Dr. Mac Culloch on Mineralogical Hammers. 7 



be directed to pay attention to the particular form of the ellip- 

 soid represented in the plate. If the longer diameter is made 

 much greater than the short one, for the purpose of securing 

 the necessary weight, the blade becomes too long, and it will 

 have the fault of the mason's hammer. If the face, again, is 

 made of a surface with too long a radius of curvature, it will 

 strike on too large a portion of the rock at once, and part of the 

 blow will be wasted. 



There are some minor conveniences arising out of the form of 

 this ellipsoid, which are worthy of notice. The steel cannot 

 easily be struck off the face, as happens at the sides of flat-faced 

 hammers wheq too much hardened ; nor does it yield and turn 

 over as when, in the same construction, they are too soft. The 

 directness of all the blows prevents over-hardened steel from 

 splintering ; and, if too soft, a second blow replaces the vacuity 

 which the first may have made. Thus also it retains a degree 

 of smoothness which those will know how to appreciate who 

 have suffered in their hands, their pockets, or their clothes, 

 from the ragged edges of a worn hammer. The durability of 

 such a hammer in practice, is in itself no small convenience ; as 

 a mineralogist is not always in a situation to get one replaced 

 or repaired, and of this superior durability, my own experience 

 has afforded ample proof. It is unnecessary for a breaking ham- 

 mer to be provided with a cutting edge, as the great weight pre- 

 vents any effectual use being made of it. That which is required 

 is best done by a lighter trimming hammer ; and thus also, the 

 breaking hammer, having two faces, has double the durability. 



I need scarcely add, that all handles should be made of ash, 

 or vine, if it can be procured, and somewhat of a conoidal form, 

 larger towards the hand, to prevent slipping ; and, that to ren- 

 der hammers portable, it is convenient to have a loop of wire 

 near the head, through which a strap may be inserted. This is 

 represented in the sketch. 



I have added another figure which I have, in practice, found 

 very convenient, where a great weight is required. It is an 

 oblate spheroid, with the polar surfaces cut away, as it is not 

 found easy by the makers to apply the steel to a whole spheroid. 



