2656 



Journal of Applied Microscopy 



up, with edge horizontal, on a level with the eye. The following observations 

 were made : 



Ho7ie A. The surface of the edge (Photomicrograph, x 280, Fig. 3), held in 

 that position, was found to be nearly plane and approximately horizontal, /. e., 

 level to slightly rolling. The projections of the cross-ridges or teeth, compara- 

 tively few, low and rounded. 



Hone VV. The surface of the edge shows a low wedge with central line, 

 which in places sinks down to a level surface. In examining a considerable 

 part of this surface, the teeth are found to be somewhat more numerous than 

 with Hone A, and more irregular both in form and size. 



Hone I. The surface of the edge was found to be somewhat rounded, with 

 great irregularities, deeply scratched, rough, and occasionally indented, though 

 level along short spaces. The teeth (Figs. 5 and 6) were many, angular, and 

 irregularly scattered, sometimes becoming actual deep nicks in the edge. 



Fig. (3. 



It may be necessary to add, in explanation, that under sufficient magnifying 

 power, the so-called edge of a cutting tool, however keen, always displays, unless 

 viewed exactly in profile, an actual flat, rough or rounded surface of varying 

 breadth, according to the attrition during sharpening it may have experienced. 

 In most of my photomicrographs it becomes visible, through a slight obliquity 

 of position from the exact vertical section. 



Any notable serration of edge, resulting from wear or from imperfect honing, 

 is subject to objections which cannot be removed by mere honing. First, the 

 increase of length of edge-line and, therefore of frictional resistance to penetra- 

 tion ; this can be better appreciated by imagining an exaggerated serration by 

 which the length of edge might be doubled, or more. Second, the increased 

 tendency to form " wire " or " feather-edge " on honing a serrated edge. Third, 

 the feeble penetration of the embayments or bases of the nicks, during cutting 

 of material, and their tendency to accumulate refuse debris. 



On the other hand, in tools used for a drawing movement, with some 

 rapidity, on softer materials, a certain degree of minute serration in the edge 

 may be adapted to corresponding inequalities of resistance in the material cut, 



