Properties of' the Two New Fluids in Minerals. 125 



numerable cavities fitted for the purposes of observation. 

 After a little practice in splitting and preparing the speci- 

 mens, the patient observer will experience no difficulty in de- 

 tecting cavities of every variety of form, and in discovering 

 the fluid as it flows from the opened cavities over the planes 

 of cleavage. Mr Sanderson, lapidary in Edinburgh, has ob- 

 tained some of the finest specimens of these new fluids ; and 

 by cutting and polishing the topazes which contain them, he 

 has been enabled to show most of the phenomena to those who 

 are interested in such pursuits. 



1. On the Number and Arrangement of' the Fluid Cavities. 



In a former paper, I had occasion to mention, that, in a 

 specimen of cymophane about one-seventh of an inch square, 

 I counted 30,000 cavities. Although this statement occasion- 

 ed great surprise, yet it was too feeble to convey any idea of 

 their number. So minute are these cavities, that the highest 

 magnifying powers are often necessary to render them visible ; 

 and we might as well attempt to number the grains of sand 

 on the sea-shore, as to count these fluid cavities when they 

 appear in this minute state. 



The strata in which these cavities are arranged, are not so 

 closely related to the primary and secondary planes of the 

 crystals, as I formerly supposed. I have found them in al- 

 most every possible direction, and intersecting one another at 

 angles, which cannot be referred to any of the crystalline 

 forms of the mineral. In a specimen of quartz observed by 

 Mr Somerville, and now in the possession of Mr Sivright, 

 they are arranged in hollow groupes, somewhat like the cells 

 of a honeycomb ; and, when they are viewed by reflected light, 

 the corresponding faces of the cavities are seen to be parallel, 

 though the cavities have every possible variety of position 

 with respect to each other. In other specimens, they form 

 planes of variable curvature, and sometimes curved surtaxes 

 of contrary flexure ; and in one specimen, belonging to Mr 

 Sivright, the longitudinal cavities are grouped and inflected, 

 SO as to resemble a curled lock of the finest hair. In a speci- 

 men of blue topaz from Brazil, belonging to Mr Spaden, la- 



