The Philosophical magazine; a journal of theoretical, experimental and applied physics . e smell of soot. When placed upon a plate of glass itcoiild be drawn along like the white of an egg, or the vitreoushumour of the eye. When dried, it left a transparent matterlike amber. This matter had no double refraction. When ex-posed to heat under the blo^^7)ipe, it became of a fine orange-redcolour. It did not burn, but by a continuance of the heat itbecame black and disappeared. In a very fine specimen of amber, belonging to the late W. , Esq., and of the size shownin the annexed diagram, t
The Philosophical magazine; a journal of theoretical, experimental and applied physics . e smell of soot. When placed upon a plate of glass itcoiild be drawn along like the white of an egg, or the vitreoushumour of the eye. When dried, it left a transparent matterlike amber. This matter had no double refraction. When ex-posed to heat under the blo^^7)ipe, it became of a fine orange-redcolour. It did not burn, but by a continuance of the heat itbecame black and disappeared. In a very fine specimen of amber, belonging to the late W. , Esq., and of the size shownin the annexed diagram, there wasa large oblong cavity ah^ in whicha fluid with its surface concave stoodat the level mn. The fluid was sosluggish, or probably viscid, that incold weather it required to be shakento make it move to the end A by in-verting it; but in warai weather(64° Fahr.) it moved with great facility. The extremity h of the cavity was sonear the surface of the specimen, thatI durst not make any experimentsupon the fluid by heating it lest the * Edinburgh Transactions, vol. x. p. 424, Account of a remarkable Fluid Cavity in Topaz. 235 cavity should burst. I founds however, that it was not veryexpansible by heat; and that it was so evaporable, thac at ordi-naiy temperatures the sides of the cavity were covered withvapour, whose particles or small globules were about the yi^dthof an inch in diameter. St. Leonards College, St. Andrews,February 28, XXXVIII. Account of a remarkable Fluid Cavity in Sir David Brewster, , , , , and Associate of the Institute of France^. THE remarkable fluid cavity in Topaz which I propose todescribe is shown in the annexed diagram. The cavityitself is of a very irregular form; its greatest length, AB, being
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