292 



Tables 304-306. 

 PERMEABILITY OF SOME OF THE SPECIMENS IN TABLE 303. 



This table gives the induction and the permeability for different values of the magnetizing force of some of the speci- 

 mens in Table 303. The specimen numbers refer to the same table. The numbers in this table have been taken 

 from the curves given by Dr. Hopkinson, and may therefore be slightly in error ; they are the mean values for 

 rising and falling magnetizations. 



Tables 305-309 give the results of some experiments by Du Bois,* on the magnetic properties of iron, nickel, and 

 cobalt under strong magnetizing forces. The experiments were made on ovoids of the metals 18 centimetres long 

 and 0.6 centimetres diameter. The specimens were as follows: (i) Soft Swedish iron carefully annealed and 

 having a density 7.82. (2) Hard English cast steel yellow tempered at 230'^ C. ; density 7.78. (3) Hard drawn 

 best nickel containing 99 % Ni with some SiOj and traces of Fe and Cu ; density 8.82. (4) Cast cobalt giving 

 the following composition on analysis: Co r^ 93.1, Ni=r 5.8, Fe = o.8, Cu:=o.2, Sirr o.i, and C=:o.3. The speci- 

 men was very brittle and broke in the lathe, and hence contained a surfaced joint held together by clamps during 

 the experiment. Referring to the columns, H, B, and fi have the same meaning as in the other tables, i" is the 

 magnetic moment per gramme, and / the magnetic moment per cubic centimetre. H and S are taken from the 

 curves published by Du Bois ; the others have been calculated using the densities given. 



Table 305. 



MAGNETIC PROPERTIES OF SOFT IRON AT 0° AND 100° C. 



Table 306. 



MAGNETIC PROPERTIES OF STEEL AT 0° AND 100= 



* " Phil. Mag." 5 series, vol. xxix. 



t The results in this and the other tables for forces above 1200 were not obtained from the ovoids above referred 

 to, but from a small piece of the metal provided with a polished mirror surface and placed, with its polished face nor- 

 mal to the lines of force, between the poles of a powerful electromagnet. The induction was then inferred from 

 the rotation of the plane of a polarized ray of red light reflected normally from the surface. (See Kerr's "Constants," 

 p. 292.) 



