WEIGHT

, or Gravity, in Physics, a quality in natural bodies, by which they tend downwards toward the centre of the earth. See Gravity.

Weight, like gravity, may be distinguished into absolute, specific, and relative.

Newton demonstrates, 1. That the Weights of all bodies, at equal distances from the centre of the earth, are directly proportional to the quantities of matter that each contains: Whence it follows, that the Weights of bodies have no dependence on their shapes or textures; and that all spaces are not equally full of matter.

2. On different parts of the earth's surface, the Weight of the same body is different; owing to the spheroidal figure of the earth, which causes the body on the surface to be nearer the centre in going from the equator toward the poles; and the increase in the Weight is | nearly in proportion to the versed sine of double the latitude; or, which is the same thing, to the square of the right sine of the latitude: the Weight at the equator to that at the pole, being as 229 to 230; or the whole increase of Weight from the equator to the pole, is the 229th part of the former.

3. That the Weights of the same body, at different distances above the earth, are inversely as the squares of the distances from the centre. So that, a body at the distance of the moon, which is 60 semidiameters from the earth's centre, would weigh only the 3600th part of what it weighs at the earth's surface.

4. That at different distances within the earth, or below the surface, the weights of the same body are directly as the distances from the earth's centre: so that, at half way toward the centre, a body would weigh but half as much, and at the very centre it would be no Weight at all.

5. A body immersed in a fluid, which is specifically lighter than itself, loses so much of its Weight, as is equal to the Weight of a quantity of the fluid of the same bulk with itself. Hence, a body loses more of its weight in a heavier fluid than in a lighter one; and therefore it weighs more in a lighter fluid than in a heavier one.

The Weight of a cubic foot of pure water, is 1000 ounces, or 62 1/2 pounds, avoirdupois. And the Weights of the cubic foot of other bodies, are as set down under the article Specific Gravity.

In the Philos. Trans. (number 458, p. 457 &c) is contained some account of the analogy between English Weights and measures, by Mr. Barlow. He states, that anciently the cubic foot of water was assumed as a general standard for liquids. This cubic foot, of 62 1/2 lb, multiplied by 32, gives 2000, the weight of a ton: and hence 8 cubic feet of water made a hogshead, and 4 hogsheads a tun, or ton, in capacity and denomination, as well as Weight.

Dry measures were raised on the same model. A bushel of wheat, assumed as a general standard for all sorts of grain, also weighed 62 1/2lb. Eight of these bushels make a quarter, and 4 quarters, or 32 bushels, a ton Weight. Coals were sold by the chaldron, supposed to weigh a ton, or 2000 pounds; though in reality it weighs perhaps upwards of 3000 pounds.

Hence a ton in Weight is the common standard for liquids, wheat, and coals. Had this analogy been adhered to, the confusion now complained of would have been avoided.—It may reasonably be supposed that corn and other commodities, both dry and liquid, were first sold by Weight; and that measures, for convenience, were afterwards introduced, as bearing some analogy to the Weights before used.

, Pondus, in Mechanics, denotes any thing to be raised, sustained, or moved by a machine; or any thing that in any manner resists the motion to be produced.

In all machines, there is a natural and sixed ratio between the Weight and the moving power: and if they be such as to balance each other in equilibria, and then the machine be put in motion by any other force; the Weight and power will always be reciprocally as the velocities of them, or of their centres of gravity; or their momentums will be equal, that is, the pro- duct of the Weight multiplied by its velocity, will be equal to the product of the power multiplied by its velocity.

, in Commerce, denotes a body of a known Weight, appointed to be put into a balance against other bodies, whose Weight is required to be known. These Weights are usually of lead, iron, or brass; though in several parts of the East Indies common flints are used; and in some places a sort of little beans.

The diversity of Weights, in all nations, and at all times, makes one of the most perplexing circumstances in commerce, &c. And it would be a very great convenience if all nations could agree upon a universal standard, and system, both of Weights and measures.

Weights may be distinguished into ancient and modern, foreign and domestic.

English Weights. By the 27th chapter of Magna Charta, the Weights are to be the same all over England: but for different commodities there are two different sorts, viz, troy Weight, and averdupois Weight.

The origin from which both of these are raised, is the grain of wheat, gathered in the middle of the ear: 32 of these, well dried, made one pennyweight, 20 pennyweights " one ounce, and 12 ounces " one pound troy; by Stat. 51 Hen. III; 31 Edw. I; 12 Henry VII.

A learned writer has shewn that, by the laws of assize, from William the Conqueror to the reign of Henry VII, the legal pound Weight contained a pound of 12 ounces, raised from 32 grains of wheat; and the legal gallon measure contained 8 of those pounds of wheat, 8 gallons making the bushel, and 8 bushels the quarter.

Henry VII. altered the old English Weight, and introduced the troy pound in its stead, being 3 quarters of an ounce only heavier than the old Saxon pound, or 1-16th heavier. The first statute that directs the use of the averdupois Weight, is that of 24 Henry VIII; and the particular use to which this Weight is thus directed, is simply for weighing butcher's meat in the market; though it is now used for weighing all sorts of coarse and large articles. This pound contains 7000 troy grains; while the troy pound itself contains only 5760 grains, and the old Saxon pound Weight but 5400 grains. Philos. Trans. vol. 65, art. 3.

