1891-92.] Prof. Knott and A. Shand on Magnetic Strains. 249 
On the Volume Effects of Magnetisation. By Prof. 
Cargill G. Knott, P.Sc., and A. Shand, Esq. 
(Read July 4, 1892.) 
{Second Note.) 
In a previous communication (see page 85) the remarkable changes 
of capacity of an iron tube when magnetised were described. In the 
present note it is proposed to record a few of the more striking results 
since obtained. 
The main object was to compare the volume changes in the 
interior of five tubes of Swedish iron, similar in every respect, 
except in size of bore, and subjected to the same magnetising forces. 
The tubes were distinguished by number. They were cut from the 
same original bar, and were as nearly as may be of the same length 
and external diameter. When prepared for experiment, each tube 
was closed at the originally open end by a screw-stopper, through 
which projected a fine capillary glass tube which was in connection 
with the interior volume. The volumes and internal radii of the 
various tubes were 
as follows : — 
Tube. 
Volume of Bore. 
Radius of Bore. 
I. 
344’83 cub. cm. 
1*60 cm. 
II. 
223*40 
1*28 „ 
III. 
127*41 „ 
•965 „ 
IV. 
67*70 
•70 „ 
V. 
18*81 
•35 „ 
The external diameter of each tube was 3 ’84 cm. 
In every case the dilatation due to magnetisation was obtained by 
dividing the measured change of volume by the corresponding total 
volume of the bore. 
One peculiar feature which was dwelt on in the previous note 
was the manner in which Tube I. behaved as the field was taken 
larger and larger. In very small fields there was jpositive dilatation 
which, however, soon changed to negative^ and continued so till 
about field 150, when it became positive again. This phenomenon 
of the initial positive dilatation was found to exist in the other 
tubes as well. But a careful study of all the circumstances showed 
that its existence depended on the previous magnetic history of the 
