370 THE YOUNG FARMER'S MANUAL. 



scope appears full of serrature more like the edge of a huge saw 

 than a razor. So with the finest cambric needle, whose point is 

 as delicate as it can be made, when viewed through a microscope 

 the point appears like a blunt, dull crowbar. When we attempt 

 to cut a very fine hair with a very sharp razor, by holding the 

 hair between the thumb and finger, with one end of the hair hang 

 ing free, we can perceive the serrature by the slipping or jerking 

 of the hair from one to another. . In the sickle the serrature may 

 be seen with the naked eye. In a scythe, and in many other 

 tools, we can feel them by drawing a finger along the edge, when 

 the tool has a good edge. When a grass scythe is in good order 

 the serrations are not as fine as they can be made, because if they 

 were the scythe would not be most effective. (See PUTTING 

 SCYTHES IN ORDER, 551.) 



529. Why may we not make a razor, or a knife blade, or any 

 other cutting instrument, out of a piece of cast or wrought iron ? 

 Why can we not make a needle or an awl out of a piece of wire? 

 Because there is not sufficient firmness and solidity between the 

 particles of such materials to retain their shape and position when 

 brought in contact with other substances. We have seen (see 

 WEDGES, Par. 344) that a piece of very tough and hard wood 

 always makes the best wedges. This holds good in respect to 

 edge tools : the cutting edge must be made of such material as is 

 capable of being made not only hard, but tough and hard. If 

 iron that is capable of being made very hard would make the 

 best edge tools, there would be nothing better than good cast- 

 iron ; because that can be made as hard as we can desire. But 

 such iron possesses no more tenacity than glass, and of course is 

 unfit for edge tools. ' If an edge tool were made of the very 

 toughest iron, it might appear to the naked eye to possess all the 

 qualities of a very effective tool. But when brought into use, 

 the edge would readily yield by bending and turning every way, 

 because the cutting edge lacks firmness and hardness in addition 

 to its toughness. And, more than these qualities already men 

 tioned, the serrations of the cutting edge of a tool made of either 

 wrought or cast-iron would be very coarse ; and if they possessed 



