Part 2

Early speculators regarded the ether as a species of fluid, which could be displaced by ordinary matter, so that upholders of the wave theory of light necessarily thought of waves like those of sound, in which the direction of vibration is in the line of transmission, for no other kind of wave can occur in a fluid. Young and Fresnel, however, insisted on the view that the movements of the medium are at right angles to the direction of propagation, and pointed out that this might be explained by supposing the medium to possess elasticity of shape. The obvious objection to the conception of a solid which permits the planets to move through it with apparently perfect freedom was met long afterwards by Stokes and Kelvin, who instanced such substances as shoemaker's wax and jelly, which are rigid enough to be capable of elastic vibration, and yet permit bodies to pass through them with more or less ease. Fresnel's work called attention to the subject of the elasticity of bodies, and led to the discovery of the general equations of vibration of an elastic solid by Navier in 1821. Navier's equations, slightly generalized, were used by Cauchy with a certain amount of success to explain reflection, refraction, and the phenomena of crystal-optics. In 1837 George Green published a variety of elastic solid theory which was a decided improvement on Cauchy's, but many difficulties remained, and it is now almost universally agreed that the vibrations of an ordinary elastic solid do not furnish an exact parallel to the vibrations which constitute light. One of the chief difficulties is that in an ordinary elastic solid two types of waves can occur, one distortional, with the displacement of a particle perpendicular to the direction of transmission, and the other dilatational, with the displacement along the line of transmission, as in sound. Waves of light must be of the distortional kind, and the velocity of the other kind of wave may be quite different from the velocity of light. A kind of ether in which this difficulty of the longitudinal wave does not occur was imagined by Cauchy and afterwards discussed by Lord Kelvin, who called it the contractile, or labile, ether. This is an elastic body with negative compressibility, like homogeneous foam which is prevented from collapsing by attachment to the sides of a containing vessel. Another type of quasi-elastic solid was brought forward by James MacCullagh in 1839. MacCullagh's solid possesses what may be called elasticity of rotation, but offers no resistance to deformations in which elementary parts of the solid preserve their orientation. The equations of motion of this ether devised by MacCullagh are very similar to those obtained much later from a very different physical point of view by Clerk Maxwell. Elastic solid theories, however, have fallen into the background before the advancing popularity of the electromagnetic theory of James Clerk Maxwell. Maxwell's equations of the electromagnetic field are deduced from easily demonstrable experimental facts, supplemented by the characteristic hypothesis that the electric current always travels in a closed circuit, even in cases where, as in the discharge of a condenser, the material circuit is open, so that the path of the current has to be completed through the ether. Other essential features of Maxwell's view are that electric, magnetic, and electromagnetic action is transmitted by means of stresses in a medium which possesses some sort of elasticity and inertia not exactly of an ordinary mechanical kind, and that the energy of all such action resides in the medium. 'Maxwell's equations', especially as modified by H. A. Lorentz so as to take account of the atomic structure of electricity, are fundamental in modern electrodynamics and the electron theory of matter. The form of Maxwell's equations shows that electromagnetic action can be propagated in waves with a definite velocity, which depends on the specific inductive capacity and the magnetic permeability of the medium. Maxwell had no difficulty in showing from experimental data that the velocity given by his theory, which turns out to depend on the ratio of the electrostatic and electromagnetic units of charge, is identical with the known velocity of light. He concludes that waves of light are electric waves. The actual production of waves by electrical means was experimentally demonstrated by Sir Oliver Lodge, and more completely by Heinrich Hertz, and is now a commonplace of wireless telegraphy and telephony. The question of the nature of the mechanical process by which physical actions are carried on in the ether weighed heavily on Maxwell, as on other nineteenth-century physicists. Mechanical models of many kinds have been devised to represent ethereal

