tube is bent through 45° the readings are only increased in the ratio of 7 to 5. The wheel barometer of Dr R. Hooke, and the steel-yard barometer, endeavour to magnify the oscillation of the mercury column by means of a float resting on the surface of the mercury in the cistern; the motion of the float due to any alteration in the level of the mercury being rendered apparent by a change in the position of the wheel or steel-yard. The pendant barometer of G. Amontons, invented in 1695, consists of a funnel-shaped tube, which is hung vertically with the wide end downwards and closed in at the upper end. The tube contains mercury which adjusts itself in the tube so that the length of the column balances the atmospheric pressure. The instability of this instrument is obvious, for any jar would cause the mercury to leave the tube.

The Siphon Barometer (fig. 1) consists of a tube bent in the form of a siphon, and is of the same diameter throughout. A graduated scale passes along the whole length of the tube, and the height of the barometer is ascertained by taking the difference of the readings of the upper and lower limbs respectively. This instrument may also be read by bringing the zero-point of the graduated scale to the level of the surface of the lower limb by means of a screw, and reading off the height at once from the surface of the upper limb. This barometer requires no correction for errors of capillarity or capacity. Since, however, impurities are contracted by the mercury in the lower limb, which is usually in open contact with the air, the satisfactory working of the instrument comes soon to be seriously interfered with. Fig. 2 shows the Cistern Barometer in its essential and simplest form. This barometer is subject to two kinds of error, the one arising from capillarity, and the other from changes in the level of the surface of the cistern as the mercury rises and falls in the tube, the latter being techBarometer. nically called the error of capacity. If a glass tube of small bore be plunged into a vessel containing mercury, it will be observed that the level of the mercury in the

FIG. 1. Siphon Barometer.

FIG. 2. · Cistern

Fortin's

this rate. The instrument in which the error of capacity is
satisfactorily (indeed, entirely) got rid of is Fortin's Barometer.
Fig. 3 shows how this is effected. The upper part
of the cistern is formed of a glass cylinder, through barometer.
which the level of the mercury may be seen. The
bottom is made like a bag, of flexible leather, against which a
screw works. At the top of the interior of the cistern is a
small piece of ivory, the point of which coincides with the zero
of the scale. By means of the screw, which acts on the flexible
cistern bottom, the level of the mercury can
be raised or depressed so as to bring the ivory
point exactly to the surface of the mercury in
the cistern. In some barometers the cistern is
fixed, and the ivory point is brought to the
level of the mercury in the cistern by raising
or depressing the scale.

In constructing the best barometers three
materials are employed, viz.:-(1) brass, for
the case, on which the scale is engraved; (2)
glass, for the tube containing the mercury;
and (3) the mercury itself. It is evident that
if the coefficient of expansion of mercury and
brass were the same, the height of the mer-
cury as indicated by the brass scale would be
the true height of the mercurial column. But
this is not the case, the coefficient of expansion
for mercury being considerably greater than
that for brass. The result is that if a baro-
meter stand at 30 in. when the temperature of
the whole instrument, mercury and brass, is
32°, it will no longer stand at 30 in. if the FIG. 3.-Fortin's
Barometer.
temperature be raised to 69°; in fact, it will
then stand at 30.1 in. This increase in the
height of the column by the tenth of an inch is not due to any
increase of pressure, but altogether to the greater expansion of
the mercury at the higher temperature, as compared Correc
with the expansion of the brass case with the engraved tions of the
scale by which the height is measured. In order, barometer
reading.
therefore, to compare with each other with exactness
barometric observations made at different temperatures, it is
necessary to reduce them to the heights at which they would
stand at some uniform temperature. The temperature to which
such observations are reduced is 32° Fahr. or o° cent.

tube is not in the line of that of the mercury in the vessel, but correction is given by the formula x=-H09-2.56;

somewhat below it, and that the surface is convex. The capillary depression is inversely proportional to the diameter of the tube. In standard barometers, the tube is about an inch in diameter, and the error due to capillarity is less than oor of an inch. Since capillarity depresses the height of the column, cistern barometers require an addition to be made to the observed height, in order to give the true pressure, the amount depending, of course, on the diameter of the tube.

