538 [April 30, 



The author states that the results already obtained by this instru- 

 ment have been so satisfactory as to leave him no cause to regret 

 the time that has been devoted to, or the expense that has been 

 incurred in the construction of this truly beautiful apparatus. 



A full description of the instrument is introduced, with several 

 diagrams showing the construction and adaptation of the different 

 parts of the apparatus, and two drawings, one showing the general 

 appearance of the instrument when prepared for observation, and the 

 other representing it as seen when viewed from above. 



II. THE BAKERIAN LECTURE. " On the Direct Correlation of 

 Mechanical and Chemical Forces." By HENRY CLIFTON 

 SORBY, F.R.S. Received April 29, 1863. 



Perhaps it may be thought somewhat strange that a geologist should 

 undertake such a subject as the correlation of forces ; but the very 

 fact of my being a geologist has led to the investigations of which 

 I now purpose to give a short preliminary account. In studying 

 general chemical and physical geology, and especially in examining 

 the microscopical structure of rocks, I have for a number of years 

 been greatly perplexed with a class of facts which pointed both to a 

 mechanical and to a chemical origin. At first I attributed them either 

 to a mechanical or a chemical action, or to the two combined ; but in 

 most cases no satisfactory explanation could be given. At length, 

 however, facts turned up which altogether precluded any supposition 

 not involving direct correlation ; for they most clearly indicated that 

 mechanical force had been resolved into chemical action in the same 

 way as, under other circumstances, it may be resolved into heat, 

 electricity, or any other modification of force, as so ably described by 

 Grove in his work ' On the Correlation of Physical Forces.' 



The effect of pressure on the solubility of salts has already been 

 made the subject of speculation and experiment *, and a considerable 

 number of facts have been described, showing that pressure will more 



* Perkins, Ann. de China, et de Phys. vol. xxiii. p. 410. Sartorius von Walters- 

 hausen, Gottinger Studien, 1857. Bunsen, Ann. der Chem. und Pharm. 1848, 

 vol. hcv. p. 70. Favre, Comptes Rendus, vol. li. p. 1027. Thomson, Proc. Roy. 

 Soc.vol.xi. p. 473(1861). 



