E occupies the fifth place in the Hebrew alphabet and those derived from it. The vowels, when arranged according to their physical affinity, would lie in the series i, e, a, o, u [ALPHABET], and accordingly the vowel e is frequently interchanged with its neighbours i and a. It is also under special circumstanes occasionally convertible with o and u.

1. E is interchanged with i. Thus in Latin the old datives heri, mani, ruri, musai, afterwards took the forms here, mane, rure, musae; and the words magis, videris, tristis, when they appeared without an 8, were written mage, videre, triste. The same interchange appears in the declension of the adjective is, ea, id, and the conjugation of the verbs eo and queo.

2. E in Latin often corresponds to oi in French. Thus many Latin infinitives in ere reappear in French with the termination oir, as habere, debere; avoir, devoir. The Latin past imperfect has the suffix eba, which passed through the forms eva and ea to oie and oi. Thus from habebam were deduced aveva, avea, avoie, and lastly avois or avais. This final s, so far as regards the first person, does not appear in the oldest forms of the French language. Other instances of the change of o into o may be seen in the Latin adjectives and other words in ensis or esis, which in French have the suffix ois, Viennensis, nois; mensis, mois. 3. E Latin into ie French, as mel, bene, ped-; miel, bien, pied. 4. E into a. This is well marked in the dialects of the Greek oopin, Ionic; σopia, Doric, &c. Hence the Latins have often an a where the common dialect of the Greek had e, as unxavn, πλnyn; Lat. machina, plaga. Both forms often coexist in Latin, as tristitia- and tristitie. The a is often changed into e in Latin, if a prefix is added, particularly if two consonants follow the vowel, as factus, confectus; pars, expers; castus, incestus; ars, iners.

5. E into o. Especially in Greek, when a strong vowel follows, as λεγω, λόγος ; νέμω, νόμος. The Latin language prefers an o, as uew, romo; TETTO, Coquo; veos, novus; ext, ob. This change is particularly common in words beginning with a w, or with what was pronounced as a w, the Latin v. Thus vester, verto, veto, were once written roster, vorto, voto. Even in our own language worm (vermis, Lat.), and work | (épyov, Gr.), are now pronounced as if written with an e. The Greek even interchanges a long o with a long e as nатηр, àñαтWρ, eÙπатшр; and so too in Latin we have Anio Aniēnis.

6. A short e often gives place in Latin to a short u when followed by one of the liquids 1, n, m, as in Siculus, (Gk. Zikeλos) perculsus (perce), tabula (Germ. tafel), decumus (decem), contumax (temno), funda (opevdóvn), faciundus (faciendus) euntem.

EAGLE, CONSTELLATION. [AQUILA.]

EAGLE, Roman Standard. The eagle, as a symbol of empire, is often seen on ancient coins and medals, and on none more frequently than on those of the Ptolemies of Egypt and the Seleucidæ of Syria. As an ensign or standard, borne upon a spear, it was used by the Persians in the time of the younger Cyrus. (Xenoph., ' Anab.' i. 10.) Pliny (Hist. Nat.' li. x., c. 4, edit. Hardouin, tom. i., p. 549) says that, till the time of C. Marius, the Romans used five different animals for standards,--the wolf, the minotaur, the horse, the boar, and the eagle, but that in Marius's second consulate they adopted the eagle as the sole ensign for their legions.

The eagle used by the Romans as a standard was of gold or silver: the latter metal, we are told by Pliny, was most frequently used, as the more glittering, and of course more readily seen. It was borne, like the Persian eagle, on the summit of a spear, and was of the size of a pigeon, with its wings displayed. It sometimes rested upon a cross-bar on the top of the spear, and sometimes upon shields piled up. On the roverses of some of the coins of Augustus and Galba, in second brass, the legionary eagle is represented holding the thunderbolt in its talons. The small size of the eagle often contributed to its concealment, when the legion to which it belonged was defeated. The name of the legion was usually engraved upon it. Tacitus, in his Annals,' 1. i. 60, relates the finding of the eagle of the nineteenth legion by Germanicus, which had been lost in the massacre of Varus. Cicero (Catilin.' i., c. 24) says that Catiline had a silver eagle in his house as his titular divinity, which was also his standard in war.

