HAMMERS AND PERCUSSION. 



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and form of the handles, the angle at which these handles should in- 

 tersect 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 modi- 

 fying 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 dif- 

 ferent purposes made of different materials. The engineer, for exam- 

 ple, uses hammers faced with steel hardened, the stone-breaker (or 

 mineralogist) hammers faced with steel softened (or rather not hard- 

 ened). Again, in another part of his progressive work, the steel ham- 

 mer 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. 



Fig. 7. 



Fig. 8. 



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OlQO 



Fig. 9. 



Fig. 10. 



Plumber's Hammers. 



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 



