Part 14

This pioneer method of Townsend's has been improved and modified in various ways by C. T. R. Wilson, Sir J. J. Thomson, H. A. Wilson, and notably by Millikan, of Chicago. Millikan's charge carriers were minute oil drops, which were given elementary charges by means of ionizing rays from radium. Observations were made of the equilibrium and motion of these charges under the combined influence of gravity and a strong vertical electric field, the intensity of which could be varied at will. A single drop could be kept in view for several minutes at a time, and note was taken of the effect of each new charge as it was picked up by the drop. On calculation, the charge was found in all cases to have very approximately the same value. It so happened, as a consequence of the method of producing the drops, that they carried a small frictional charge, and incidentally Millikan was able to verify that this was always an integral multiple of the electronic charge e. Millikan's result, which is most probably the best yet found, is that e = 4.774 x 10^{-10} absolute electrostatic units, or 1.591 x 10^{-20} absolute electromagnetic units.

An indirect but very interesting method of determining e was devised independently by Regener and by Rutherford and Geiger. The special feature of this method is the actual counting of the number of [alpha]-particles (see _Radio-activity_) shot out per second through a given solid angle by a small speck of radium. Each [alpha]-particle produces a scintillation on a sensitive screen placed in its path, and these scintillations are counted one by one by the observer. The total quantity of electricity carried by the [alpha]-particles emitted in one second is measured independently. The charge on each particle is then found by simple division. This charge is found to be almost exactly twice Millikan's value for e, as it ought to be, as it is practically certain that the [alpha]-particle is an atom of helium which has lost two electrons.

The value of e/m, as determined by Thomson's method described above, is 1.76 x 10^7 e.m.u. per gramme, or 5.29 x 10^{17} e.s.u. per gramme. Taking this with Millikan's value for _e_, we find n = 0.902 x 10^{-27} grammes. The exact determination of e has made it possible to assign precise values to several other important physical constants, which formerly were only known roughly from data depending on the Kinetic Theory of Gases. Thus Avogadro's constant N, or the number of molecules in one gramme-molecule (molecular weight in grammes) of any gas can be connected with e by the exact measurements of electrolysis, which give Ne = 9650 e.m.u. It follows that N = 6.06 x 10^{23}, and that the number of gas molecules per cubic centimetre at 0deg C and 76 centimetres pressure is 2.70 x 10^{19}. We find at once also the mass of the hydrogen atom as 1.66 x 10^{-24} grammes, the density of hydrogen being known to be .0899 grammes per litre. The mass of the electron is therefore about 1/1840 of the mass of the hydrogen atom, which till the isolation of the electron was the smallest mass known.

It is necessary, however, to scrutinize with some care the meaning of the word mass as applied to an electron. The determination of the mass of the hydrogen atom ultimately depends on weighing, that is, on finding its gravitational inertia. We cannot weigh an electron, but must determine its mass by experiments involving its motion, the word mass here meaning the ratio of the force acting on the electron to the acceleration produced, and the force being calculated from the charge and velocity of the electron on the principles of electrodynamics. An electron being entirely different in its physical nature from ordinary matter, the question arises whether its mass, as calculated in this way, is actually a definite constant, as it is for a material particle, according to the accepted principles of Newtonian dynamics. It can even be shown, as was first done by Sir J. J. Thomson, that a moving charged body possesses inertia in virtue of the mere fact that it carries a charge. The value of this inertia, or electromagnetic mass, when the velocity is small compared with that of light is, in a vacuum, for a small sphere of radius a, 2/3e^2/a, where e is the charge. If the velocity is greater than, say, 1/10 the velocity of light, the formula for the electromagnetic mass is more complicated, and, indeed, cannot be calculated without some assumption as to the internal distribution of charge in the electron itself. Two formulae for the mass have been given, one by Abraham, the other by H. A. Lorentz. Abraham started from the supposition that the electron is a rigid sphere carrying a uniform surface charge. Lorentz showed that a simpler theory could be obtained by the hypothesis that the electron contracts, in the direction of its motion, by a certain definite amount depending on its velocity. On both theories the value found for the mass depends on the relation between the direction of the force and the direction of the motion. On Lorentz's theory the longitudinal mass, or mass when the force is in the direction of the motion, is m_0/(1-[beta]^2)^{3/2}; and the transverse mass, or mass when the force is perpendicular to the velocity, is m_0/(1-[beta]^2)^{1/2}; where m_0 is the mass for very small speeds, and [beta] is v/c, the ratio of the velocity of the electron to the velocity of light. The two theories have been tested by various experimenters, with somewhat conflicting results. On the evidence of experiments by Bucherer, however, Lorentz's theory of the contractile electron is now generally accepted, and it is regarded as highly probable that electrons are devoid of all mass except the electromagnetic mass due to their charge of negative electricity.

