A C H A G I 97 among these a hundred were greater than any then used in Europe. 60,000 men were embarked, with the king and his women. On the death of Iskandar s successor in 1641, the widow was placed on the throne; and as a female reign favoured the oligarchical tendencies of the Malay chiefs, three more queens were allowed to reign successively. Though this series of female sovereigns lasted only fifty-eight years alto gether, so dense is apt to be the ignorance of recent history, that long before the end of that period it had become an accepted belief among foreign residents at Acln n that there never had been any sovereigns in A chin except females; and hence, by an easy inference, that the Queen of Sheba had been Queen of Achin ! In 1699 the Arab or fanatical party suppressed female government, and put a chief of Arab blood on the throne. The remaining history of Achin is one of rapid decay. Thirty sovereigns in all have reigned from the beginning of the 16th century to the present day. After the restoration of Java to the Netherlands in 1816, a good deal of weight was attached by the neighbouring English colonies to the maintenance of our influence in Achin; and in 1819 a treaty of friendship was concluded with the Calcutta Government, which excluded other European nationalities from fixed residence in Achin. When the home Government, in 1824, made a treaty with the Netherlands, surrendering our remaining settlements in Sumatra in exchange for certain possessions on the con tinent of Asia, no reference was made in the articles to the Indian treaty of 1819; but an understanding was exchanged that it should be modified by us, whilst no proceedings hostile to Achin should be attempted by the Dutch. This reservation was formally abandoned by our Govern ment in a convention signed at the Hague, November 2, 1871; and little more than a year elapsed before the government of Batavia declared war upon Achin. Doubt less there was provocation, as there always will be between such neighbours; but the necessity for war has been greatly doubted, even in Holland. A Dutch force landed at Achin in April 1873, and attacked the palace. It was defeated with considerable loss, including that of the general (Kohler). The approach of the south-west mon soon was considered to preclude the immediate renewal of the attempt ; but hostilities were resumed, and Achin fell in January 1874. (De-Barros; Faria y Souza; Valentyn, vol. v. ; Beaulieu (in Thcvenot s Collection); Dampier; Marsden; Crawfurd s Hist, and Decl. of the Ind. Archip.; J. of Ind. Archip.; Dulaurier in J.A&iatigue, 3d s. vol. viii.; Anderson s Acheen, 1840; Veth, Atchin, &c. Leyden, 1873, <fcc.) (H. y.) ACHMET, or AHMED, the name of three emperors or sultans of Turkey, the first of the name reigning from 1 603 to 1617, the second from 1691 to 1695. Achmet III. succeeded his brother Mustapha II., whom the Janissaries deposed in 1703. After the battle of Pultowa in 1709, Charles XII. of Sweden took refuge with him, and incited him to war with Peter the Great, Czar of Russia. Achmet recovered the Morea from the Venetians (1715); but his expedition into Hungary was less fortunate, his army being defeated at Peterwardein by Prince Eugene in 1716, and again near Belgrade the year after. The empire was dis tracted during his reign by political disturbances, which were occasioned, in part at least, by his misgovernment ; and the discontent of his soldiers at last (1730) drove him from the throne. He died in prison in 1736. ACHRAY, a small picturesque lake in Perthshire, near Loch Katrine, 20 miles W. of Stirling, which has obtained notoriety from Scott s allusion to it in the Lady of the Lake ACHROMATIC GLASSES are so named from being specially constructed with a view to prevent the confusion of colours and distortion of images that result from the use of lenses in optical instruments. When white light passes through a lens, the different-coloured rays that con stitute it are refracted or bent aside at different angles, and so converge at different foci, producing a blurred and coloured image. To remedy this compound lenses have been devised, which present a well-defined image, unsur- rounded by coloured bands of light. To instruments fitted with lenses of this kind has been given the name achromatic, from d privative, and xpw/xa, colour. The celebrated opti cian, John Dollond, was the first to surmount this practical difficulty, about the year 1757, by the use of a combination of crown and flint glass. See OPTICS, MICROSCOPE, itc. ACI REALE, a city and seaport of Sicily, in the Italian province of Catania, near the base of Mount Etna. It stands on solidified lava, which has here been deposited by different streams to a deptli of 560 feet. The town, which has been almost entirely re-erected since the earth quake of 1693, is built of lava, contains many handsome edifices, and is defended by a fortress. Linen, silks, and cutlery are manufactured, and the trade in cotton, flax, grain, and wines is considerable. The place is celebrated for its cold sulphurous mineral waters. Near Aci Reale is the reputed scene of the mythical adventures of Acis and Galatea; and on this account several small towns in the neighbourhood also bear the name of Aci, such as Aci Castello, Aci Terra, <fec. Aci Reale has a population of 24,151. ACID, a general term in chemistry, applied to a group of compound substances, possessing certain very distinctive characteristics. All acids have one essential property, viz., that of combining chemically with an alkali or base, forming a new compound that has neither acid nor alkaline characters. The new bodies formed in this way are termed salts. Every acid is therefore capable of producing as many salts as there are basic substances to be neutralised; and this salt-forming power is the best de finition of an acid substance. The majority of acids possess the following contingent properties : 1. When applied to the tongue, they excite that sensation which is called sour or acid. 2. They change the blue colours of vegetables to a red. The vegetable blues employed for this purpose are generally tincture of litmus and syrup of violets or of radishes, which have obtained the name of re-agents or tests. If these colours have been previously converted to a, green by alkalies, the acids restore them. All these secondary properties are variable; and if we attempted to base a definition on any one of them, many important acids would be excluded. Take the case of a body like silica, so "widely diffused in nature. Is pure silicious sand or flint an acid or a neutral substance 1 ? When it is examined, it is found to be insoluble in water, to be devoid of taste, and to possess no action on vegetable colour ing matters ; yet this substance is a true acid, because when it is heated along with soda or lime, it forms the new body commonly called glass, which is chemically a salt of silicic acid. Many other acids resemble silica in properties, and would be mistaken for neutral bodies if the salt-forming power was overlooked. Another method of regarding an acid, which is found of O O 7 great importance in discussing chemical reactions, is to say an acid is a salt whose baso is water. This definition is very apparent if we regard what takes place in separating the acid from a salt. In this decomposition the acid would appear to be left without having any substitute for the removed alkali. This is not however the case, as water is found to enter into union instead of the base. Thus every
true acid must contain hydrogen; and if this is displaced
