Endothermic Reactions effected by Mechanical Force. 351 



the example worked in the paper referred to*. We have 

 for a A the determinant 



1 -8 -9 



■8 

 •9 



1 



for — , -r-, -£, &c, respectively the values of corresponding 



minors, viz. '35, —'08, — '26, &c, and, for -r-, lx'36 — 'Sx'OS 



-•9 x '26 = *062. Dividing -36, &c, by '062 we obtain the 

 same values for the coefficients as those reached in the paper 

 referred to by a more circuitous route: viz. p 1 = 5 , 806, &c. 

 The saving of trouble in the case of four variables f is sub- 

 stantial. 



AU Souls College, Oxford. 



XXXVII. On Endothermic Reactions effected by Mechanical 

 Force. {First Part.) By M. Carey Lea %. 



IN a previous paper the effects of pressure on the silver 

 haloids were described. These salts were readily black- 

 ened and so gave evidence of partial reduction. That inves- 

 tigation was undertaken with the object of bringing into 

 complete harmony the effects upon these haloids of the differ- 

 ent forms of energy. It had been previously shown with 

 respect to all the other forms of energy that a slight impres- 

 sion made upon the haloids caused an effect not visible to the 

 eye but capable of indefinite increase by the application of a 

 reducing agent. Also it had been shown in the case of me- 

 chanical force that a slight application would cause an invisible 

 effect which could be rendered evident by the application of 

 a reducing agent. It seemed to follow almost necessarily 

 that a powerful application of the same agent would bring 

 about an effect visible to the eye. Experiment proved this to 

 be the case. 



It next appeared worth while to examine whether the same 

 agent, mechanical force, would not be capable of bringing 

 about analogous chemical changes in other compounds. For 

 the nature of these changes was something quite different from 

 anything that had been previously described. In Prof. Spring's 

 well-known investigation, combination was brought about 



* Phil. Mag. 1892, xxxiv. p. 196. 

 X Communicated dv the Author. 



t Ibid. p. 202. 



