as they result in producing motion or not, constitute cases in STATICS or DYNAMICS. These two terms are frequently used to designate the two great divisions of mechanics-Statics, including all cases where equilibrium is produced, and Dynamics, those in which motion results. The term dynamics is, however, not confined exclusively to the motions of solid bodies. When applied to describe the laws of motion in fluids, it is termed hydrodynamics, and electrodynamics when used to comprehend the phenomena of electricity in motion. See FORCES, MOTION, &c.

DYNAMOMETER. An instrument employed to measure the comparative

strengths of men and cattle, and to ascertain the force required in drawing

carriages upon land, and vessels upon canals. These effects are usually estimated by the compression or distension of a strong spring, or by a steelyard upon the principle of a bent lever balance; but in both these constructions the instrument is subject to great vibration, owing to inequalities in the resistance and in the moving force, which render the indications very uncertain. This objection to spring dynamometers has been obviated by Mr. H. R. Palmer, as follows::-a piston, fitting loosely in a cylinder filled with oil, so as to allow the oil to escape slowly past its sides as it moves up and down, is connected with the springs by means of a fine steel wire passing through stuffing boxes at each end of the cylinder; the friction, therefore, is so extremely slight as not to be worth taking into account in any experiments, whilst it prevents that vibratory motion of the index, from jerks, and allows the resistance to be ascertained with the greatest accuracy. The preceding engraving is a representation of the instrument. a a represents the back of the dial plate of any ordinary spring weighing machine, the front of which is shown separate in Fig. 2 (but without the graduated scale, as being unnecessary); bb are two spiral springs enclosed in cylindrical cases, (similar to the well-known domestic article called pocket steelyards,) the upper ends of which are fixed to a sliding frame c c, and at their lower ends they are hooked to a cross bar f, which bar is made fast to a piece of metal o at the back of a a; d is the cylinder of oil, which is firmly fixed at the back of a a; to this cylinder is fixed four pieces of metal e e e e, having angular grooves, in which the frame c c slides when the springs are acted upon. The piston in the cylinder is shown by dots, the rod to which (a fine steel wire) passes through stuffing boxes at each end of the cylinder, and each Now the bar g, which pro

end of the rod is then made fast to the frame c c. ceeds from the circular box a a, and acts upon the spring, is connected at the swivel ring with the upper end of the frame e c, as one solid piece; therefore when the ring k is made fast to a carriage, and power applied to the rope at i, the bar g is drawn out of a, while the frame c e acts simultaneously upon the steelyard springs c c, which move along with them the piston in the fixed cylinder d; the oil therein being incompressible, is compelled to pass from one side of the piston to the other, through the extremely narrow interstice between the periphery and the cylinder.

In the dynamometer invented by Mr. Milne, of Edinburgh, an iron plunger is by the force exerted in traction caused to descend in an open vessel containing mercury, by which means the latter rises to a height indicated by a glass tube open at top, and connected to the mercurial vessel at bottom by a neck, the bore of which is contracted to diminish the vibrations of the mercurial column; half the height in inches of the mercury in the tube multiplied by the area of the base of the plunger in inches will be the amount of the force of traction in pounds.

E.

EARTHS. A name commonly assigned to a class of solid substances composing, in various states of combination, the crust of the globe; the general qualities of which are, that they are incombustible, not convertible into metals by the ordinary methods of reduction, and their specific gravity not exceeding five times that of water. The number of these substances is ten; viz. barytes, strontites, lime, magnesia, alumina, or clay, silica, glucina, zerconia, yttria, and thorina. But although these substances are generally termed earths, the experiments of Sir H. Davy have shown that a portion of them, viz., barytes, strontites, and lime, as well as the alkalies, potash and soda, are, in reality, combinations of metallic bases with oxygen and lead, and determine, by most probable analogies, that the whole of them belong to the metallic class. EARTHENWARE. Articles made of baked or vitrified earth. See

POTTERY.

