Whatever be the number of divisions in the scale of variation, and in the vernier, the height of the mercury in the barometer is easily discovered by a process similar to that already mentioned.

There are several other kinds of barometers, of which it will be sufficient to give a short description.

1. In the portable barometer, the lower part of the tube is bent upwards, and wider than the rest of the tube; and in this recurvated part the mercury is exposed to the pressure of the atmosphere; or the mercury in the bason is contained in a flexible leathern bag, exposed to the same pressure. In this last, the mercury is forced into the tube so as to fill it, by a screw fixed in the bottom of a wooden box containing the bag, lest the motion of the mercury should break the tube.

2. In the diagonal barometer, (fig. 11) the scale of variation is bent into the direction DR, making an obtuse angle with the vertical part BD. The scale of variation is by this barometer increased in the ratio of DR: DA; but this increase does not compensate for the friction and attraction of cohesion upon the lower side of DR. And when the angle RDA is greater than 45°, the instrument is rendered useless by the separation of globules of mercury from the column.

3. The wheel-barometer, (fig. 12) is a compound tube, SERBD, open at D and closed at E, the diameter of the highest part, SER, being much greater than that of the rest, and filled with mercury from D to SR, and above that vacuous. Upon the surface of the mercury in the recurved leg there is an iron ball in equilibrio with another, H, by a string passing over a pully, P. As the ball at D rises and falls with the mercury, the string turns the pulley, and an index, IN, fixed to it, which points to different parts of a graduated circle. It is clear, that by increasing the diameter of the circle, this contrivance will shew the minutest variations of the air, provided the friction be inconsiderable, which is seldom true.

4. The pendent barometer, (fig. 13) is composed of a tube of a very small bore, a little conical or tapering, closed at the smaller orifice, A, and filled with prepared mercury from A to B, whose distance is equal to the greatest altitude, or about 31 inches. Let the tube be suspended vertically, and the mercury will subside, and be quiescent in that part whose length is equal to the VOL. I.

=

standard altitude at that time; and sup posing that to be the least, it will occupy a space FE equal to 28 inches; and consequently A F is the scale of variation. If AE 60 inches, then AF=32, when in the common barometer it is only 3 inches. The diameter of this barometer tube is very small, and consequently the attraction of cohesion considerable, which prevents the freedom of motion necessary to ascertain minute variations of the air's pressure.

5. In the horizontal rectangular barometer, (fig.14) the highest part of the tube, opposite to the scale of variation, is wider than the rest of the tube; and the mercury, descending 3 inches from A to D, will describe a much longer space in the horizontal leg FG, these spaces being to each other inversely as the squares of the diameters of the tubes, and, that of FG being very small, its motion will be extremely sensible. But the free motion of the mercury in FG is impeded by friction, and the attraction of cohesion, which from the smallness of the tube is considerable; and besides this, globules of mercury are apt to be separated from M, and flow out at G.

By the above, and other expedients, as using water, or water and mercury, the scale of variation is enlarged; but the common barometer is the best, being subject to the fewest inconveniences. In the construction and use of it, the following particulars are to be observed. 1. The diameter of the tube should be id or 4th of an inch, to prevent the effects of the attraction of cohesion; the length of the tube 33 or 34 inches, with a bulb upon the top, into which the air may be diffused, should any remain in the mercury. 2. The diameter of the cistern containing the mercury should be large (at least ten times greater than that of the tube) that the addition or subtraction of the mercury, contained between the greatest and least altitudes, may not sensibly affect its depth; for the numbers, marked upon the side of the tube, shew their distance from a fixed point, and cannot shew the height of the column above the mercury in the cistern, unless its surface coincide with this point, and be immovable. 3. The mercury should be free from any mixture of other metals, and purged of air by being boiled in a glazed earthen vessel, closely covered, and poured, when hot, through a glass funnel, with a long capillary tube, into the barometer tube washed with a rectified spirit, and cleaned with a piston of shammy

