The only exception to this is to be found in the blows given to minerals which are to be cleft, and not crushed. In their case it is desired to give only such a blow as shall accomplish the cleaving; any surplusage of energy, if expended on the material, would, of course, produce fractures over and above the required cleavage. Provision must be made for the dissipation of this superfluous energy, and it is done by placing the mineral in an elastic holding, the nature of the required elasticity being determined by experience, as different substances require different elasticities in the supports by which they are held for cleavage. Illustrations of the principle here enunciated are seen in the breaking of stones on the highway, where the elasticity is transferred from the mineral support to the handle of the hammer; also in the flaking of flints, where the elasticity is obtained by holding the mineral in the hand and supporting it on the knees. The splitting of the diamond is a case where these principles and considerations claim the greatest care.
The anvil used by the diamond-splitter is of wood, in shape not unlike a ninepin, but tapered at the lower end so as to be placed upright in a coned hole in a small block of lead. On the head of the ninepin is a flat, on which, by means of cement, the diamond to be split can be firmly fixed. Placed here so that the plane of intended cleavage shall be vertical when the wooden anvil is in the lead block, a deep scratch is made by a second diamond, in which scratch the edge of the splitter's chisel is to be planted. The diamond-splitter's chisel is very like an old razor. This chisel the workman holds in his left hand, in his right he holds that which is his hammer. The hammer is a plain steel rod, about eight inches in length, and tapering from about half an inch diameter in the middle to three-quarters of an inch at the end. The very construction of this peculiar hammer gives the operator a large range for precise and graduated blows; within certain limits he can most carefully arrange that the path of the centre of percussion, the place of impact, the line bisecting the angle of his razor-like chisel, and the expected plane of cleavage of the diamond, shall coincide; hence, with great coolness and the absence of all hesitation, he gives a blow, upon the effect of which many hundreds of pounds may depend.
In dealing with hammers—including under that term for the present purpose axes, hatchets, adzes, and picks—the following question claims consideration: What power or energy is in a hammer of known weight, moving at a known velocity, if brought to a state of rest by impact on a block? Another question also suggests itself: Can this impact effect of a hammer be converted into simple pressure, and be stated as a load or weight placed, where the impact was requisite, to produce the same effect as the impact did? If the mode of solving the first question can be made clear, then the answer to the second can be easily obtained. The measurable elements which affect the
