 



9,800 



142 



12,370 



2570 



7,800 



220 



28,870 



5-81 



153 



9,990 



148 



12,890 



2900 



8,810 



250 



29,350 



7-60 



157* 



10,280 



154 



13,410 



3130 



9,500 



260 



30,200 



11 



160 



10,450 



157 



13,670 



3220 



9,780 



270 



30,680 



13 5 



161 



10,520 



160 



13,930 



3410 



10,360 



290 



30,830 



16-2 



164 



10,710 



164 



14,280 



3570 



10,840 



300 



31,370 



2l'6 



165 



10,780 



166 



14,460 



3680 



11,180 



310 



31,560 



26-8 



In another test of Lowmoor iron, conducted in the same way, a still 

 higher value of was reached, namely, 32,880. This is the highest 

 induction that has been recorded in these experiments. 



A similar experiment with a piece of Swedish wrought iron, of the 

 form and dimensions shown in fig. 2, gave 32,310 for the greatest value 

 of |p, the magnetic force in the ring of space surrounding the iron 

 neck being then 11,250. 



The amount of residual magnetism retained by a Lowmoor sample 

 of this form (Sample B) was determined by comparing the effect of 

 withdrawing the test-piece with the effect of reversing it. The results 

 showed that within the range of magnetic force used in these experi- 

 ments, namely, from about 4000 to 11,000 C.G.S. units, the residual 

 magnetism is nearly constant. Its mean value in a number of 

 determinations was — 



For Lowmoor iron, residual induction, ^ r = 510 per sq. cm. 



For Swedish iron, residual induction, §) r = 500 per sq. cm. 



These results showed that pieces of the form of Sample B (fig. 2) 

 retained only a small part (less than 1/60) of their greatest induction 

 when withdrawn from the field. The proportion of residual; to 