6

A Roman eagle in steel, found at Silchester, presumed to have been a legionary eagle, was exhibited to the Society of Antiquaries in 1788 by the then bishop of Carlisle.

The reader will see a great deal of learning displayed upon this and the standard of the cohorts in M. Le Beau's Quatorzième Mémoire sur la Legion Romaine; Des Enseignes.' Mem. de l'Académie des Inscript. tom. xxxv., 4to, Par. 1770, pp. 277-308.

The eagle has also been adopted as the standard in the modern French army. It is borne perched at rest on a small base at the top of the banner-staff. Austria bears a double-headed eagle on her banners; and Prussia and Russia have taken the eagle as their national

EAR TRUMPET, a curved tube employed to aid defective hearing. The rays of sound, proceeding from any source, enter the tube nearly parallel, and its inner surface is so curved that, after one or more reflections, they converge upon the membrane of the tympanum, and thus act with increased force.

In early notices of acoustic instruments there is some difficulty in distinguishing such as were intended to be applied to the ear, to assist in collecting sound, from such as were employed in aid of the voice, to enable a speaker to produce articulate sounds in such a manner as to insure their transmission to a considerable distance. [SPEAKING TRUMPET.] To a certain extent, indeed, such instruments may be employed for either purpose, some speaking-trumpets being so formed that, if applied to the ear, they would act as hearing- or ear-trumpets.

The common ear-trumpet is a conical tube of metal, the larger end of which expands like the mouth of a trumpet, while the smaller is so shaped as to enter the ear, and conduct the vibrations of sound collected at the wide end direct to the membrane of the tympanum. The smaller end is frequently curved, in order that it may be applied properly to the car while the mouth is directed forwards to receive sounds from a speaker in front of the person using it. For the sake of portability, ear-trumpets are frequently made in two, three, or more portions, sliding within one another, somewhat in the same manner as the tubes of an opera-glass.

Various other instruments, of doubtful value, are more or less employed in aid of defective hearing: among these may be mentioned, the auricle, a small shell-like instrument, formed of gold, and worn in the ear, so that nothing but the expanded mouth is visible; car-cornets, which are small instruments, made of various shapes and sizes, somewhat resembling a French horn or a musical trumpet in appearance, applied to the ears and held in their place by slender springs; speaking or conversation tubes, which are flexible elastic tubes of India-rubber and silk, kept open by spiral wire springs, and terminating at one end in an ear-piece, and at the other in an open bell-shaped vessel, which is held before the mouth of the speaker; and table sonifers, which consist of a revolving trumpet-shaped cowl mounted on a pedestal, which may be placed upon a table, so as to be turned towards any part of the room where conversation may be going on, and of communicating the sound through a flexible tube to the ear of the deaf person. When flexible tubes are employed for such a purpose, their effect is increased by making them of a tapered or conical shape. An ingenious instrument of the ear-trumpet kind is made in the form of a walking-stick. Another, which is held so as to reflect sound into the ear, is styled the ear-conch, and may be termed an auxiliary ear: it is formed of plated metal. The commoner kinds of acoustic instruments are made of tinplate, japanned; but the better sorts are sometimes formed of silver, or of gong-metal, which is supposed by some to be the best metal for the purpose.

Hebert (Engineer's and Mechanic's Encyclopædia,' vol. i., p. 463) quotes an opinion from Dr. Morrison, of Aberdeen, that that end of an ear-trumpet which is applied to the ear should not be made so small as to enter the ear, but should be large enough to include the whole of the external ear; for that gentleman, having been deaf for many years, experienced no relief from ordinary ear-trumpets, but found one which he had made of block-tin, on the proposed plan, to succeed.

