102 RESEARCH WITH SIR LYON PLAYFAIR. 



In this lecture he " made it evident that an increase of 

 length in a bar of iron was produced by magnetizing it, and 

 therein also states his reasons for believing that, whilst the 

 bar was increased in length by the magnetic influence, it 

 experienced a contraction at right angles to the magnetic 

 axis, so as to prevent any change taking place in the bulk 

 of the bar. In the meantime this inquiry has been taken 

 up by De la Rive, Matteucci, Wertheim, Wartmann* 

 Marrian, Beatson, and others, whose ingenious experiments 

 have invested the subject with additional interest." Joule 

 now made a complete investigation, which he published in 

 the Philosophical Magazine. 



The other investigation which Joule was engaged upon 

 at this time was on " Atomic Volume and Specific Gravity," 

 which he undertook in conjunction with Sir Lyon Playfair. 

 Of this investigation, Joule says in a note to the reprint in 

 1885 :— 



" My work with Dr., now the Right Hon. Sir Lyon 

 Playfair, K.C.B., was commenced at about the time when he 

 occupied the post of Chemist to the Royal Manchester 

 Institution. It is only just to observe that the important 

 theoretical results arrived at with regard to atomic volumes, 

 are almost entirely due to him, while I took the principal 

 part in the experiments on the expansion of salts, the 

 maximum density of water, &c. My own individual work 

 was done at Oak Field House, Upper Chorlton Road, 

 Manchester."— Note, 1885, J. P. J. 



The amount of experimental work done in this investiga- 

 tion, which was completed in 1847, was very great; the 

 results being communicated in no less than seventeen papers 

 to the Chemical Society. 



