2658 



Journal of Applied Microscopy 



lies between the extremes of divergence of the edge-band, as it waves or is sud- 

 denly bent in places from side to side (Fig 8). The differences of this virtual 

 thickness of edge therefore much exceeds, with the different hones, those of 

 the actual thickness above reported. 



Fig. 8. 



Again, this virtual thickness, or breadth of edge, ought to be adapted, in 

 honing, to the size of cells or texture of the material to be penetrated by the 

 tool. Thus, an edge like that prepared by Hone I would present a virtual 

 breadth of at least '23 microns, and would tend to crush rather than to penetrate 

 wood cells having a diameter of 11 microns, as in Willow, but would tend to 

 penetrate cells of 28 microns, as in Ash. 



III. TRANSVERSE OR CROSS SECTION, 



/. <?., from end view of the edge, when the line of the edge is directed toward the eye. 

 The actual ends of a chisel edge, however, have been so much rounded 



and worn, during grinding and honing, that they do not show a satisfactory 

 cross section. This can be best obtained by nicking a chisel 

 edge by sharp blow and mounting the fragment of edge, 

 thus struck out, in such a way as to present the cross section 

 to advantage. From such a minute splinter, a photomicro- 

 graph of the cross section was made (x 170, Fig. 7), which 

 shows the extremity of the cutting edge to consist of three 

 parts : 



Core. This is the wedge-shaped end of the interior 

 material of the steel part of the chisel, and presents a very 

 finely granular, crystalline mass, sparkling at the center of 

 the wedge. Below that point its thickness is from 30 to 50 

 microns (^i^j - -ji^ inch). 



Lateral Plate. This is the dark coating of tempered 

 steel on each face of the core, generally reaching about 38 

 microns (-^^^ inch) in thickness. It consists of finely fibrous 

 metal, with fibres normal to faces of the core, so that a fine 

 cross-fibration becomes apparent in the section, though not 

 distinguishable in the photomicrograph. 



Terminal Wedge. The two lateral plates unite toward 

 the edge-line to form this wedge, which, in the specimen 

 photographed, was 83 microns (-^^q inch) in length, from 

 their junction to the edge-line. The contour of the cross 

 section of this wedge, toward the edge-line, displays sig- 

 nificant modifications with the different hones which can be 



most clearly explained by means of a diagram (Fig. 9). 



Ifo/ie A. This cross section has been presented in the photomicrograph, 



Fig. y. 



