38 SALMON FLIES 



trate deeply, though it penetrates easily (see 

 Fig. 4). 



As soon, however, as the blade of the 

 chisel is inclined so that it ceases to shave 

 off parings, but bites deeper and deeper 

 into the wood and jambs, then we have a 

 representation of a hook point with a large 

 angle of impact. Such a point not only 

 engages at once, but penetrates deeply, and 

 the larger the angle of impact the deeper 

 (within certain limits) will be the penetration, 

 but the less easy the penetration (see Fig. 5). 



Finally, the blade may be so inclined that, 

 though the bevelled surface is still uppermost, 

 it does not bite at all, but merely scrapes along 

 the surface of the wood. In this case it repre- 

 sents the point of a hook which has a very 

 large angle of impact in fact, almost a right 

 angle. It will neither engage nor penetrate, 

 and we have the same result observed in our 

 first illustration, though produced by totally 

 different causes (see Fig. 6). 



Though it by no means disposes of the 

 question, I think that the above homely illus- 

 tration will serve to indicate the principles to 

 observe and the features to avoid in a hook. 



