206 



Prof. J. A. Ewing and Mr. W. Low. [Mar. 24, 



These figures agree very well with those in the preceding table, 

 which related to another sample of different form cut from the same 

 bar. Probably 500 is in this case also a fair estimate of the residual 

 induction, and by adding that to the values given above we arrive at 

 probable values of g}. 



Lowmoor wrought iron. Form of Sample A. Dimensions as above. 

 Current in field magnets = 20*4 amperes. Loss of induction on 

 withdrawing the bobbin (§) — |fr) = 31,660. Allowing for the residual 

 magnetism, this gives an induction exceeding 32,000. 



Soft Hammered Scrap. Form of Sample A. Dimensions as above. 

 Current in field magnets. |j) — |5 r . 



20*4 31,230 

 26-2 31,520 



The remaining experiments relate to cast iron. The following 

 results are for a sample of the form shown in fig. 2, except that the 

 neck was of considerably larger diameter, namely 0*962 cm. The 

 sample was tested by turning it end for end in the magnetic field. 



Section of neck = 0*727 sq. cm. 



Section within middle of inner induction coil = 0*767 sq. cm. 

 Space to be corrected for = 0*040 sq. cm. 

 Section within middle of outer induction coil = 1*195 sq. cm. 

 Space between coils = 0*328 sq. cm. 



Cast Iron. 



Field round 

 iron neck 

 per sq. cm. 



Correction 



to be 

 subtracted 

 from Xi. 



14,450 

 16,200 

 16,910 

 17,420 

 18,240 

 18,490 

 19,030 



15,730 

 18,300 

 19,440 

 20,070 

 21,260 

 21,670 

 22,510 



1280 

 2100 

 2530 

 2650 

 3020 

 3180 

 3480 



3,900 

 6,400 

 7,710 

 8,080 

 9,210 

 9,700 

 10,610 



160 

 260 

 310 

 320 

 370 

 390 

 420 



19,660 

 21,930 

 22,830 

 23,520 

 24,580 

 24,900 

 25,600 



Another set of readings were taken with this sample at the same 

 time, by drawing it suddenly out of the field, in order to determine 

 the residual induction. The results showed that throughout the 

 range of magnetic forces employed here, the residual induction had a 

 nearly constant value of 400 C.Gr.S. units per sq. cm. 



A bobbin of cast iron of a form resembling Sample A, fig. 1, was 