No fundamental positive electron has been isolated which at all corresponds to the negative electron, or corpuscle, as it is called by Sir J. J. Thomson. The nearest approach to a positive electron is the nucleus of the hydrogen atom, which carries a positive charge of the same magnitude as the charge on an electron. Practically the whole mass of the atom resides in this nucleus. According to the modern theory of the structure of matter, the neutral atom of any element is built up of a comparatively small number of electrons and an equal number of these positive nuclei. Electrons being present everywhere, and their action influencing all natural phenomena, their properties will naturally come up for consideration from various points of view in other articles. See _Ionization_; _Isotopes_; _Matter_; _Radio-activity_; _Rays_, _Electric._--BIBLIOGRAPHY: J. A. Crowther, _Ions, Electrons, and Ionizing Radiations_; R. A. Millikan, _The Electron_; N. R. Campbell, _Modern Electrical Theory_; O. W. Richardson, _The Electron Theory of Matter_; H. A. Lorentz, _Theory of Electrons_.

ELECTRO-PLATING, the process of depositing a coating of some selected metal on a given surface by means of electrolysis (q.v.). The most important classes of electro-plating commonly carried out are nickel-plating, used very largely for a variety of articles made of iron, steel, &c.; copper-plating, used for facing printing-blocks and as a first coating to non-metallic substances prior to silver- or gold-plating; silver-plating, for imitation silverware and for cutlery, &c.; gold-plating, for ornamental ware, jewellery, &c. Previous to plating it is necessary to remove all grease, dirt, oxide, &c., from the surface, this cleansing of the articles being the first step in the operations necessary. The exact procedure for cleansing varies with the nature of the articles to be plated, but for the removal of grease a strong caustic alkali bath is generally used. To remove oxide and dirt, scratch-brushing is used, also scouring with pumice-stone. Acid-dipping baths are also employed, muriatic acid or sulphuric acid for iron or steel articles, dipping-acid, which is a mixture of sulphuric acid and nitric acid, for brass. For the actual deposition an electrolytic cell is prepared, containing a solution of a suitable salt of the metal to be deposited, with an anode, generally consisting of a plate of the same metal, attached to the positive pole of the battery used, the article to be treated being connected with the negative pole and thus forming the cathode. When a current of electricity is passed through the solution, a thin coating of metal is deposited on the article forming the cathode, and an equivalent portion is carried into solution from the anode. In the case of nickel-plating, the solution used is made from the double chloride or sulphate of nickel and ammonium, to which salt, sal-ammoniac, &c., may be added. The bath is used at a temperature of 100deg F., and cast-nickel plates are used as anodes. For copper-plating the bath used generally consists of an acid solution of sulphate or acetate of copper, cyanide of potash also being added; in case the article is made of zinc, an alkaline bath is used. The bath may be used cold, but is sometimes kept at about 120deg F. For iron simple dipping is sometimes used, as copper is readily deposited on iron without the use of an electric current. For electroplating of copper, anodes of metallic copper, having a surface equal to that of the articles to be coated, are used. For silver-plating the solution consists of the double cyanide of silver and potash, and may be used either hot or cold. An article to be silver-plated is often prepared by a preliminary dip in a solution of nitrate of mercury, which causes a slight amalgamation with mercury. After this preliminary treatment it is placed in the bath and a slight deposit of silver obtained, after which it is removed, well brushed, washed, and replaced in the bath. A silver plate is used as an anode. A density of 1-1/4 to 1-1/2 ounces of silver to the square foot gives an excellent plate about the thickness of common writing-paper. In gold-plating baths, a hot solution of the double cyanide of gold and potash is used at 170deg F., and for the anode platinum foil is frequently used, the strength of the bath being maintained by the addition of fresh quantities of chloride of gold. After all kinds of plating as described above, the goods are thoroughly washed in water, and dried by means of saw-dust or in a drying-chamber. In ordinary circumstances the deposited metal presents a dead or matted appearance, and if a bright polished effect is desired, it is burnished and buff-polished. Certain chemicals added to the solution will cause the original deposit to have a metallic lustre.

