MORE CONCERNING MECHANICAL TOOLS. 177 



drawn to follow the fibre, should it lead inward. Suppose, however, 

 that in the progress of the work such a place has been reached as 

 would have so drawn the chisel inward. What will happen ? Either 

 the strength of the indrawing fibre will be so great that the work- 

 man will be unable to propel the tool, or, if not thus impeded, he 

 must by extra effort separate the fibre and so release the tool. This 

 separation, however, will not be by the process of cutting, but by 

 that of tearing, and shavings so torn off will have left their marks 

 in the roughnesses which attend the tearing asunder of fibrous 

 woods. Thus the tool will defeat the very object for which it was 

 designed. 



Now, what is it which so forcibly draws, or tends to draw, the tool 

 downward below the surface of the timber ? The forces in operation 

 are the hand of the workman and the tenacity of the fibre. If the 

 tenacity is greater than the power, the workman must stop. That 

 the tool cannot follow the direction of the fibre is clear, because the 

 front part of the wooden sole forbids the penetration ; but that it may 

 be brought to a standstill, or must tear off the fibre, is also very 

 clear. The mechanician has therefore to consider how to defeat these 

 tendencies, which, as now sketched, result from a collision between 

 the indrawing strength of the fibre and the power of the man to cross- 

 cut the fibre by the tool, or else to tear it asunder and leave the sur- 

 face rough. 



Since the tool, as now contrived, cannot efficiently cross-cut the 

 resisting fibre, and since that fibre has to be removed, the object 

 must be either to prevent such an accumulation of fibres as will stop 

 the progress of the tool, or to destroy the fibre piecemeal as it is 

 operative for hinderance. Both plans have been adopted. A consid- 

 eration of the former may prove introductory to the latter, which ap- 

 pears in almost all attempts to perfect this tool and its appended 

 contrivance. 



As the tool pi-ogresses, and the fibres become more and more im- 

 peding, it will be clear that a portion of this impediment results from 

 a condensation of the fibre in the mouth of the wooden box. The 

 more numerous the fibres admitted here, the greater will be the con- 

 densation. This state of affairs can be partially obviated by a nar- 

 rowing of the mouth of the plane ; such an act, of course, requires that 

 the introduced chisel should enter less deeply into the timber being 

 operated upon. Although thus abated, the cause is not removed, and 

 even if so far abated as to prove no real impediment to the workman, 

 yet the quantity of material removed on each occasion will be so 

 small that the tool becomes one for finishing work only, and not for 

 those various operations to which its present powers enable artisans 

 to apply it. 



To be the useful tool it is, the mouth must not be so narrowed, nor 

 the inserted chisel so withdrawn, that the shaving is thus the thinnest 



VOL. X. 12 



