in the Cavities of Minerals. 3 



sed about 10 times more than atmospheric air ; and that in the 

 naphtha cavity there was almost a perfect vacuum *, 



Such was the state of the subject, when my attention was 

 again turned to the examination of these cavities. 



In resuming this enquiry, I have been fortunate, not only in 

 possessing many excellent specimens of my own, but in having 

 the free use of an interesting collection, belonging to Mr Siv- 

 RIGHT of Meggetland ; and though I have employed only the 

 microscope, and the agency of heat and of light, I have been led 

 to results of considerable generality and interest. This physical 

 method of determining the properties of minute quantities of 

 matter, though often very difficult, and sometimes perplexing in 

 its manipulations, carries with it a degree of evidence not infe- 

 rior to that of chemical analysis ; while it possesses the advantage 

 of examining the substance in its original and unchanged condi- 

 tion, and may be applied, in many cases, where the chemist can- 

 not avail himself of any of the resources of his art. 



When the cavities in crystals are very large, which seems to 

 be the case principally when they contain water, the elegant me- 

 thod pursued by the distinguished President of the Royal Socie- 

 ty of London will afford precise results, and may be expected to 

 add greatly to our knowledge of this mysterious subject. Lea- 

 ving, therefore, this branch of the enquiry in the skilful hands of 

 Sir HUMPHRY DAVY, I have pursued the subject under a more 

 general form, and have studied the phenomena in their various 

 relations to the principles and methods of general physics. 



Philosophical Transactions, 1822, p. 367. 

 A 2 