## action. Were it sufficient for the purpose, certainly nothing could be

simpler than the elastic solid model. Other models of much interest are the gyrostatic ether and the vortex sponge ether of Lord Kelvin, and the molecular vortex ether of Maxwell. It is recorded that the celebrated mathematician Gauss had made out a theory of electrodynamics, but always declined to publish it because he was unable to devise a mental picture of the physical action represented by his mathematics; and it was probably a similar reason that led Lord Kelvin to declare, so late as 1904, that "the electromagnetic theory has not helped us hitherto". Sir J. J. Thomson has developed a theory of moving tubes of electric force, which produce magnetic fields by their motion. Possibly light may consist of tremors in these tubes, and if the tubes are discrete, it may become practicable to reconcile the modern quantum theory (q.v.) with the phenomena of interference of light, with which at present it seems to be utterly inconsistent.

The extraordinary developments in both theoretical and experimental physics during recent years have diverted attention to some extent from the question of the constitution of the ether, and the problem of its mode of working is more frequently considered from a mathematical and pseudo-metaphysical point of view than from the old standpoint of Newtonian dynamics. It was from a question about the ether, however, that the theory of relativity, the most important of recent speculations, took its origin. Is the ether fixed, or does it move? Is it carried along with the earth in its motion round the sun, or does the ether pass through the atoms of material bodies as the sea passes through the meshes of a net? The elastic solid analogy, and the simplicity of the classical explanation of the aberration of light, are evidence in favour of a fixed ether. But the celebrated interference experiment of Michelson and Morley, which was capable of detecting a comparatively small relative velocity of earth and ether, gave a null result. Various electrical experiments also point to the conclusion that the medium in which optical and electrical effects take place is carried along with the earth in its motion. We are thus placed in a dilemma. We must either reconcile the idea of a fixed ether with the Michelson-Morley and kindred experiments, or we must explain aberration on the supposition that earth and ether move together. Both alternatives have had their supporters. Those who, like Sir Joseph Larmor and Sir Oliver Lodge, believe in a fixed ether rely on the hypothesis of the 'Fitzgerald contraction', according to which bodies moving through the ether with velocity v are contracted in the direction of their motion by the fraction [sqrt](1 - v^2/c^2) of their length, c being the velocity of light. This contraction is in ordinary cases very small, amounting only to a few inches for the diameter of the earth when moving round the sun. The hypothesis follows naturally enough from the accepted theory of the motion of electrons, and leads to a perfectly simple explanation of the Michelson-Morley result. The most prominent champion of a moving ether was Sir George Stokes. He assumed that, so far as the earth's motion through it is concerned, the ether behaves as a perfect liquid, so that it moves along with the earth, and he proved that aberration would be unaffected by this motion, provided it is everywhere irrotational, or free from spin. Stokes's theory has been extended by Larmor so as to cover a very important set of phenomena found by Arago and Airy, and explained in a general way by Fresnel. These phenomena relate to the velocity of light in material media which are in motion relative to the earth, running water for example. Fresnel proved that all the experimental results are explained if the velocity of light in the water, with respect to the earth, is given by the formula c' + v(1 - 1/m^2), where c' is the velocity of light in still water, v is the velocity of the water relative to the earth, and m is the index of refraction of water. At present the fashionable view of all the phenomena is that taken in Einstein's theory of relativity (q.v.), which makes revolutionary suppositions with respect to the measurement of space and time, and assumes that the velocity of light is a universal constant, independent of the motion either of the source of light or of the observer. Once its initial assumptions are granted, the theory undoubtedly gives simple and natural explanations of the chief optical and electrical phenomena, and in particular leads at once to Fresnel's formula given above. Most English writers on the subject, among whom A. S. Eddington, E. Cunningham, and A. N. Whitehead are prominent, continue to believe that an ether exists, in spite of the fact that as relativists they hold that no experiment can ever enable us to determine our motion through it.--BIBLIOGRAPHY: E. T. Whittaker, _History of the Theories of Aether and Electricity_; Sir Joseph Larmor, _Aether and Matter_; A. S. Eddington, _Space, Time, and Gravitation_; O. W. Richardson, _Electron Theory of Matter_; R. W. Wood, _Physical Optics_.

