130 Mr. C. Hood on Changes in the Structure of Iron 



this assumption is never made by writers on the molecular 

 hypothesis, nor do I know that it is requisite ; at least, before 

 we can admit any argument based on it, we require to be 

 shown that it is actually or virtually made in the application 

 of the hypothesis against which the objection is raised. We 

 are not aware that any one has attempted to show how vi- 

 brations are generated: the question is how they are propa- 

 gated. Now in order to the propagation of a vibration it is 

 assuredly requisite that the force put in play by a relative 

 series of displacements, should, on each particle, act in the 

 line of the displacement. But this force is not a statical 

 force ; it is due to the actions of the displaced particles, and 

 dependent altogether on their displacement ; in a medium of 

 symmetry, and on the Newtonian law. (See my Memoir, 

 Trans. Camb. Phil. Soc. vii. p. 244.) The whole line of 

 argument, therefore, is inadmissible. No objection based on 

 the want of fulfilment of the conditions of vibration can be 

 valued, unless it distinctly recognises all those conditions. 



P.S. Since writing the above, Professor Braschmann of 

 Moscow has favoured me with a sight of his " Theory of 

 Equilibrium," which contains M. Mossotti's views. It is 

 written in Russ, but as the author promises me a copy of 

 the work with manuscript translations of some of the more 

 important passages, I hope in a future communication to pro- 

 fit by it. 



XXII. On some peculiar Changes in the Internal Structure of 

 Iron, independent of, and subsequent to, the several Pro- 

 cesses of its Manufacture. By Charles Hood, Esq., 

 F.R.A.S., $c*. 

 nPHE important purposes to which iron is applied have al- 

 -*■ ways rendered it a subject of peculiar interest ; and at 

 no period has its importance been so general and extensive 

 as at the present time, when its application is almost daily ex- 

 tending, and there is scarcely anything connected with the 

 arts, to which, either directly or indirectly, it does not in some 

 degree contribute. My object in the present paper is to 

 point out some peculiarities in the habitudes of iron, which 

 appear almost wholly to have escaped the attention of scien- 

 tific men; and which, although in some degree known to 

 practical mechanics, have been generally considered by them 

 as isolated facts, and not regarded as the results of a general 

 and important law. The circumstances, however, well de- 

 serve the serious attention of scientific men, on account of the 

 very important consequences to which they lead. 



* Communicated by the Author : having been read before the Institu- 

 tion of Civil Engineers, June 21, 1842. 



