THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



■ 



[SIXTH SERIES.] 



JANUARY 1911. 



I. On Magnetic Testing. By JaMES G. GkaY, D.Sc, 

 F.R.S.E., Lecturer on PJiysics in the University of Glasgow, 

 and Alexander D. Ross, M. A., B.Sc, F.R S.E., Lecturer 

 on Natural Pliilosophy in the University of Glasgow *. 



THE methods in use for the experimental determination 

 of the magnetic constants of materials have been 

 brought to a high state" of perfection, and are thoroughly 

 understood by the majority of the investigators engaged in 

 carrying out research work in magnetism. But the pre- 

 cautions which must be taken in order that the results 

 yielded by application of these methods maybe accurate, are, 

 however, not so well understood. It is proposed in the 

 present paper to bring forward some facts bearing on this 

 point which have been brought to light by recent work 

 carried out in the Physical Institute of the University of 

 Glasgow. 



It is well known, and is pointed out in all the text-books, 

 that the magnetic properties of a test specimen depend on its 

 previous magnetic history. In this connexion Ewingt has 

 drawn attention to the very interesting fact that it is possible 

 to put a specimen — say, a long rod of iron having uniformity 

 of physical structure throughout its length — through a series 

 of magnetic operations such that it is left devoid of residual 



* Communicated by the Authors. 



t J. A. Ewing, " Experimental Researches in Magnetism," Trans. Boy. 

 Soc. clxxvi. p. 533. 



Phil Mag. S. 6. Vol. 21. No. 121. Jan, 1911. B 



