* Its anlogy to these and other combustible bodies was inferred by Sir Isaac Newton, owing to the highly refractive power of the diamond; this has been subsequently proved; although as a combustible body it submits alone to the action of the oxy hydrogen blowpipe, before which it is dissipated in carbonic acid gas.

The high refractive power of the diamond has led to its employment for the construction of small lenses for single microscopes, because compared with glass leasee of the same focal length, the diamond requires much less curvature of surface, it therefore admits of the employment of a larger pencil of rays, and gives more light The ruby, sapphire, and garnet, havethe same properties in inferior degrees, but the heterogeneous structure of these jewels has caused their employment as lenses) to bo abandoned. See article Microscope, in the Penny Cyclopedia; also Pritchard' works on the Microscope.

The numbers upon the Scale of Chemical Equivalents for Diamond and Quarts have been very recently pronounced to be alike; this has opened a wide field for speculation.

In cutting diamonds, two stones are operated upon at once; they are cemented in the ends of two sticks, which are supported on the edges of a box three or four inches wide, rested against two pins as fulcra, and forcibly rubbed against each other; by which means they abrade each other in nearly flat planes and remove a fine dust called diamond powder, which falls through the fine holes in the bottom of the box, and is there collected.

The diamonds are lastly polished upon an iron lap or skive, charged with diamond powder, the stone being guided mechanically; it is fixed by soft solder in a copper cup, or dop, attached by a stout copper-wire to the end of the pincers, a flat board terminating at the other extremity in two feet, which rest upon a fixed support, the whole forming a long and very shallow triangular stool, loaded at the end near the stone. In the last two processes the stone is re-adjusted for producing every separate facet.* We will now proceed to the applications of the diamond as tools.

The invaluable instrument, the glazier's diamond, although employed for a considerable period, was for the first time investigated scientifically by Dr. Wollaston in 1816,† who pronounced its operation to depend upon a peculiarity of crystallization in the diamond, the facets of which are frequently round instead of flat, and therefore the edges are circular instead of straight. The rounded edge first indents the glass, and then slightly separates its particles, forming a shallow fissure, with a splitting rather than a cutting action, cutting action of the material being removed.*

* The reader will find an excellent account of splitting, cutting, and polishing, diamonds, read by the late Mr. Edmund Turrell before the Royal Institution, and published by him in Gill's Technological Repository, 1827, p. 1, etc. The subject is also noticed in Mawe's Treatise on Diamonds, 2nd Edition, p. 67.

† Set Transactions of the Royal Society, 1816, p. 265. Transcribed by Turrell with additions, at pp. 66 - 8, of Gill's Tech. Repos., 1827.

Fig. 61.

Topaz 8 Sapphire Ruby 9 Part 2 10043

62.

Topaz 8 Sapphire Ruby 9 Part 2 10044Topaz 8 Sapphire Ruby 9 Part 2 10045

* The primitive form of the diamond is that of a regular octohedron which is represented in fig. 61; it is like two square pyramids joined base to base; the four sides of the pyramids meet at the angle of 90°, their bases at the angle of 100° or thereabouts. Many of the diamonds merge from the form of the octohedron, into that of the sphere, or a very long egg, in which cases although a disposition to the development of the six points, each formed by the meeting of four surfaces, exists. they are curiously twisted and contorted. The Count de Bournon has published upwards of one hundred forms of crystallisation of the diamond, but the irregular octohedrons with round facets are those proper for glaziers' diamonds.

The extreme point of any diamond may be employed to scratch glass with a broad white streak, and detach its particles in a powder, but such glass will break with difficulty, (if at all,) through such a scratch; whereas the almost invisible assure, made when the rounded edge is slid over the glass with but slight pressure and almost without causing any sound, is that which produces the effective cut; and the cut or split thus commenced will be readily extended through the entire thickness of the glass, when the extremities of the sheet are bent with the fingers or appropriate nippers.

If we could obtain a diamond in the form of a circular button, the edges of which were turned to the angle of 90 or 100 degrees, it would be the perfection of the instrument, as there would be then no point to interfere with its action, and any fart of its edge might be used. But as the natural diamond, unaltered by the artisan, is always employed, it must be so applied upon the glass, that one of its curved edges bears upon the intended line of division of the glass, and with the extreme point just out of contact, this in so small an object, necessarily confines the position within very narrow limits.

The patent swivel diamond ensures the one condition, by placing the edge of the stone upon the line of the cut, and a few trials at different elevations, generally

70 to 80 degrees, will soon giro the other position. At the commencement a slight force is applied, until the stone appears to bite or hang to the glass; it is drawn steadily along, with but little pressure, and the good cut will be scarcely either seen or heard.

To show that the diamond possesses nothing in itself that should adapt it to cutting glass, beyond its peculiar form and hardness, Dr. Wollaeton succeeded with great labour in giving the same form to the ruby, the spinel ruby, topaz, and rock crystal, with all of which likewise he effected the cutting of glass, but they were of course far less economical than the natural angle of the diamond itself, which requires no such tedious preparation, and lasts very much longer.