ELECTROTYPE. The production of copper facsimiles by the electric current is called _electrotype_, and is the oldest branch of electro-metallurgy. One of its most important applications is the copying of type set up for printing, and of wood blocks for wood-cuts. A mould is first obtained in gutta-percha or some similar material. This, being a non-conductor, is brushed over with plumbago in its interior, so as to give it a conducting surface to receive the deposit. After several hours the deposit is detached from the mould and backed by pouring in melted solder, the surface being first moistened with chloride of zinc to make the solder adhere. In the copying of steel engravings the mould is obtained by electro-deposition of copper on the steel, the surface of which must first be specially prepared to prevent adhesion; and a second electro-deposition of copper, on the mould thus obtained, gives the required copy, from which impressions can be printed.

ELEC'TRUM (Gr. _[=e]lektron_), in antiquity, a term applied to native gold, which frequently contains notable quantities of silver, copper, and other metals. According to Pliny, the term electron was applied to native gold containing at least 20 per cent of silver. The term was afterwards transferred from this native alloy to the artificial alloy of gold and silver on account of its colour and inferior lustre. The word originally meant 'amber', and was given to impure gold on account of a supposed resemblance. Electrum was used since the eighth or seventh century B.C.

ELEC'TUARY, or CONFECTION, is a pharmacopoeial preparation. It is solid, but of soft consistence, and contains sugar or honey, impregnated with some more active body. The best known is the confection of senna.

ELE'GIT, in English law, a writ by which a creditor who has obtained a judgment against a debtor, and is hence called the _judgment-creditor_, may be put in possession of the lands and tenements of the person against whom the judgment is obtained, called the _judgment-debtor_, until the debt is fully paid. The writ is addressed to the sheriff, who enforces it. The writ of elegit was first authorized by the Statute of Westminster the Second, which gave the _judgment-creditor_ the right to choose between a writ against the debtor's land, and until 1883 his goods also, and an execution by writ against the latter's person or chattels. The new writ, representing the choice of the creditor, was therefore called an elegit, Lat., he has chosen. See _Fieri Facias_.

EL'EGY (Gr. _elegos_, mourning, song), a mournful and plaintive poem or funeral song, or any serious poem of a melancholy contemplative kind. In classic poetry what is known as _elegiac verse_ is composed of couplets consisting of alternate hexameter and pentameter lines. In English we generally understand by elegies lyric poems which are laments over the dead, such as Milton's _Lycidas_, or Shelley's _Adonais_.

ELEMEN'TAL SPIRITS, according to a belief common in the Middle Ages, spirits proper to and partaking of the four so-called elements, viz. salamanders or fire spirits, sylphs or aerial spirits, gnomes or earth spirits, and undines or water spirits.