EARL. The title of count or earl, in Latin comes, is the most

ancient and widely spread of the subordinate or subject titles. This dignity exists under various names in almost every country in Europe. By the English it is called earl, a name derived to us from the ealderman of the Anglo-Saxons and the eorle of the Danes. By the French it is called comte; by the Spaniards conde; and by the Germans graf, under which generic title are included several distinct degrees of rank, -landgraves, or counts of provinces; palsgraves, or counts palatine, of which there are two sorts; markgraves, or counts of marches, or frontiers (whence marchio, or marquess); burghgraves, or counts of cities; counts of the empire; counts of territories; and several others. [COUNT; BARON.]

After the battle of Hastings, William the Conqueror recompensed his followers with grants of the lands of the Saxon nobles who had fallen in the battle, to be held of himself as strict feuds; and having annexed the feudal title of earl to the counties of the Saxon earls (with whom the title was only official), he granted them to his principal captains.

These earldoms were of three kinds, all of which were by tenure. The first and highest was where the dignity was annexed to the seisin or possession of a whole county, with jura regalia. In this case the county became a county palatine, or principality, and the person created earl of it acquired royal jurisdiction and seigniory. In short, a county palatine was a perfect feudal kingdom in itself, but held of a superior lord. The counties of Chester, Pembroke, Hexham, and Lancaster, and the bishopric of Durham, have, at different times, been made counties palatine; but it does not appear that the title of earl palatine was given to the most ancient and distinguished of them namely, the earl of Chester-before the time of Henry II., surnamed Fitz-Empress, when the title of palatine was probably introduced from the empire. The earls of Chester created barons and held parliaments, and had their justiciaries, chancellors, and barons of their exchequer. This county palatine reverted to the crown in the reign of Henry III. The second kind of earls were those whom the king created earls of a county, with civil and criminal jurisdiction, with a grant of the third part of the profits of the county court, but without giving them actual seisin of the county. The third kind was where the king erected a large tract of land into a county, and granted it with civil and criminal jurisdiction to be held per servitium unius comitatûs.

Under the early Norman kings, all earls, as well as barons, held their titles by the tenure of their counties and baronies; and the grant, or even purchase, with the licence of the sovereign of an earldom or a barony, would confer the title on the grantee or purchaser; but with the solitary exception of the earldom of Arundel, earldoms by tenure have long since disappeared, and in late times the title has been conferred by letters patent under the great seal. Earls have now no local jurisdiction, power, or revenue, as a consequence of their title, which is no longer confined to the names of counties or even of places; for several earls, as Earl Spencer, Earl Grey, and others, have chosen their own names instead of local titles.

The coronet of an English earl is of gold surmounted with pearls, which are placed at the extremity of raised points or rays, placed alternately with foliage. The form of their creation, which has latterly been superseded by the creation by letters patent, was by the king's girding on the sword of the intended earl, and placing his cap and coronet on his head and his mantle on his shoulders. The king styles all earls, as well as the other ranks of the higher nobility of peerage, his cousins. An earl is entitled right honourable, and takes precedence next after marquesses, and before all viscounts and barons. When a marquess has an earldom, his eldest son is called earl by courtesy ; but notwithstanding this titular rank, he is only a commoner, unless he be summoned to the House of Lords by such title. So the eldest sons of dukes are called earls where their fathers have an earldom but no marquisate, as the Duke of Norfolk, &c.

The number of English earls in the House of Lords is at present (1859) 110. Of Scotch earls there are 42, and of Irish earls 65, of whom many have seats in the House of Lords in consequence of possessing a British peerage also.

EARL MARSHAL OF ENGLAND, one of the great officers of state, who marshals and orders all great ceremonials, takes cognisance of all matters relating to honour, arms, and pedigree, and directs the proclamation of peace and war. The curia militaris, or court of chivalry, was formerly under his jurisdiction, and he is still the head of the heralds' office, or college of arms. Till the reign of Richard II., the possessors of this office were styled simply marshals of England; the title of earl marshal was bestowed by that king, in 1386, on Thomas Lord Mowbray, Earl of Nottingham. The office is now hereditary in the family of Howard, and is enjoyed by the Duke of Norfolk. EARTH (Astronomy). In the language of astronomers, the earth is rarely treated as a planet. All the phenomena connected with its motion are seen in the apparent motion of the SUN, to which article we therefore refer.

