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WEIGHTS AND MEASURES

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Originally appearing in Volume V28, Page 481 of the 1911 Encyclopedia Britannica.
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WEIGHTS AND MEASURES. This subject may he most conveniently considered under three aspects—I. Scientific; II. Historical; and III. Commercial. Nll, ,.lirh 61 'I ,',1111.11'' IH I From the Notice issued by the Standards Department of the Board of Trade, by permission of the Controller of H.M. Stationery Office. end in readiness for the next load. All of this is effected automatically as follows: The machine,is driven continuously by a belt from a motor which wraps round the large drum at the right-hand side of the machine. On the same axle as the drum and behind it is a small pulley which is keyed upon the axle and is connected with the small pulley (which runs idle on its shaft) at the left-hand side of the machine by a crossed belt. Thus these two small pulleys are always running, but in opposite directions. The drum-shaft is connected by a friction I. SCIENTIFIC I. Units.—In the United Kingdom two systems of weights and measures are now recognized—the imperial and the metric. The fundamental units of these systems arc of length, the yard and metre; and of mass, the pound and kilogram. The legal theory of the British system of weights and measures is—(a) the standard yard, with all lineal measures and theft squares and cubes based upon that; (b) the standard pound of 7000 grains, with all weights based upon that, with the troy pound of 5760 grains for trade purposes; (c) the standard gallon (and multiples and fractions of it), declared to contain so lb of water at 62° F., being in volume 277.274 cub. in., which contain each 252'724 grains of water in a vacuum at 62°, or 252.458 grains of water weighed with brass weights in air of 62° with the barometer at 30 in. Of the metric units international definitions have been stated as follows: (a) The unit of volume for determinations of a high degree of accuracy is the volume occupied by the mass of 1 kilogram of pure water at its maximum density and under the normal atmospheric pressure; this volume is called litre. . (b) In determinations of volume which do not admit of a high degree of accuracy the cubic decimetre can be taken as equivalent to the litre; and in these determinations expressions of volumes based on the cube of the unit of linear measure can be substituted for expressions based on the litre as defined above. (c) The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.' (d ~ The term " weight " denotes a magnitude of the same nature as a force; the weight of a body is the product of the mass of the body by the acceleration of gravity; in particular, the normal weight of a body is the product of the mass of the body by the normal acceleration of gravity. The number adopted for the value of the normal acceleration of gravity is 980.665 cm/sect. 2. Standards.—The metre (metre-d-traits) is represented by the distance marked by two fine lines on an iridio-platinum bar (t=o° C.) deposited with the Standards Department. This metre (m.) is the only unit of metric extension by which all other metric measures of extension—whether linear, superficial or solid—are ascertained. The kilogram (kg.) is represented by an iridio-platinum standard weight, of cylindrical form, by which all other metric weights, and all measures having reference to metric weight, are ascertained in the United Kingdom. From the above four units are derived all other weights and measures (W. and M.) of the two systems. The gallon is the standard measure of capacity in the imperial system as well for liquids as for dry goods. In the United Kingdom the metric standard of capacity is the litre, represented (Order in Council, 19th May 1890) by the capacity of a hollow cylindrical brass measure whose internal diameter is equal to one-half its height, and which at o° C., when filled to the brim, contains one kg. of distilled water of the temperature of 4° C., under an atmospheric pressure equal to 76o millimetres at o° C. at sea-level and latitude 45°; the weighing being made in air, but reduced by calculation to a vacuum. In such definition an attempt has been made to avoid former confusion of expression as to capacity, cubic measure, and volume; the litre being recognized as a measure of capacity holding a given weight of water. For the equivalent of the litre in terms of the gallon, see below III. Commercial. In the measurement of the cubic inch it has been found that2 the specific mass of the cubic inch of distilled water freed from air, and weighed in air against brass weights (A=8.13), at the temperature of 62° F., and under an atmospheric pressure equal to 30 in. (at 32° F.), is equal to 252'297 grains weight of water at its maximum density (4° C.). Hence a cubic foot of water would weigh 62.281 lb avoir., and not 62.321 lb as at present legally taken. For the specific mass of the cubic decimetre of water at 4° C., under an atmospheric pressure equal to 76o mm., Guillaume and Chappuis of the Comite International des Poids et Mesures at Paris (C.I.P.M.) have obtained 0.9999707 kg.,3 which has been accepted by the committee. The two standards, the cubic inch and the cubic decimetre, may not be strictly comparable owing to a difference in the normal temperature (Centigrade and Fahrenheit scales) of the two units of extension, the metre and the yard. ' Troisieme Conference Generale des Poids et Mesures (Paris, 1901). Metric Units Com. Roy. Soc. (1898). 