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the hand at h. The spiral spring on which the lever rests at d is intended to compensate for the effects of alterations of temperature. The actual movement at the centre of the exhausted box, whence the indications emanate, is very slight, but by the action of the levers is multiplied 657 times at the point of the hand, so that a movement of the 220th part of an inch in the box carries the point of the hand through three inches on the dial. The effect of this combination is to multiply the smallest degrees of atmospheric pressure, so as to render them sensible on the index. Vidie's instrument has been improved by Vaudet and Hulot. Eugène Bourdon's aneroid depends on the same principle. The aneroid requires, however, to be repeatedly compared with a mercurial barometer, being liable to changes from the elasticity of the metal chamber changing, or from changes in the system of levers which work the pointer. Though aneroids are constructed showing great accuracy in their indications, yet none can lay any claim to the exactness of mercurial barometers. The mechanism is liable to get fouled and otherwise go out of order, so that they may change 0.300 in. in a few weeks, or even indicate pressure so inaccurately and so irregularly that no confidence can be placed in them for even a few days, if the means of comparing them with a mercurial barometer be not at hand.

The mercurial barometer can be made self-registering by concentrating Barographs. the rays from a source of light by a lens, so that they strike the top of the mercurial column, and having a sheet of sensitized paper attached to a frame and placed behind a screen, with a narrow vertical slit in the line of the rays. The mercury being opaque throws a part of the paper in the shade, while above the mercury the rays from the lamp pass unobstructed to the paper. The paper being carried steadily round on a drum at a given rate per hour, the height of the column of mercury is photographed continuously on the paper. From the photograph the height of the barometer at any instant may be taken. The principle of the aneroid barometer has been applied to the construction of barographs. The lever attached to the collapsible chamber terminates in an ink-fed style which records the pressure of the atmosphere on a moving ribbon. In all continuously registering barometers, however, it is necessary, as a check, to make eye-observations with a mercury standard barometer hanging near the registering barometer from four to eight times daily.

See Marvin, Barometers and the Measurement of Atmospheric Pressure (1901); and C. Abbe, Meteorological Apparatus (1888). Reference may also be made to B. Stewart and W. W. H. Gee, Practical Physics (vol. i. 1901), for the construction of standard barometers, their corrections and method of reading.

BAROMETRIC LIGHT, the luminous glow emitted by mercury in a barometer tube when shaken. It was first observed by Jean Picard, and formed the subject of many experiments at the hands of Francis Hawksbee. The latter showed that the Torricellian vacuum was not essential to the phenomenon, for the same glow was apparent when mercury was shaken with air only partially rarefied. The glow is an effect of the electricity generated by the friction of the mercury and the air in the barometer tube.

BARON, MICHEL (1653-1729), French actor (whose family name originally was Boyron), was born in Paris, the son of a leading actor (d. 1655) and of a talented actress (d. 1662). At the age of twelve he joined the company of children known as the Petits Comédiens Dauphins, of which he was the brightest star. Molière was delighted with his talent, and with the king's permission secured him for his own company. In consequence of a misunderstanding with Molière's wife, the actor withdrew from the dramatist's company, but rejoined in 1670, reappearing as Domitien in Corneille's Tite et Bérénice, and in his Psyche. He remained in this company until Molière's death. He then became a member of the company at the Hôtel de Bourgogne, and from this time until his retirement in 1691 was undisputed master of the French stage, creating many of the leading rôles in Racine's tragedies, besides those in two of his own comedies, L'Homme à bonnes fortunes (1686), and La Coquette (1687). He also wrote Les Enlèvements (1685), Le Débauché (1689), and translated and acted two plays of Terence. In 1720 Baron reappeared at the Palais Royal, and his activity on the stage was renewed in a multitude of parts. He died on the 22nd of December 1729.

His son Étienne Michel Baron (1676-1711) was also a fine actor, and left a son and two daughters who also played at the Comédie Française.

See George Monval, Un Comédien amateur d'art (1893); also the Abbé d'Allanial's Lettres a mylord XXX. sur Baron et la demoiselle Lecouvreur, in F.G.J.S Andrieux's Collection des mémoirer sur l'art dramatique (1822).

BARON. This word, of uncertain origin, was introduced into England at the Conquest to denote "the man" (i.e. one who had done him "homage") of a great lord, and more especially of the king. All who held "in chief" (i.e. directly) of the king were alike barones regis, bound to perform a stipulated service, and members, in theory at least, of his council. Great nobles, whether earls or not, also spoke of their tenants as "barons," where lesser magnates spoke of their "men" (homines). This was especially the case in earldoms of a palatine character, such as Chester, where the earl's barons were a well-recognized body, the Venables family, "barons of Kinderton," continuing in existence down to 1679. In the palatinate of Durham also, the bishop had his barons, among whom the Hiltons of Hilton Castle were usually styled "Barons of Hilton" till extinct in 1746. Other families to whom the title was accorded, independently of peerage dignity and on somewhat uncertain grounds, were "the barons of Greystock," "the barons of Stafford," and the Cornwalls, "barons of Burford." Fantosme makes Henry II. speak of "mes baruns de Lundres"; John's charter granting permission to elect a mayor speaks of "our barons of our city of London," and a London document even speaks of "the greater barons of the city." The aldermen seem to have been loosely deemed equivalent to barons and were actually assessed to the poll-tax as such under Richard II. In Ireland the palatine character of the great lordships made the title not uncommon (e.g. the barons of Galtrim, the barons of Slane, the barons of the Naas).

As all those who held direct of the crown by military service (for those who held "by serjeanty" appear to have been classed apart), from earls downwards, were alike "barons," the great difference in their position and importance must have led, from an early date, to their being roughly divided into "greater" and "lesser" barons, and indeed, under Henry II., the Dialogus de Scaccario already distinguishes their holdings as "greater" or "lesser" baronies. Within a century of the Conquest, as we learn from Becket's case (1164), there arose the practice of sending to the greater barons a special summons to the council, while the lesser barons, it is stipulated in Magna Carta (1215), were to be summoned only through the sheriffs. Thus was introduced a definite distinction, which eventually had the effect of restricting to the greater barons the rights and privileges of peerage.

Thus far the baron's position was connected with the tenure of land; in theory the barons were those who held their lands of the king; in practice, they were those who so held a large amount of land. The great change in their status was effected when their presence in that council of the realm which became the House of Lords was determined by the issue of a writ of summons, dependent not on the tenure of land, but only on the king's will. Camden's statement that this change was made by Henry III. after "the Barons' War" was long and widely accepted, but it is now assigned, as by Stubbs, to Edward I., and the earliest writs accepted as creating hereditary baronies are those issued in his reign. It must not, however, be supposed that those who received such summons were as yet distinguished from commoners by any style or title. The only possible prefix at that time was Dominus (lord), which was regularly used by simple knights, and writs of summons were still issued to the lowest order of peers as knights (chevaliers) only. The style of baron was first introduced by Richard II. in 1387, when he created John de Beauchamp, by patent, Lord de Beauchamp and baron of Kidderminster, to make him "unum parium et baronum regni nostri." But it was not till 1433 that the next "baron" was created, Sir John Cornwall being then made baron of Fanhope. In spite, however, of these innovations, the former