1893-94.] Prof. C. G. Knott and A. Shand on Nickel Tubes. 291 
for the steel tubes in the same field we obtained the total inductions 
proportional to 
590, 604, 570, 605, 593. 
In general, then, in low fields, the magnetic inductions in iron or 
steel tubes of the same material and external dimensions tend to 
equality, being independent of the size of the bore. In other 
words, the apparent average permeability in low fields is inversely 
as the cross section of the metal. 
In very high fields again, the magnetic moments are proportional 
to the cross section of the metal, or the apparent average permea- 
bilities tend to equality. 
These few results are here introduced to facilitate a comparison 
with the results for nickel. 
In our experiments four nickel bars were used, three of which 
were hollow. All were of the same length (47 cm.) and the same 
external diameter (4*2 cm.). The internal diameters and the areas 
of section of the metal were as follows : — 
Tube. 
Diameter of Bore in cm. 
Area of Section of 
Metal in cm.^. 
I. . 
2-543 
8-776 
11. . 
1-586 
11-879 
III. . 
0-692 
13-478 
IV. . 
0 
13-854 
Ko. I. nickel corresponds fairly well, as regards its various 
relative dimensions, with No. II. of Iron or Steel; and No. III. 
nickel corresponds with No. V. of Iron or Steel. The tubes were 
all cut from the same original bar of rolled nickel ; and the solid 
cylinder (No. IV.) from another bar rolled from the same original 
casting.* 
In high fields, the result obtained with the nickel is the same as 
* The long bars were supplied to order by Henry Wiggin & Co., Birming- 
ham, and the tubes were turned and bored by Aitken & Allan, Edinburgh. 
