See also:

• PHYSICAL

PHYSICAL See also:

• UNITS, DIMENSIONS OF
• PHYSICAL UNITS

UNITS  . In See also:

• ORDER
• ORDER (through Fr. ordre, for earlier ordene, from Lat. ordo, ordinis, rank, service, arrangement; the ultimate source is generally taken to be the root seen in Lat. oriri, rise, arise, begin; cf. " origin ")
• ORDER, HOLY

order that our acquaintance with any See also:

• PART

part of nature may become exact we must have not merely a qualitative but a quantitative knowledge of facts . Hence the moment that any See also:

• BRANCH (from the Fr. branche, late Lat. branca, an animal's paw)

branch of See also:

• SCIENCE (Lat. scientia, from scire; to learn, know)

science begins to develop to any extent, attempts are made to measure and evaluate the quantities and effects found to exist . To do this we have to select for each measurable magnitude a unit or See also:

• STANDARD
• STANDARD, BATTLE OF THE

standard of reference (Latin, unitas, unity), by comparison with which amounts of other like quantities may be numerically defined . There is nothing to prevent us from selecting these fundamental quantities, in terms of which other like quantities are to be expressed, in a perfectly arbitrary and See also:

• INDEPENDENT

independent manner, and as a See also:

• MATTER

matter of fact this is what is generally done in the See also:

• EARLY
• EARLY, JUBAL ANDERSON (1816-1894)

early stages of every science . We may, for instance, choose a certain length, a certain See also:

• VOLUME

volume, a certain See also:

• MASS (O.E. maesse; Fr. messe; Ger. Messe; Ital. messa; from eccl. Lat. missa)
• MASS, IN

mass, a certain force or See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power as our See also:

• UNITS, DIMENSIONS OF
• UNITS, PHYSICAL

units of length, volume, mass, force or power, which have no See also:

• SIMPLE

simple or See also:

• DIRECT

direct relation to each other . Similarly we may select for more See also:

• SPECIAL

special measurements any arbitrary electric current, electromotive force, or resistance, and See also:

• CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

call them our units . The progress of knowledge, however, is greatly assisted if all the measurable quantities are brought into relation with each other by so selecting the units that they are related in the most simple manner, each to the other and to one See also:

• COMMON

common set of measurable magnitudes called the fundamental quantities . The progress of this co-ordination of units has been greatly aided by the See also:

• DISCOVERY

discovery that forms of See also:

• PHYSICAL

physical See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy can be converted into one another, and that the See also:

• CONVERSION (Lat. conversio, from convertere, to turn or ,change)

conversion is by definite See also:

• RULE

rule and amount (see ENERGY) . Thus the See also:

• MECHANICAL

mechanical energy associated with moving masses can be converted into See also:

• HEAT (0. E. haktu, which like " hot," Old Eng. hat, is from the Teutonic type haita, hit, to be hot; cf. Ger. hitze, heiss; Dutch, hitte, heet, &c.)

heat, hence heat can be measured in mechanical energy units . The amount of heat required to raise one gramme of See also:

• WATER

water through 1° C. in the neighbourhood of to° C. is equal to See also:

• FORTY

forty-two million ergs, the erg being the kinetic energy or energy of See also:

• MOTION (Lat. motio, from movere, to move)
• MOTION, LAWS OF

motion associated with a mass of 2 grammes when moving uniformly, without rotation, with a velocity of 1 cm. per second . This number is commonly called the " mechanical See also:

• EQUIVALENT

equivalent of heat," but would be more exactly described as the " mechanical equivalent of the specific heat of water at to° C." Again, the fact that the See also:

• MAINTENANCE (Fr. maintenance, from maintenir, to maintain, support, Lat. manu tenere, to hold in the hand)

maintenance of an electric current requires energy, and that when produced its energy can be wholly utilized in See also:

• HEATING

heating a mass of water, enables us to make a similar statement about the energy required to maintain a current of one See also:

• AMPERE, ANDRE MARIE (1775–1836)
• AMPERE, JEAN JACQUES (1800-1864)

ampere through a resistance of one See also:

• OHM, GEORG SIMON (1787-1854)

ohm for one second, and to define it by its equivalent in the energy of a moving mass .

Physical units have therefore been selected with the See also:

• OBJECT

object of establishing simple relations between each of them and the fundamental mechanical units . Measurements based on such relations are called See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

absolute measurements . The science of See also:

• DYNAMICS
• DYNAMICS (from Gr. bbvayts, strength)

dynamics, as far as that part of it is concerned which deals with the motion and energy of material substances, starts from certain See also:

• PRIMARY

primary See also:

• DEFINITIONS

definitions concerning the measurable quantities involved . In constructing a See also:

• SYSTEM

system of physical units, the first thing to consider is the manner in which we shall connect the various items . What, for instance, shall be the unit of force, and how shall it be determined by simple reference to the units of mass, length and See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time ? The See also:

• MODERN

modern absolute system of physical measurement is founded upon dynamical notions, and originated with C . F . See also:

• GAUSS, KARL FRIEDRICH (1777-1855)

Gauss . We are for the most part concerned in studying motions in nature; and even when we find bodies at See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest in See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium it is because the causes of motion are balanced rather than absent . Moreover, the postulate which lies at the See also:

• BASE

base of all See also:

• PRESENT

present-See also:

• DAY (O. Eng. dreg, Ger. Tag; according to the New English Dictionary, " in no way related to the Lat. dies")
• DAY, JOHN (1574-1640?)
• DAY, THOMAS (1748-1789)

day study of physics is that in the ultimate issue we must seek for a mechanical explanation of the facts of nature if we are to reach any explanation intelligible to the human mind . Accordingly the See also:

• ROOT (late O.E. rot, adopted from Scand., cf. Norw. and Swed. rot, Dan. rod; the true O.E. word was wyrt, plant, represented in Ger. Wurz or Wurzel; the ultimate root is the same in both words, and is seen in Lat. radix)
• ROOT, ELIHU (1845– )

root of all science is the knowledge of the See also:

• LAWS

laws of motion, and the enunciation of these laws by See also:

• NEWTON
• NEWTON, ALFRED (1829–1907)
• NEWTON, JOHN (1725-1807)
• NEWTON, JOHN (1823-1895)
• NEWTON, SIR CHARLES THOMAS (1816-1894)
• NEWTON, SIR ISAAC (1642-1727)

Newton laid the See also:

• FOUNDATION (Lat. fundatio, from fundare, to found)

foundation of a more exact knowledge of nature than had been possible before . Our fundamental scientific notions are those of length, time, and mass .