Hence there are now in common use in England, two different Weights, viz, troy Weight, and averdupois Weight, the former being employed in weighing such fine articles as jewels, gold, silver, silk, liquors, &c; and the latter for coarse and heavy articles, as bread, corn, flesh, butter, cheese, tallow, pitch, tar, iron, copper, tin, &c. and all grocery wares. And Mr. Ward supposes that it was brought into use from this circumstance, viz, as it was customary to allow larger Weight, of such coarse articles, than the law had expressly enjoined, and this he observes happened to be a 6th part more. Apothecaries buy their drugs by averdupois Weight, but they compound them by troy Weight, though under some little variation of name and divisions. |

The troy or trone pound Weight in Scotland, which by statute is to be the same as the French pound, is commonly supposed equal to 15 3/4 English troy ounces, or 7560 grains; but by a mean of the standards kept by the dean of gild of Edinburgh, it weighs 7599 1/16 or 7600 grains nearly.

The following tables shew the divisions of the troy and averdupois Weights.

Mr. Ferguson (Lect. on Mech. p. 100, 4to) gives the following comparison between troy and averdupois Weight.

The moneyers, jewellers, &c, have a particular class of Weights, for gold and precious stones, viz, carat and grain; and for silver, the pennyweight and grain. The moneyers have also a peculiar subdivision of the troy grain: thus, dividing

The dealers in wool have likewise a particular set of Weights; viz, the sack, weigh, tod, stone, and clove, the proportions of which are as below: viz,

Also 12 sacks make a last or 4368 pounds. Farther, 56 lb of old hay, or 60 lb new hay, make a truss. 40 lb of straw make a truss. 36 trusses make a load, of hay or straw. 14 lb make a stone. 5 lb of glass a stone.

French Weights. The common or Paris pound Weight, is to the English troy pound, as 21 to 16, and to the averdupois pound as 27 to 25; it therefore contains 7560 troy grains; and it is divided into 16 ounces like the pound averdupois, but more particularly thus: the pound into 2 marcs; the marc into 8 ounces; the ounce into 8 gros, or drams; the gross or dram into 3 deniers, Paris scruples or pennyweights; and the pennyweight into 24 grains; the grain being an equivalent to a grain of wheat. So that the Paris ounce contains 472 1/2 troy grains, and therefore it is to the English troy ounce as 63 to 64. But in several of the French provinces, the pound is of other different Weights. A quintal is equal to 100 pounds.

The Weights above enumerated under the two articles of English and French Weights, are the same as are used throughout the greatest part of Europe; only under somewhat different names, divisions, and proportions. And besides, particular nations have also certain Weights peculiar to themselves, of too little consequence here to be enumerated. But to shew the proportion of these several Weights to one another, there may be here added a reduction of the divers pounds in use throughout Europe, by which the other Weights are estimated, to one standard pound, viz, the pound of Amsterdam, Paris, and Bourdeaux; as they were accurately calculated by M. Ricard, and published in the new edition of his Traité de Commerce, in 1722.

1. The Weights of the ancient Jews, reduced to the English troy Weights, will stand as below:

2. Grecian and Roman Weights, reduced to English troy Weight, are as in the following table:

The Roman ounce is the English averdupois ounce, which they divide into 7 denarii, as well as 8 drachms: and as they reckoned their denarius equal to the Attic drachm, this will make the Attic Weights one-eighth heavier than the correspondent Roman Weights. Arbuth.

Regulation of Weights and Measures. This is a branch of the king's prerogative. For the public convenience, these ought to be universally the same throughout the nation, the better to reduce the prices of articles to equivalent values. But as Weight and measure are things in their nature arbitrary and uncertain, it is necessary that they be reduced to some sixed rule or standard. It is however impossible to fix such a standard by any written law or oral proclamation; as no person can, by words only, give to another an adequate idea of a pound Weight, or foot-rule. It is therefore expedient to have recourse to some visible, palpable, material standard; by forming a comparison with which, all Weights and measures may be reduced to one uniform size. Such a standard was anciently kept at Winchester: and we find in the laws of king Edgar, near a century before the conquest, an injunction that that measure should be observed throughout the realm.

Most nations have regulated the standard of measures of length from some parts of the human body; as the palm, the hand, the span, the foot, the cubit, the ell (ulna or arm), the pace, and the fathom. But as these are of different dimensions in men of different proportions, ancient historians inform us, that a new standard of length was fixed by our king Henry the first; who commanded that the ulna or ancient ell, which answers to the modern yard, should be made of the exact length of his own arm.

A standard of long measure being once gained, all others are easily derived from it; those of greater length by multiplying that original standard, those of less by dividing it. Thus, by the statute called compositio ulnarum et perticarum, 5 1/2 yards make a perch; and the yard is subdivided into 3 seet, and each foot into 12 inches; which inches will be each of the length of 3 barley corns. But some, on the contrary, derive all measures, by composition, from the barley corn.

