Part 298

+------+-----+-----+-----+-----+-----+-----+ |Ounces| 0 | 1 | 2 | 3 | 4 | 5 | +------+-----+-----+-----+-----+-----+-----+ | 0 | 0 |1·256|1·583|1·811|1·994|2·148| +------+-----+-----+-----+-----+-----+-----+ | 1 |2·706|2·793|2·876|2·953|3·027|3·098| +------+-----+-----+-----+-----+-----+-----+

Diameters and Heights of Cylindric Powder Measures, holding from 1 to 15 Pounds.

+------+-----+-----+-----+-----+-----+-----+ |Pounds| 0 | 1 | 2 | 3 | 4 | 5 | +------+-----+-----+-----+-----+-----+-----+ | 0 | 0 |3·165|3·988|4·565|5·024|5·412| +------+-----+-----+-----+-----+-----+-----+ | 1 |6·890|7·039|7·245|7·442|7·628|7·805| +------+-----+-----+-----+-----+-----+-----+

The above are in inches and decimals.

MEASURE-angle, a brass instrument to measure angles, either saliant or rentrant, for exactly ascertaining the number of degrees and minutes, to delineate them on paper.

MEASURING, MENSURATION, in military mathematics, the assuming any certain quantity, and expressing the proportion of other similar quantities to the same; or the determining, by a certain known measure, the precise extent, quantity, or capacity of any thing.

MEASURING, in general, constitutes the practical part of geometry; and from the various subjects which it embraces, it acquires various names, and constitutes various arts, viz.

LONGIMETRY, ALTIMETRY, LEVELLING, GEODESIA, or SURVEYING, STEREOMETRY, SUPERFICIES, and SOLIDS, &c. which see.

MEASURING. See CHAIN.

MECHANICS, a mixed mathematical science, which considers motion and moving powers, their nature and laws, with the effects thereof, in machines, &c. The word is derived from the Greek. That part which considers motion arising from gravity, is sometimes called statics, in contradistinction from that part which considers the mechanical powers and their application, properly called mechanics: it is, in fine, the geometry of motion.

MECHANICS. The whole momentum or quantity of force of a moving body, is the result of the quantity of matter, multiplied by the velocity with which it is moved; and when the product arising from the multiplication of the particular quantities of matter in any two bodies, by their respective velocities are equal, their momentum will be so too. Upon this easy principle depends the whole of mechanics; and it holds universally true, that when two bodies are suspended on any machine, so as to act contrary to each other; if the machine be put in motion, and the perpendicular ascent of one body multiplied into its weight, be equal to the perpendicular descent of the other, multiplied into its weight, those bodies, how unequal soever in their weights, will balance each other in all situations: for, as the whole ascent of the one is performed in the same time as the whole descent of the other, their respective velocities must be as the spaces they move through; and the excess of weight in one is compensated by the excess of velocity in the other. Upon this principle it is easy to compute the power of any engine, either simple or compound; for it is only finding how much swifter the power moves than the weight does, (i. e. how much further in the same time,) and just so much is the power increased by the help of the engine.

The simple machines usually called mechanic powers, are six in number, viz. the lever, the wheel and axle, the pulley, the inclined plane, the wedge, and the screw.

There are four kinds of levers: 1st, where the prop is placed between the weight and the power. 2d, where the prop is at one end of the lever, the power at the other, and the weight between them. 3d, where the prop is at one end, the weight at the other, and the power applied between them. 4th, the bended lever, which differs from the first in form, but not in property.

In the first and 2d kind, the advantage gained by the lever, is as the distance of the power from the prop, to the distance of the weight from the prop. In the 3d kind, that there may be a balance between the power and the weight, the intensity of the power must exceed the intensity of the weight, just as much as the distance of the weight from the prop exceeds the distance of the power from the prop. As this kind of lever is disadvantageous to the moving power, it is seldom used.

Wheel and axle. Here the velocity of the power is to the velocity of the weight, as the circumference of the wheel is to the circumference of the axle.

Pulley. A single pulley, that only turns on its axis, and does not move out of its place, serves only to change the direction of the power, but gives no mechanical advantage. The advantage gained in this machine, is always as twice the number of moveable pullies; without taking any notice of the fixed pullies necessary to compose the system of pullies.

Inclined plane. The advantage gained by the inclined plane, is as great as its length exceeds its perpendicular height. The force wherewith a rolling body descends upon an inclined plane, is to the force of its absolute gravity, as the height of the plane is to its length.

Wedge. This may be considered as two equally inclined planes, joined together at their bases. When the wood does not cleave at any distance before the wedge, there will be an equilibrium between the power impelling the wedge, and the resistance of the wood acting against its two sides; when the power is to the resistance, as half the thickness of the wedge at the back, is to the length of either of its sides; because the resistance then acts perpendicular to the sides of the wedge: but when the resistance on both sides acts parallel to the back, the power that balances the resistance on both sides will be, as the length of the whole back of the wedge is to double its perpendicular height. When the wood cleaves at any distance before the wedge, (as it generally does) the power impelling the wedge will be to the resistance of the wood, as half the length of the back is to the length of either of the sides of the cleft, estimated from the top, or acting part of the wedge.

Screw. Here the advantage gained is as much as the circumference of a circle described by the handle of the winch, exceeds the interval or distance between the spirals of the screw.

There are few compound engines, but what, on account of the friction of parts against one another, will require a third part more power to work them when loaded, than what is required to constitute a balance between the power and the weight.

MECHANICAL, something relating to mechanics.

MECHANICAL philosophy, that which explains the phenomena of nature, and the operations of corporeal things, on the principles of mechanics; namely, the motion, gravity, figure, arrangement, &c. of the parts which compose natural bodies.

MECHANICAL powers. When two heavy bodies or weights are made by any contrivance to act against each other, so as mutually to prevent each other, from being put into motion by gravity, they are said to be in equilibrio. The same expression is used with respect to other forces, which mutually prevent each other from producing motion.

Any force may be compared with gravity, considered as a standard. Weight is the action of gravity on a given mass. Whatever therefore is proved concerning the weights of bodies will be true in like circumstances of other forces.

Weights are supposed to act in lines of direction parallel to each other. In fact, these lines are directed to the centre of the earth, but the angle formed between any two of them within the space occupied by a mechanical engine is so small, that the largest and most accurate astronomical instruments are scarcely capable of exhibiting it.

The simplest of those instruments, by means of which weights or forces are made to act in opposition to each other, are usually termed mechanical powers. Their names are, the lever, the axis or axle, and wheel, the pully or tackle, the inclined plane, the wedge, and the screw.

Of the Lever.

The lever is defined to be a moveable and inflexible line, acted upon by three forces, the middle one of which is contrary in direction to the other two.