2 Phil. ,Trans. (1892) ; and Proc. Roy. Soc. (1895), p. 143. Proc. Verb. Com. Intern. des Poids et Mesures (1900), p. 84. Congres International de Physique reuni a Paris en 1900. For the weight of the cubic decimetre of water, as deduced from the experiments made in London in 1896 as to the weight of the cubic inch of water, D. Mendeleeff (Proc. Roy. Soc., 1895) has obtained the following results, which have been adopted in legislative enactments in the United Kingdom : Temperature on Weight of Water in vacuo. the Hydrogen Thermometer Scale. Of a Cubic Of a Cubic Of a Cubic — Decimetre in Lich in Inch in C. F. Grammes. Grains. Russian Dolis. 0° 32°.0 999'716 252.821 368.686 4 39.2 999.847 252.854 368.734 15 59.0 998'979 252.635 368.414 163 62.o 998.715 252.568 368.316 20 68•o 998.082 252.407 368.083 In this no account is taken of the compressibility of water—that is to say, it is supposed that the water is under a pressure of one atmosphere. The weight of a cubic decimetre of water reaches i000 grammes under a pressure of four atmospheres; but in vacuo, at all temperatures, the weight of water is less than a kilogram. 3. National Standards.—National standards of length are not legally now referred to natural standards or to physical con- Total length of bronze bar, 38 in.; distance a a', 36 in., or the imperial yard; a a', wells sunk to the mid-depth of the bar, at the bottom of each of which is inserted a gold stud, having the defining line of the yard engraved on it. . stants,4 but it has been shown by A. A. Michelson that a standard of length might be restored, if necessary, by reference to the measurement of wave-lengths of light. Preliminary experiments have given results correct to to•5 micron, and it appears probable that by further experiments, results correct to t 1•oµ may be obtained. That is to say, the metre might be redetermined or restored as to its length within one ten-millionth part, by reference to, e.g., 1553163'5 wave-lengths of the red ray of the spectrum of cad- mium, in air at 15° C. and 76o mm. In all countries the national standards of weights and measures are in the custody of the state, or ) of some authority administering the ,government of the country. The standards of the British Empire, so far as they relate to the imperial and metric systems, are in the custody of the Board of Trade. Scientific research is not, of course, bound by official standards. For the care of these national FIG. 2.—Imperial Standard standards the Standards Department Pound, 1844• was developed, under the direction of a Royal Commissions (of which the Platinum pound avoirdulate Henry Williams Chisholm was a pois, of cylindrical form, with leading member), to conduct all com- groove at a for lifting the parisons and other operations with weight. reference to weights and measures in aid of scientific research or otherwise, which it may be the duty of the state to undertake. Similar standardizing offices are established 4 Valeur du Metre, A. A. Michelson (Paris, 1894) ; Units, Everett, Illustrations of C.G.S. System; Unites et Etalons, Guillaume (Paris, 189o) ; Lupton's Numerical Tables, 1892; Metric Equivalent Cards, 1901; Dictionary of Metric Measures, L. Clark (1891) ; Glazebrook and Shaw's Physics (1901). s Report Standards Commission, 187o. Section of bar. 0 Section at a a'. 01 in other countries (see STANDARDS). Verified " Parliamentary Copies " of the imperial standard are placed at the Royal Mint, with the Royal Society, at the Royal Observatory, and in the Westminster Palace. The forms of the four primary standards representing the four units of extension and mass are shown in figs. I to 4. A secondary standard measure for dry goods is the bushel of 1824, containing 8 imperial gallons, represented by a hollow bronze cylinder having a plane base, its internal diameter being double its depth. The imperial standard measure of capacity is a hollow cylinder (fig. 5) made of brass, with a plane base, of equal height and diameter; which when filled to the brim, as determined by a plane glass disk, contains ro lb weight of water at 1=62° F.B. = 30 in., weighed in air against brass weights. 4. Atmospheric Pressure, and Materials.