No metaphysical discussion has been able to resolve these ideas into anything simpler or to derive them from each other . Hence in selecting units for physical measurements we have first to choose units for the above three quantities . Fundamental Units.—Two systems of fundamental units are in common use: the See also:

• BRITISH

British system, having the yard and See also:

• POUND
• POUND (2)—(a)

pound as the standard units of length and mass, frequently termed the " See also:

• FOOT

foot-pound-second " (F.P.S.) system; and the " centimetre-gramme-second " system (C.G.S.), having the centimetre and gramme as standard units of length and mass, termed the " metric " system . The fundamental unit of time is the same in both systems, namely, the " mean See also:

• SOLAR, SOLLER (Lat. solarium, Fr.• galetas, Ital. solaio)

solar second," 86,400 of which maker solar day (see TIME) . Since these systems and the corresponding See also:

• STANDARDS

standards, together with their factors of conversion, are treated in detail in the See also:

• ARTICLE (from Lat. articulus, a joint)

article WEIGHTS AND See also:

• MEASURES

MEASURES, we need only See also:

• DEAL

deal here with such units as receive special scientific use, i.e. other than in See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary commercial practice . The choice of a unit in which to See also:

• EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express any quantity is determined by the magnitude and proportional See also:

• ERROR (Lat. error, from errare, to wander, to err)

error of the measurement . In See also:

• ASTRONOMY (from Gr. &arpov, a star, and v ,usiv, to classify or arrange)

astronomy, where immense distances have to be very frequently expressed, a common unit is the mean See also:

• RADIUS

radius of the See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth's See also:

• ORBIT (from Lat. orbita, a track, orbis, a wheel)

orbit, the " astronomical unit " of length, i.e . 92,900,000 See also:

• MILES, NELSON APPLETON (1839— )

miles . But while this unit serves well for the region of our solar system, its use involves unwieldy numerical coefficients when stellar distances are to be expressed . Astronomers have therefore adopted a unit of length termed the " See also:

• LIGHT

light See also:

• YEAR

year," which is the distance traversed by light in a year; this unit is 63,000 times the mean radius of the earth's orbit . The relative merits of these units as terms in which astronomical distances may be expressed is exhibited by the values of the distance of the See also:

• STAR

star a Centauri from our earth, namely, 25,000,000,000,000 miles = 275,000 astronomical units = 4.35 light years . As another example of a physical unit chosen as a matter of convenience, we may refer to the magnitudes of the See also:

• WAVE

wave-lengths of light .

These quantities are extremely small, and admit of correct determination to about one part in ten-thousand, and range, in the visible spectrum, from about 6 to 4 ten-millionths of a See also:

• METRE ((terpuc?, sc. rFxvf, from Gr. Or poi', measure)

metre . Since their values are determined to four significant figures, it is desirable to choose a unit which represents the value as an integer number; the unit is therefore a ten-thousandmillionth of a metre, termed a " tenth metre," since it is io 10 metres . Sometimes the thousand-millionth of a metre, the " micromillimetre," denoted by µµ, serves as a unit for wave lengths . Another relatively See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute unit is the " micron," denoted by µ, and equal to orie-millionth of a metre; it is especially used by bacteriologists . Units in See also:

• MECHANICS

Mechanics . --The quantifies to be measured in mechanics (q.v.) are velocity and See also:

• ACCELERATION (from Lat. accelerare, to hasten, celer, quick)

acceleration, dependent on the units of length and time only, momentum, force, energy or See also:

• WORK

work and power, dependent on the three fundamental units . The unit of velocity in the British system is r foot, i yard, or r mile per second; or the time to which the distance is referred may be expressed in See also:

• HOURS, CANONICAL

hours, days, &c., the choice depending upon the actual magnitude of the velocity or on See also:

• CUSTOM (from O. Fr. costume, costume or coustume; Low Lat. costuma, a shortened form of consuetudo)

custom . Thus the muzzle velocity of a See also:

• RIFLE

rifle or See also:

• CANNON (a word common to Romance languages, from the Lat. canna, a reed, tube, with the addition of the augmentative termination -on, -one)

cannon shot is expressed in feet per second, whereas the See also:

• SPEED, JOHN (1552–1629)

speed of a See also:

• TRAIN (M. Eng. trayn or trayne, derived through Fr. from Late Lat. trahinare, to drag, draw, Lat. trahere, cf. trail, trace, ultimately from the same source)

train is usually expressed in miles per See also:

• HOUR

hour . Similarly, the unit on the metric system is s metre, or any decimal multiple thereof, per second, per hour, &c . Since acceleration is the See also:

• RATE

rate of increase of velocity per unit time, it is obvious that the unit of acceleration depends solely upon the units chosen to express unit velocity; thus if the unit of velocity be one foot per second, the unit of acceleration is one foot per second per second, if one metre per second the unit is one metre per second per second, and similarly for other units of velocity . Momentum is defined as the product of mass into velocity; unit momentum is therefore the momentum of unit mass into unit velocity; in the British system the unit of mass may be the pound, ton, &c., and the unit of velocity any of those mentioned above; and in the metric system, the gramme, kilogramme, &c., may be the unit of mass, while the metre per second, or any other metric unit of velocity, is the remaining See also:

• TERM

term of the product . Force, being measured .by the See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change of momentum in unit time, is expressed in terms of the same units in which unit momentum is defined .

The common British unit is the poundal," the force which in one second retards or accelerates the velocity of a mass of one pound by one foot per second . The metric (and scientific) unit, named the " dyne," is derived from the centimetre, gramme, and second . The poundal and dyne are related as follows:—r poundal= 13,825.5 dynes . A common unit of force, especially among See also:

• ENGINEERS, MILITARY

engineers, is the " See also:

• WEIGHT

weight of one pound," by which is meant the force equivalent to the gravitational attraction of the earth on a mass of one pound . This unit obviously depends on gravity; and since this varies with the See also:

• LATITUDE (Lat. latitudo, latus, broad)

latitude and height of the See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place of observation (see EARTH, FIGURE oF), the " force of one pound " of the engineer is not See also:

• CONSTANT, BENJAMIN (1845-1902)

constant . Roughly, it equals 32.17 poundals or 98o dynes . The most frequent uses of this engineer's unit are to be found in the expressions for pressure, especially in the boilers and cylinders of See also:

• STEAM
• STEAM (0. Eng. steam, vapour, smoke, cf. Du. steam; the origin is unknown)

steam engines, and in structures, such as See also:

• BRIDGES
• BRIDGES, ROBERT (1844– )

bridges, See also:

• FOUNDATIONS

foundations of buildings, &c . The expression takes the See also:

• FORM (Lat. forma)

form: pounds per square foot or See also:

• INCH (O. Eng. ynce from Lat. uncia, a twelfthpart; cf. " ounce," and see As)

inch, meaning a force equivalent to so many pounds' weight distributed over a square foot or inch, as the See also:

• CASE
• CASE, JOHN (d. 1600)

case may be . Other units of pressure (and therefore special units of force) are the " See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere " (abbreviated atmo "), the force exerted on unit See also:

• AREA

area by the See also:

• COLUMN (Lat. columna)

column of See also:

• AIR (from an Indo-European root meaning " breathe," " blow ")
• AIR, or ASBEN

air vertically above it; the " millimetre or centimetre of See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

mercury," the usual scientific units, the force exerted on unit area by a column of mercury one millimetre or centimetre high; and the " foot of water," the column being one foot of water . All these units admit of ready conversion:—I atmo -s-- 76o mm. mercury—32 feet of water =1,013,600 dynes . Energy of work is measured by force acting over a distance . The scientific unit is the " erg," which is the energy expended when a force of one dyne acts over one centimetre .

