The rolling machines through which the ingots are passed are adjustable, the space between the rollers being governed by the operator. About two hundred ingots are run through per hour on each pair of rollers.
When the rolling is completed the strip of metal is about six feet long. As it is impossible to roll perfectly true, it is necessary to “draw” these strips, after being softened by annealing. The drawing benches resemble long tables, with a bench on either side, at one end of which is an iron box secured to the table. In this are fastened two perpendicular steel cylinders. These are at the same distance apart that the thickness of the strip is required to be. It is drawn between the cylinders, which reduces the whole to an equal thickness.
These strips are now taken to the cutting machines, each of which will cut 225 planchets per minute. The press used consists of a vertical steel punch. From a strip worth $1,100 about $800 of planchets will be cut. These are then removed to the adjusting room, where they are adjusted. After inspection they are weighed on very accurate scales. If a planchet is too heavy, but near the weight, it is filed off at the edges; if too heavy for filing, it is thrown aside with the light ones to be remelted.
The planchets, after being adjusted, are taken to the coining and milling rooms, and are passed through the milling machine. They are fed to this machine through an upright tube, and as they descend are caught upon the edge of a revolving wheel and carried about a quarter of a revolution, during which the edge is compressed and forced up. By this apparatus 560 nickels can be milled in a minute; for large pieces the average is 120.
The massive but delicate coining presses coin from 80 to 100 pieces a minute. These presses do their work in a perfect manner. After being stamped the coins are taken to the coiner’s room. The light and heavy coins are kept separate in coining, and when delivered to the treasurer they are mixed in such proportions as to give him full weight in every delivery. By law, the deviation from the standard weight, in delivering to him, must not exceed three pennyweights in one thousand double eagles.
The coinage of the United States mints since the organization of the government has amounted to nearly 6,000,000,000 pieces, valued at over $4,000,000,000.
How does a Bird Fly?
The wing of a bird is an elastic, flexible organ, with a thick anterior and a thin posterior margin; hence the wing does not act like a solid board, but is thrown into a succession of curves. When a bird rises from the ground it leaps up with head stuck out and expanded tail, so that the body is in the position of a boy’s kite when thrown up. The wings are strongly flapped, striking forward and downward, and the bird quickly ascends. It has been shown that the wing describes a figure 8 in its action, the margin being brought down so that the tip of the wing gives the last blow after the part next the trunk has ceased to strike; hence, standing in front of a bird, the wing would be divided into two, the upper surface of one-half and the lower surface of the other being visible at the same time. These portions are reversed when the wing is drawn back and towards the body, before beginning another stroke; but it will be observed that during retraction the wing is still sloped, so that the resemblance to a kite is maintained. There are many varieties of flight among birds; of these the most remarkable is the sailing motion, in which the wings are but slightly moved. Probably the original impetus is maintained by the kite-like slope of the wing, and advantage may be taken of currents by a rotation of the wing at the shoulder, a movement invisible at any distance.