—In the verification of a precise standard of length there may be taken into account the influence of the variation of atmospheric pressure. Taking the range of the barometer in Great Britain from 28 to 31 in., giving a difference of 3 in. (76 millimetres), which denotes a variation of 103 grammes per square centimetre in the pressure of the atmosphere, the change caused thereby in the length of a standard of linear measurement would appear to be as follows: For the yard measure of the form shown in fig. i a difference of length equal to 0.000002 in. is caused by the variation of atmospheric pressure from 28 to 31 in. For the metre of the form shown in fig. 3 the difference in length for a variation of 76 mm, in the barometer would be o•000048 mm. on the metre. With reference to the materials of which standards of length are made, it appears that the Matthey alloy iridio-platinum (90% platinum, lo g% iridium) is probably of all substances the least affected by time or circumstance, and of this costly alloy, Metre, 1897. perial yard has been made. There appears, however, to be some Iridio-platinum bar of Tresca objection to the use of iridiosection as shown at A. The two platinum for weights, as, owing microscopic lines are engraved to its great density (A=21.57), on the measuring axis of the bar the slightest abrasion will make an at b, one near to each end of the appreciable difference in a weight; bar. The standard metre (metre- sometimes, therefore, quartz or a-traits) was supplemented by rock-crystal is used; but to this the delivery to Great Britain, also there is some objection, as in 1898, of an end standard owing to its low density (0=2.65) metre (metre-a-bouts) also made there is a large exposed surface of iridio-platinum, and also of the mass. For small standard verified by the C.I.P.M. A corn- weights platinum (A =21.45) and parison of the yard with the aluminium (A=2.67) are used, and metre was made by the C.I.P.M. also an alloy of palladium (6o %) in 1896, and of the pound and and silver (40 %) (A =11.00). kilogram in 1883–1885 (see III. For ordinary standards of Commercial). length Guillaunie's alloy (invar) of nickel (35'7%) and steel (64.3%) is used, as it is a metal that can be highly polished, and is capable of receiving fine graduations. Its coefficient of linear expansion is only o•oo00008 for 1° C.' 5. Electrical Standards.—Authoritative standards and instruments for the measurement of electricity, based on the fundamental units of the metric system, have been placed in the Electrical Laboratory of the Board of Trade? These include Current measuring ) The standard ampere, and sub-standards instruments. from I to 2500 amperes. Potential measuring ( The standard volt, and sub-standards instruments. j( for the measurement of pressure from 25 to 3000 volts. Resistance measuring ( The standard ohm, sub-standards up instruments. j( to roo,000 ohms, and below I ohm to ohm. Rapport du Yard, Dr Benoit (1896). 2 Orders in Council (1894). 6. Temperature.—In the measurement of temperature the Fahrenheit scale is still followed for imperial standards, and the Centigrade scale for metric standards. At the time of the construction of the imperial standards in 1844, Sheepshanks's Fahrenheit thermometers were used; but it is difficult to say now what the true temperature then, of 62° F., may have been as compared with 62° F., or 16.667° C., of the present normal hydrogen scale. For metrological purposes the C.I.P.M. have adopted as a normal thermometric scale the Centigrade scale of the hydrogen thermometer, having for fixed points the temperature of pure melting ice (o°) and that of the vapour of boiling distilled water (roo°), under a normal atmospheric pressure; hydrogen being taken under an initial manometric pressure of r metre, that is to say, at W''00 = times the normal atmospheric pressure. This latter is represented by the weight of a column of mercury 76o mm. in height; the specific gravity of mercury being now taken as 13'5950, after Volkmann and Marek, and at the normal in-tensity followed under this pressure. The value of this intensity is equal to that of the force of gravity at the Bureau International, Paris (at the level of, the Bureau), divided by 1.000332; a co-efficient which allows for theoretical reduction to the latitude 45° and to the level of tha sea. The length of the metre is independent of the thermometer so far that it has its length at a definite physical point, the temperature of melting ice (o° C.), but there is the practical difficulty that for ordinary purposes measurements cannot be always carried out at o° C. The International Geodetic Committee have adopted the metre as their unit of measurement. In geodetic measurements the dimensions of the triangles vary with the temperature of the earth, but these variations in the same region of the earth are smaller than the variations of the temperature of the air, less than roe C. Adopting as a co-efficient of dilatation of the earth's crust 0.000002, the variations of the distances are smaller than the errors of measurement (see GEODESY). 7. Standardizing Institutions.