The error of capacity arises in this way. The height of the barometer is the perpendicular distance between the surface of the mercury in the cistern and the upper surface of the mercurial column. Now, when the barometer falls from 30 to 29 inches, an inch of mercury must flow out of the tube and pass into the cistern, thus raising the cistern level; and, on the other hand, when the barometer rises, mercury must flow out of the cistern into the tube, thus lowering the level of the mercury in the cistern. Since the scales of barometers are usually engraved on their brass cases, which are fixed (and, consequently, the zeropoint from which the scale is graduated is also fixed), it follows that, from the incessant changes in the level of the cistern, the readings would be sometimes too high and sometimes too low, if no provision were made against this source of error.

A simple way of correcting the error of capacity is-to ascertain (1) the neutral point of the instrument, or that height at which the zero of the scale is exactly at the height of the surface of the cistern, and (2) the rate of error as the barometer rises or falls above this point, and then apply a correction proportional to

1000,

If English units be used (Fahrenheit degrees and inches), this in the centigrade-centimetre system the correction is 0001614 HT (H being the observed height and T the observed temperature). Devices have been invented which determine these corrections mechanically, and hence obviate the necessity of applying the above formula, or of referring to tables in which these corrections for any height of the column and any temperature are given.

The standard temperature of the English yard being 62° and not 32°, it will be found in working out the corrections from the above formula that the temperature of no correction is not 32° but 28.5°. If the scale be engraved on the glass tube, or if the instrument be furnished with a glass scale or with a wooden scale, different corrections are required. These may be worked out from the above formula by substituting for the coefficient of the expansion of brass that of glass, which is assumed to be 0.00000498, or that of wood, which is assumed to be o. Wood, however, should not be used, its expansion with temperature being unsteady, as well as uncertain.

If the brass scale be attached to a wooden frame and be free to move up and down the frame, as is the case with many siphon barometers, the corrections for brass scales are to be used, since the zero-point of the scale is brought to the level of the lower limb; but if the brass scale be fixed to a wooden frame, the corrections for brass scales are only applicable provided the zero of the scale be fixed at (or nearly at) the zero line of the column, and be free to expand upwards. In siphon barometers, with which an observation is made from two readings on the scale, the

three barometers, to reduce them to the same temperature, so as to neutralize the inequalities arising from the expansion of the scales by heat.

scale must be free to expand in one direction. Again, if only | it is necessary, before comparing observations made with the the upper part of the scale, say from 27 to 31 in., be screwed to a wooden frame, it is evident that not the corrections for brass scales, but those for wooden scales must be used. No account need be taken of the expansion of the glass tube containing the mercury, it being evident that no correction for this expansion is required in the case of any barometer the height of which is measured from the surface of the mercury in the cistern.

Position of

In fixing a barometer for observation, it is indispensable that it be hung in a perpendicular position, seeing that it is the perpendicular distance between the surface of the barometer, mercury in the cistern and the top of the column which is the true height of the barometer. The surface of the mercury column is convex, and in noting the height of the barometer, it is not the chord of the curve, but its tangent which is taken. This is done by setting the straight lower edge of the vernier, an appendage with which the barometer is furnished, as a tangent to the curve. The vernier is made to slide up and down the scale, and by it the height of the barometer may be read true to 0.002 or even to o-oor in.

It is essential that the barometer is at the temperature shown by the attached thermometer. No observation can be regarded as good if the thermometer indicates a temperature differing from that of the whole instrument by more than a degree. For every degree of temperature the attached thermometer differs from the barometer, the observation will be faulty to the extent of about 0.003 in., which in discussions of diurnal range, &c., is a serious amount.

Before being used, barometers should be thoroughly examined as to the state of the mercury, the size of cistern (so as to admit of low readings), and their agreement with some known standard instrument at different points of the scale. The pressure of the atmosphere is not expressed by the weight of the mercury sustained in the tube by it, but by the perpendicular height of the column. Thus, when the height of the. column is 30 in., it is not said that the atmospheric pressure is 14.7 lb on the square inch, or the weight of the mercury filling a tube at that height whose transverse section equals a square inch, but that it is 30 in., meaning that the pressure will sustain a column of mercury of that height.

