224 Mr. H. Tomlinson. The Influence of [Mar. 31, 



than what one might have expected, is the very great distance to 

 which the point 1 descends at ordinary temperatures. It would be 

 interesting to compare the forms of these parts of the curve for 

 several liquids, and see whether there was any connexion between it 

 and the capillarity. 



III. " The Influence of Stress and Strain on the Physical Pro- 

 perties of Matter. Part III. Magnetic Induction." By 

 Herbert Tomlinson, B.A. Communicated by Professor 

 W. Grylls Adams, M.A., F.R.S. Received March 17, 

 1887. 



(Abstract.) 



The author lays before the Society the results of experiments 

 extending over a period of ten years on the effects of stress and strain 

 on the magnetic permeabilities of iron, nickel, and cobalt. 



Two methods were employed. In one the metal to be tested — 

 usually in the form of wire — was placed with its axis coincident with 

 that of a magnetising solenoid, in most cases of considerable length 

 as compared with the diameter of the wire ; round the central portion 

 of the solenoid was wrapped a secondary coil. A similar pair of 

 primary and secondary coils, with a similar piece of the same speci- 

 men of metal, was balanced against the first by means of resistance 

 coils, so that on closing the magnetising circuit no deflection was pro- 

 duced in a delicate Thomson's galvanometer suitably connected up 

 with the resistance coils and secondary coils. The alteration of mag- 

 netic permeability produced by stress was measured by the change 

 necessary to be made in the resistance coils in order to restore the 

 balance. 



In the second method the resistance coils were dispensed with, and 

 only a metal core used in one of the two pairs of solenoids which were 

 connected in series each to each. The arrangements were such that 

 the pairs of solenoids, when without any cores, balanced each other's 

 effects on the galvanometer, so that the deflections of the latter instru- 

 ment were due only to the magnetic permeability of the metal to be 

 tested. The alteration of permeability was in this case measured 

 by the change of deflection produced in the Thomson's galvanometer. 

 The second method was the one principally employed. 



In all cases, where it is advisable, the results are either given in 

 C.G.S. units, or data are supplied for reducing to these units ; more- 

 over, the author has endeavoured to separate, as far as possible, the 

 effects of stress on the permanent and on the temporary permeabilities of 



