Page:Popular Science Monthly Volume 9.djvu/33

Rh and form of the handles, the angle at which these handles should intersect the axial line of the hammer-head, the position of the centre of gravity with respect to the intersection of this axial line, the length and elasticity of the handle. If the centre of gravity is not in the central line or longitudinal axis of the hammer-head, then there is a tendency to bring the hammer down on the edge of the face and not on the face. If this defective construction were great, the muscles of the wrist might not be strong enough to counteract the tendency. If the defective construction is slight, then the work is often marked with angular indents. Arrangements, too, may be required for modifying the intensity of the blow, while retaining the effects resulting from a heavy hammer where a light one would be inefficient.

It is curious to see how in the same trade the hammers are for different purposes made of different materials. The engineer, for example, uses hammers faced with steel hardened, the stone-breaker (or mineralogist) hammers faced with steel softened (or rather not hardened). Again, in another part of his progressive work, the steel hammer with which the engineer commenced his operations gives place to a bronze or copper one, and this is sometimes displaced by one of lead alloyed with tin, and the handle entirely discarded.



The plumber dismisses all these, and for direct action upon the material employed in his trade he uses a hammer of wood, discarding not only the material but also the form of hammers used in allied crafts. Indeed, one of his hammers (Fig. 7) serves a double purpose, for, if at one moment it is a hammer, at the next it is used as a swage. Fig. 9 is his ordinary hammer, but when carrying on his allied trade of a glazier, not content with this, even the handle (Fig. 10) is finished