DIAMOND MICROSCOPES were first suggested by Dr. Goring, and have been well executed by Mr. Pritchard. Previ ous to grinding a diamond into a spheri cal figure, it should be ground flat and parallel upon both sides, that by looking through it, as opticians try flint glass, we may see whether it has a double or triple refractive power, as many have, which would render it useless as a lens. Among the fourteen different crystalline forms of the diamond, probably the octahedron and the cube are the only ones that will give single vision. It will, in many cases, be advisable to grind diamond lenses plano-convex, both because this figure gives a low spherical aberration, and be cause it saves the trouble of grinding one side of the gem. A concave tool of cast iron, paved with _diamond-powder, ham mered into it by a hardened steel punch, was employed by Mr. Pritchard. This ingenious artist succeeded in completing a double convex of equal radii, of about one-twenty-fifth of an inch focus, bear ing an aperture of one-thirtieth of an inch with distinctness upon opaque ob jects, and its entire diameter upon trans parent ones. This lens gives vision with
a trifling chromatic aberration ; in other respects, like Dr. Goring's Amician Re Sector, but without its darkness ; its light is said to be superior to that of any com pound microscope whatever, acting with the same power and the same angle of aperture. The advantage of seeing an object without aberration by the interpo sition of only a single magnifier, instead of looking at a picture of it with an eye glass, is evident. We thus have a simple direct view, whereby we shall see more accurately and minutely the real texture of objects.