paratively soft, and became harder as the outside was cut away.
The intense hardness of the diamond can be illustrated by the following experiment. On the flattened apex of a conical block of steel place a diamond, and upon it bring down a second cone of steel. On forcing together the two steel cones by hydraulic pressure the stone is squeezed into the steel blocks without injuring it in the slightest degree.
In an experiment I made at Kimberley the pressure gauge showed 60 atmospheres, and the piston being 3-2 inches diameter, the absolute pressure was 3-16 tons, equivalent on a diamond of 12 square mm. surface to 170 tons per square inch of diamond.
The use of diamond in glass-cutting I need not dwell on. So hard is diamond in comparison to glass, that a suitable splinter of diamond will plane curls off a glass plate as a carpenter's tool will plane shavings off a deal board. The illustration (Fig. 17) shows a few diamond-cut glass shavings. 92
