1891-92.] Prof. Knott and Mr Shancl on Magnetic Strains, 85 
Not© on Certain Remarkable Volume Effects of Mag- 
netisation. By Professor Cargill G. Knott, D.Sc., and A, 
Shand, Esq. 
(Read May 16, 1892.) 
In June of last year one of us gave before the Society a short 
account of certain preliminary experiments on the volume effects of 
magnetisation.* These experiments had been made in Japan ; and 
the results obtained evidently called for a more thorough investi- 
gation. The facilities of the Physical Laboratory of Edinburgh 
University were kindly placed at our disposal by Professor Tait. 
Five tubes of Swedish iron, all cut from the same original bar 
but made with different bores, were prepared for study in much 
the same manner as formerly. Many experimental difficulties 
encountered us; and only now have these been satisfactorily over- 
come. For it must be remembered that the effect to be observed is 
very minute, and can be measured only in one way, viz., by the 
motion of the meniscus along the narrow capillary tube which is in 
connection with the iron tube, the whole being filled with fluid. 
But such an arrangement is obviously a very delicate thermometer ; 
and, as a matter of fact, we have seldom got the meniscus really 
steady. Generally it is moving at a rate which, though as inappre- 
ciable to the naked eye as the motion of an hour hand, is only too 
evident under the microscopic power necessary for the observation 
of the magnetic effect. 
To diminish the temperature effect upon the liquid contained in 
the tube, we used Professor Tait’s device of filling up most of the 
volume by a hollow glass bulb nearly the same length and width as 
the bore. But there still remained the effect of temperature upon 
the iron walls. At first it might be supposed that with the three 
substances, iron, glass, and liquid, it would be a comparatively easy 
matter by calculation to so adjust the size of the glass bulb to the 
* “On the Effect of Longitudinal Magnetisation on the Interior Volume of 
Iron and Nickel Tubes,” by Professor Knott, D.Sc., F.R.S.E., Proc. Boy. Soc. 
Edin., 1891. 