Superficial measures are derived by squaring those of length; and measures of capacity by cubing them.

The standard of Weights was originally taken from grains or corns of wheat, whence our lowest denomination of Weights is still called a grain; 32 of which are directed, by the statute called compositio mensurarum, to compose a pennyweight. 20 of which make an ounce, and 12 ounces a pound, &c.

Under king Richard the first it was ordained, that there should be only one Weight and one measure throughout the nation, and that the custody of the assize or standard of Weights and measures, should be committed to certain persons in every city and borough; from whence the ancient office of the king's ulnager seems to have been derived. These original standards were called pondus regis, and mensura domini regis, and are directed by a variety of subsequent statutes to be kept in the exchequer chamber, by an officer called the clerk of the market, except the wine gallon, which is committed to the city of London, and kept in Guildhall.

The Scottish standards are distributed among the oldest boroughs. The elwand is kept at Edinburgh, the pint at Stirling, the pound at Lanark, and the firlot at Linlithgow.

The two principal Weights established in Great Britain, are troy Weight, and avoirdupois Weight, | as before mentioned. Under the head of the former it may farther be added, that

A carat is a Weight of 4 grains; but when the term is applied to gold, it denotes the degree of fineness. Any quantity of gold is supposed divided into 24 parts. If the whole mass be pure gold, it is said to be 24 carats fine; if there be 23 parts of pure gold, and one part of alloy or base metal, it is said to be 23 carats fine, and so on.

Pure gold is too soft to be used for coin. The standard coin of this kingdom is 23 carats fine. A pound of standard gold is coined into 44 1/2 guineas, and therefore every guinea mould weigh 5 dwts 9 39/<*> grains.

A pound of silver for coin contains 11 oz 2 dwts pure silver, and 18 dwts alloy: and standard silverplate, 11 ounces pure silver, with 1 ounce alloy. A pound of standard silver is coined into 62 shillings; and therefore the Weight of a shilling should be 3 dwts 20 28/31 grains.

Philosophers, from their habits of generalizing, have often made speculations for forming a general standard for Weights and measures through the whole world. These have been devised chiefly of a philosophical nature, as best adapted to universality. After the invention of pendulum clocks, it first occurred that the length of a pendulum which should vibrate seconds, would be proper to be made a universal standard for lengths; whether it should be called a yard, or any thing else. But it was found, that it would be difficult in practice, to measure and determine the true length of such a pendulum, that is the distance between the point of suspension and the point of oscillation. Another cause of inaccuracy was afterwards discovered, when it was found that the seconds pendulum was of different lengths in all the different latitudes, owing to the spheroidal figure of the earth, which causes that all places in different latitudes are at different distances from the centre, and consequently the pendulums are acted upon by different forces of gravity, and therefore require to be of different lengths. In the latitude of London this is found to be 39 1/8 inches.

The Society of Arts in London, among their many laudable and patriotic endeavours, offered a handsome premium for the discovery of a proper standard for Weights and measures. This brought them many frivolous expedients, as well as one which was an improvement on the method of the pendulum, by one Hatton. This consisted in measuring the difference of the lengths of two pendulums of different times of vibration; which could be performed more easily and accurately than that of the length of one single pendulum. This method was put in practice, and fully explained and illustrated, by the late Mr. Whitehurst, in his attempt to ascertain an Universal Standard of Weights and Measures. But still the same kind of inaccuracy of measurement &c, obtains in this way, as in the single pendulum, though in a smaller degree.

Another method that has been proposed for this purpose, is the space that a heavy body falls freely through in 1 second of time. But this is an experiment more difficult than the former to be made with accuracy; on which account, different persons will all make the space fallen to be of different quantities, which would give as many different standards of length. Add to this, that the spheroidal form of the earth here again introduces a diversity in the space, owing to the different distances from the centre, and the consequent diversity in the force of gravity by which the body falls. This space has been found to be 193 inches, or 16 1/12 feet, in the latitude of London; but it will be a different quantity in other latitudes.

Many other inferior expedients have also been proposed for the purpose of universal measures, and Weights, but there is another which now has the best prospect of success, and is at present under particular experiments, by the philosophers both of this and the French nation. This method is by the measure of the degrees of latitude; which would give a large quantity, and admit of more accurate measures, by subdivision, than what could be obtained by beginning from a small quantity, or measure, and thence to proceed increasing by multiples. This measure might be taken either from the extent of the whole compass of the earth, or of all the 360 degrees, or a medium degree among them all, or from the measure of a degree in the medium latitude of 45 degrees. It will also be most convenient to make the subdivisions. of this measure, when found, to proceed decimally, or continually by 10ths.

The universal standard for lengths being once established, those of Weights, &c, would easily follow. For instance, a vessel, of certain dimensions, being filled with distilled water, or some other homogeneous matter, the Weight of that may be considered as a standard for Weights.

Weight of the Air, Water, &c. See those articles severally. See also Specific Gravity.