EL'EMENTS, the simplest constituent principles or parts of anything; in a special sense, the ultimate indecomposable constituents of any kind of matter. In ancient philosophies the term was applied to fire, air, earth, and water. The mediaeval chemists, however, absorbed in the study of metals and mineral substances, supposed that the metals consisted of an elemental sulphur and an elemental mercury mixed together more or less perfectly and in different proportions. To these were subsequently added salt and some others, so that about the middle of the seventeenth century the first principles amounted to five, divided into two classes; the active, consisting of mercury or spirit, sulphur or oil, and salt; and the passive, consisting of water or phlegm, and earth or the terrestrial part. The names remained, not so much as denoting substances or ultimate principles as gradually coming to denote functions; the first great modification being the expansion of the idea of elemental sulphur into phlogiston by Stahl, as the result of which the adherents of the phlogistic theory applied the term phlogiston to the gases then discovered, the mineral, vegetable, and animal acids, the alkalies, earths, and metallic calces, oil, alcohol, and water. The substances considered as simple naturally changed with the change of theory introduced by Lavoisier, who considered as elements, oxygen, nitrogen, hydrogen, sulphur, phosphorus, and carbon, the metals and the earths, and, as Boyle had already suggested, practically defined an element as a body not yet decomposed, the definition now commonly adopted. For list of known elements see _Chemistry_.

EL'EMI, the fragrant resinous exudation from various trees, such as the _Canarium commune_, from which the Eastern or Manila elemi is obtained; the _Ic[=i]ca Ic[=i]car[=i]ba_, the source of the American or Brazilian elemi; and the _Elaphrium elemif[)e]rum_, from which the Mexican elemi comes. It is a regular constituent of spirit varnishes, and is used in medicine, mixed with simple ointment, as a plaster.

EL'EPHANT, the popular name of a genus, family, or sub-order of five-toed proboscidian mammals, usually regarded as comprehending two species, the Asiatic (_Elephas indicus_) and the African (_E. afric[=a]nus_). From a difference in the teeth, however, the two species are sometimes referred to distinct genera (Euelephas and Loxodon). The so-called white elephants are merely albinos. The African elephant is distinguished from the Asiatic species by its greater height, its larger ears, its less elevated head and bulging or convex forehead, the closer approximation of the roots of the tusks, and the greater density of the bone. It has also only three external hoofs on the hind-feet, while the Asiatic has four. All elephants are remarkable for their large, heavy, short bodies supported on columnar limbs, a very short neck, a skull with lofty crown and short face-bones, with the exception of the premaxillaries, which are enlarged to form tusk-sockets. To compensate for the short neck, they have the long proboscis, often 4 or 5 feet in length, produced by the union and development of the nose and upper lip. It is made up of muscular and fibrous tissue. The trunk is of great strength and sensibility, and serves alike for respiration, smell, taste, suction, touch, and prehension. The tusks, which are enormously developed upper incisor teeth, are not visible in young animals, but in a state of maturity they project in some instances 7 or 8 feet. The largest on record (undoubtedly that of an extinct species) weighed 350 lb. Elephants sometimes attain the height of 12 feet or more, but their general height is about 9 or 10 feet. Their weight ranges from 4000 to 9000 lb. The period of gestation is twenty months, and the female seldom produces more than one calf at a birth: this, when first born, is about 3 feet high, and continues to grow till it is sixteen or eighteen years of age. It is said that they live to the age of 150 years. They feed on vegetables, the young shoots of trees, grain, and fruit. They are polygamous, associating in herds of a considerable size under the guidance of a single leader. An elephant leaving or driven from a herd is not allowed to join another, but leads a lonely, morose, and destructive life. Such solitary elephants are known as 'rogues'. Elephants are caught either singly or in herds. In the former case it is necessary to catch adroitly one of the elephant's legs in the noose of a strong rope, which is then quickly attached to a tree; another leg is then caught, until all are securely fastened. His captors then encamp beside him, until under their treatment he becomes tractable. When a herd is to be caught a strong enclosure is constructed, and into this the elephants are gradually driven by fires, noise, &c. With the aid of tame elephants the wild ones are tied to trees and subjected to the taming process. The domesticated elephant requires much care, and a plentiful supply of food, being liable to many ailments. The daily consumption of a working elephant is, according to Sir J. E. Tennent, 2 cwt. of green food, about half a bushel of grain, and about 40 gallons of water. Their enormous strength, docility, and sagacity make them of great value in the East for road-making, building, and transport. They are used by the great on occasions of pomp and show, being often richly caparisoned, and bearing on their back a howdah containing one or more riders, besides the mahout or driver sitting on the animal's neck. Tiger-shooting is often practised from an elephant's back. Several extinct species are known, the most notable being the mammoth (_E. primigenius_), a contemporary of prehistoric man. The allied genus Mastodon was of very wide distribution, and the Tertiary deposits of the Fayum (Egypt) have yielded the remains of types that bridge over the gap between elephants and more typical quadrupeds. See _Mammoth_; _Mastodon_.--BIBLIOGRAPHY: Andersson, _The Lion and the Elephant_; Sir. J. E. Tennent, _The Wild Elephant in Ceylon_; Sanderson, _Wild Beasts of India_; R. Lydekker, _The Game Animals of Africa_.

