7. In 1841, Walter Hunt, of New-York, invented a double reciprocating nail engine, which is owned by the New-York Patent Nail Company. This machine works with surprising rapidity, it being capable of cutting five or six hundred ten-penny nails in a minute. One hand can tend three engines, as he has nothing more to do than to place the heated plate in a perpendicular position in the machine. 8. This manufacture includes, also, that of tacks and spikes; but since, in the production of these, the same general methods are pursued, they need no particular notice. The different sizes of tacks are distinguished by a method which indicates the number per ounce; as two, three, or four hundred per ounce. Spikes are designated by their length in inches, and nails by the terms, two-penny, three-penny, four-penny, ten-penny, and so on up to sixty-penny. [Illustration: CUTLER.] THE CUTLER. 1. Under the head of cutlery, is comprehended a great variety of instruments designed for cutting and penetration, and the business of fabricating them is divided into a great number of branches. Some manufacture nothing but axes; others make plane-irons and chisels, augers, saws, or carvers' tools. Others, again, make smaller instruments, such as table-knives, forks, pen-knives, scissors, and razors. There are also cutlers who manufacture nothing but surgical instruments. 2. The coarser kinds of cutlery are made of blistered steel welded to iron. Tools of a better quality are made of shear steel, while the sharpest and most delicate instruments are formed of cast steel. The several processes constituting this business may be comprised in forging, tempering, and polishing; and these are performed in the order in which they are here mentioned. 3. The general method of _forging_ iron and steel, in every branch of this business, is the same with that used in the common blacksmith's shop, for more ordinary purposes. The process, however, is somewhat varied, to suit the particular form of the object to be fashioned; for example, the blades and some other parts of the scissors are formed by hammering the steel upon indented surfaces called _bosses_. The bows, which receive the finger and thumb, are made by first punching a hole in the metal, and then enlarging it by the aid of a tool called a _beak-iron_. 4. The steel, after having been forged, is soft, like iron, and to give it the requisite degree of strength under the uses to which the tools or instruments are to be exposed, it is hardened. The process by which this is effected is called _tempering_, and the degree of hardness or strength to which the steel is brought is called its _temper_, which is required to be _higher_ or _lower_, according to the use which is to be made of the particular instrument.