36 Mr. S. Seaward's Description of an improved Gauge 



mica, of which there are some small plates interposed, even in 

 the substance of the girasol. This gangue contains, in the 

 interior of its substance, a considerable quantity of pale-blue 

 crystallized spinelle, among which, however, there are some 

 crystals of so deep a blue that they appear black. M. Les- 

 chenault only found this rock on the bank of a river seven 

 miles to the north-east of Candy, on the route to the province 

 of Fassagram, where he met with it in isolated masses. 



The sixth gangue of Ceylon spinelle, which is still more 

 particular, is a rock of a granitic aspect, in which the mica is 

 replaced by molybdena in small thin laminae. This rock is 

 principally composed of transparent granular felspar, and 

 of these laminae of molybdena. One may observe, besides, 

 some little plates of brown mica, which are thinly dissemi- 

 nated, and a great number of very pale-red crystals of spinelle. 

 This rock was found by M. Leschenault, seven miles to the 

 north-east of Candy, in the same district as the preceding, 

 and likewise in isolated masses upon the bank of the same 

 river. 



I may add to the description of these gangues of spinelle, 

 that of a seventh, which is the second of those I have de- 

 scribed in the paper on Corundum, printed in the Philosophical 

 Transactions for 1802. This gangue consists principally of 

 transparent felspar or adularia, pure in one part, and mixed 

 in the other with magnetic pyrites and a little carbonate of 

 lime. Some small crystals of spinelle are disseminated in it, 

 but more thinly than in the other gangue mentioned in the 

 same memoir. 



VII. Description of an improved Gauge for ascertaining with 

 Precisioti the Pressure of highly compressed Steam, Gases, 

 and Fluid Bodies. By Mr. Samuel Seaward. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 TJEItMIT me to offer you the accompanying description of 

 a gauge for measuring the pressure of highly compressed 

 fluids or gases, which I shall feel gratified by your introducing 

 into your valuable Magazine, if you consider it deserving of 

 that distinction. 



I am, gentlemen, yours, &c. 



3 Charles Street, City Road, Samuel Seaward. 



Jan. 14, 1824. 



Dcscrip- 