EARTH, CONTROVERSY ON THE MOTION OF THE. [MoTION OF THE EARTH.]

EARTH, FIGURE OF THE. [GEODESY.]

EARTH, MEAN DENSITY OF THE. The quantity of matter which the earth contains must ultimately be our only guide to that of any other planet, The relative masses of two planets can be found by

calculation of the effects which they produce upon any third body; but the mass of a planet with reference to any given substance, as water, cannot be directly determined upon any instance except our own earth. Perhaps a problem could hardly be proposed which would seem more impracticable to the ordinary reader than that of determining the mean density of the earth. It amounts to asking this:If it were required to substitute for the earth a solid globe of the same size, but of uniform material, in such a manner that the absolute weight of bodies on its surface should remain the same, and the attraction of the whole on other planets remain the same-what must the material be?

Of necessity this question was started by Newton, whose system was the first in which it became of much interest. Having no means of submitting it to experiment, he made one of those sagacious guesses which, had they been collected and preserved, would alone have kept his memory alive. "Unde cum terra communis suprema quasi duplo gravior sit quam aqua, et paulo inferius in fodinis quasi triplo vel quadruplo aut etiam quintuplo gravior reperiatur: verisimile est quod copia materiæ totius in terrâ quasi quintuplo vel sextuplo major sit quam si tota ex aquâ constaret." (Principia,' iii. 10.) That is, he judged the earth to be between five and six times as massive as the same bulk of water; which is the truth.

The relative masses of two planets are determined by the observation of their effects upon a third. Two preliminaries are required: first, the great assumption of the theory of gravitation, that any two particles of matter must attract one another with forces which at different distances are directly as their masses, and inversely as the squares of those distances; secondly, the mechanical consequence of this law of action, namely, that two spheres, having their centres at any given distance, attract one another in the same manner as if each were collected in its centre. Without describing the mode of arriving at such a result from observation, suppose it is ascertained that two planets, A and B, whose distances from a third are as 4 to 3, attract that third with forces which are as 7 to 2. If both planets be brought to the distance 1 from the third, the attraction of the first will be made (4 x 4, or) 16 times as great as before, and that of the second (3 x 3, or) 9 times. Consequently, the new attractions will be as 7 x 16 to 2 x 9, or as 112 to 18. But at equal distances the attractions are in the proportion of the masses; therefore these masses are as 112 to 18. Now suppose the radii of the planets to be as 3 to 2; then their solidities are as 27 to 8, and if the densities (mean) are 8 and 8', the masses are as 278 to 88'. Therefore 276: 86' :: 112: 18, or 8::: 112 x 8: 18 x 27: 896: 486. If then the mean density of either planet be known, that of the other can be found.

The principle of the preceding process exists in every attempt which has been made to find the mean density of the earth. The earth itself is made one of the planets; some known substance, a mountain or a ball of lead, is made the other planet. The attracted body is not a planet, but a pendulum or a plumb-line, and the effect of the mountain or ball of lead upon the plumb-line is measured, that of the earth being either measured or previously known. The actual attraction of the mountain or ball of lead being thus determined, its effect as it would be if placed at the centre of the earth can be calculated; which effect is to the effect of the earth as the mass of the mountain or ball of lead to that of the whole earth. The result of this process, as usual, is condensed into a formula, in which the mode of making the steps is lost sight of: but the above is not the less the manner in which the experiment must be explained.