ETHER, or ETHYL ETHER, (C_2H_5)_2O, a colourless, inflammable liquid produced by distillation of alcohol with concentrated sulphuric acid. It is almost immiscible with water, lighter than alcohol, has a sweet taste, and evaporates rapidly in air, producing extreme cold. The vapour of ether mixed with air forms an explosive mixture. Ether is a valuable solvent for many organic substances, fats, oils, &c., and is also used in surgery as an anaesthetic.

ETHEREGE (eth'[.e]-rej), Sir George, English writer of comedy, born about 1635, died about 1691. He studied at Cambridge, travelled afterwards on the Continent, and then returned to enter himself at one of the Inns of Court. Devoting himself less to legal studies than to literature and society, he wrote several plays. In 1664 he had his first comedy represented, _The Comical Revenge, or, Love in a Tub_, which was well received. Four years later his _She Would if She Could_ appeared, a brilliant play, though frivolous and immoral. Eight years afterwards (1676) he produced his best comedy, _The Man of Mode, or Sir Fopling Flutter_. Etherege's plays are witty and sparkling, and the characters, genuine portraits of the men and women he saw, are vividly if lightly drawn.

ETHICAL CULTURE. It has been said by a prominent leader of the movement for ethical culture that the one dogma admitted is the doctrine of personality. The movement eliminates from its teaching all hitherto received religions, admits no Christian symbolism, and acknowledges neither a personal Creator nor a personal Saviour. Christ is, however, highly reverenced as a man. The world as it _should be_ is regarded not as an unattainable though beautiful ideal to be admired and longed for, but as a possible reality to be achieved by strenuous concerted action. The means by which it is hoped to bring about this much-to-be-desired result is the reaction on each other of carefully selected and highly cultivated personalities. Such virtues, therefore, as kindness, pity, justice, charity, temperance, and chastity are deemed less necessary as a personal moral duty in each human being than as a means by which a perfect world may be attained. Man's duty is towards no divine being, but to his fellow-man. In place of that help from above which theologians deem needful to attain even a short step in the direction of perfection, the power of conscience is considered as sufficient for all needs, and disciples are counselled that they should

More strictly, then, the inward judge obey,

since they no longer believe in divine anger or approval.

Germs of the movement may be found in many writers, and Emerson seems to have foreseen it when he said: "The mind of this age has fallen away from theology to morals. I conceive it to be an advance." But the obvious founder of ethical societies was Felix Adler (born 1851), who, in 1876, established in New York a Society of Ethical Culture. He also set in motion such useful work as training-schools, kindergartens, and nursing. In 1885 his associate, W. Salter, established the Chicago Ethical Society. Both have written extensively on the subject; while English supporters of the movement include Sir Leslie Stephen, Sir J. Seeley, Professor Sidgwick, and others. Several ethical societies exist in Britain, carrying out much educational and philanthropic work. There are both Sunday services and Sunday schools, and in many cases the branches are more or less closely affiliated with labour and its associations. With regard to this community of work and aim, it may be noted that while ethical culturists look forward to a time when no man shall exploit his fellow human beings for personal ends, absolute equality for all is not promised, being recognized as impossible.--BIBLIOGRAPHY: Felix Adler, _Creed and Deed_; W. M. Salter, _Ethical Religion_.

