in Ancient Geography, a town of Boeotia, to the west of Thebes, or lying between Platæa and Thespiae, where the Lacedemonians had a great defeat given them by Epaminondas and Pelopidas, the Theban generals. The Theban army consisted at most but of 6000 men, whereas that of the enemy was at least thrice that number; but Epaminondas trusted most in his horse, wherein he had much the advantage, both in their quality and good management; the rest he endeavoured to supply by the disposition of his men, and the vigour of the attack. He even refused to suffer any to serve under him in the engagement, but such as he knew to be fully resolved to conquer or die. He put himself at the head of the left wing, opposite to Cleombrotus king of Sparta, and placed the main stress of the battle there; rightly concluding, that if he could break the body of the Spartans, which was but 12 men deep, whereas his own was 50, the rest would be soon put to flight. He closed his own with the sacred band, which was commanded by Pelopidas; and placed his horse in the front. His right, from which he had drawn so many men, he ordered to fall back, in a slanting line, as if they declined to fight, that they might not be too much exposed to the enemy, and might serve him for a corps of reserve in case of need. This was the wise disposition which the two Theban generals made of these few but resolute forces; and which succeeded in every part, according to their wish. Epaminondas advanced with his left wing, extending it obliquely, in order to draw the enemy's right from the main body; and Pelopidas charged them with such desperate speed and fury, at the head of his battalion, before they could reunite, that their horse, not being able to stand the shock, were forced back upon their infantry, which threw the whole into the greatest confusion: so that though the Spartans were of all the Greeks the most expert in recovering from any surprise, yet their skill on this occasion either failed them or proved of no effect; for the Thebans, observing the dreadful impression they had made on them with their horse, pushed furiously upon the Spartan king, and opened their way to him with a great slaughter.

Upon the death of Cleombrotus, and several officers of note, the Spartans, according to custom, renewed the fight with double vigour and fury, not so much to revenge his death as to recover his body, which was such an established point of honour as they could not give up without the greatest disgrace. But here the Theban general wisely chose rather to gratify them in that point, than to hazard the success of a second onset; and left them in possession of their king, whilst he marched straight against their other wing, commanded by Archidamus, and consisting chiefly of such auxiliaries and allies as had not heartily engaged in the Spartan interest: these were so discouraged by the death of the king and the defeat of that wing, that they took themselves to flight, and were presently followed by the rest of the army. The Thebans, however, pursued them so closely, that they made a second dreadful slaughter among them; which completed Epaminondas's victory, who remained master of the field, and erected a trophy in memory of it. This was the conclusion of the famed battle of Leuctra, in which the Lacedemonians lost 4000 men, and the Thebans but 300.

**LEVEL** is an instrument which enables us to find a line parallel to the horizon, or concentric with the circumference of the earth, and to continue it to any distance—to form a surface exactly level, having all its parts at equal distances from the earth's centre, or to find the difference of ascent between several places for the purpose of making roads, conducting water, draining low grounds, rendering rivers navigable, forming canals, &c. &c.

Among the great variety of instruments which have been invented for these purposes, the following are the most important and useful.

**Air-Level**, that which shows the line of level by means of a bubble of air inclosed with some liquor in a glass tube of an indeterminate length and thickness, whose two ends are hermetically sealed. When the bubble fixes itself at a certain mark, made exactly in the middle of the tube, the plane or ruler wherein it is fixed is level. When it is not level, the bubble will rise to one end. This glass tube may be set in another of brass, having an aperture in the middle, through which the bubble of air may be observed. The liquor with which the tube is filled is oil of tartar, or aqua secunda; these not being liable to freeze as common water, nor to rarefaction and condensation, as spirit of wine is. This application of a bubble of air was the invention of Dr Hooke.

