8 Dr. Mac Culloch on Minerahgkal Hammers. 



It is unnecessary to dilate further on the advantages of this 

 form ; as it is, for all purposes of use, a sphere. From the ex- 

 tent of face, it is almost eternal ; and it is not difficult to con- 

 struct, by welding a ring of bar steel on a nucleus of iron. 



The drawings which accompany this communication, repre- 

 sent also the particular form of those hammers for trimming 

 or shaping specimens, which I have found, in practice, to exceed 

 all others. 



The ordinary trimming hammer has two cutting edges only, 

 one at each end, and placed in a reverse direction, or like an axe 

 and an adze. Doubtless, this answers its purpose, but not 

 equally well with the construction here represented. 



In that there are only two edges, and they soon wear, as these 

 hammers must be made of hard steel. In this there are, at 

 first, four edges ; and, as the handle may then be turned, there 

 are thus acquired four more ; so that each hammer of this con- 

 struction is at least as durable as four of the former. 