EAR TRUMPET. A contrivance for the benefit of deaf persons; as usually constructed, it resembles in shape a marine speaking trumpet, but smaller, seldom exceeding six or eight inches in length. The party using the

trumpet inserts the small end within his ear, and the speaker applies his mouth to the wide end. Dr. Morrison, of Aberdeen, however, contends that this construction is erroneous, and that the end which is applied to the ear should be large enough to include the whole ear, instead of being inserted within it. The Doctor states, that having laboured under a deafness for a number of years, he applied in every quarter for the most improved ear trumpet; but from none of them could he derive the most trivial benefit. He at length ordered one to be made of the finest block tin, constructed as above recommended, and found it to answer beyond his most sanguine hopes. The annexed cut is a representation of a flexible ear trumpet, invented by Mr. T. Hancock, of Fulham. It is made of Indian rubber, covered with a net-work of gold or

silver wire, and, from its flexibility, is rendered more convenient for portability and for ready application in any situation that may be required. Mr. Hancock has successfully applied tubes of this description as speaking pipes, to communicate verbally with the various parts of an extensive manufactory.

EASEL. A frame used by painters for supporting their pictures while in progress, and admitting of being adjusted to any convenient angle by means of a movable prop at the back.

EAU-DE-LUCE. A volatile preparation, which is thus made:-12 grains of white soap are dissolved in 4 ounces of spirit of wine; this solution being strained, a drachm of rectified oil of amber is added, and the whole filtered. Afterwards, some strong volatile spirit of sal ammonia is to be mixed with the solution.

EAU-DE-COLOGNE. A celebrated odoriferous liqueur: the following is the true mode of preparing it. Take of the essence of bergamot, lemon peel, lavender, and orange flower, of each 1 ounce; essence of cinnamon, half an ounce; spirit of rosemary, and of the spirituous water of melisse, each 15 ounces; strong alcohol, 7 pints. Mix the whole together, and let the mixture stand for the space of a fortnight; after which introduce it into a glass retort, the body of which is immersed in boiling water, contained in a vessel placed over a lamp, while the beak is introduced into a large glass reservoir well luted. By keeping the water to the boiling point, the mixture in the retort will distill over into the reservoir, which should be covered with wet cloths. In this manner will be obtained pure eau-de-Cologne.

EAVES. The edge or margin of the roof of a house, which projects beyond the walls to throw off the water therefrom.

EBONY. An exceedingly hard and heavy wood, susceptible of a fine polish. There are many kinds of ebony; the most usual are the black, red, and green, all of them the product of the island of Madagascar. The black ebony is preferred to that of any other colour, but it is not so much in request as formerly, since the discovery of so many ways of giving other hard woods a black colour. This may be done by boiling smooth, clean box wood in oil till it becomos perfectly black; or by washing pear wood with aquafortis, and drying it in a

shady place in the open air; after which common writing ink should be repeatedly passed over it, and the wood dried in a similar manner till it acquire a deep black colour. It may then be polished with wax and a woollen cloth, which will give it a fine lustre. An excellent black is also produced by first applying a solution of copper and aquafortis, and afterwards brushing the wood over with a decoction of logwood.

ECCENTRIC, in Geometry, denotes two circles or spheres, one of which is contained within the other, but the centres of the two do not coincide. In mechanics, the name is given to a contrivance frequently substituted for a crank, for obtaining a reciprocating motion from a circular. It consists of a circular disc placed eccentrically upon a shaft, and revolving within a hoop formed at one end of the connecting rod. The valves of most steam engines which work with a fly-wheel are moved by an eccentric.

EDGE TOOLS is a general name applied to the coarser kinds of cutting instruments, such as chisels, axes, adzes, gouges, augers, saws, &c.

EFFECT (USEFUL.), in Mechanics; the measure of the real power of any machine, after deducting that portion which is lost or expended in overcoming the inertia and friction of the moving parts, and in giving them the required velocity, and every other source of loss. The greatest useful effect which a horse can produce, was estimated by Bolton and Watt at 33,000 lbs. raised one foot high per minute; and upon the introduction of the steam engine to perform the labour which was before performed by horses, their power was expressed by that of the number of horses which they were equal to; and from the convenience of this mode of expression, it has since been generally adopted to express the power of all kinds of machinery. It is at all times desirable to know the real effective power of any machine: when water is to be raised, the effect is readily computed, but in most other species of work it is difficult to estimate the resistance, and consequently whether the engine be really equal to its nominal power; in this case, Mr. Tredgold observes, the most convenient and simple mode of measuring the effect is by friction. If the rim of a brake wheel of known diameter upon an engine shaft be pressed with a force producing a known degree of friction, which is exactly equal to the effect of the engine at its working speed, then it is clear that if the friction this pressure produces be ascertained, the power of the engine will be equal to the friction multiplied by the velocity of the rubbing surface. To apply this, let A B be a lever with a friction strap, that may be tightened upon the cylindrical surface of the shaft or wheel C, and let it be tightened by the screw at B (the lever being stopped by the stop at D), till the friction be equal to the power of the engine when all other work is thrown off; then while the engine is still in motion, add such a weight at E as retains the lever in a horizontal position.

