508 E T H -
Ethelred as usual did nothing to oppose them, but bought them off with a large sum of money. His efforts at conciliation were completely successful with Olaf, who, after being converted to Christianity, and adopted by Ethelred as his soil, remained faithful ever afterwards to his promise of friendship. In the years 997, 99S, and 999 the Danes ravaged the coasts of Wessex, Sussex, and Kent. In 1000 Ethelred, energetic at the wrong time and for wrong objects, invaded Normandy, "but suflered a disastrous defeat. He concluded a treaty with that country soon afterwards, and in 1002 married Emma, daughter of Richard duke of Normandy. In the spring a treaty had been concluded with the Danes, but in the winter of the same year, Ethelred suspecting that they were plotting treachery, ordered a general massacre of all the Danes in England. Among others murdered was Gunold, sister of Swend ; and the Danish king, to revenge her death and that of his countrymen, invaded the coast of Devonshire with a large force. He met with scarcely any opposition, and committed the usual ravages till 1007, when peace was concluded by Ethelreds consenting, as at other times, to the payment of a large sum of money. In 1009 Ethelred collected the largest fleet that had been seen in the reign of any king, but it was soon afterwards nearly wholly destroyed by a violent storm, just bsfore the Danes renewed their invasion. Ethelred, though he had gathered an army, wras dissuaded from attacking them by Edric, and afterwards the English, through the treachery of their leaders, suffered a series of defeats; but in 1012 peace was again bought, and Thurkill, one of the Danish leaders, entered the English service. In 1013 Swend, with a more formidable fleet than any he had yet collected, sailed up the Humber, and then marched southward to London; but meeting there with a strenuous resistance, he was compelled to give up the attack and marched to Bath. Here he was proclaimed king, apparently by the Witan, and with the general consent of the English people, who were doubtless wearied of Ethelreds in competency, of the treachery of the nobles, and of the oppressive taxes which had been paid for no purpose. London itself soon acknowledged the Danish king, and Ethelred, after for a time taking refuge in Thurkills ileet, escaped to Normandy. Swend died on February 1014, and on his death Ethelred was recalled by the Witan, on the promise of ruling better in future. In the same year he defeated Cnut, son of Swend, but in 1015 Cnut renewed his attack with a large fleet, and being joined by the traitor Edric, ravaged Wessex and Mercia, and was preparing to attack London, when Ethelred died April 23, 101G. (See Palgraves History of the Anglo-Saxons; Freemans Norman Conquest, vol. i.; and Greens History of the English People.)
ETHELWULF, or /Ethelwulf, an Anglo-Saxon king, succeeded his father Egbert about 83G. 11 is reign, like that of his father, was almost wholly occupied with wars against the Danish invaders. For along time he held them in cheek, and when in 851 they took Canterbury and London, and defeated Beohrtwulf, king of the Mercians, he met them at Ockley in Surrey, and there made the greatest slaughter among the heathen army that we have heard tell of unto the present day, and there got the victory. But the Northmen were persevering in their efforts; and it is stated that in 855 they, for the first time, remained over winter in Sheppsy. In the same year Ethelwulf made a journey to Rome, accompanied by his youngest and favourite son Alfred, to get the latter consecrated as his successor; and his first wife Osburga had been for some time dead, he delayed a few months in France to marry Judith, daughter of the king of the Franks. Ethelbald, his eldest surviving son, indignant at his*youngest brother being preferred to him as successor to his fathers throne, took advantage of his
-E T H
fathers absence to stir up a revolution against him, and obtained the support of so powerful a party that an unnatural civil war was only prevented by Ethelwulf agreeing to grant to his son the government of "Wessex, he himself being recognized as over-lord, and retaining the rest of the kingdom. He died in 858.
