A scale of resistance to abrasion based on the following method: if specimens of different materials are mounted so that they present surfaces substantially in the same plane, and if the surfaces are subjected to a lapping operation with a properly selective abrasive, the harder materials will stand out in relief, whereas the softer ones will be cut or worn to a depth, depending upon their hardness. By averaging several readings, a scale of hardness was established by which the quantitative values of the hardness of various materials could be determined. On the Woodell scale, diamond has approx. 2 times the hardness of boron carbide, 3.5 times that of tungsten carbide, and nearly 5 times that of corundum.