This unit is too small for measuring the quantity of energy associated, for instance, with engines; for such purposes a unit ten-million times as See also:

• GREAT

great, termed the " See also:

• JOULE, JAMES PRESCOTT (1818–1889)

joule," is used . The British absolute unit is the " poundal-foot." As we noticed in the case of units of force, common-See also:

• LIFE

life experience has led to the introduction of units dependent on See also:

• GRAVITATION (from Lat. gravis, heavy)

gravitation, and therefore not invariable; the common British See also:

• PRACTICAL

practical unit of this class is the " foot-pound "; in the metric system its congener is the " kilogramme-metre." Power is the rate at which force does work; it is therefore expressed by " units of energy per second." The metric unit in use is the " See also:

• WATT, JAMES (1736-1819)

watt," being the rate equal to one joule per second . Larger units in practical use are: " kilowatt,' equal to See also:

• I000

I000 See also:

• WATTS, ALARIC ALEXANDER (1797-1864)
• WATTS, GEORGE FREDERICK (1817-1904)
• WATTS, ISAAC (1674-1748)

watts; the corresponding energy unit being the kilowatt-second, and 3600 kilowatt-seconds or I kilowatt-hour called a " See also:

• BOARD (O. Eng. bord)

Board of See also:

• TRADE (O. Eng. trod, footstep, from tredan, to tread; in M. Eng. the forms teed, trod and trade appear, the last in the sense of a beaten track)
• TRADE, BOARD OF

Trade unit " or a " See also:

• KELVIN, WILLIAM THOMSON, BARON (1824-1907)

kelvin." This last is a unit of energy, not power . In British See also:

• ENGINEERING

engineering practice the common unit of power is the " See also:

• HORSE (a word common to Teutonic languages in such forms as hors, hros, ros; cf. the Ger. ross)

horse-power " (I-P), which equals 55o foot-pounds performed per second, or 33,000 foot-pounds per minute; its equivalent in the metric system is about 746 watts, the ratio varying, however, with gravity . Units of Heat.—In studying the phenomena of heat, two measurable quantities immediately present themselves: (1) temperature or thermal potential, and (2) quantity of heat . Three arbitrary scales are in use for measuring temperature (see See also:

• THERMOMETRY (Gr. Bepµos, warm; µerpov, a measure)

THERMOMETRY), and each of these scales affords units suitable for the expression of temperature . On the Centigrade See also:

• SCALE
• SCALE (1) A

scale the unit, termed a " Centigrade degree," is one-hundredth of the See also:

• INTERVAL

interval between the temperature of water boiling under normal barometric pressure_ (76o mm. of mercury) and that of melting See also:

• ICE (a word common to Teutonic languages; cf. Ger. Eis)

ice; the " See also:

• FAHRENHEIT, GABRIEL DANIEL (1686–1936)

Fahrenheit degree " is one-hundredand-eightieth, and the " See also:

• REAUMUR, RENE ANTOINE FERCHAULT DE (1683-1757)

Reaumur degree " is one-eightieth of the same difference . In addition to these scales there is the " thermo-dynamic scale," which, being based on dynamical reasoning, admits of correlation with the fundamental units . This subject is discussed in the articles See also:

• THERMODYNAMICS (from Gr. Bepµos, hot, Siva trs, force)

THERMODYNAMICS and THERMOMETRY . Empirical units of " quantity of heat " readily suggest them-selves as the amount of heat necessary to heat a unit mass of any substance through unit temperature . In the metric system the unit, termed a " calorie," is the quantity of heat required to raise a gramme of water through one degree Centigrade . This quantity, however, is not constant, since the specific heat of water varies with temperature (see See also:

• CALORIMETRY

CALORIMETRY) .

In defining the calorie, therefore, the particular temperatures must be specified; consequently there are several calories particularized by special designations:—(r) conventional or common gramme-calorie, the heat required to raise I gramme of water between 150° C. and 17° C. through 1° C.; (2) " mean or See also:

• AVERAGE

average gramme calorie," one-hundredth of the See also:

• TOTAL

total heat required to raise the temperature of I gramme of water from o° C. to See also:

• ROE (or Row), SIR THOMAS (c. 1581—1644)
• ROE, EDWARD PAYSON (1838-1888)

roe C.; (3) " zero gramme calorie," the heat required to raise r gramme of water from o° C. to I° C . These units are thus related: common calorie= 1.987 mean calories= 0.992 zero calories . A unit in common use in thermo-See also:

• CHEMISTRY
• CHEMISTRY (formerly "chymistry"; Gr. xvµela; for derivation see ALCHEMY)

chemistry is the See also:

• MAJOR
• MAJOR (Lat. for " greater ")
• MAJOR (or MAIR), JOHN (1470-1550)

major calorie, which refers to one kilogramme of water and I° C . In the British system the common unit, termed the " British Thermal Unit " (B.Th.U.), is the amount of heat required to raise one pound of water through one degree Fahrenheit . A correlation of these units of quantity of heat with the fundamental units of mass, length and time attended the recognition of the fact that heat was a form of energy; and their quantitative relationships followed from the experimental determinations of the so-called " mechanical equivalent of heat," i.e. the amount of mechanical energy, expressed in ergs, joules, or foot-pounds, equivalent to a certain quantity of heat (cf . CALORIMETRY) . These results show that a See also:

• GRAM

gram-calorie is equivalent to about 4.2 joules, and a British thermal unit to 78o foot-pounds . See also:

• ELECTRICAL
• ELECTRICAL (or ELECTROSTATIC) MACHINE

Electrical Units.—The next most important units are the electrical units . We are principally concerned in electrical work with three quantities called respectively, electric current, electromotive force, and resistance . These are related to one another by Ohm's See also:

• LAW
• LAW (0. Eng. lagu, M. Eng. lawe; from an old Teutonic root lag, " lie," what lies fixed or evenly; cf. Lat. lex, Fr. loi)
• LAW, JOHN (1671—1729)
• LAW, WILLIAM (1686-1761)

law, which states that the electric current in a See also:

• CIRCUIT (Lat. circuitus, from circum, round, and ire, to go)

circuit is directly as the electromotive force and inversely as the resistance, when the current is unvarying and the temperature of the circuit constant . Hence if we choose units for two of these quantities, the above law defines the unit for the third . Much discussion has taken place over this question, .