The sympiezometer was invented in 1818 by Adie of Edinburgh. It is a revived form of Hooke's marine barometer. It consists of a glass tube, with a small chamber at the top and Symplex an open cistern below. The upper part of the tube ometer. is filled with air, and the lower part and cistern with glycerin. When atmospheric pressure is increased, the air is compressed by the rising of the fluid; but when it is diminished the fluid falls, and the contained air expands. To correct for the error arising from the increased pressure of the contained air when its temperature varies, a thermometer and sliding-scale are added, so that the instrument may be adjusted to the temperature at each observation. It is a sensitive instrument, and well suited for rough purposes at sea and for travelling, but not for exact observation. It has long been superseded by the Aneroid, which far exceeds it in handiness.

Aneroid Barometer.-Much obscurity surrounds the invention
of barometers in which variations in pressure are rendered
apparent by the alteration in the volume of an elastic chamber.
The credit of the invention is usually given to Lucien Vidie,
who patented his instrument in 1845, but similar instruments
were in use much earlier. Thus in 1799 Nicolas Jacques Conté
(1755-1805), director
of the aerostatical
school at Meudon,
and a man of many
parts - a chemist,
mechanician and
painter,-devised an
instrument in which
the lid of the metal
chamber
was sup-

ported by internal
springs; this instru-
ment was employed
during the Egyptian
campaign for measur-
ing the altitudes of
the war-balloons. Al-
though Vidie patented
FIG. 4.-Aneroid Barometer.
his device in 1845, the
commercial manufacture of aneroids only followed after
E. Bourdon's patent of the metallic manometer in 1849,
when Bourdon and Richard placed about 10,000 aneroids on
the market. The production was stopped by an action taken
by Vidie against Bourdon for infringing the former's patent,
and in 1858 Vidie obtained 25,000 francs (£1000) damages.

It is essential in gasometry to fix upon some standard pressure to which all measurements can be reduced. The height of the standard mercury column commonly used is 76 cms. (29-922 in.) of pure mercury at o°; this is near the average height of the barometer. Since the actual force exerted by the atmosphere varies with the intensity of gravity, and therefore with the position on the earth's surface, a place must be specified in defining the standard pressure. This may be avoided by expressing the force as the pressure in dynes due to a column of mercury, one square centimetre in section, which is supported by the atmosphere. If H cms. be the height at o°, and g the value of gravity, Fig. 4 represents the internal construction, as seen when the the pressure is 13.596 Hg dynes (13-596 being the density of face is removed, but with the hand still attached, of an aneroid mercury). At Greenwich, where g= 981-17, the standard pressure which differs only slightly from Vidie's form. a is a flat circular at o° is 1,013,800 dynes. At Paris the pressure is 1,013,600 metallic box, having its upper and under surfaces corrugated dynes. The closeness of this unit to a mega-dyne (a million in concentric circles. This box or chamber being partially dynes) has led to the suggestion that a mega-dyne per square exhausted of air, through the short tube b, which is subsequently centimetre should be adopted as the standard pressure, and it made air-tight by soldering, constitutes a spring, which is affected has been adopted by some modern writers on account of its by every variation of pressure in the external atmosphere, the convenience of calculation and independence of locality. corrugations on its surface increasing its elasticity. At the centre The height of the barometer is expressed in English inches of the upper surface of the exhausted chamber there is a solid in England and America, but the metric system is used in all cylindrical projection x, to the top of which the principal lever scientific work excepting in meteorology. In France cde is attached. This lever rests partly on a spiral spring at and most European countries, the height is given ind; it is also supported by two vertical pins, with perfect freedom readings. millimetres, a millimetre being the thousandth part of motion. The end e of the lever is attached to a second or small of a metre, which equals 39-37079 English inches. lever f, from which a chain g extends to h, where it works on a Up to 1869 the barometer was given in half-lines in Russia, which, drum attached to the axis of the hand, connected with a hair equalling the twentieth of an English inch, were readily reduced spring at h, changing the motion from vertical to horizontal, to English inches by dividing by 20. The metric barometric and regulating the hand, the attachments of which are made to scale is now used in Russia. In a few European countries the the metallic plate i. The motion originates in the corrugated French or Paris line, equalling o-088814 in., is sometimes used. elastic box a, the surface of which is depressed or elevated as The English measure of length being a standard at 62° Fahr., the weight of the atmosphere is increased or diminished, and the old French measure at 61-2°, and the metric scale at 32°, this motion is communicated through the levers to the axis of

