^{page 407 note *} See Page 1. of this Volume.

^{page 410 note *} This Cyanogen was made by Dr Turner. Mr Faraday, who first rendered it fluid, remarks “that its refractive power is rather less, perhaps, than that of water.” Phil. Trans. 1819, p. 286.

^{page 410 note †} This is a mean between Dr Wollaston's result and mine.

^{page 410 note ‡} This experiment is a very interesting one to the spectator; the new fluid, appearing quite transparent at a temperature of 60°, seems quite opaque when it is made to fill the tube, by a slight increase of temperature, as if it had become black by heat.

^{page 416 note *} Patrin, if we recollect rightly, speaks of crystals of Beryl in Siberia, which were so soft that they broke like a piece of apple.

^{page 418 note *} See Phil. Trans. 1816, p. 73.

^{page 418 note †} One of the largest vapour cavities that I have seen is one-twelfth of an inch every way. It is less than half full of fluid, and hence it is driven into vapour by heat. During the precipitation of the vapour it becomes perfectly opaque.

^{page 419 note *} In Fig. 4. of Plate XIX, I have represented another vapour cavity, which is remarkable for having a very small portion of the expansible fluid, and also, for having several crystalline forms within the dense fluid.

^{page 423 note *} Some of the fluids in quartz seem to be entirely gaseous, while in sulphate of barytes the fluid appears to be the mineral itself in a fluid state; see p. 425. and note on p. 427.

^{page 424 note *} Mr William Nicol, Lecturer on Natural Philosophy and Chemistry, has shewn me some fine specimens of Amber containing cavities. The inner surface of these cavities is rough, like finely ground glass, and many of them contain a fluid with a moveable globule of air. In a specimen of calcareous spar, in the possession of Mr Sanderson, there is a fluid cavity about two inches long, an inch wide, and one-eighth of an inch deep.

^{page 425 note *} These balls are of the same size as the seeds of Lycopodium, which amount to 32 parts of Dr Young’s eriometrical scale. Their diameter is therefore = th part of an inch.

^{page 425 note †} I have since opened several of these cavities by the blow of a hammer. In a second or two the fluid was entirely gone, without leaving a trace of its existence behind. The spherical balls remained in the cavities. They were not acted upon either by the muriatic or the sulphuric acids.

^{page 427 note *} Since this Paper was written, Mr William Nicol has shewn me a very remarkable specimen of Sulphate of Barytes, with fluid cavities of the same general character with those which I described in my former paper (Trans, vol. x. p. 36.), but much larger than any which I had seen. Upon grinding down on a dry stone, one of the faces of this specimen, the largest cavity burst, and discharged its fluid contents through the fissure upon the ground surface of the specimen. The fluid lay in drops of different sizes along the line of die fissure, and in this condition Mr Nicol put it into his cabinet. Upon looking at the specimen about twenty-four hours afterwards, each drop of fluid had become a crystal of Sulphate of Barytes. These crystals had the primitive form of the mineral.

This very curious fact is analogous to the uncrystallised water in the ice-cavities mentioned above, the crystallisation in both cases being prevented by pressure. When that pressure was removed, a portion of the water and the fluid sulphate of barytes were immediately crystallised. Mr Nicol distinctly remarked, that the crystals occupied as much space as the drops of the fluid; so that the crystals of sulphate of barytes were not deposited from an aqueous solution, but bore the same relation to the fluid from which they were formed, as ice does to water.