ETH'ICS, otherwise called _Moral Philosophy_ or _Morals_, is the science which treats of the nature and laws of the actions of intelligent beings, considered as to whether they are _right_ or _wrong_, _good_ or _bad_. Its subject-matter is human conduct and character in view of a standard or ideal. It refers to constant elements in human nature, and, like aesthetics and logic, is of universal application. The science is more or less closely connected with theology, psychology, politics, political economy, and jurisprudence, but what most strictly belongs to it is the investigation of the principles and basis of duty or the moral law, and an inquiry into the nature and origin of the faculty by which duty is recognized. Various answers have been given to the question why we call an action good or bad, such as that it is consistent or not with the will of God, or with the nature of things, or with the greatest happiness of the greatest number, or that an inward faculty decides it to be such or such; and a great variety of _ethical_ systems has been proposed. The foundations of the leading systems were laid in antiquity, the names of Socrates, Plato, Aristotle, Epicurus, the Cynics, and the Stoics being especially prominent. All the Greek philosophers, however, considered ethics from an individualistic standpoint, and paid little attention either to politics or to sociology. The introduction of Christianity brought a new element into ethical speculation, and among Christians ethics were intimately associated with theology, and morality was regarded as based on and regulated by a definite code contained in the sacred writings. The speculations of the Greeks were not, however, disregarded, and some of the ablest Christian moralists (as Augustine, Peter Lombard, Erigena, Anselm, and Aquinas) endeavoured to harmonize the Greek theories with the Christian dogmatics. Most modern ethical systems consider the subject as apart from theology and as based on independent philosophical principles, and they fall into one of two great classes--the utilitarian systems, which recognize as the chief good, happiness, or the greatest possible satisfaction of the tendencies of our nature; and the rationalistic systems, which recognize that ideas of law and obligation can have their source only in reason. _Utilitarianism_ has been rightly called universal hedonism, as distinguished from the hedonism of Epicurus, which was egoistic. The first of the modern Utilitarian school in England was Hobbes (1588-1679). Among subsequent names are those of Cudworth, Locke, Clarke, Shaftesbury, Butler, Hutcheson, Hume, Adam Smith, Reid, Paley, Whewell, Bentham, J. S. Mill, &c. Paley held that men ought to act so as to further the greatest possible happiness of the race, because God wills the happiness of men, and rewards and punishes them according to their actions, the divine commands being ascertained from Scripture and the light of nature. Bentham's utilitarianism is considerably different from Paley's. It was entirely dissociated from theology or Scripture, and maintained that increase of happiness ought to be the sole object of the moralist and legislator, pleasure and pain being the sole test of actions. To utilitarianism as a special development belong the later 'evolution ethics' represented by Herbert Spencer, in which biological conceptions, such as 'the preservation of the human race', take the place of the Benthamite criterion for determining what is good and bad in actions. Another theory of ethics places the moral principle in the sentimental part of our nature, that is, in the direct sympathetic pleasure or sympathetic indignation we have with the impulses which prompt to action or expression. By means of this theory, which he treats as an original and inexplicable fact in human nature, Adam Smith explains all the phenomena of the moral consciousness. In considering the ethical systems of the Rationalistic school, systems which recognize that the ideas of law and obligation can have their source only in reason, the question, what is the source of the laws by which reason governs, gives rise to a number of psychological theories, amongst which we may notice Clarke's view of the moral principles as rational intuitions or axioms analogous to those of mathematics; Butler's theory of the natural authority of conscience; the position of Reid, Stewart, and other members of the later Intuitional school, who conceive a moral faculty implanted in man which not only perceives the 'rightness' or 'moral obligation' of actions, but also impels the will to perform what is seen to be right. Very similar, as far as classification goes, is the position of Kant, who holds that reason recognizes the immediate obligation of certain kinds of conduct, and that an action is only good when done from a good motive, and that this motive must be essentially different from a natural inclination of any kind.--BIBLIOGRAPHY: H. Sidgwick, _The Method of Ethics_; A. C. Bradley, _Ethical Studies_; H. Spencer, _Principles of Ethics_; L. Stephen, _The Science of Ethics_; _The English Utilitarians_; W. Wundt, _Ethics_; J. Martineau, _Types of Ethical Theory_; A. Sutherland, _The Origin and Growth of the Moral Instinct_; E. Westermarck, _The Origin and Development of Moral Ideas_; W. R. Sorley, _The Moral Life_; C. Read, _Natural and Social Morality_.

