large crystals fresh from the mine. By way of safeguard against explosion some dealers imbed large diamonds in raw potato to ensure safe transit to England.
The anomalous action which many diamonds exert on polarised light is not such as can be induced by heat, but it can easily be conferred on diamonds by pressure, showing that the strain has not been produced by sudden cooling, but by sudden lowering of pressure.
The illustration of this peculiarity is not only difficult, but sometimes exceedingly costly difficult because it is necessary to arrange for projecting on the screen the image of a diamond crystal between the jaws of a hydraulic press, the illuminating light having to pass through delicate optical polarising apparatus and costly because only perfectly clear crystals can be used, and crystals of this character sometimes fly to pieces as the pressure rises. At first no colour is seen on the screen, the crystal not 106