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leather, if both ends were not hermetically sealed when it was made, and heated and rendered electrical by rubbing. 4. Unless the temperature of the air remain the same, the dimensions of a given quantity of mercury will be variable, and the altitude of the mercury is an uncertain measure of the weight of the atmosphere, because it is dilated by heat, and contracted by cold,when perhaps the weight of the atmosphere is unaltered. If very great exactness be therefore required, the difference of temperature, at the different times of observation, and the depression or elevation of the mercury produced by it, must be ascertained, before the height of the column, raised by the weight of the atmosphere, can be discovered. See WEATHER, rules for judging of. The barometer applied to the measuring of altitudes.—The secondary character of the barometer, namely as an instrument for measuring accessible heights or depths, was first proposed by Pascal, and Descartes and succeeding philosophers have been at great pains to ascertain the proportion between the fall of the barometer and the height to which it is carried; as Halle, Mariotte, Shuckburgh, Roy, and more especially by De Luc, who has given a critical and historical detail of most of the attempts that have at différent times been made for applying the motion of the mercury in the barometer to the measurement of accessible heights. And for this purpose serves the portable barometer already described, which should be made with all the accuracy possible. Various rules have been given by the writers on this subject, for computing the height ascended from the given fall of the mercury in the tube of the barometer, the most accurate of which was that of Dr. Halley, till it was rendered much more accurate by the indefatigable researches of De Luc, by introducing into it the corrections of the columns of mercury and air, on account of heat. This rule is as follows:

M viz. 10000 x log. of is the altitude in fa

thoms, in the mean temperature of 31°; and for every degree of the thermometer above that, the result must be increased by so many times its 435th part, and diminished when below it: in which theorem M denotes the length of the column of mercury in the barometer tube at the bottom, and m that at the top of the hill, or other eminence; which lengths may be expressed in any one and the same sort of measures, whether feet, or inches, or tenths, &c. and either

English, or French, or of any other nation; but the result is always in fathoms, of 6 English feet each. The following rules must be attended to.

1. Observe the height of the barometer at the bottom of any height or depth, proposed to be measured; together with the temperature of the mercury, by means of the thermometer attached to the barometer, and also the temperature of the air in the shade by another thermometer which is detached from the barometer.

2. Let the same thing be done also at the top of the said height or depth, and as near to the same time with the former as may be. And let those altitudes of mercury be reduced to the same temperature, if it be thought necessary, by correcting either the one or the other, viz. augmenting the height of the mercury in the colder temperature, or diminishing that in the warmer, by its 9600th part for every degree of difference between the two; and the altitudes of mercury so corrected, are what are denoted by M and m, in the algebraic formula above.

3. Take out the common logarithms of the two heights of mercury, so corrected, and subtract the less from the greater, cutting off from the right hand side of the remainder three places for decimals; so shall those on the left be fathoms in whole numbers, the tables of logarithms being understood to be such as have seven places of decimals.

4. Correct the number last found, for the difference of the temperature of the air, as follows; viz. take half the sum of the two temperatures of the air, shewn by the detached thermometers, for the mean one; and for every degree which this differs from the standard temperature of 31°, take so many times the 435th part of the fathoms above found, and add them if the mean temperature be more than 31°, but subtract them if it be below 31°; so shall the sum or difference be the true altitude in fathoms, or being multiplied by 6, it will give the true altitude in English feet.

Ex. 1. Let the state of the barometers and thermometers be as follows, to find the altitude; viz.

BARON, in British customs, a degree of nobility next to a viscount, but the highest in point of antiquity. In the House of Peers dukes, marquisses, earls, viscounts, and barons, are all equal members, whence they are collectively called a House of Peers, or equals; but, in other respects, they claim and enjoy certain honours and distinctions, peculiar to their respective ranks and the date of their creations. See PRECEDENCE.

The original, by writ, Camden refers to King Henry III. and barons, by letters patent or creation, commenced in the reign of Richard II. to these is added a third kind of barons, called barons by tenure. The chief burgesses of London were in former times barons, before there was a lord-mayor; the earl-palatines had anciently their barons

under them; but no barons, except those who held immediately under the king, were peers of the realm.

BARONS of the exchequer, the four judges to whom the administration of justice is committed, in causes between the king and his subjects, relating to matters concerning the revenue. They were formerly barons of the realm, but of late are generally persons learned in the laws. Their office is also to look into the accounts of the king, for which reason they have auditors under them.

BARON and feme, in our law, a term used for the husband in relation to his wife, who is called feme; and they are deemed but one person, so that a wife cannot be witness for or against her husband, nor he for or against his wife, except in cases of high

treason.

BARON and feme, in heraldry, is when the coats of arms of a man and his wife are borne per pale in the same escutcheon, the man's being always on the dexter side, and the woman's on the sinister; but here the woman is supposed not an heiress, for then her coat must be borne by the husband on an escutcheon of pretence.

BARONS of the Cinque-ports, are sixteen members of the House of Commons, elected by the Cinque-ports; two for each port.

