290 Proceeclings of Royal Society of Edinburgh. [sess. 
Note on Magnetic Induction in Nickel Tubes. By 
Professor C. G. Knott, D.Sc., and A. Shand, Esq. 
(Read June 18, 1894.) 
This paper is a continuation of a paper communicated to the 
Society in July of last year, the publication of which was withheld 
until the whole subject could be treated as one. In the previous 
paper we discussed the magnetic induction in Iron and Steel Tubes. 
These tubes, and the nickel tubes now under discussion, were con- 
structed primarily for the purpose of investigating their changes of 
volume under magnetisation but it seemed advisable to study as 
many of their magnetic properties as possible. 
In the meantime an interesting paper by Professor Grotrian on 
“ The Magnetisation of Hollow and Solid Iron Cylinders ” has been 
published in Wiedemann’s Annalen (Band 50, 1893). His tubes 
were considerably shorter than ours, and had much thinner walls. 
Many of the results obtained are, however, very similar. In a 
recent paper (Wiedemann’s Ann., Band 51, 1894) Dr H. du Bois 
discusses the most important of these results as illustrative of self- 
demagnetisation in magnetic bodies whose linear dimension is not 
very great compared to their breadth. 
This mode of regarding the subject is a very suggestive one, and 
seems sufficient as an explanation of the broad result that in weak 
fields the magnetic moment of a hollow bar is equal to the magnetic 
moment of a solid bar of the same length and breadth. Thus, with 
the six iron bars, five of which were hollow, we obtained in a field 
of 20 C. G. S. units total magnetic inductions proportional to the 
numbers 
665, 700, 702, 709, 703, 724, 
where the first refers to the tube of widest bore, and so on in order of 
diminishing bore to the last, which refers to the solid bar. Similarly 
* Ptoc. Boy. Soc. Edin., vol. xix. pp. 85, 249, 1892. 