ETHER, (C2H5)20, the jEllier or JEllier Sulphuricus of pharmacy, is a colourless, volatile, highly inflammable liquid, of specific gravity 0*723, boiling-point when pure 35*0 C, and fusing-point 31 C. It has a strong and characteristic odour, and a hot sweetish taste, is soluble in ten parts of water, and in all proportions in alcohol, and dissolves bromine, iodine, and, in small quantities, sulphur and phosphorus, also the volatile oils, most fatty and resinous substances, gun-cotton (see Collodiox, vol. vi., p. 149), caoutchouc, and certain of the vegetable alkaloids. The vapour mixed with oxygen or air is violently explosive. The making of ether by the action of sulphuric acid on alcohol was known to Raymond Lully, who wrote in the 13th century; and later Basil Valentin and Valerius Cordus described its preparation and properties. The name ether appears to have been applied to the drug only since the times of Froben, who in 1730 termed it spiritus celhereus. Ether is manufactured by the distillation of 5 parts of 90 per cent, alcohol with 9 parts of concentrated sulphuric acid, at a temperature of 140-145 C., a constant stream of alcohol being caused to flow into the mixture during the operation. (See Chemistry-, vol. v. p. 5GG). It is purified by treatment with lime and calcium chloride, and subsequent redistillation. According to P. Stefanelli (Ber. deutsch. Ghem. G'es., 1875, p. 439), the presence of as small a quantity as 1 per cent, of alcohol may be detected in ether by the colour imparted to it by aniline violet; if water or acetic acid be present, the ether must be shaken with anhydrous potassium carbonate before the application of the test. Ether when drunk has a rapid though evanescent intoxicating effect, estimated to be more than three times that of the same bulk of whisky, instead of which it is largely consumed in some parts of Ireland. (See H. N. Draper, Med. Press and Circular, iv. 117). Mixed with twice its volume of rectified spirit, it is administered internally as a remedy for nervous headache, flatulence, hiccough, hysteria, and spasmodic vomiting and asthma, occasionally also in angina pectoris, intermittent fevers and typhus, and as an antidote for narcotic poisons, and for relieving the pain caused by biliary calculi. It has been shown by Longet that ether when swallowed even in fatal doses does not at any time produce amusthesia. Much heat being rendered latent by its evaporation, ether is sometimes employed as a refrigerant in the reduction of hernia. By the use of Dr Richardsons ether spray apparatus for effecting local anaesthesia, a temperature of - G F. can be obtained. When not allowed to evaporate, ether acts as a rubefacient. Its vapour when inhaled causes at first considerable irritation of the air-passages, and increased rapidity of the pulse, accompanied by much excitement. With the establishment of complete anaesthesia the pulse sinks to G0 or 70. the face becomes pallid, and the muscles are relaxed. Ether occasions more excitement, and requires a somewhat longer period for its exhibition than chloroform, but does not exercise upon the heart the sedative influence of that drug. A history of the employment of ether as an anaesthetic will be found under Anaesthesia, vol. i. p. 78G. See also Chloroform, vol. v. p. G80.
ETHER, or AEther (uiOyp, probably from aWw, I burn, though Plato in his Cralylus (410, b) derives the name from its perpetual motionon del 0ei irfpl tov atpa />W, aeiOajp Si/caiw? av KaXotTo), a material substance of a more subtle kind than visible bodies, supposed to exist in those parts of space which are apparently empty.
ETHER
569
The hypothesis of an retlier has been maintained by different speculators for very different reasons. To those who maintained the existence of a plenum as a philosophical principle, natures abhorrence of a vacuum was a sufficient reason for imagining an all-surrounding aether, even though every other argument should be against it. To Descartes, who made extension the sole essential property of matter, and matter a necessary condition of extension, the bare existence of bodies apparently at a distance was a proof of the existence of a continuous medium between them.
But besides these high metaphysical necessities for a medium, there were more mundane uses to be fulfilled by aethers. /Ethers were invented for the planets to swim in, to constitute electric atmospheres and magnetic effluvia, to convey sensations from one part of our bodies to another, and so on, till all space had been filled three or four times over with lethers. It is only when we remember the extensive and mischievous influence on science which hypotheses about aethers used formerly to exercise, that we can appreciate the horror of aethers which sober-minded men had during the 18th century, and which, probably as a sort of hereditary prejudice, descended even to the late Mr John Stuart Mill.
The disciples of Newton maintained that in the fact of the mutual gravitation of the heavenly bodies, according to Newtons law, they had a complete quantitative account of their motions; and they endeavoured to follow out the path which Newton had opened up by investigating and measuring the attractions and repulsions of electrified and magnetic bodies, and the cohesive forces in the interior of bodies, without attempting to account for these forces.