—Besides the State departments dealing with weights and measures, there are other standardizing institutions of recent date. In Germany, e.g. there is at Charlottenburg (Berlin) a technical institute (Physikalisch - technische-Reichsanstalt) established under Dr W. Forster in 18871 which undertakes researches with reference to physics and mechanics, particularly as applied to technical industries.' In FIG. 5 —Present Imperial Standard England a National Gallon, 1824 Physical Laboratory (N.P.L.) has been established, based on the German institute, and has its principal laboratory at Bushey House, near Hampton, Middlesex. Here is carried out the work of standardizing measuring instruments of various sorts in use Wissenschaftliche Abhandlungen der physikalischen Reichsanstall, Band ii. (Berlin, 1900); Denkschrift betreffend die Tatigkeit der K. Norm.-Aichungs Kommn. (1869–1900). Kilogram, 1897. by manufacturers, the determination of physical constants and the testing of materials. The work of the Kew Observatory, at the Old Deer Park, Richmond, has also been placed under the direction of the N.P.L. (see III. Commercial)). The C.I.P.M. at Paris, the first metrological institution, also undertakes verifications for purely scientific purposes. A descriptive list of the verifying instruments of the Standards Department, London, has been published? In the measurement of woollen and other textile fabrics, as to quality, strength, number of threads, &c., there exists at Bradford a voluntary standardizing institution known as ,the Conditioning House (Bradford Corporation Act 1887), the work of which has been extended to a chemical analysis of fabrics. 8. Ancieni Standards of England and Scotland.—A " troy pound" and a new standard yard, as well as secondary standards, were constructed by direction of parliament in 1758-1760, and were deposited with the Clerk of the House of Commons. When the Houses of Parliament were burned down in 1834, the pound was lost and the yard was injured. It may here be mentioned that the expression " imperial " first occurs in the Weights and Measures Act of 1824. The injured standard was then lost sight of, but it was in 1891 brought to light by the Clerk of the Journals, and has now been placed in the lobby of the residence of the Clerk of the House, together with a standard " stone " of 14 lb .3 In the measurement of liquids the old " wine gallon " (231 cub. in.) was in use in England until 1824, when the present imperial gallon (fig. 5) was legalized; and the wine gallon of 1707 is still referred to as a standard in the United States. Together with the more ancient standard of Henry VII. and of Queen Elizabeth, this standard is deposited in the Jewel Tower at Westminster. They are probably of the Norman period, and were kept in the Pyx Chapel at Westminster, now in the custody of the Commissioners of Works. A sketch of these measures is given in fig. 6.4 Besides these ancient standards of England (1495, 1588, 16oi) there are at the council chambers of Edinburgh and Scotland, as or half-pint, of the same English Weights and Measures Abolished.—The yard and handful, or 40 in. ell, abolished in 1439. The yard and inch, or 37 in. ell (cloth measure), abolished after 1553; known later as the Scotch ell= 37.06. Cloth ell of 45 in., used till 1600. The yard of Henry VII. 35.963 in. Saxon moneyers.pound, or Tower pound, 5400 grains, abolished in 1527. Mark, a pound =3600 grains. Troy pound in use in 1415, established as monetary pound 1527. Troy weight was abolished, from the 1st of January 1879, by the Weights and Measures Act 1878, with the exception only of the Troy ounce, its decimal parts and multiples, legalized in 1853, 16 Viet. c. 29, to be used for the sale of gold and silver articles, platinum and precious stones. Merchant's pound, in 1270 established for all except gold, silver and medicines =6750 grains, generally superseded by avoirdupois in 1303. Mer- • Treasury Committee on National Physical Laboratory, Parliamentary Paper, 1898. 2 Descriptive List of Standards and Instruments, Parliamentary Paper, 1892. 2 Report on Standards deposited in House of Commons, 1st November 1891. ' S. Fisher, The Art Journal, August 1900. ' Buchanan, Ancient Scotch Standards.chant's pound of 7200 grains, from France and Germany, also superseded. ( Avoirdepois " occurs in 1336, and has been thence continued: the Elizabethan standard was probably 7002 grains.) Ale gallon of 16oi =282 cub. in., and wine gallon of 1707 =231 cub. in., both abolished in 1824. Winchester corn bushel of 8X268.8 cub. in. and gallon of 2744 are the oldest examples known (Henry or Half-Pint, 1555. Troy Weight, 1618. French Weights and Measures Abolished.