Page:Proceedings of the Royal Society of London Vol 1.djvu/145

Rh In order to raise her, Mr. W'hidbey had recourse to another Dutch vessel of 1063 tons burthen, and four ﬁghters of 100 tons each. In what manner he slung the frigate through the ports, and across the decks, and by proper purchases and other expedients first overcame the powerful effect of cohesion at the bottom, and then having ﬂoated her brought her safe into harbour, and completely recovered her, can only be clearly understood by perusing the paper, and at the same time inspecting the drawing which accompanies it. Mr. W'hidbey, at the end of his paper, acknowledges that he does not apprehend that there is anything new in the mode he has adopted in weighing this frigate, unless it be the expedient he had recourse to in order to remove the effect of cohesion : and he declares his opinion, that if a similar principle had been applied in the attempt made to weigh the Royal George, it would most probably have succeeded.

The new carbonate of lime here treated of was ﬁrst noticed in a group of hexahedral pyramidal crystals in Mr. Greville’s collection. The Count, observing that the exterior appearance of these crystals was very different from that which is peculiar to carbonate of lime, endeavoured in the ﬁrst place, in order to determine their nature by their conﬁguration, to reduce them, by splitting, into the rhomboidal form of this substance; but he soon found, to his surprise, that not only he failed in producing such a fracture, but that it was with the greatest difﬁculty he could break them into any regular form what- ever. Their hardness he found to be much greater than that of common carbonate of lime, being such as would scratch very easily the ﬂuates of lime, and even glass. Their speciﬁc gravity was 2912. They were colourless, and in general perfectly transparent. When heated they are slightly phosphorescent. They dissolve quickly, and with great effervescence, in nitric acid.

After various attempts, he found at length that these crystals would admit of being divided into two directions, tending to produce a rhomboidal tetrahedral prism. A great part of the paper is taken up in describing the angles produced by these fractures, and also the ﬁgures of all the different crystals he had opportunities of observing; which descriptions are illustrated by drawings.

This substance, upon further inquiry, does not appear to be very scarce, there being no less than twelve specimens in Mr. Greville’s collection, most of which came from Carinthia and Transylvania, and some from Scotland. The delicate stalactitical substance, hitherto known by the name of ﬁns ferri, belongs to this species of carbonate, of which the crystals, though ever so minute, have so singular a degree of hardness as to resist the common efforts of the ﬁngers to break them.

The matrix of this kind of carbonate is generally a brown oxide of