VOL. XLIII.] PHILOSOPHICAL TRANSACTIONS. 13 



parallelepiped stones, like those above, only smaller : also, after having broken to 

 pieces several little bits of slate, certain black spots were observed; which, by the 

 help of a microscope, he found to be real figured stones. 



Besides every one of these stones, as long as it remains in the rock, is always 

 found between two bundles or clusters of transparent fibres, of which generally 

 one is placed on the one, and the other on the opposite side. These bundles are 

 larger in great stones : those which seem, to the naked eye, to be but small black 

 spots, are yet accompanied by their bundles. 



The stone of the mountain of Barege, on which the asbestos grows, breaks also 

 constantly into fragments of the same figure. 



Having seen several productions of nature, in which we discover, that the 

 above figure so remarkably prevails, he was nevertheless surprised, when he found 

 the same figure in the sediment of the water of the Fontaine de Salut. He had 

 let a considerable quantity of the water of the mineral spring evaporate : there re- 

 mained a shining dust, in which he could distinguish nothing. He then looked 

 at it through a microscope ; and, among several crystals of a less regular figure, he 

 found many which were quite regular and well-shaped, with 6 faces, and oblique 

 angles. 



The waters of this spring contain no iron, as it is commonly believed. When 

 you put the tincture of galls in it, it grows neither black nor red : this mixture only 

 turns it a little, and makes it look whitish, after having stood some hours. 



When these waters are evaporated by a mild and equal heat, the small crystals 

 are found swimming on the surface; where they join, and form a film on the water; 

 some of which stick also to the sides and the bottoms of the vessel. Those 

 crystals which are formed first, are insipid ; but those which are produced towards 

 the end of the evaporation, are indeed of the same shape, but of a tart and saltish 

 taste. There remains yet a little of this matter, which cannot be reduced to very 

 regular crystals : it is of a very sharp and pungent savour, but has nothing of the 

 prevailing character of acid or alkali ; at least it makes no sensible impression on 

 blue paper. 



Mr. S. has also found at Bagneres, a particular aquatic plant, which he had 

 seen, for the first time, in the great basin of the boiling spring at Dax: it bears 

 neither fruit nor flower, as far as appears ; its substance is entirely composed of 

 small bladders full of air; its surface is like net-work or canvas; it grows only in 

 the hottest mineral springs. 



It is well known, that the greatest degree of heat in common water, is that 

 which it acquires by boiling ; that is, if water be put on the fire, it grows by de- 

 grees hotter and hotter, till it quite boils ; but after that, though there be ever 

 so much fire added, and it stand ever so long on it, it will never grow hotter than 

 it was on the first instant, when it began to boil. Hence the degree of heat of 

 boiling water is considered as fixed and invariable. 