The hint given by Bouguer, the experiment of Maskeleyne, and those of Cavendish and Zach, have been briefly described in ATTRACTION. Since their time two repetitions of Cavendish's experiment have been made the first, by Dr. Reich, of Freyberg, of which an account was published in 1838; the second, by Mr. Baily, at the desire of the Astronomical Society, and at the expense of the government. (Mem. Ast. Soc., vol. xiv.) The former obtained the same result as Cavendish, but the experiments were few in number; the latter obtained a result slightly differing from that of Cavendish, but in so many different ways and by so large a number of experiments, that it is impossible to doubt the superior correctness of the conclusion. We shall give such a slight general account of this process (which is substantially that of Cavendish) as our limits will admit, referring to the volume already cited for more detail: very few experiments have been either so well performed or so satisfactorily described.

A TORSION pendulum (76 inches long) was provided, moving on a single or double metal wire, or on a double silk line, the mode of sus pension being varied from time to time. At each end was suspended à metal or other ball; and these balls (a and b) were the principal attracted substances. The whole torsion-rod with the suspension was inclosed in a case, with a glass at one end. Large leaden balls (A and B) of about twelve inches diameter (the attraction of which on the torsion pendulum is the quantity to be measured in the experiment) were made to travel on a frame in such manner that they could quickly be brought up laterally on opposite sides of the balls, as in the diagram. We must leave out the whole account of the precautions against electricity or radiation, the manner of noting the actual position of the pendulum, &c., and confine ourselves to the principle of the experiment.

When a torsion pendulum, such as that described, is left to itself,

one side and the other. Even this mean position is continually shifting its direction, so that it cannot be permitted to take a series of observations and make use of them all in determining one mean place. The mode of finding the point of rest, that is of deducing it from observing the extremes of the vibration, is described in the work cited. As soon as the line of rest of the undisturbed pendulum is ascertained, and the large balls are brought into the attracting positions at a and B, on continuing the observation an immediate alteration of the line of rest is seen towards the large balls; say that it becomes nn'. Then the position of equilibrium of the pendulum is altered by the angle nom, in consequence of the approach of the balls.* The precautions taken are abundantly sufficient to assure us that the alteration is no consequence of heat, electricity, magnetism, or any of the variable accidents of matter; there is nothing to which it can be referred except that attraction which, when the earth is the agent, we know under the name of weight, and the assumption of which, as a universal property of matter, led Newton to his explanation of the planetary motions. Many of those who were content to receive Newton's hypothesis to this extent, that the planets attract each other, were staggered by the idea that every particle in the universe attracts every other. Such objectors might have here received conviction from the evidence of their own senses, which would have rendered obvious not only the attraction of the balls upon each other, but its transmission through the wood, flannel, and gilding, which it was found necessary ultimately to interpose between the attracting substances and the torsion-rod in order to destroy the effects of radiant heat.

Two observations are necessary, that of the time of oscillation of the pendulum, and that of the displacement of the line of rest which the approach of the larger balls produces. The first observation, the time, enables the observer to deduce the force of torsion, or the quantity of pressure required to produce any given displacement. And in this particular it was found that the pendulum altered its character from one quarter of an hour to another; showing that the instrument was so delicate, that circumstances of which no explanation can be given were continually altering its character. The consequence was, that at every new trial, both the time and displacement had to be scrupulously observed together, in order that to each displacement produced the proper producing attraction might be applied. The complete formula for calculating the mean density of the earth, implies,-1. The calculation of the character of the pendulum, or the amount of attraction necessary to alter its line of rest by a given quantity; 2. The determination of the attraction actually employed, namely, that of the larger balls, by means of the displacement actually observed; 3. The determination of the attraction which the larger ball would exert, if it had been at the centre of the earth, instead of at the distance employed; 4. The number of times the whole earth would contain such a leaden ball, and its easy consequence, namely, the number of times the whole earth would contain a similar bulk of water; 5. All the necessary corrections for the attraction of the other parts of the apparatus upon the torsion pendulum.

The larger masses were leaden balls, but the smaller balls attached to the torsion pendulum were changed from time to time, and different substances were used. The following table of results will be more interesting than any description we could give in the same space. It shows the result of the experiments made after the effects of radiation were removed ‡ by additional precautions. The first column In making the experiment the effect was usually doubled by placing the large balls first on one side of the smaller ones, and then on the other, and noting the whole of the double displacement.

