38 DR BREWSTER on the Existence of Two New Fluids 



It is unnecessary to extend these details to all the artificial 

 crystals enumerated at the beginning of this paper, as I have 

 not observed in them any phenomena different from those which 

 have already been described. 



There is another class of cavities which require to be studied 

 with some attention, namely, those which are entirely full of 

 fluid, or entirely empty. Mr SIVRIGHT first observed cavities in 

 the diamond *, and in garnet ; but, though I have examined 

 them in various specimens, I have not been able to determine 

 whether they are entirely filled with fluid, or are entirely emp- 

 ty. I have found cavities of a similar kind in cinnamon-stone, 

 where they are beautifully crystallized, in sulphate of Strontian, 

 in sulphur, in analcime, and in chabasie ; but I observed no ap- 

 pearance of air-bubbles, and have no certain evidence that they 

 contain a fluid f . 



It would be improper to conclude this paper, without noti- 

 cing the relations which are supposed to subsist between this class 

 of phenomena and the two contending Geological Theories. 

 The existence of highly rarified gas in the cavities of crystals, 

 has been regarded by the distinguished President of the Royal 

 Society of London, as " seeming to afford a decisive argument in 

 favour of the igneous origin of crystalline rocks ;" and the " fact 

 of almost a perfect vacuum existing in a cavity containing an ex- 

 pansible but difficultly volatile substance," (as naphtha), he like- 

 wise considers as highly favourable to the same theory. The 

 discovery of compressed gas in similar cavities might have been 

 regarded as neutralizing, in some degree, the first of these argu- 



See the Edinburgh Philosophical Journal, vol. iii. p. 98., for an account of 

 the polarising structure which sometimes exists round the cavities in diamond. 



+ This point may be easily determined by grinding the specimens, and exa- 

 mining the light reflected at the surfaces of the cavities. 



