and Laboratory Methods. 2661 



lateral plate has led Mr. Waterhouse to the conclusion " that the superficial film 

 was homogeneous." By study of the side fracture of that film, however, under 

 the higher magnification obtained by length of camera, I could readily distinguish 

 the cross fibration to which I have referred ; the superficial film which he studied 

 was made up of the minute ends of these fibres. The core of the cutting edge 

 is shown to consist of hardenite cells in a meshwork of cementite. 



RESUME. 



To sum up these observations in the reverse Oider in which they have been 

 recorded, and so far as it seems safe to generalize from the limited series of experi- 

 ments, the following appeir to be the effects of successive application of coarse 

 to fine hones to the edges of such a tool : 



First, the effect of a coarse hone is to produce a roughly rounded thick edge, 

 more or less deeply indented, waving along its line both vertically and laterally, 

 and deeply scratched and nicked in places into rather angular teeth. 



Its faces are also deeply scratched, the pair nearest the edge inclined at a 

 wide angle, with several others below producing a series of inclined shoulders. 

 Much of this irregular attrition has been undoubtedly caused by isolated grains, 

 loosened from the coarse hone. 



Second, the effect of a hone of medium grain is to produce a much thinner, 

 straighter and more uniform edge, with finer scratches and serration. The faces 

 nearest the edge present a low wedge, with smaller angle than before, and the 

 secondary faces or shoulders occur in much smaller number. 



Third, with a fine hone the results approximate the properties desirable in a 

 wedge of most efficient penetration, viz.: only two, continuous, terminal planes 

 at a small angle and without shoulders ; a thin and nearly straight edge, so 

 feebly scratched as to show but a minute and rounded serration and almost pol- 

 ished faces on sides of the wedge. 



In conclusion, I have yet to refer to the surprising softness and flexibility 

 of the true edge of the wedge, that part which reaches beyond its stiff core. It 

 is illustrated by the sudden indentations and bendings noted on both the verti- 

 cal and the horizontal sections, by the split shown at the extremity of the wedge 

 in the photomicrograph (Fig. 7), and by the actual curling of the metal, observed 

 in many cases under a light blow. This would probably indicate a loss of the 

 rigidity or stiffness once acquired during tempering. Can this be due to the 

 high temperature of the thin wedge, occasioned by friction, during the process 

 of honing? If so, it may be suggested that it might be desirable, at least for 

 tools of the higher class, worthy of the additional time and labor, to renew the 

 original temper of the terminal wedge by a second and local tempering, after the 

 honing has been completed. 



It is also probable that the finish of the edge of a razor upon a strop or of a 

 microtome-knife upon plate glass is effective, not merely by removal of remnants 

 of feather-edge, but by straightening the line of the softened and flexible margin 

 of the terminal wedge. Alexis A. Julien. 



Columbia University. 