This distance of course was accurately measured.

An enormous mass of experiments was made and rejected in the course of

the attempts to remove singular discordances, of which no explanation could be given. The mean result of these would not have differed much from those of the more correct sets, but would, of course, have been less satisfactory. The removal of the discordances was due to the suggestion of Professor Forbes, of Edinburgh, who continued to believe they might arise from radiation long after others thought the precautions then already taken must have been sufficient to remove that source of disturbance.

ARTS AND SCI. DIV. VOL. III.

24-inch brass

single copper. bifilar silk

415

.0178

ments.

8

6.154

brass rod alone

bifilar iron

177

20

5.993

415

79

5.839

20

5.787

2-inch ivory

. 0178

The results of individual experiments vary considerably, but it is important to observe that there is nothing which indicates that different kinds of matter attract each other according to different laws. If the large ball of lead exerted different attractions upon particles of brass and ivory of the same weight, the effect would be to give the whole earth one mean density or another, according as the smaller ball is of brass or ivory. Now it is true that the experiments give all manner of results from 5:500 to 6:154, but on examining the results, there appears no evidence whatever of the larger balls attracting the different smaller ones differently. If such were the case, undoubtedly the mean densities obtained from different substances would be different; but though such is the case in the preceding list, and even though it would seem that the lighter balls give the larger densities, yet there is every reason to suppose that the effect is to be attributed to the alteration of the pendulum. Thus it will be seen that there is not so much difference between the results of 2-inch ivory and lead balls susbetween the results of 2-inch lead balls suspended by bifilar iron pended in the same way by a single copper wire, as there is wires, and the same suspended by bifilar brass wires, and also that ivory balls differently suspended give results which have differences as great as any. The mode of suspension and the effect of merely increasing the weight of the smaller balls, appear much to exceed that of applying different substances; but not according to any law. In fact, the differences are altogether of that character to which the term discordance is applied; following no settled rule, and exhibiting every appearance of as often affecting the truth by a positive as by a negative error. The first three sets, in which a brass rod alone is used, were rather a defiance to the apparatus to fail if it could, than seriously intended to help the result. Almost all the experiments were made with a light wooden torsion-rod, and comparatively heavy balls appended. The trying a brass rod by itself, that is, the attempt at obtaining a mean density by noting the attraction of the larger balls upon the torsion-rod only, was the introduction of an extreme case, to increase confidence in the more ordinary experiments.

The mean of the whole is 5.6747, and, rejecting the experiments of which the character would be à priori most doubtful (though it is not certain they ought to be rejected) it is reduced to 5-6604. From the

That it is not the case, is also established without a doubt by pendulum experiments. 81

experiments, by the usual rules of the theory of probabilities it is an even chance that the error of this result is within 04. Cavendish's result was 5'48.

Besides the confirmation of some of the most material points of the theory of gravitation which results from this experiment, it furnishes a presumption of the strongest kind that the earth is solid to the centre, and not, as many have supposed in every age, a hollow shell. The mean density 5 is very much greater than that of the substances which abound at the surface. All common rocks are under 3, and nothing under the ores of the heavier metals comes up to 53. The earth is as massive as if it were all composed of silver-ore, from the centre to the circumference, so that there must be an increase of density towards the centre. If those who think the earth to be a shell were to presume that its solidity ceased at five hundred miles below the surface, they would then be compelled to give to the terrestrial matter, one part with another, a density greater than that of mercury, in order that the whole shell, the hollow part included, might have the mean density which is found by this experiment.

