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lliC Injiuencc of f\Ioleculav Coiistitutio)i and Tenipevciture on Mufjnetic 
Part IV.~ Further Applicatioris of the Molecular Field. 
Bij Major A. E. Oxi^ey, R.A.F., MA., D.Sc., Mackmnon Student of the 
Royal Society. 
Communicated hy Prof. J. W. Nicholson, F.R.S. 
Received May 1,—Read June 26, 1919. 
Contents. 
(1) Introduction.. 
(2) On the energy and ultimate tensile strength associated with crystalline media or gels 
(3) A comparison of the elastic constants of diamagnetic, paramagnetic, and ferro-magnetic 
crystalline media. 
(4) On the change of volume on crystallization interpreted as a magneto-striction effect of the 
molecular field.. 
(5) Further discussion of the nature of the molecular field. 
(6) On a magnetic theory of chemical combination. 
(7) On some anomalies of the Faraday effect. 
(8) Summary of conclusions. 
Rage 
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(1) Introduction. 
The present work is a continuation of that published in ‘ Phil. Trans., Eoyal Society,’ 
vol. 214, pp. 109-146, 1914 (Parts I. and II.) and vol. 215, pp. 79-103, 1915 (Part 
III.).* It will lead to clearness in the following development of the subject if a brief 
resume of these papers is given. At the same time, I wish to discuss one or two 
points in connexion with the views which have been previously advanced and tbe 
relation between mechanical and molecular theory. 
In Part I. the experimental evidence brought forward has justified the hypothesis 
of molecular distortion enunciated at the outset. We have thereby been led to 
regard the molecular contiguration of a material medium as a distorted one, and this 
applies particularly to a substance which is crystalline. The extent of this distortion 
is small, but is sufficient to account for the observed change of specific susceptibility 
which occurs on crystallization. Such change will naturally depend upon the 
particular crystalline symmetry assumed by the substance. 
The theoretical treatment given in Part II. is an attempt to account for the 
phenomena observed by extending the electron theory developed by Langevin so 
* For brevity, reference to these researches is given under Parts L, II., and III. 
VOL. CCXX. A 578. 2 M [Published, April 9, 1920. 