Baro

metric

woman's on the sinister. But in this case the woman is supposed
not to be an heiress, for then her coat must be borne by the
husband on an escutcheon of pretence. (See HERALDRY.)
The foreign title of baron is occasionally borne by English
subjects, but confers no precedence in the United Kingdom. It
may be Russian, e.g. Baron Dimsdale (1762); German, eg.
Baron Stockmar, Baron Halkett (Hanoverian); Austrian, eg.
Baron Rothschild (1822), Baron de Worms; Italian, e.g. Baron
Heath; French, e.g. Baron de Teissier; French-Canadian, e.g.
Baron de Longueil (1700); Dutch, e.g. Baron Mackay (Lord
Reay).
(J. H. R.)

was only summoned to parliament by the style of "John | escutcheon, the man's being always on the dexter side, and the Beauchamp of Kidderminster," and the latter by that of "John Cornwall, knight." Such creations became common under Henry VI., a transition period in peerage styles, but "Baron " could not evict "Sire," " Chevalier " and " Dominus." Patents of creation contained the formula "Lord A. (and) Baron of B.," but the grantee still styled himself "Lord" only, and it is an historically interesting fact that to this day a baron is addressed in correspondence, not by that style, but as "the Lord A.," although all peers under the rank of Duke are spoken of as "lords," while they are addressed in correspondence by their proper styles. To speak of " Baron A." or " Baron B." is an unhistorical and quite recent practice. When a barony, however, is vested in a lady it is now the recognized custom to speak of her as baroness, e.g. Baroness Berkeley.

The solemn investiture of barons created by patent was performed by the king himself, by enrobing the peer in the scarlet "robe of estate" during the reading of the patent, and this form continued till 13 Jac. I., when the lawyers declared that the delivery of the letters patent without ceremony was sufficient. The letters patent express the limits of inheritance of the barony. The usual limit is to the grantee and heirs male of his body, occasionally, in default of male issue, to a collateral male relative (as in the case of Lord Brougham, 1860)or (as in the case of Lord Basset, 1797, and Lord Burton, 1897) to the heirsmale of a daughter, and occasionally (as in the case of Lord Nelson, 1801) to the heirs-male of a sister. Sometimes also (as in the case of the barony of Rayleigh, 1821) the dignity is bestowed upon a lady with remainder to the heirs-male of her body. The coronation robes of a baron are the same as those of an earl, except that he has only two rows of spots on each shoulder; and, in like manner, his parliamentary robes have but two guards of white fur, with rows of gold lace; but in other respects they are the same as those of other peers. King Charles II. granted to the barons a coronet, having six large pearls set at equal distances on the chaplet. A baron's cap is the same as a viscount's. His style is "Right Honourable "; and he is addressed by the king or queen, "Right Trusty and Wellbeloved." His children are by courtesy entitled to the prefix 66 The Honourable."

