In an overshot wheel, the power is the product of the descent from the head to the bottom, and the weight of the water expended in a second. The power is to the effect as 10 to 6.6.
The velocity at a maximum load is three feet in a second.
The velocity is the square root of the space Mien through. For the same stream Exiling, turns a wheel 57 times iu a minute, and directed to the centre as in an undershot wheel, turns it but 88.5 times, which are as 1 to 1.414, the square root of 1 and 2 nearly.
Therefore, the verecities will be as the square roots of their diameters, in all overshot wheels.
Portable horse mills.—The horse is at tached to the extremity of a cast-iron le ver, which puts in motion a large hori zonlal wheel, the upright axis of which is sunk into the earth, and having a groove around its rim, which is armed with points of iron ; these points enter the links of a chain, which passes around the great wheel, and through two east iron trunks, or tubes, which are buried in the earth, under the horse-walk. This chain very conveniently communicates the motion to any distance, and in any direction required ; and either of each may be varied ad infinitum, without much loss of time, or the employment of any considerable quantity of materials. Two men only were able to re-establish a mill in the course of an hour in a fresh situa tion in the open air. The horse is at tached to the outer end of the lever, by means of a swingle-tree and traces, which should be as short as possible.
Mr. Bogardus, of IN ew York, has in vented an universal eccentric mill for wheeling, cutting, and grinding, which is one of the most useful and important inventions of the time. His patent has been extended by special act of Congress 14 years, in consideration of its great merit.
In Mr. Bogardus's mill the principle is entirely new, both plates revolve in the same direction (with nearly equal speed) on centres, which are apart from each other one inch, more or less ; the centre of the one, or axis thereto affixed, resting on, or revolving upon a stationary point, whilst the prime mover, by means of a belt or gearing, communicates motion to the other plate. The circles which are cut in the plates act like revolving shears, i cutting every way, which, when in opera tion, causes a peculiar cutting, wrench ing or twisting, and sliding motion, ad mirably adapted for every species of grinding. From the position of the two
centres it is named the eccentric mill. The following are some of its advantages : 1. The peculiar motion of the plates will of itself discharge the ground sub stance ,• so that many substances can be ground thereby which would altogether choke other mills.
2. In other mills, a given point in one of the plates continually describes the same circle on the other ; but in this mill it traverses on the other plate at an infinite variety of angles, every point within two concentric circles apart from each other twice the distance of the cen tres of the plates, thereby rendering the wear and tear of the plates uniform, and preserving the grinding action of every point.
8. In other mills the grinding power of each point increases with its distance from the centre ; rut in this mill every point, from the centre to the circumference, has the same grinding power. A consider ably smaller mill will therefore effect a given purpose, and the eccentric mill is therefore more portable than other mills. t 4. The ever changing action of the mill and the quick discharge of the substance ground prevented from becoming heated, so that the eccentric mill may be profit ably employed in grinding substances which, in other mills, would be either spoiled or deteriorated in quality, or, by their melting, be impossible to be ground. If other mills were driven with that speed which can be safely applied to the eccen tric mill, they would be made red-hot in a few minutes.
Bogardus's mills have been successful ly introduced for the following purposes : Hulling rice, coffee, and olives. Grind ing grain of all kinds ; paints of all kinds, in water or oil : iron, zinc, copper, and gold ores, plumbago and manganese; bones for manure, and bones for sugar refining, flint and quartz, charcoal, plas ter, putty, printers' inks, drugs and dye stuffs; snuffs, mustard, coffee, spices, loaf-sugar, starch, gums, resins, asphalt um, india-rubber, flax-seed, and oil-cake.