The choice is decided by the nature of the quantities themselves . Since resistance is a permanent quality of a substance, it is possible to select a certain piece of See also:

• WIRE (A.S. wir, a wire; cf. Swed. vire, to twist, M.H.G. wiere, a gold ornament, Lat. viriae, armlets, ultimately from the root wi, to twist, bind)

wire or See also:

• TUBE (Lat. tuba)

tube full of mercury, and declare that its resistance shall be the unit of resistance, and If the substance is permanent we shall possess an unalterable standard or unit of resistance . For these reasons the practicalunit of resistance, now called the See also:

• INTERNATIONAL, THE

international ohm, has been selected as one of the above three electrical units . It has now been decided that the second unit shall be the unit of electric current . As an electric current is not a thing, but a See also:

• PROCESS

process, the unit current can only be reproduced when desired . There are two available methods for creating a standard or unit electric current . If an unvarying current is passed through a neutral See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution of See also:

• SILVER

silver nitrate it decomposes or electrolyses it and deposits silver upon the negative See also:

• POLE (FAMILY)
• POLE, REGINALD (1500-1558)
• POLE, RICHARD DE LA (d. 1525)
• POLE, WILLIAM (1814—1900)

pole or See also:

• CATHODE

cathode of the electrolytic See also:

• CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell . According to See also:

• FARADAY, MICHAEL (1791-1867)

Faraday's law and all subsequent experience, the same current deposits in the same time the same mass of silver . Hence we may define the unit current by the mass of silver it can liberate per second . Again, an electric current in one circuit exerts mechanical force upon a magnetic pole or a current in another circuit suitably placed, and we may measure the force and define by it a unit electric current . Both these methods have been used . Thirdly, the unit of electromotive force may be defined as equal to the difference of potential between the ends of the unit of resistance when the unit of current flews in it .

Apart, however, from the relation of these electrical units to each other, it has been found to be of great importance to establish a simple relation between the latter and the absolute mechanical units . Thus an electric current which is Absolute passed through a conductor dissipates its energy as electrical heat, and hence creates a certain quantity of heat units . per unit of time . Having chosen our units of energy and related unit of quantity of heat, we must so choose the 'Init of current that when passed through the unit of resistance it shall dissipater unit of energy in 1 unit of time . A further See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration has weight in selecting the See also:

• SIZE

size of the units, namely, that they must be of convenient magnitude for the ordinary measurements . The founders of the British modern system of practical electrical units were a Assoclacommittee appointed by the British Association in tioa 1861, at the See also:

• SUGGESTION

suggestion of See also:

• LORD
• LORD (O. Eng. hldford, i.e. hldfweard, the warder or keeper of bread, hlIf, loaf; the word is not represented in any other Teutonic language)
• LORD, JOHN (1810-1894)

Lord Kelvin, which made its units. first See also:

• REPORT (O.Fr. report or raport, modern rapport, from O.Fr. reporter, mod. rap porter, Lat. reportare, to bring back, in poetical use only, of bringing back an account, news, &c.)

report in 1862 at See also:

• CAMBRIDGE
• CAMBRIDGE, EARLS AND DUKES OF
• CAMBRIDGE, RICHARD OWEN (1717-1802)

Cambridge (see B . A . Report) . The five subsequent reports containing the results of the See also:

• COMMITTEE (from commute, an Anglo-Fr. past participle of commettre, Lat. committere, to entrust; the modern Fr. equivalent comite is derived from the Eng.)

committee's work, together with a large amount of most valuable matter on the subject of electric units, were collected in a volume edited by Prof . Fleeming Jenkin in 1873, entitled Reports of the Committee on Electrical Standards . This committee has continued to sit and report annually to the British Association since that date . In their second report in 1863 (see B.A .

Report, See also:

• NEWCASTLE
• NEWCASTLE, DUKES OF

Newcastle-on-See also:

• TYNE

Tyne) the committee recommended the See also:

• ADOPTION (Lat. adoptio, for adoptalio, from adoptare, to choose for oneself)

adoption of the absolute system of electric and magnetic units on the basis originally proposed by Gauss and See also:

• WEBER, CARL MARIA FRIEDRICH ERNEST VON (1786–1826)
• WEBER, WILHELM EDUARD (1804-1891)

Weber, namely, that these units should be derived from the fundamental dynamical units, but assuming the units of length, mass and time to be the metre, gramme and second instead of the millimetre, milligramme and second as proposed by Weber . Considerable See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences of See also:

• OPINION (Lat. opinio, from opinari, to think)

opinion existed as to the choice of the fundamental units, but ultimately a suggestion of Lord Kelvin's was adopted to select the centimetre, gramme, and second, and to construct a system of electrical units (called the C.G.S. system) derived from the above fundamental units . On this system the unit of force is the dyne and the unit of work the erg . The dyne is the See also:

• UNIFORM

uniform force which when acting on a mass of r gramme for I second gives it a velocity of I centimetre per second . The erg is the work done by I dyne when acting through a distance of I centimetre in its own direction . The electric and magnetic units were then derived, as previously suggested by Weber, in the following manner: If we consider two very small See also:

• SPHERES, MUSIC OF THE

spheres placed with centres I centimetre apart in air and charged with equal quantities of See also:

• ELECTRICITY

electricity, then if the force between these bodies is I dyne each See also:

• SPHERE (Gr. vclsa?pa, a ball or globe)

sphere is said to be charged with I unit of electric quantity on the electrostatic system . Again, if we consider two isolated magnetic poles of equal strength and consider them placed r centimetre apart in air, then if the force between them is r dyne these poles are said to have a strength of I unit on the electromagnetic system . Unfortunately the committee did not take into See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account the fact that in the first case the force between the electric charges depends upon and varies inversely as the di-electric constant of the See also:

• MEDIUM

medium in which the experiment is made, and in the second case it depends upon the magnetic See also:

• PERMEABILITY, MAGNETIC

permeability of the medium in which the magnetic poles exist . To put it in other words, they assume that the See also:

• DIELECTRIC

dielectric constant of the circumambient medium was unity in the first case, and that the permeability was also unity in the second case . The result of this choice was that two systems of measurement were created, one depending upon the unit of electric quantity so chosen, called the electrostatic system, and the other depending upon the unit magnetic pole defined as above, called the electromagnetic system of C.G.S. units . Moreover, it was found that in neither of these systems were the units of very convenient magnitude . Hence, finally, the committee adopted a third system of units called the practical system, in which convenient decimal multiples or fractions of the electromagnetic units were selected and named for use .

