the Seychelles, and forming a dependency of Mauritius.

Amlwch (am´löh), a seaport in North Wales, Island of Anglesey. Pop. (1921), 2694 (urb. dist.).

Ammana´ti, Bartolomeo, a sculptor and architect, born at Florence in 1511, died 1592; executed the Leda at Florence, a gigantic Neptune for St. Mark's Place at Venice, a colossal Hercules at Padua, and after the inundation in 1557, which destroyed all the bridges of the Arno, built the celebrated Trinity Bridge at Florence, finished in 1570. He was an imitator of Michael Angelo without his inspiration and genius.

Ammergau (a˙m´er-gou), a district in Upper Bavaria, having its centre in the villages of Ober and Unter Ammergau. The former village is famous on account of the Passion Play which is performed there, at intervals usually of ten years.

Ammeter.—Front removed to show details.

A. Large magnet. B. Soft-iron keeper magnetized by magnet and acting as resistance. D. Cylinder turning within B, and actuated by current entering at C1, and flowing through spiral wire (not shown) at base of D, and through coil on cylinder to terminal C2. E. Hair-spring regulating pointer. F. Pointer stops.

Am´meter (short for ampere-meter), an instrument used for the measurement of electric currents. For commercial use the scale is marked so as to read amperes directly, but for experimental purposes it is usual to have a scale with divisions numbered in tens, in which case the reading multiplied by a suitable constant gives the value of the current in amperes. By employing suitable shunts this admits of the one instrument being used for a number of ranges.

The types of ammeter and the principles upon which they work are as follows: (a) Soft-iron type, the action of a magnetic field on a piece of soft iron; (b) moving-coil type and dynamometer type, the action of a magnetic field on a current-carrying coil; (c) hot-wire type, the expansion of a conductor due to the heating produced by the current; (d) induction type, the action of a magnetic field on the eddy currents produced in a metal disc.

The "soft-iron" ammeter can be used for both direct and alternating currents, is inexpensive, and is sufficiently accurate for commercial use.

For direct-current measurements where a high degree of accuracy is of first importance, a "moving-coil" ammeter is invariably used.

In alternating-current circuits its place is taken by the dynamometer type, which reads both direct and alternating currents.

In cases where absence of inductance in the instrument is important, e.g. in the measurements in wireless-telegraph and telephone circuits, the "hot-wire" ammeter is used. It measures both direct and alternating currents, and, when properly used, has a high degree of accuracy.

The "induction" type cannot be used for direct currents, and has the limitation that with alternating currents it will read correctly only at the frequency for which it is calibrated.

Almost invariably an ammeter gives its full-scale reading when a small current, say of the order of one-tenth of an ampere, is passing through the instrument itself. In order to read larger currents a device is employed whereby a definite fraction of the current to be measured

passes through the instrument.—Bibliography: J. A. Fleming, A Handbook for the Electrical Laboratory and Testing Room (2 vols.); G. D. Aspinall Parr, Electrical Measuring Instruments.

Ammia´nus Marcelli´nus, a Roman historian, born at Antioch in Syria about 320, died about 390. He wrote in 31 books (of which the first 13 are lost) a history of the Cæsars, from Nerva to Valens, which was highly thought of by Gibbon for its fidelity. His MS. was printed for the first time at Rome in 1474.

Ammon.

Am´mon (often called Ammon-Ra, i.e. Ammon-Sun), an ancient Egyptian deity, one of the chief gods of the country, identified by the Greeks with their supreme god Zeus, while the Romans regarded him as the representative of Jupiter; represented as a ram, as a human being with a ram's head, ornamented with the solar disc, or simply with the horns of a ram. There was a celebrated temple of Ammon in the Oasis of Siwah in the Libyan desert.

Ammon, Oasis of. See Siwah.

Ammo´nia, an alkaline substance, which differs from the other alkalies by being gaseous, and is hence sometimes called the volatile alkali. It is a colourless pungent gas, composed of nitrogen and hydrogen; formula, NH₃. It was first prepared by Priestley, who termed it alkaline air. He obtained it from sal-ammoniac by the action of lime, by which method it is yet generally prepared. It is used for many purposes, both in medicine and scientific chemistry; not, however, in the gaseous state, but frequently in solution in water, under the names of liquid ammonia, aqueous ammonia, or spirits of hartshorn. It is generally prepared from the ammoniacal liquor obtained as a by-product on distilling coal. Combined with acids, ammonia forms salts which are of immense value to agriculture. The well-known odour of farmyard manure is very largely due to the formation of ammonia during the rotting of the dung. Many animal substances, such as bones, clippings and shavings of horn, hoof, &c., and certain vegetable matters yield ammonia when heated. Sal-ammoniac is ammonium chloride.

Ammoni´ăcum, a gum-resinous exudation from an umbelliferous plant, the Dorēma ammoniăcum. It has a fetid smell, is inflammable, soluble in water and spirit of wine; used as an antispasmodic, stimulant, and expectorant in chronic catarrh, bronchitic affections, and asthma; also used for plasters.

Ammo´niaphone, an instrument, consisting of a metallic tube containing some substance saturated with ammonia, peroxide of hydrogen, and a few flavouring compounds, fitted with a mouthpiece to breathe through, which is said to render the voice strong, clear, rich, and ringing by the inhalation of the ammoniacal vapour. It was invented by Dr. Carter Moffat, and was suggested by the presence of ammonia in some quantity in the atmosphere of Italy—the country of fine singers.

Ammonites obtusus. Ammonites varians

Am´monites, a group of fossil cephalopods, now divided into a large number of genera, ranging from the Coal Measures (Texas) to the uppermost cretaceous strata. The ammonites differ from the nautili in having the tube connecting the chambers placed on the outer margin of the coiled shell, while the calcareous neck where it passes through the partitions is directed forwards. The partitions are much folded, producing markings like the fronds of ferns where they meet the inner wall of the shell. The name arises from confusion with a coiled gastropod, which was held to resemble the horns of the Egyptian deity Jupiter Ammon.

Am´monites, a Semitic race frequently mentioned in Scripture, descended from Ben-Ammi, the son of Lot (Gen. xix, 38), often spoken of in conjunction with the Moabites. A predatory and