ETHIOPIA, or AETHIOPIA (Heb. _Cush_), in ancient geography, the country lying to the south of Egypt, and comprehending the modern Nubia, Kordofan, Abyssinia, and other adjacent districts; but its limits were not clearly defined. It was vaguely spoken of in Greek and Roman accounts as the land of the _Ichthyophagi_ or fish-eaters, the _Macrobii_ or long-livers, the _Troglodytes_ or dwellers in caves, and of the _Pygmies_ or dwarf races. In ancient times its history was closely connected with that of Egypt, and about the eighth century B.C. it imposed a dynasty on Lower Egypt, and acquired a predominant influence in the valley of the Nile. In sacred history Ethiopia is repeatedly mentioned as a powerful military kingdom (see particularly _Is._ xx, 5). In the sixth century B.C. the Persian Cambyses invaded Ethiopia; but the country maintained its independence till it became tributary to the Romans in the reign of Augustus. Subsequently Ethiopia came to be the designation of the country now known as Abyssinia (q.v.), and the Abyssinian monarchs still call themselves rulers of Ethiopia.

ETHIOPIAN LANGUAGE, THE, or more accurately the _Geez_ language, is the old official and ecclesiastical language of Abyssinia, introduced into that kingdom by settlers from South Arabia. In the fourteenth century it was supplanted as the language of the Christian Church of Abyssinia by the Amharic. It is a Semitic language resembling Aramaic and Hebrew as well as Arabic. It has a Christian literature of some importance. The principal work is a translation of the Bible, including the Old and New Testaments and _Apocrypha_, to which are appended some non-canonical writings, such as the _Shepherd of Hermas_ and the _Book of Enoch_. The language is to some extent represented by the modern dialects of Tigre, and by that spoken by some nomadic tribes of the Sudan. For the Ethiopian or Abyssinian Church, see _Abyssinia_ and _Copt_.

ETH'MOID BONE (Gr. _[=e]thmoeides_, like a sieve), a light spongy bone situated in the upper part of the cavity of the nose. The olfactory nerves pass upward through its numerous perforations to reach the brain.

ETHNOL'OGY AND ETHNOG'RAPHY, sciences dealing with man, the aim of the former being to analyse and interpret the meaning of the social phenomena of mankind, as shown in their customs, languages, institutions, &c., the latter being more concerned with descriptive details and the orderly collection of facts relating to particular tribes and localities. Both terms, however, are used very loosely and in a variety of ways, often being confused with _anthropology_, the general science or natural history of mankind, of which the other two are parts. Anthropology, again, is sometimes used in the narrower sense implied in the word _somatology_, the study of the physical structure and distinctive characteristics of the various races of mankind. When the term ethnology is used by the politician or journalist, in most cases it is intended to refer to the racial components in a given territory; in other words, it is used in the sense in which the scientific writer would employ the word anthropology. For instance, when the endeavour was made in the earlier part of the nineteenth century to liberate the Greeks from Turkish dominion, the plea was put forward that they differed in race; and the delimitation of the territory of the Greek state was claimed on what was called 'the ethnological basis', the geographical distribution of people of Greek nationality. Even since then, and especially during the European War and the subsequent attempt at a settlement, claims have been put forward to fix the boundaries of Italy, Yugo-Slavia, Czecho-Slovakia, Poland, &c., on the basis of race and nationality. But further confusion arises from the attempt to apply this anthropological or ethnological test in deciding whether physical type, language, religion, or social traditions and usages are to be the test of nationality. In this article it will be convenient to give the term ethnology its widest meaning, and to consider not merely the customs, beliefs, and institutions of various peoples, but also the early history of the human family, its differentiation into races and the significance of their geographical distribution, and the different phases of culture which are found in the various communities even of the same race.

[Illustration: The Piltdown Skull.

As restored by Dr. Smith Woodward and Mr. Frank O'Barlow. The dark portions are those actually recovered.]