This system, moreover, is not only consistent with itself, but may be considered to be derived from a system of dynamical units in which the unit of length is the earth quadrant or ro million metres, the unit of mass is Io 11 of a gramme and the unit of time is i second . The units on this system have received names derived from those of eminent discoverers . Moreover, there is a certain relation between the size of the units for the same quantity on the electrostatic (E.S.) system and that on the electromagnetic (E.M.) system, which depends upon the velocity of light in the medium in which the measurements are supposed to be made . Thus on the E.S. system the unit of electric quantity is a point See also:

• CHARGE
• CHARGE (through the Fr. from the Late Lat. carricare, to load in a carrus or wagon; cf. " cargo ")

charge which at a distance of r cm. acts on another equal charge with a force of r dyne . The E.S. unit of electric current is a current such that I E.S. unit of quantity flows per second across each See also:

• SECTION
• SECTION (Lat. sectio, cutting, secare, to cut)

section of the circuit . On the E.M. system we start with the See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition that the unit magnetic pole is one which acts on another equal pole at a distance of r cm. with a force of 1 dyne . The unit of current on the E.M. system is a current such that if flowing in circular circuit of r cm. radius each unit of length of it will See also:

• ACT (Lat. actus, actum)

act on a unit magnetic pole at the centre with a force of r dyne . This E.M. unit of current is much larger than the E.S. unit defined as above . It is v times greater, where v = 3 X r o10 is the velocity of light in air expressed in See also:

• EMS

ems. per second . The See also:

• REASON (Lat. ratio, through French raison)

reason for this can only be understood by considering the dimensions of the quantities with which we are concerned . If L, M, T denote length, mass, time, and we adopt certain sized units of each, then we may measure any derived quantity, such as velocity, acceleration, or force in terms of the derived dynamical units as already explained . Suppose, however, we alter the size of our selected units of L, M or T, we have to consider how this alters the corresponding units of velocity, acceleration, force, &c .

To do this we have to consider their dimensions . If the unit of velocity is the unit of length passed over per unit of time, then it is obvious that it varies directly as the unit of length, and inversely as the unit of time . Hence we may say that the dimensions of velocity are L/T or LT-'; similarly the dimensions of acceleration are L/T2 or LT-2, and the dimensions of a force are MLT-2 . For a See also:

• FULLER, ANDREW (1954-1815)
• FULLER, GEORGE (1822—1884)
• FULLER, M
• FULLER, MARGARET, MARCHIONESS
• FULLER, MELVILLE WESTON (1833-1910)
• FULLER, THOMAS (16o8-1661)
• FULLER, WILLIAM (1670--c. 1717)

fuller explanation see above (UNITS, DIMENSIONS OF), or See also:

• EVERETT
• EVERETT, ALEXANDER HILL (1790-1847)
• EVERETT, CHARLES CARROLL (1829-1900)
• EVERETT, EDWARD (1794–1865)

Everett's Illustrations of the C.G.S . System of Units . Accordingly on the electrostatic system the unit of electric quantity is such that f= q2/Kd2, where q is the quantity of Flectro- the two equal charges, d their distance, f the mechanical staticand force or stress between them, and K the dielectric electro- constant of the dielectric in which they are See also:

• IM(K2+a2+h2—2 ah cos 0)

im- magnetic mersed . Hence since f is of the dimensions MLT-2, q2 units . must be of the dimensions of KML3T-2, and q of the dimensions M1 LIT 'KI . The dimensions of K, the dielectric constant, are unknown . Hence, in accordance with the suggestion of See also:

• SIR

Sir A . Rucker (Phil . Mag., See also:

• FEBRUARY

February 1889), we must treat it as a fundamental quantity .

The dimensions of an electric current on the electrostatic system are therefore those of an electric quantity divided by a time, since by current we mean the quantity of electricity conveyed per second . Accordingly current on the E.S. system has the dimensions MiLIT-2KI . We may obtain the dimensions of an electric current on the magnetic system by observing that if two circuits traversed by the same or equal currents are placed at a distance from each other, the mechanical force or stress between two elements of the circuit, in accordance with Ampere's law (see ELECTRO-See also:

• KINETICS (from Gr. taveiv, to move)

KINETICS), varies as the square of the current C, the product of the elements of length ds, ds' of the circuits, inversely as the square of their distance d, and directly as the permeability p of the medium in which they are immersed . Hence C2dr ds'g/d2 must be of the dimensions of a force or of the dimensions MLT-2 . Now, ds and ds' are lengths, and d is a length, hence the dimensions of electric current on the E.M . system must be MlLIT 'p 1 . Accordingly the dimensions of current on the E.S. system are MILIT-2 K1, and on the E.M. system they are M1LIT' 1, where u and K, the permeability and di- electric constant of the medium, are of unknown dimensions, and therefore treated as fundamental quantities . The ratio of the dimensions of an electric current on the two systems (E.S. and E.M.) is therefore LT 1K'µ1 . This ratio must be a See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere numeric of no dimensions, and therefore the dimensions of SKµ must be those of the reciprocal of a velocity . We do not know what the dimensions of u and K are separately, but we do know, therefore, that their product has the dimensions of the reciprocal of the square of a velocity . Again, we may arrive at two dimensional expressions for electromotive force or difference of potential . Electrostatic difference of potential between two places is measured by the mechanical work required to move a small conductor charged with a unit electric charge from one place to the other against the electric force .

Hence if V stands for the difference of potential between the two places, and Q for the charge on the small conductor, the product QV must be of the dimensions of the work or energy, or of the forceXlength, or of ML2T-2 . But Q on the electrostatic system of measurement is of the dimensions MILlT-'KI ; the potential difference V must be, therefore, of the dimensions MiLiT 'KI . Again, since by Ohm's law and Joule's law electromotive force multiplied by a current is equal to the power expended on a circuit, the dimensions of electromotive force, or, what is the same thing, of potential difference, in the electromagnetic system of measurement must be those of power divided by a current . Since mechanical power means rate of doing work, the dimensions of power must be ML2T-3 . We have already seen that on the electromagnetic system the dimensions of a current are MiLIT 'p 1 • therefore the dimensions of electromotive force or potential on the electromagnetic system must be MILIT-2µI . Here again we find that the ratio of the dimensions on the electrostatic system to the dimensions on the electromagnetic system is L-1TK 1p 1 . In the same manner we may recover from fundamental facts and relations the dimensions of every electric and magnetic quantity on the two systems, starting in one case from electrostatic phenomena and in the other case from electromagnetic or magnetic . The electrostatic dimensional expression will always involve K, and the electromagnetic dimensional expression will always involve p, and in every case the dimensions in terms of K are to those in terms of p for the same quantity in the ratio of a power of LT-'K1µ1 . This therefore confirms the view that whatever may be the true dimensions in terms of fundamental units of µ and K, their product is the inverse square of a velocity . Table I. gives the dimensions of all the See also:

• PRINCIPAL

principal electric and magnetic quantities on the electrostatic and electromagnetic systems . It will be seen that in every case the ratio of the dimensions on the two systems is a power of LT-'K'1µ1, or of a velocity multiplied by the square root of the product K and p; in other words, it is the product of a velocity multiplied by the geometric mean of K and p . This quantity i/s/Kµ must therefore be of the dimensions of a velocity, and the questions arise, What is the absolute value of this velocity? and, How is it to be determined ?