ELEPHAN'TA ISLE, or GHARAPURI, a small island in the Bay of Bombay, between Bombay and the mainland, 6 miles north-east of the former; circumference about 5 miles. It consists of two long hills chiefly overgrown with wood. A city is supposed to have flourished on the island between the third and tenth centuries, but now it has only a few inhabitants, who rear sheep and poultry for the Bombay market. It is celebrated for its rock temples or caves, the chief of which is a cave-temple supposed by Fergusson to belong to the tenth century, 130 feet long, 123 broad, and 18 high. It is supported by pillars cut out of the rock, and containing a colossal figure of the trimurti or Hindu Trinity: Brahma, Vishnu, and Siva. The temple is still used by the Bania caste for the Sawa at certain festivals.

ELEPHANT-FISH (_Callorhynchus antarcticus_), a fish of the sub-class Elasmobranchii (rays and sharks), so named from a proboscis-like structure on the nose: called also Southern Chimaera. It inhabits the Antarctic seas, and is palatable eating.

ELEPHANTIASIS is a disease characterized by progressive enlargement of a limb, or portion of the body, and occurs most frequently in the legs. The enlargement begins below the knee and gradually involves the entire limb. The onset may be slow and painless, or sudden with fever and rapid swelling. The disease is common in all countries in which the Filariae prevail. No drug destroys the embryos in the blood, and in infected districts the drinking-water should be boiled or filtered. In rapid cases rest, liquid diet, purgation, and firm bandaging of the legs are indicated. Surgical treatment for removal of adult Filariae in enlarged glands has met with some success.

ELEPHANTI'NE, the Greek name of a small island of Egypt, in the Nile, just below the First Cataract and opposite Assouan (Syene). It is partly covered with ruins of various origins--Egyptian, Roman, Saracen, and Arabic, the most important being a gateway of the time of Alexander, a small temple dedicated to Khnum and founded by Amenophis III, and the ancient Nilometer mentioned by Strabo. The latter was restored in 1870 by the Khedive Ismail Pasha. The northern part is low, the southern elevated and rocky.

ELEPHANT LORE. The cult of the elephant is found among many nations in Asia and Africa. It exists in Indo-China, Cambodia, Abyssinia, Siam, and Sumatra. The Aryo-Indian god Indra rides on an elephant. Buddha had a white elephant form. One of the Sanskrit names for the elephant is _Naga_, which connects the animal with the sacred snake, possibly on account of its trunk; another name is _Hastin_, 'having a hand'. The Wambuwegs believe the elephant to be the abode of the souls of their ancestors. It is a bad omen, according to the _Talmud_, to dream of an elephant.

ELEPHANT RIVER, a river of Cape Colony, running into the Atlantic after a course of 140 miles,

ELEPHANT-SEAL, the Proboscis Seal, or Sea-elephant, the largest of the seal family (Phocidae). There are probably two species, one (_Macrorhinus angustirostris_) found only on the coast of California and Western Mexico, the other (_Macrorhinus leoninus_) found in Patagonia, Kerguelen Island, Heard's Island, and other parts of the Southern Seas. They vary in length from 12 to 30 feet, and in girth at the chest from 8 to 18 feet. The proboscis of the male is about a foot long when the creature is at rest, but elongates under excitement. The females have no proboscis and are considerably smaller than the male. Both species are becoming rare owing to the wholesale slaughter of them which takes place.