Dr. Mac Culloch on Mimralogical Hammers. 5 



Nor is the missing of a blow attended with impunity ; as the 

 length of the lever afforded by the blade, twists the handle in 

 the hand, and injures the wrist if too strongly grasped, as it 

 always will be by an inexpert practitioner. The mineralogical 

 hammer generally in use, is not, it is true, so long or narrow as 

 that used by masons ; but, having a broad flat face, it is a feeble 

 instrument, and produces a small effect in proportion to its 

 weight; while it cannot be increased in size so as to compensate 

 this defect, as it becomes inconvenient to carry, and requires too 

 much strength to give it the requisite velocity. 



The construction by which these defects are remedied, and 

 the greatest effect produced with the least possible weight and 

 strength of arm, is that where the face of the hammer is round, 

 or spheroidal. Theoretically, an obtuse wedge would, perhaps, 

 be generally preferable ; but it is scarcely possible to give the 

 blow in such a manner that the centre of percussion should fall 

 in the true line ; and, in such a form, the slightest deviation 

 causes the blow to be wasted. A hammer in the form of a 

 sphere, would, indeed, ensure the effect of every blow, but it is 

 very difficult to steel such a figure all round, and it cannot be 

 made all of steel, since it will not stand without a centre of iron. 

 Besides, with a weight of three and a half or four pounds, the 

 surface of the sphere becomes somewhat less curved than is con- 

 venient for making the impulse on one point. 1 have, therefore, 

 preferred the form of an ellipsoid, and the particular figure will 

 be better understood from the accompanying drawing, than from 

 any description. 



