28 Mr. Carl Barus on the 



at identical stress-points needs not be in the same chemical 

 condition while stress is being removed, in which it was when 

 stress was being applied ; for there will be certain groups of 

 particles, uniformly distributed throughout the solid, which 

 during the " stress on " phase pass from a first molecular con- 

 dition to second, and which, in virtue of the volume-lag, do not 

 regain their original state at identical pressures of the " stress 

 off'" phase. The march in the two cases is not a symmetrical 

 one. This I take to be the inherent nature of the phenomena 

 studied by Cohn*, Warburg f, and others, and to which 

 Ewingf, after much original research, has given the generic 

 name hysteresis. In my note I pointed out the important 

 bearing of the volume-lag on the molecular behaviour of 

 matter §, though I have yet to specify my views in detail. 

 The occurrence of hysteresis, therefore, implies a favourable 

 molecular mechanism of the kind indicated, and one would not 

 expect to find it at once in all substances. 



Conformably with the above, the interpretation given by 

 Mr. C. A. Carus-Wilson || of his important discovery (to 

 which I alluded in a former paper), is much more than an 

 analogy. 



27. Warburg and Ewing have proved that hysteresis is not 

 only associated with mechanical stress, but may be very 

 clearly evoked by magnetic stress. Curiously enough, the 

 evidence in favour of the views expressed in § 26 is here 

 directly forthcoming. Remsen'sIF discovery of the chemical 

 influence of the magnetic field, additionally substantiated as 

 it now is by the ingenious experiments of Rowland and Bell **, 

 proves beyond a doubt that magnetic iron is more electro- 

 negative than unmagnetic iron. Conformably with the above 

 paragraphs, I therefore infer that this phenomenon is to be 

 interpreted as directly evidencing a chemical difference be- 

 tween magnetic and unmagnetic iron, and as such I consider 

 it an exceedingly important step towards an ion theory of mag- 

 netism |f. Thus the occurrence of the chemical difference in 



* E. Cohn, Wied. Ann, vi. p. 388 (1878). 



t Warburg, Wied. Ann. xiii. p. 141 (1881). 



X Ewing, Phil. Trans, ii. p. 545 (1885). 



§ American Journal, xxxviii. p. 408 (1889). 



|| Carus-Wilson, Phil. Mag. xxix. p. 200 (1890). 



5[ Remsen, American Chemical Journal, iii. p. 157 (1881). 



** Rowland and Bell, Phil. Mag. [5] xxvi. p. 105 (1888). 



tt I 11 ' Nature ' (xli. p. 370, 1890) I pointed out that closed helical paths 

 of molecular dimensions, each consisting of a right- and a left-hand screw- 

 thread, with their ends joined, can be generated by the symmetrical 

 interpenetration of two congruent Bravais nets. I inferred that electrical 

 charges urged along and around the said closed helical paths by the action 