Newton himself, however, endeavoured to account for gravitation by differences of pressure in an aether (see art. Attraction, vol. iii. p. Gi); but he did not publish his theory, because he was not able from experiment and observation to give a satisfactory account of this medium, and the manner of its operation in producing the chief phenomena of nature.
On the other hand, those who imagined tethers in order to explain phenomena could not specify the nature of the motion of these media, and could not prove that the media, as imagined by them, would produce the effects they were meant to explain. The only aether which has survived is that which was invented by Huygens to explain the propagation of light. The evidence for the existence of the luminiferous aether has accumulated as additional phenomena of light and other radiations have been discovered ; and the properties of this medium, as deduced from the phenomena of light, have been found to be precisely those required to explain electromagnetic phenomena.
Function of the (ether in the propagation of radiation. The evidence for the undulatory theory of light will be given in full, under the article on Light, but we may here give a brief summary of it so far as it bears on the existence of the aether.
That light is not itself a substance may be proved from the phenomenon of interference. A beam of light from a single source is divided by certain optical methods into two parts, and these, after travelling by different paths, are made to reunite and fall upon a screen. If either half of the beam is stopped, the other falls on the screen and illuminates it, but if both are allowed to pass, the screen in certain places becomes dark, and thus shows that the two portions of light have destroyed each other.
Now, we cannot suppose that two bodies when put together can annihilate each other; therefore light cannot be a substance. What we have proved is that one portion of light can be the exact opposite of another portion, just as +a is the exact opposite of-a, whatever a may
be. Among physical quantities we find some which are capable of having their signs reversed, and others which are not. Thus a displacement in one direction is the exact opposite of an equal displacement in the opposite direction. Such quantities are the measures, not of substances, but always of processes taking place in a substance. Wc therefore conclude that light is not a substance but a process going on in a substance, the proccss going on in the first portion of light being always the exact opposite of the process going on in the other at the same instant, so that when the two portions are combined no process goes on at all. To determine the nature of the process in which the radiation of light consists, we alter the length of the path of one or both of the two portions of the beam, and we find that the light is extinguished when the difference of the length of the paths is an odd multiple of a certain small distance called a half wave-length. In all other cases there is more or less light; and when the paths are equal, or when their difference is a multiple of a whole wave-length, the screen appears four times as bright as when one portion of the beam falls on it. In the ordinary form of the experiment these different cases are exhibited simultaneously at different points of the screen, so that we see on the screen a set of fringes consisting of dark lines at equal intervals, with bright bands of graduated intensity between them.
If we consider what is going on at different points in the axis of a beam of light at the same instant, we shall find that if the distance between the points is a multiple of a wave-length the same process is going on at the two points at the same instant, but if the distance is an odd multiple of half a wave-length the process going on at one point is the exact opposite of the process going on at the other.
Now, light is known to be propagated with a certain velocity (3OO-t x 1010 centimetres per second in vacuum, according to Cornu). If, therefore, we suppose a movable point to travel along the ray with this velocity, we shall find the same process going on at every poiut of the ray as the moving point reaches it. If, lastly, we consider a fixed point in the axis of the beam, we shall observe a rapid alternation of these opposite processes, the interval of time between similar processes being the time light takes to travel a wave-leugth.
These phenomena may be summed up in the mathematical expression
u = A cos (ut - px + a)
which gives u, the phase of the process, at a point whose distance measured from a fixed point in the beam is x, and at a time t.
We have determined nothing as to the nature of the process. It may be a displacement, or a rotation, or an electrical disturbance, or indeed any physical quantity which is capable of assuming negative as well as positive values. Whatever be the nature of the process, if it is capable of being expressed by an equation of this form, the process going on at a fixed point is called a vibration; the constant A is called the amplitude; the time is called
the period; and nt - px+ a is the phase.
The configuration at a given instant is called a ivave, and
the distance is called the wave-lenyth. The velocity V
of propagation is n/p. When we contemplate the different
parts of the medium as going through the same process in succession, we use the word undulatory to denote this character of the process without in any way restricting its physical nature.
VIII. 72