A

F

E

B

To calculate the power, multiply together the length of the lever F C in feet, the weight E in lbs. the number of revolutions of C per minute, and the number 6.2832; the result will be the number of pounds raised one foot per minute, and divided by 33,000 it is the horses' power. Thus if a shaft make 20 revolutions per minute, and the length EC of the lever be 10 feet, and if it be found that a weight of 240 lbs. is sufficient to retain the lever in a horizontal position, then 6.2832 x 10 × 240 × 25=376992 lbs. raised one foot high, or nearly eleven and a half horses' power.

EFFERVESCENCE. The commotion produced in fluids by some part of the mass taking suddenly the elastic form, and escaping rapidly in numerous bubbles.

EFFLORESCENCE. The effect which takes place when bodies spontaneously become converted into a dry powder. It is almost always occasioned by the loss of the water of crystallization in saline bodies.

EGGS. The envelope which contains the foetus of various animals, and which, being voided by the parent, is subsequently matured by incubation. This may also be effected by means of prolonged artificial heat; and in Egypt the art of hatching chickens by means of ovens has long been practised, but it is there only known to the inhabitants of a single village, named Berme, and to those that live at a small distance from it. Towards the beginning of autumn they scatter themselves all over the country, where each person among them is ready to undertake the management of an oven, each of which is of a different size, but in general they are capable of containing from forty to fourscore thousand eggs. The number of these ovens placed up and down the country is about 386, and they usually keep them working for about six months; as, therefore, each brood takes up in an oven, as under a hen, only twenty-one days, it is easy in every one of them to hatch eight different broods of chickens. Every Bermean is under the obligation of delivering to the person who entrusts him with an oven, only two-thirds of as many chickens as there have been eggs put under his care; and he is a gainer by this bargain, as more than two-thirds of the eggs usually produce chickens. In order to make a calculation of the number of chickens yearly so hatched in Egypt, it has been supposed that only two-thirds of the eggs are hatched, and that each brood consists of at least 30,000 chickens; and thus it would appear that the ovens of Egypt give life yearly to at least 92,640,000 of these animals. As it is of great importance in a zoological, and, to a certain extent, even in an economical point of view, to be able to transport eggs fresh from one country to another, it has been proposed, as the best method of effecting this, to varnish them with gum arabic, and then imbed them in pounded charcoal, which being a non-conductor of heat, a uniform temperature will be preserved.

ELAINE. The oily principle of solid fats, the remaining or solid portion being named stearine,—names assigned to these substances by the discoverer, Mr. Chevreul. If tallow be squeezed between the folds of porous paper, the elaine soaks into it, whilst the stearine remains. The paper being then soaked in water and pressed, yields up its oily impregnation. Elaine has very much the appearance and properties of vegetable oil, and is liquid at the temperature of 60°. Cocoa nut oil, which in England usually is concrete, or at most semi-fluid, has of late years been resolved into the above-named constituents by mechanical pressure, and the solid part manufactured into candles, whilst the liquid forms a valuable oil for lamps. See FAT.

ELASTICITY. A property of bodies to resume their form upon the removal of any force by which they may have been deflected from it. In this respect all bodies which come within our knowledge are comprehended under one of these three distinctions. If two bodies, when pressed together, suffer an alteration in their form, and if afterwards, on removing that pressure, they recover their original figures, they are called elastic; if, when pressed, their forms are not in the least altered, they are called hard; and if, when pressed as above, they alter their forms, and retain the same after the pressure is discontinued, they are called soft; and both these last kinds of bodies are termed non-elastics. It is doubtful, however, whether any bodies are either perfectly hard, or soft, or elastic, -the air not being perfectly elastic, and water (which was for a long time held to be perfectly incompressible and non-elastic,) being in the opinion of many persons shown to be compressible, by the experiments of Canton and of Perkins. ELECTRICITY. The name assigned to a certain mysterious natural principle or element, with the nature of which we are totally unacquainted, as it can only be inferred from its effects, in which respect it resembles the principles of light, heat, and magnetism. For a brief outline of the science of electricity, see CHEMISTRY.