Barons of the Exchequer were formerly six judges (a chief baron and five puisne barons) to whom the administration of justice was committed in causes betwixt the king and his subjects relative to matters of revenue. Selden, in his Titles of Honour, conjectures that they were originally chosen from among the barons of the kingdom, and hence their name; but it would probably be more exact to say that they were officers of a branch of the king's Curia, which was theoretically composed of his "barons." The title has become obsolete since 1875, when the court of exchequer was merged in the High Court of Judicature. Barons of the Cinque Ports (originally Hastings, Dover, Hythe, Romney and Sandwich) were at first the whole body of their freemen, who were so spoken of in royal charters. But the style was afterwards restricted to their mayors, jurats, and (prior to 1831) members of the House of Commons elected by the Cinque Ports, two for each port. Their right to the title is recognized in many old statutes, but in 1606 the use of the term in a message from the Lower House drew forth a protest from the peers, that "they would never acknowledge any man that sitteth in the Lower House to the right or title of a baron of parliament" (Lords' Journals). It was the ancient privilege of these "barons" to bear a canopy over the sovereign at his or her coronation and retain it as their perquisite. They petitioned as "barons of the Cinque Ports" to attend the coronation of Edward VII., and a deputation was allowed to do so.

Baron and Feme, in English law, is a phrase used for husband and wife, in relation to each other, who are accounted as one person. Hence, by the old law of evidence, the one party was excluded from giving evidence for or against the other in civil questions, and a relic of this is still preserved in the criminal law.

Baron and Feme, in heraldry, is the term used when the coatsof-arms of a man and his wife are borne per pale in the same

"

The Foreign Tille.-On the continent of Europe the title baron, though the same in its origin, has come, owing to a variety of causes, to imply a rank and status very different from its connotation in the United Kingdom, and again varies considerably in different countries. Originally baro meant no more than "man," and is so used in the Salic and other "barbarian" laws; e.g. Si quis mortaudit barum vel feminam, &c. (Lex Aleman. tit. 76). In this way, too, it was long preserved in the sense of "husband," as in the Assize of Jerusalem (MSS. cap. 98): Si l'on appelle aucune chose femme qui aura baron, et il la veut deffendre, il la peut deffendre de son cors, &c. Gradually the word seems to have come to mean a strong or powerful man," and thus generally "a magnate." Finally, in France in the 12th century the general expression barones was introduced in a restricted sense, as applied properly to all lords possessing an important fief, subject to the rule of primogeniture and thus not liable to be divided up, and held of one overlord alone. Sometimes it included ecclesiastical lordships of the first rank. In the 13th century the Register of King Philip Augustus places the barones regis Francie next to the dukes and counts holding in chief, the title being limited to vassals of the second rank. Towards the end of the century the title had come to mean that its bearer held his principal fief direct from the crown, and was therefore more important than that of count, since many counts were only mediate vassals. Thus the kings in granting a duchy or countship as an apanage to their brothers or sons used the phrase in comitatum et baroniam. From this period, however, the title tends to sink in comparative importance. When, in the 14th century, the feudal hierarchy was completed and stereotyped, the barons are ranked not only below counts, but below viscounts, though in power and possessions many barons were superior to many counts. In any case, until the 17th century, the title of baron could only be borne by the holder of a territorial barony; and it was Louis XIV. who first cheapened the title in France by creating numerous barons by royal letters. This entire dissociation of the title from the idea of feudal rights and obligations was completed by Napoleon's decree of March 1, 1808, reviving the ancient titles. By this instrument the title of baron was to be borne ex officio by a number of high officials, e.g. ministers, senators, councillors of state, archbishops and bishops. It was given to the 37 mayors who attended the coronation, and could be claimed by any mayor who had served to the emperor's satisfaction for ten years, and by any member of an electoral college who had attended three sessions. The title was made to descend in order of primogeniture to legitimate or adopted sons and to the nephews of bishops, the sole condition being that proof must be presented of an actual income of 15,000 fr., of which one-third should descend with the title. The creation of barons was continued by Louis XVIII., Charles X. and Louis Philippe, and, suspended at the revolution of 1848, was revived again on a generous scale by Napoleon III. The tolerant attitude of the Third Republic towards titles, which it does not officially recognize, has increased the confusion by facilitating the assumption of the title on very slender grounds of right. The result has been that in France the title of Baron, unless borne by the recognized representative of a historic name, not only involves no political status, but confers also but very slight social distinction. The same is true, mutatis mutandis, of most other European countries, and notably of Italy. In Austria and Germany the