Recently, Mr. Airy, the present Astronomer Royal, has determined the mean density of the earth by means of observations of the rate of oscillation of a pendulum made at the top and bottom of a coal-mine in the county of Durham. As early as the year 1826 he endeavoured, in conjunction with Dr. Whewell and the late Mr. Sheepshanks, to effect the same object by means of pendulum experiments in the Dolcoath mine in Cornwall, but the project was frustrated by local accidents; and a similar attempt in 1828 proved equally fruitless. The principal obstacle to the success of the experiments on those occasions consisted in the difficulty of comparing the clocks at the top and bottom of the mine. In more recent times the application of galvanic electricity to the transmission of signals suggested to Mr. Airy an easy method of conquering this impediment. He accordingly resolved to repeat the experiment, and chose for that purpose the Harton colliery, near South Shields, the bottom of which is no less than 1260 feet beneath the earth's surface. The application of pendulum experiments made at the earth's surface, and at some distance beneath it, to the determination of the mean density of the earth, rests on two principles of attraction, both of which were originally established by Newton. The first is, that the attraction exercised upon an external particle by a sphere of uniform density, or one consisting of concentric strata of different densities, but of uniform density throughout each stratum, is the same as if all the matter of the sphere were collected at the centre. The second is, that a hollow spherical shell of matter exercises no effective attraction on a particle placed anywhere within it. Now, in the case of experiments made with a pendulum at the top and bottom of a coal-mine, the pendulum is acted upon in the former instance by a force equivalent to the attraction which the whole quantity of matter contained in the earth would exert if it were collected at the centre; in the latter instance the quantity of attracting matter is less than in the former by the spherical shell, whose thickness is equal to the distance between the top and bottom of the mine, but the distance of the particle from the centre of attraction is less. It is clear then, that experiments founded on the principles to which we have just alluded, enable us to weigh the whole mass of the earth against an exterior shell of a given thickness; and therefore if the density of the shell (or at any rate the density of the parts which are nearest the mouth of the mine, and on which the attraction exerted by the shell upon the pendulum mainly depends), be ascertained by observation, we shall hence readily deduce the value of the mean density of the earth. Mr. Airy's experiments on the rate of oscillation of the pendulum at the top and bottom of the Harton colliery were made in the summer of 1854. Several English observatories co-operated in their execution by furnishing assistant observers. The Electric Telegraph Company supplied the means of establishing simultaneous galvanic signals between the upper and lower stations. The observations consisted of 104 hours of incessant observations of one pendulum ▲, above, and another pendulum B, below; then of 104 hours with в above, and ▲ below; then of 60 hours with A above and B below: then of 60 with B above and a below. It appeared from these experiments that the lower pendulum was accelerated 2.25" per day, or in other words, that the force of gravity was more intense at the lower station than at the upper byth part. The final conclusion which Mr. Airy deduced from these experiments was, that the mean density of the earth is 6623, the mean density of water being represented by unity. This result, it will be seen, is considerably higher than any value of the same element hitherto found.

The most recent operations for determining the mean density of the earth are due to Colonel James, Superintendent of the Ordnance Survey, who, in 1855, caused a series of celestial observations to be made to the north and south of Arthur's Seat, near Edinburgh, for the purpose of ascertaining the amount of deflection caused by the attraction of the mountain. The resulting value of the mean density was found to be 5:316, with a probable error of 0.054. Colonel James purposes, as soon as the details of the survey of Ben Nevis have been completed, to obtain a new solution of the important problem of the mean density of the earth by determining the amount of deflection caused by the attraction of that mountain, which is the highest in the British Isles, and appears to be in other respects well adapted for the object in view.

