Mr. A. Gages on the Study of some Metamorphic Rocks. 169 



As to the gravitating force, I do not presume to say that I 

 have the least idea of what occurs in two particles when their 

 power of mutually approaching each other is changed by their 

 being placed at diflFerent distances ; but I have a strong convic- 

 tion, through the influence on my mind of the doctrine of con- 

 servation, that there is a change; and that the phsenomena 

 resulting from the change will probably appear some day as the 

 result of careful research. If it be said that " 't were to con- 

 sider too curiously to consider so," then I must dissent : to 

 refrain to consider would be to ignore the principle of the con- 

 servation of force, and to stop the inquiry which it suggests, — 

 whereas to admit the proper logical force of the principle in 

 our hypotheses and considerations, and to permit its guidance 

 in a cautious yet courageous course of investigation, may give 

 us power to enlarge the generalities we already possess in respect 

 of heat, motion, electricity, magnetism, &c., to associate gravity 

 with them, and perhaps enable us to know whether the essen- 

 tial force of gravitation (and other attractions) is internal or 

 external as respects the attracted bodies. 



Returning once more to the definition of the gravitating 

 power as " a simple attractive force exerted between any two or 

 all the particles or masses of matter at every sensible distance, 

 but with a strength varying inversely as the square of the 

 distance," I ought perhaps to suppose there are many who 

 accept this as a true and sufficient description of the force, and 

 who therefore, in relation to it, deny the principle of conserva- 

 tion. If both are accepted and are thought to be consistent with 

 each other, it cannot be difficult to add words which shall make 

 " varying strength" and " conservation " agree together. It can- 

 not be said that the definition merely applies to the effects of gra- 

 vitation as far as we know them. So understood, it would form 

 no barrier to progress ; for, that particles at different distances are 

 urged towards each other with a power varying inversely as the 

 square of the distance, is a truth : but the definition has not that 

 meaning; and what I object to is the pretence of knowledge which 

 the definition sets up when it assumes to describe, not the par- 

 tial effects of the force, but the nature of the force as a whole. 



XXV. On a Method of Observation applied to the study of some 

 Metamorphic Rocks; and on some Molecular Changes exhibited by 

 the action of Acids upon them. 5// Alphonse Gages, M.R.I.A.* 



CHEMICAL analysis makes us acquainted with the consti- 

 tuents of rocks, and with the relative proportions in which 

 they are combined ; but, generally speaking, it can tell us no- 



* Communicated by the Author, having been read at the Meeting of the 

 BritiHh Association at Leeds. 



Phil. May. S. 4. Vol. 17. No. 113. March 1859. N 