The See also:

• ANSWER (derived from and, against, and the same root as swear)

answer is, that the value of the velocity in See also:

• CONCRETE
• CONCRETE (Lat. concretes, participle of concrescere, to grow together)

concrete See also:

• NUMBERS, BOOK OF
• NUMBERS, PARTITION OF

numbers maybe obtained by measuring the magnitude of any electric quantity in two ways, one making use only of electrostatic phenomena, and the other only of electromagnetic . To take one instance :—It is easy to show that the electrostatic capacity of a sphere suspended in air or in vacuo at a great distance from other conductors is given by a number equal to its radius in centimetres . Suppose such a sphere to be charged and discharged rapidly with electricity from any source, such as a See also:

• BATTERY (Fr. batterie, from battles, to beat)

battery . It would take electricity from the source at a certain rate, and would in fact act like a resistance in permitting the passage through it or by it of a certain quantity of electricity per unit of time . If K is the capacity and n is the number of discharges per second, then nK is a quantity of the dimensions of an electric conductivity, or of the reciprocal of a resistance . If a conductor, of which the electrostatic capacity can be calculated, and which has associated with it a commutator that charges and discharges it n times per second, is arranged in one branch of a See also:

• WHEATSTONE, SIR CHARLES (1802–1875)

Wheatstone's See also:

• BRIDGE

Bridge, it can be treated and measured as if it were a resistance, and its equivalent resistance calculated in terms of the resistance of all the other branches of the bridge (see Phil . Mag., 1885, 20, 258) . Accordingly, we have two methods of measuring the capacity of a conductor . One, the electrostatic method, depends only on the measurement of a length, which in the case of a sphere in See also:

• FREE

free space is its radius; the other, the electromagnetic method, deter-mines the capacity in terms of the quotient of a time by a resistance . The ratio of the electrostatic to the electromagnetic value of the same capacity is therefore of the dimensions of a velocity multiplied by a resistance in electromagnetic value, or of the dimensions of a velocity squared . This particular experimental measurement has been carried out carefully by many observers, and the result has been always to show that the velocity v which expresses the ratio is very nearly equal to 30 thousand million centimetres per second; v =nearly 3 X 10'0 . The value of this important constant can be determined by experiments made to measure electric quantity, potential, resistance or capacity, both in electrostatic and in electromagnetic measure .

For details of the various methods employed, the reader must be referred to standard See also:

• TREATISES

treatises on Electricity and See also:

• MAGNETISM
• MAGNETISM, TERRESTRIAL

Magnetism, where full particulars will be found (see See also:

• MAXWELL
• MAXWELL, JAMES CLERK (1831–1879)

Maxwell, See also:

• TREATISE

Treatise on Electricity and Magnetism, vol. ii. ch. xix . 2nd ed.; also Mascart and See also:

• JOUBERT, BARTHELEMY CATHERINE (1769–1799)
• JOUBERT, JOSEPH (1754–1824)
• JOUBERT, PETRUS JACOBUS (1834–1900)

Joubert, Treatise on Electricity and Magnetism, vol. ii. ch. viii., Eng. trans. by See also:

• ATKINSON, EDWARD (1827—1905)
• ATKINSON, SIR HARRY ALBERT (1831—1892)

Atkinson) . Table II. gives a See also:

• LIST (O.E. lisle, a Teutonic word, cf. Dut. lust, Ger. Leiste, adapted in Ital. lista and Fr. lisle)
• LIST, FRIEDRICH (1789-1846)

list of some of these determinations of v, with references to the See also:

• ORIGINAL

original papers . It will be seen that all the most See also:

• RECENT

recent values, especially those in which a comparison of capacity has been made, approximate to 3 X tO'0 centimetres per second, a value which is closely in See also:

• ACCORD (from Fr. accorder, to agree)

accord with the latest and best determinations of the velocity of light . We have in the next place to consider the question of Practical practical electric units and the determination and units. construction of concrete standards . The committee of the British Association charged with the See also:

• DUTY (from " due," that which is owing, O. Fr. deu, dil, past participle of devoir; Lat. debere, debitum; cf. " debt ")

duty of arranginga system of absolute and magnetic units settled also on a system of practical units of convenient magnitude, and gave names to them as follows:- Io9 absolute electromagnetic units of resist- ance = I ohm Ios „ „ units of electro- See also:

• MOTIVE (from Lat. movere, to move)

motive force = r volt th of an „ unit of current =1 ampere -i,° th of an „ „ unit of quantity = I See also:

• COULOMB, CHARLES AUGUSTIN (1736-1806)

coulomb Io-9 „ ,, units of capacity=1 farad Io is ,, 11 units of capacity =1microfarad Since the date when the preceding terms were adopted, other multiples of absolute C.G.S. units have received practical names, thus: Io7 ergs or absolute C.G.S. units of energy = I joule Io7 ergs per second or C.G.S. units of power = I watt •Io9 absolute units of inductance = r See also:

• HENRY
• HENRY (1129-1195)
• HENRY (c. 1108-1139)
• HENRY (c. 1174–1216)
• HENRY (Fr. Henri; Span. Enrique; Ger. Heinrich; Mid. H. Ger. Heinrich and Heimrich; O.H.G. Haimi- or Heimirih, i.e. " prince, or chief of the house," from O.H.G. heim, the Eng. home, and rih, Goth. reiks; compare Lat. rex " king "—" rich," therefore " mig
• HENRY, EDWARD LAMSON (1841– )
• HENRY, JAMES (1798-1876)
• HENRY, JOSEPH (1797-1878)
• HENRY, MATTHEW (1662-1714)
• HENRY, PATRICK (1736–1799)
• HENRY, PRINCE OF BATTENBERG (1858-1896)
• HENRY, ROBERT (1718-1790)
• HENRY, VICTOR (1850– )
• HENRY, WILLIAM (1795-1836)

henry I0 absolute units of magnetic See also:

• FLUX (Lat. fluxus, a flowing; this being also the meaning of the English term in medicine, &c.)

flux = i weber, 1 absolute unit of magnetomotive force = 1 gauss, An Electrical See also:

• CONGRESS (Lat. congressus, coming together, from congredi; cum, with, and gradus, step)

Congress was held in See also:

• CHICAGO
• CHICAGO, UNIVERSITY OF

Chicago, U.S.A., in See also:

• AUGUST (originally Sextilis)

August 1893, to consider the subject of international practical electrical units, and the result of a See also:

• CONFERENCE

conference between scientific representatives of Great See also:

• BRITAIN (Gr. Hperavuml vi7vot, Bperravia; Lat. Britannia, rarely Britannia)

Britain, the See also:

• UNITED

United States, See also:

• FRANCE
• FRANCE, ANATOLE (1844– )

France, See also:

• GERMANY
• GERMANY (Ger. Deutschland)

Germany, See also:

• ITALY
• ITALY (Italia)

Italy, See also:

• MEXICO
• MEXICO (Span. Mejico, or Mexico,)
• MEXICO, FEDERAL DISTRICT OF
• MEXICO, GULF OF

Mexico, See also:

• AUSTRIA
• AUSTRIA, LOWER (Ger. Niederosterreich or Osterreich unter der Enns, " Austria below the river Enns ")
• AUSTRIA, UPPER (Ger. Oberosterreich or Osterreich ob der Enns, " Austria above the river Enns ")

Austria, See also:

• SWITZERLAND

Switzerland, See also:

• SWEDEN
• SWEDEN [Sverige]
• SWEDEN, NORWAY AND

Sweden and British See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

North See also:

• AMERICA

America, after deliberation for six days, was a unanimous agreement to recommend the following resolutions as the definition of practical international units . These resolutions and definitions were confirmed at other conferences, and at the last one held in See also:

• LONDON

London in See also:

• OCTOBER

October 1908 were finally adopted . It was agreed to take : ” As a unit of resistance, the International Ohm, which is based upon the ohm equal to Io9 units of resistance of the C.G.S. system of electromagnetic units, and is represented by the resistance offered to an unvarying electric current by a column of mercury at the temperature of melting ice 14.4521 grammes in mass, of a constant See also:

• CROSS

cross-sectional area and of the length of Io6.3 cm . " As a unit of current, the International Ampere, which is one-tenth of the unit of current of the C.G.S. system of electromagnetic units, and which is represented sufficiently well for practical use by the unvarying current which, when passed through a solution of nitrate of silver in water, depasits silver at the rate of x•00111800 of a gramme per second . " As a unit of electromotive force, the International Volt, which is the electromotive force that, steadily applied to a conductor whose resistance is one international ohm, will produce a current of one international ampere . It is represented sufficiently well for practical purposes by ioea of the E.M.F. of a normal or saturated See also:

• CADMIUM (symbol Cd, atomic weight 112.4 (0=16))

cadmium See also:

• WESTON, THOMAS (1737-1776)

Weston cell at 20° C., prepared in the manner described in a certain See also:

• SPECIFICATION (from Med. Lat. specificatio, specificare, to enumerate or mention in detail)

specification . " As a unit of quantity, the International Coulomb, which is the quantity of electricity transferred by a current of one international ampere in one second .

As the unit of capacity, the International Farad, which is the capacity of a See also:

• CONDENSER

condenser charged to a potential of one international volt by one international coulomb of electricity . " As a unit of work, the Joule, which is equal to Io7 units of work in the C.G.S . System, and which is represented sufficiently well for practical use by the energy expended in one second by an international ampere in an international ohm . " As a unit of power, the Watt, which is equal to Io7 units of power in the C.G.S . System, and which is represented sufficiently well for practical use by the work done at the rate of one joule per second . As the unit of inductance, the Henry, which is the See also:

• INDUCTION (from Lat. inducere, to lead into; cf. Gr. ilrayu yli)

induction in a circuit when an electromotive force induced in this circuit is one international volt, while the inducing current varies at the rate of one ampere per second.” Neither the weber nor the gauss has received very See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general adoption, although recommended by the Committee of the British Association on Electrical Units . Many different suggestions have been made as to the meaning to be applied to the word " gauss.” The practical electrical engineer, up to the present, prefers to use one ampere-turn as his unit of magnetomotive force, and one See also:

• LINE

line of force as the unit of magnetic flux, equal respectively to Io/47r times and I times the C.G.S. absolute units . Very frequently the kiloline,” equal to woo lines of force, is now used as a unit of magnetic flux . Quantity . See also:

• SYMBOL (Gr. o-uµ(3oXov, a sign)

Symbol . Dimensions Dimensions Ratio of E.S to on the Electro- on the Electro- static System magnetic EM . E.S .

System E.M . Magnetic per-) (µ) L 2 Ts K 1 µ L Tz K i µ meability . (H) Li Mi T KI L i MI T u I L T' KI µi Magnetic force o r See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field . (B) Ll MI K i L i MI T1 µi L ' T K µ Magnetic (Z) Li MI K i Li MI T-' µi L' T K µ' flux den- (I) L x Mi K' L i MI T' µi L' T K µi sity or In- duction T n ticl mag- flux . Magnetization Magnetic pole (m) LI MI KI L' Mi T , L1 T KTµ i µi strength (M) Li MI KI L° MI T, µi La ,Kip 1 M a n n e t i c LI MI T µ- T LJ Tz L T ' KI µi Lz T1 K µ Magnetic .M.FI L M M I T I KI poagnelor~ (M .) to- magneto_ motiveforce Specific in- ductive ca- (K) K pacity (e) L4 MIT'K 4 Li M' TI µi L1 T K A-1 1 Electric force . Electric dis- (D) LiMI T t KI L Mi µ L T 1 KI µi placement . (Q) LI MI T i KI L' Mi L T 'KI µi Electricquan- my Electric cur- (A) Li M' T1 Kt Li MI T ' i L T 1 KI See also:

• RENT

rent (V) 1 Li MIT ' K i , T K IA -I Electric Ls MI T1 potential Electromo- (E.M.F.) L1 T K' L T 1' L z T2 K' tive force (R) µ' Electric re sistance (C) L K µ Lz T1 K µ Electric ca- L 1 Tz µ l pacity . Self Induct- (L) -i i -z z -i ance Mutual in- (M) L Tz K L µ L T K-iµ ductance Date . Name . Reference . Electric v in Quantity Centimetres Measured. per Second . 1856 W .

Weber and Electrodynamisc he Quantity 3•Io7XIo'o R . Kohlrausch Massbeslimmungen and Pogg . See also:

• ANN

Ann . xcix., August 10, 1856 1867 Lord Kelvin Report of British Potential 2-81 X1o'o 1868 and W . F . See also:

• KING
• KING (O. Eng. cyning, abbreviated into cyng, cing; cf. O. H. G. chun- kuning, chun- kunig, M.H.G. kiinic, kiinec, kiinc, Mod. Ger. Konig, O. Norse konungr, kongr, Swed. konung, kung)
• KING [OF OCKHAM], PETER KING, 1ST BARON (1669-1734)
• KING, CHARLES WILLIAM (1818-1888)
• KING, CLARENCE (1842–1901)
• KING, EDWARD (1612–1637)
• KING, EDWARD (1829–1910)
• KING, HENRY (1591-1669)
• KING, RUFUS (1755–1827)
• KING, THOMAS (1730–1805)
• KING, WILLIAM (1650-1729)
• KING, WILLIAM (1663–1712)

King Assoc., 1869, p . 434; x868 J . Clerk Maxwell . and Reports on Elec- „ 2'84 XIO10 trical Standards, F . Jenkin, p . 186 Phil . Trans . See also:

• ROY, WILLIAM (1726-1790)

Roy .

See also:

• SOC

Soc., 1868, p . 643 1872 Lord Kelvin and Phil . Trans . Roy . „ z'89 XIo10 Dugald M'Kich- Soc .. 1873, p . 409 1878 an See also:

• LAWN

lawn . Soc . Tel . Eng . Capacity 2.94 X1010 W . E .

See also:

• AYRTON, WILLIAM EDWARD (1847-1908)

Ayrton and 188o J . See also:

• PERRY
• PERRY (from Fr. Moire, from poire, a pear)
• PERRY, MATTHEW CALBRAITH (1794–1858)
• PERRY, OLIVER HAZARD (1785-1819)

Perry vol. viii. p . 126 Potential 2.955X I010 Lord Kelvin and Phil . Mag., 188o, vol . Shida x . P . 431 1881 A . G . Stoletow . Soc . See also:

• FRANC

Franc. de Phys., Capacity 2.99 Xioto 188r 1882 F . Exner .

