1894 



THE MICROSCOPE. 



ner that the entire edge is always toward the front as 

 shown in Fig. 1. It is necessary that the mentioned thread 

 be formed on the concave side only, in order that the 

 amount ground off on the flat side be as little as possible. 

 Should the ground surface on the lower flat side be 

 too large, it will no longer be possible to obtain a per- 

 fect cut and the knife must be first of all reground on 

 the flat surface. As soon as the thread appears, the 

 knife is drawn equally to the right and left in the indi- 

 cated directions, see Figure No. 1, without exerting the 

 least pressure of the hand on the stone. After a uniform 



keenness has been obtained by light and continued sharp- 

 ening its quality can be judged by passing the edge of 

 the knife lightly over the moistened tip of the thumb, 

 and if the feeling that the knife will enter the skin be 

 apparent, it shows that a suflBcient keenness has been 

 obtained on the stone and that its perfection can then be 

 only attained by passing it over the strop. The knife 

 is then carefully cleaned with an old linen cloth held 

 between thumb and index finger, but in such a manner 

 that this cloth does not touch the edge. After cleaning, 

 it is lightly and carefully drawn across the strop with 