Vases

The reader may consult the following recent works on this subject: Experiments with the Torsion-rod, for determining the mean density of the Earth,' by Francis Baily, Esq. (Mem. Ast. Soc., vol. xiv.); Account of Pendulum Experiments undertaken in the Harton Colliery, for the purpose of determining the mean density of the Earth' (with a Supplement), by G. B. Airy, Esq. (Phil. Trans.' 1856, vol. cxlvi.); 'On the deflection of the plumb-line at Arthur's Seat, and the mean specific gravity of the Earth,' by Capt. Clarke,* R.E. (Phil. Trans,' 1856, vol. cxlvi.) EARTHENWARE. The art of moulding earthen vessels for domestic use appears to have been practised in the earliest ages, and among the rudest nations. It is at once the most ancient and the most widely diffused of the arts. In newly-discovered countries it has been found that the use of earthen vessels is familiar among people otherwise little acquainted with the arts of civilised life. have been discovered in the ruins of temples and palatial buildings, constructed by the Aztecs, and other aboriginal tribes of central America; and there is strong evidence for believing that these vessels were the manufacture of the country in which they were found. The potter's wheel is represented in the sculpture and painting of ancient Egypt; frequent reference is made to it in the scriptures of the Old Testament; it must have been in use from a very remote date in ancient Assyria, China, and Japan. In Greece, Rome, and Etruria the potter's art was cultivated with the greatest diligence from the earliest and rudest period of their respective histories, to that of their highest prosperity and refinement. The art indeed arrived at a point of great advancement among the oldest of these nations. In ancient Egypt were made vases and other articles of very elegant forms, as well as common ware for domestic use. From the analyses made at the laboratory of the Museum of Practical Geology, it appears that the pastes or bodies used in making Egyptian earthenware, as seems indeed to have been the case with most ancient pottery, were merely "the natural clays selected for their fitness to the purposes for which they were intended." Glazes or enamels were used by the Egyptians for covering small figures made of a frit of sand, but it is believed that it was not till the later periods of their history that they acquired the art of applying vitreous glazes to their earthenware proper. The Assyrian and Babylonian pottery, as Mr. Birch remarks in his 'History of Ancient Pottery,' "although it bears a general resemblance in shape, form, and use, to that of Egypt, has certain specific differences. As a general rule it may be stated to be firmer in its paste, brighter in its colour, employed in thinner masses, and for purposes not known in Egypt." The Assyrians were, from a very early period, fully acquainted with the use of siliceous and metallic glazes or enamels, and produced them of brilliant colours. Very little of their earthenware has, however, been recovered.

In the hands of the Greeks, vessels of earthenware assumed forms of the most perfect grace and symmetry; and much additional interest was imparted to them for future ages by the practice of painting on them designs which serve now as the truest reflex of Greek painting of the several periods, and afford an almost limitless store of illustration of Greek customs, mythology, &c. The earliest remaining examples of Greek fictile vases are of a pale yellow clay, and have the designs rudely painted of a dark reddish brown. Later, the figures were painted in a black glaze on a pale or red ground. But in the best period of Greek art the earthenware was formed of a reddish substance. which was glazed black; the figures of the design being left of the natural red of the ground. The shapes are of almost infinite variety, but almost invariably marked by the most beautiful simplicity of outline. The pottery of Athens was the most celebrated in Greece, and Athenian vases were offered as prizes in the public games. That of Samos was famous in the days of Homer. With the decline of Greece, all its arts gradually declined, and eventually perished together. Ancient Greek vases are among the most esteemed objects in museums of antiquities: during the last century in particular, extraordinary prices were given for fine specimens: a famous vase, containing a representation of the last night of Troy, was purchased for the Museo Borbonico for 1500l. But owing to the vast numbers of them, and of Etruscan vases, which are essentially similar in character, which have been found, the prices have fallen considerably, though very high prices are still readily given for superior examples. [VASES.]

Roman pottery is, in an artistic point of view, of far less value than that of Greece, but as a manufacture much of it is of a very superior quality. The use of earthenware for domestic purposes was almost universal with the Roman people, and wherever they settled they appear to have carried the manufacture with them; not only Roman pottery, but traces of kilns for the firing of the ware having been found in most of the countries in which were Roman settlements. The ware itself is usually of a bright red colour, given to it by the introduction of a peroxide of iron into the paste, and it bears a brilliant glaze. M. Brongniart calls particular attention to the perfection of workmanship exhibited in this ware, in the making of which he says most of the processes now in use appear to have been employed.

With the fall of the Roman empire the arts for a time perished also.

Communicated by Colonel James, under whose superintendence the whole operation was conducted.