—Often needed in reading older works. ligne, 12=ponce, 12 =pied, 6=toise, 2000=lieue de poste. •08883 in. 1.0658 12.7892 76.735 2.42219 miles. grain, 72 = gros, 8=once, 8=mare, 2 =poids de mart. .8197 gr. 59.021 472.17 3777.33 1.0792 lb. Rhineland foot, much used in Germany, =12.357 in. =the foot of the Scotch or English cloth ell of 37•o6 in., or 3X12.353. (H. J. C.) II. ANCIENT HISTORICAL Though no line can be drawn between ancient and modern metrology, yet, owing to neglect, and partly to the scarcity of materials, there is a gap of more than a thousand 'years over which the connexion of units6 of measure is mostly guess-work. Hence, except in a few cases, we shall not here consider any units of the middle ages. A constant difficulty in studying works on metrology is the need of distinguishing the absolute facts of the case from the web of theory into which each writer has woven them—often the names used, and sometimes the very existence of the units in question, being entirely an assumption of the writer. Again, each writer has his own leaning: A. Bockh, to the study of water-volumes and weights, even deriving linear measures therefrom; V. Queipo, to the connexion with Arabic and Spanish measures; J. Brandis, to the basis of Assyrian standards; Mommsen, to coin weights; and P. Bortolotti to Egyptian units; but F. Hultsch is more general, and appears to give a more equal representation of all sides than do other authors. In this article the tendency will he to trust far more to actual measures and weights than to the statements of ancient writers; and this position seems to be justified by the great in-crease in materials, and their more accurate means of study. The usual arrangement by countries has been mainly abandoned in favour of following out each unit as a whole, without recurring to it separately for every locality. The materials for study are of three kinds. (1) Literary, both in direct statements in works on measures (e.g. Elias of Nisibis), medicine (Galen) and cosmetics (Cleopatra), in ready-reckoners (Didymus), clerk's (katib's) guides, and like handbooks, and in indirect explanations of the equivalents of measures mentioned by authors (e.g. Josephus). But all such sources are liable to the most confounding errors, and some passages relied on have in any case to submit to conjectural emendation. These authors are of great value for connecting the monumental information, s In the absence of the actual standards of ancient times the units of measure and of weight have to be inferred from the other remains; hence unit in this division is used for any more or less closely defined amount of length or weight in terms of which matter was measured. Linlithgow some of the interesting standards of the Stirling jug or Scots pint, 1618; the choppin 1555 (fig. 7); the Lanark troy and tron weights periods (fig. 8).5 but must yield more and more to the increasing evidence of actual weights and measures. Besides this, all their evidence is but approximate, often only stating quantities to a half or quarter of the amount, and seldom nearer than 5 or 10%; hence they are entirely worthless for all the closer questions of the approximation or original identity of standards in different countries; and it is just in this line that the imagination of writers has led them into the greatest speculations, unchecked by accurate evidence of the original standards. (2) Weights and measures actually remaining. These are the prime sources, and as they increase and are more fully studied, so the subject will be cleared and obtain a fixed basis. A difficulty has been in the paucity of examples, more due to the neglect of collectors than the rarity of specimens. The number of published weights did not exceed 600 of all standards in 1880; but the collections from Naucratis (28),1 Defenneh (29) and Memphis (44) have supplied over six times this quantity, and of an earlier age than most other examples, while existing collections have been more thoroughly examined. It is above all desirable to make allowances for the changes which weights have undergone; and, as this has only been done for the above Egyptian collections and that of the British Museum, conclusions as to the accurate values of different standards will here be drawn from these rather than continental sources. (3) Objects which have been made by measure or weight, and from which the unit of construction can be deduced. Buildings will generally yield up their builder's foot or cubit when examined (Inductive Metrology, p. 9). Vases may also be found bearing such relations to one another as to show their unit of volume. And coins have long been recognized as one of the great sources of metrology—valuable for their wide and detailed range of information, though most unsatisfactory on account of the constant temptation to diminish their weight, a weakness which seldom allows us to reckon them as of the full standard. Another defect in the evidence of coins is that, when one variety of the unit of weight was once fixed on for the coinage, there was (barring the depreciation) no departure from it, because of the need of a fixed value, and hence coins do not show the range and character of the real variations of -units as do buildings, or vases, or the actual commercial weights.
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