Wien . Ber., 1882 Potential 2-92 X into 1883 Sir J . J . See also:

• THOMSON, JAMES (1822-1892)
• THOMSON, JAMES (1834-1882)
• THOMSON, JAMES (r700-1748)
• THOMSON, JOHN (1778-184o)
• THOMSON, JOSEPH (1858-1895)
• THOMSON, SIR CHARLES WYVILLE (1830-1882)
• THOMSON, THOMAS (1773-1852)
• THOMSON, WILLIAM (1819-189o)

Thomson Phil . Trans . Roy . Capacity 2.963X See also:

• ROW, JOHN (c. 1525—1580)

row Soc., 1883, p . 707 1884 I . Klemencic Journ . Soc . Tel . Eng., ii 3.019 X 1010 I887, p .

162 1888 F . Himstedt . . Electrician, See also:

• MARCH
• MARCH (1) (from Fr. marcher, to walk; the earliest sense in French appears to be " to trample," and the origin has usually been found in the Lat. marcus, hammer; Low Lat. marcare, to hammer; hence to beat the road with the regular tread of a soldier: cf.
• MARCH, AUZIAS (c. "1395-1458)
• MARCH, EARLS OF
• MARCH, FRANCIS ANDREW (1825– )

March 23, „ 3'007X1010 1888, vol. xx. p . 530 1888 Lord Kelvin, See also:

• AYR

Ayr- British Association, Potential 2.92 X1010 ton and Perry See also:

• BATH
• BATH, THOMAS THYNNE
• BATH, WILLIAM

Bath; and Elec- trician, See also:

• SEPT

Sept . 28, 1888 1888 H . Fison Electrician, vol. ma . Capacity 2.965X1010 p . 215; and Proc . Phys . Soc . See also:

• LAND

Land., See also:

• JUNE

June 9, 1888 2889 Lord Kelvin . Proc .

Roy . Inst., 1889 Potential 3'094Xlolo 1889 H . A . See also:

• ROWLAND, HENRY AUGUSTUS (1848-1901)

Rowland , Phil..Mag., 1888 Quantity 2.981XroIo 1889 E . B . See also:

• ROSA, CARL AUGUST NICHOLAS (1843-1889)
• ROSA, MONTE
• ROSA, SALVATOR (1615-1673)

Rosa Phil . Mag., 1889 Capacity 3.~XIO10 1890 Sir J . J . Thomson Phil . Trans., 1890 2995X1010 1887 and G . F . C .

Searle Wied . Ann . 1897 Alternating 3.o15X 1010 M . E . Maltby . . currents In connexion with the numerical values in the above definitions much work has been done . The electrochemical equivalent of silver or the weight in grammes deposited per second by r C.G.S. electromagnetic unit of current has been the subject of much See also:

• RESEARCH (O. Fr. recerche, from recercher, re- and cercer, mod. chercher, to search; Late Lat. circare, to go round in a circle, to explore)

research . The following determinations of it have been given by various observers: Name . Value . Reference . E . E .

N . Mascart . 0.011156 Journ. de physique, 1884, (2), 3, 283 . F. and W . Kohlrausch . o•oi 1183 Wied . Ann., 1886, 27, I . Lord See also:

• RAYLEIGH, JOHN WILLIAM STRUTT

Rayleigh and Mrs 0.011179 Phil . Trans . Roy . Soc., See also:

• SEDGWICK, ADAM (1785-1873)
• SEDGWICK, JOHN (1813–1864)

Sedgwick 1884, 2, 411 . J . S .

H . Pellat and 0.011192 Journ. de Phys., 1890, (2), A . Potier 9, 381 . Karl Kahle 0.011183 Wied . Ann., 1899, 67, I . G . W . Patterson and 0.011192 Physical See also:

• REVIEW (Fr. revue, from revoir, to see again, Lat. re and videre)

Review, 1898, 7, K . E . Guthe 251 . J . S .

H . Pellat and S . A. o•ot 1195 Comptes rendus, 1903, Leduc 136, 1649 . Although some observers have urged that the 0.01119 is nearer to the true value than o•o1118, the preponderance of the See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence seems in favour of this latter number and hence the value per ampere-second is taken as o•oolISoo gramme . The exact value of the electromotive force of a See also:

• CLARK, FRANCIS EDWARD (1851- )
• CLARK, GEORGE ROGERS (1752—1818)
• CLARK, JOHN BATES (1847— )
• CLARK, JOSIAH LATIMER (1822—1898)
• CLARK, SIR ANDREW
• CLARK, SIR JAMES (1788—1870)
• CLARK, THOMAS (1801—1867)
• CLARK, WILLIAM (1770-1838)
• CLARK, WILLIAM GEORGE (1821—1878)

Clark cell has also been the subject of much research . Two forms of cell are in use, the simple tubular form and the H-form introduced by Lord Rayleigh . The See also:

• BERLIN
• BERLIN, CONGRESS AND TREATY OF
• BERLIN, ISAIAH (1725–1799)

Berlin Reichsanstalt has issued a specification for a particular H-form of Clark cell, and its E.M.F. at 15° C. is taken as 1.4328 international volts . The E.M.F. of the cell set up in accordance with the British Board of Trade specification is taken as 1.434 international volts at 15° C . The detailed specifications are given in See also:

• FLEMING, PAUL (1609-1640)
• FLEMING, RICHARD (d. 1431)
• FLEMING, SIR SANDFORD (1827- )
• FLEMING, SIR THOMAS (1S44-1613)

Fleming's See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

Hand-See also:

• BOOK

book for the Electrical Laboratory and Testing See also:

• ROOM

Room (1901), vol. i. See also:

• CHAP

chap . 1; in the same book will be found copious references to the scientific literature of the Clark cell . One objection to the Clark cell as a concrete standard of electromotive force is its variation with temperature and with slight impurities in the mercurous sulphate used in its construction . The Clark cell is a voltaic cell made with mercury, mercurous sulphate, See also:

• ZINC

zinc sulphate, and zincas elements, and its E.M.F. decreases o.o8 % per degree Centigrade with rise of temperature .

In 1891 Mr Weston proposed to employ cadmium and cadmium sulphate in place of zinc and zinc sulphate and found that the temperature coefficient for the cadmium cell might be made as See also:

• LOW, SETH (1850- )
• LOW, WILL HICOK (1853- )

low as 0.004 % per degree Centigrade . Its E.M.F. is, however, 1•o184 international volts at 20 C . For details of construction and the literature of the subject see Fleming's Handbook for the Electrical Laboratory, vol. i. chap. i . In the British Board of Trade laboratory the ampere and the volt are not recovered by immediate reference to the electrochemical equivalent of silver or the Clark cell, but by means of See also:

• INSTRUMENTS

instruments called a standard ampere See also:

• BALANCE (derived through the Fr. from the Late Lat. bilantia, an apparatus for weighing, from bi,