HAMMERS AND PERCUSSION. i 9 



The only exception to this is to be found in the Moavs 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 sub- 

 si ances 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 up- 

 right 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 hesi- 

 tation, 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 pres- 

 ent 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 