BARONET, a modern degree of honour, next to a baron, created by King James I. in order to propagate a plantation in Ulster, in Ireland, for which purpose each of them was to maintain thirty soldiers in Ireland, for three years, after the rate of eight pence sterling per day to each soldier. The honour is hereditary, and they have the precedence of all knights, except those of the garter, bannerets, and privy-counsellors. They are stiled baronets in all writs, and the addition of Sir is attributed to them, as the title of Lady is to their wives. No honour is to be created between barons and baronets.

BARONETS of Ireland, a dignity instituted 30 Sept. 1619.

BARONY, the honour and territory which gives title to a baron, whether he be a layman or a bishop. According to Bracton, a barony is a right indivisible; wherefore, if an inheritance is to be divided among coheirs, though some capital messuages may be divided, yet if the capital messuage be the head of a county or barony, it may not be parcelled; and the reason is, lest by this division many of the rights of counties and baronies by degrees come to nothing, to the

BARRA, in commerce, a long measure used in Portugal and some parts of Spain, to measure woollen cloths, linen cloths, and serges.

BARRACAN, in commerce, a sort of stuff not diapered, something like camblet, but of a coarser grain. It is used to make cloaks, surtouts, and such other garments to keep off the rain.

BARRACKS, places for soldiers to lodge in, especially in garrisons. Barracks were formerly reckoned as highly dangerous to the constitution of the realm; within these last ten years, however, they have increased so much in number and extent, that there is scarcely a moderate sized town in the kingdom without its barracks; and one might infer from the rapid increase of these buildings, that our very existence depends upon them.

a thousand herrings. The barrel of salmon must contain forty-two gallons. The barrel of eels the same. The barrel of soap must weigh two hundred and fifty-six pounds.

BARREL, fire, in military affairs, is mounted on wheels, filled with a composition, and intermixed with loaded grenades, and the outside full of sharp spikes: some are placed under ground to act as mines: others are used to roll down a breach to prevent the enemy's entrance. These are rarely used now in any country.

BARREL, in mechanics, a term given by watch-makers to the cylinder about which the spring is wrapped: and by gun-smiths to the cylindrical tube of a gun, pistol, &c. through which the ball is discharged.

BARRERIA, in botany, named after Peter Barrere, a French physician, a genus of the Syngenesia Monogymia class and order. Essential character; calyx fivetoothed, very small; corol five-parted; style short; stigma trifid. There is only one species, viz. B. guianensis. This tree rises forty or fifty feet in height, and is two feet and a half in diameter; the bark is ash-coloured, and the wood is reddish brown,

BARRATRY, in a ship-master, is his cheating the owners. If goods delivered on shipboard are embezzled, all the mariners ought to contribute to the satisfaction of the party that lost his goods, by the maritime law; and the cause is to be tried in the admiralty. In a case where a ship was insured against the barratry of the master, &c. and the jury found that the ship was lost by the fraud and negligence of the master, the court agreed that the fraud was barratry, though not named in the covenant; but that negligence was not.

BARREL is a measure of liquids. The English barrel, wine measure, contains the eighth part of a tun, the fourth part of a pipe, and one half of an hogshead; that is to say, it contains thirty-one gallons and a half: a barrel, beer-measure, contains thirty-six gallons.

BARREL also denotes a certain weight of several merchandises, which differs according to the several commodities: a barrel of Essex butter weighs one hundred and six pounds, and of Suffolk butter, two hundred and fifty-six pounds. The barrel of herrings ought to contain thirty-two gallons winemeasure, which amount to about twenty

the top a great number of branches, which rise and spread in all directions. These branches are loaded with twigs, on which are alternate leaves ending in a point. It is a native of Guiana, and flowers there in November.

BARRICADE, or BARRICADO, a warlike defence, consisting of empty barrels and such like vessels filled with earth, stones, carts, trees cut down, against an enemy's shot, or assault; but generally trees cut with six faces, which are crossed with battoons as long as a half-pike, bound about with iron at the feet.

In a vessel of war, the vacant spaces between the stancheons are commonly filled with rope, mat, cork, or pieces of old cable, and the upper part which contains a double rope netting above the sail, is stuffed full with hammocks, to intercept the motion, and prevent the execution of small shot in the line of battle.

BARRIER, in fortification, a kind of fence made at a passage, retrenchment, &c. to

stop up the entry thereof, and is composed of great stakes, about four or five feet high, placed at the distance of eight or ten feet from one another, with transums, or over thwart rafters, to stop either horse