4 Dr. Mac Culloch on Mineralogical Hammers. 



here adopted, a very small weight will thus be found adequate to 

 liroduce an effect which would be in vain expected frpm the same 

 acting- on a larger surface, or exposing a broad face of contact. It 

 is true, that, in the ordinary practice of masons and quarrymen, a 

 flat-faced hammer will detach a fragment, by communicating ' 

 motion to the whole of it, while the mass is comparatively at 

 rest ; but it will at the same time be recollected, with how little 

 effort blocks of granite and marble are split into two parts by 

 the comparatively slight blows given on the feather wedges, and 

 how hopeless an attempt it would be to separate such masses by 

 any practicable momentum applied to one half of them. The ob- 

 ject of the improvement here suggested is, as in other cases of 

 mechanics, to oeconomize power ; and though the arm of a 

 practised quarryman may render such expedients of compara- 

 tively little value to him, that of a mineralogist is seldom in a 

 condition to despise them. 



The ordinary mason's hammer, used for breaking rough stones 

 for rubble work, is formed of two frusta of pyramids on a com- 

 mon parallelogramic base, (to describe it mathematically,) and 

 the blade is of considerable length. The faces, it is true, are 

 thus somewhat narrow in proportion to their length, but yet 

 they present far too large a surface. This hammer is attended 



with another serious inconvenience, in consequence of the length 

 of the blade. If the blow is not given in such a manner that 

 the line joining the centre of gravity (or percussion) with the 

 point of impulse, is vertical to the surface of the stone struck, 

 the blow fails ; or, at least, a portion of the momentum is lost. 



