VOL. L.] PHILOSOPHICAL TRANSACTIONS* 97 



he supposed these waters might prove a more beneficial medicine than any others 

 of the ferrugineous kind, whose mineral contents are not so intimately commixed 

 with the aqueous fluid. 



But to sum up the evidence, which these experiments, taken all together, 

 afforded concerning the mineral ingredients of this spa : he thought they deter- 

 mined with some degree of certainty, that it contains 1 different principles of 

 iron, both of which are fixed. The one, which is the ochrous earth, is a true 

 minera ferri, and though it be a crude mineral, exists in the water in a very fine 

 and subtile form ; the other, which is the cremor or pellicle, whose parts are 

 also extremely attenuated in the water, appeared to be iron, not in its mineral 

 but in its metalline form, and when thrown up to the surface of the water, 

 showed itself like an extreme thin lamina of that metal. There seemed also to be 

 some small proportion of sulphur joined with the metalline cremor. The other 

 mineral ingredient, which entered into the composition of this spa, was a consi- 

 derable proportion of an aluminous salt, conjoined with a small quantity of a 

 light brown-coloured earth (probably a part of the matrix whence the salt is 

 formed), and still more intimately connected with some of the chalybeate parts of 

 the water, which were not separable from it eitlier by elixation or evaporation. 

 Whether these were saline or terrestrial, he could not determine. 



Then follow some reflections on the origin of steel waters, and particularly of 

 this spa (the Hartfell spa) ; the mineral impregnation of which he attributes 

 ti the adjacent strata of cliffery rock.* He concludes with this query; viz. 

 Whether or not from such a knowledge of the origin of mineral waters, we may 

 nov acquire (prepare) artificial ones of as great or perhaps greater medicinal uses 

 thai I those which are naturally produced ? 



XyilL On the State of the Thermometer at the Hague on the Qth of January 

 1757. Extracted from a Letter of Mr, Abraham Tremhley^ F.R.S. p. 148. 



I carefully observed the thermometer during the cold days, which we have had 

 this winter. I made use of the same thermometer with which I made my ob- 

 servations in 1 740, and for that purpose fixed it in the same place where it was 

 that year, viz. in a window directly exposed to the north, and open to a large 

 square. In 1740 Fahrenheit's thermometer was at 2 degrees below O. This 

 year, on the Qth day of January in the morning, it was at 3 degrees above O ; 

 that is, only 5 degrees higher than in 1740. 



XIX. Experimental Examination of Platina. By IV. Lewis, M.B., F.R.S. p. 148. 

 Paper V. The account of this extraordinary mineral, formerly read to this So- 



* Aluminous schistus and argillaceous stone, intermixed with martial pyrites. 

 VOL. XI. O ., , 