There is one of these instruments made with sights, which is an improvement upon that last described, and which, by a little additional apparatus, becomes more commodious and exact. It consists of an air level (fig. i.), about eight inches long, and seven or eight lines in diameter, set in a brass tube 2, with an aperture in the middle, C. The tubes are supported by a straight ruler a foot long; at whose end are fixed two sights, 3, 3, exactly perpendicular to the tubes, and of an equal height, having a square hole, formed by two fillets... of brass crossing each other at right angles, in the middle of which is drilled a very small hole, through which a point on a level with the instrument is observed. The brass tube is fastened on the ruler by means of two screws; one of which, marked 4, serves to raise or depress the tube at pleasure, for bringing it towards a level. The top of the ball and socket is rivetted to a little ruler that springs, one end whereof is fastened with a screw to the great ruler, and at the other end has a screw, 5, serving to raise and depress the instrument when nearly level.

The instrument just described, however, is still less commodious than the following one; for though the holes be ever so small, they will take in too great a space to determine the point of level precisely.

The instrument alluded to consists of an air-level, with telescopic sights. This level (fig. 2.) is like the last; with this difference, that, instead of plain sights, it carries a telescope to determine exactly a point of level at a great distance. The telescope is a little brass tube, about 15 inches long, fastened on the same ruler as the level. At the end of the tube of the telescope, marked 1, enters the little tube 1, carrying the eyeglass and a hair placed horizontally in the focus of the object-glass, 2; which little tube may be drawn out, or pushed into the great one, for adjusting the telescope to different sights; at the other end of the telescope is placed the object-glass. The screw 3, is for raising or lowering the little fork, for carrying the hair, and making it agree with the bubble of air when the instrument is level; and the screw 4, is for making the bubble of air, D or E, agree with the telescope; the whole is fitted to a ball and socket. M. Huygens is said to be the first inventor of this level; which has this advantage, that it may be inverted by turning the ruler and telescope half round; and if then the hair cut the same point that it did before, the operation is just.

It may be observed, that one may add a telescope to any kind of level, by applying it upon, or parallel to, the base or ruler, when there is occasion to take the level of remote objects.

Dr Desaguliers contrived an instrument, by which he could take the difference of level of two places, which could not be taken in less than four or five days with the best telescopic levels, may be taken in as few hours. The instrument is as follows. To the ball C (fig. 3.) is joined a recurve tube BA, with a very fine bore, and a small bubble at top A, whose under part is open. It is evident from the make of this instrument, that if it be inclined in carrying, no injury will be done to the liquor, which will always be right both in the ball and tube when the instrument is set upright. If the air at C be so expanded with heat, as to drive the liquor to the top of the tube, the cavity A will receive the liquor, which will come down again and settle at D, or near it, according to the level of the place where the instrument is, as soon as the air at C returns to the same temperament as to heat and cold. To preserve the same degree of heat, when the different observations are made, the machine is fixed in a tin vessel EF, filled with water up to g h, above the ball, and a very sensible thermometer has also its ball under water, that one may observe the liquor at D, in each experiment, when the thermometer stands at the same height as before. The water is poured out when the instrument is carried; which one may do conveniently by means of the wooden frame, which is set upright by the three screws, S, S, S, (fig. 4.), and a line and plummet PP, (fig. 5.). At the back part of the wooden frame, from the piece at top K, hangs the plummet P, over a brass point at N; M m are brackets to make the upright board KN continue at right angles with the horizontal one at N. Fig. 6. represents a front view of the machine, supposing the fore part of the tin vessel transparent; and here the brass socket of the recurve-tube, into which the ball is screwed, has two wings at II, fixed to the bottom, that the ball may not break the tube by its endeavour to emerge when the water is poured in as high as g h.

After the doctor had contrived this machine, he considered, that as the tube is of a very small bore, if the liquor should rise into the ball at A (fig. 3.) in carrying the instrument from one place to another, some of it would adhere to the sides of the ball A, and upon its descent in making the experiment, so much might be left behind, that the liquor would not be high enough at D to show the difference of the level; therefore, to prevent that inconvenience, he contrived a blank screw, to shut up the hole at A, as soon as one experiment is made, that in carrying the machine, the air in A may balance that in C, so that the liquor shall not run up and down the tube, whatever degree of heat and cold may act upon the instrument, in going from one place to another. Now, because one experiment may be made in the morning, the water may be so cold, that when a second experiment is made at noon the water cannot be brought to the same degree of cold it had in the morning; therefore, in making the first experiment, warm water must be mixed with the cold, and when the water has stood some time, before it comes to be as cold as it is likely to be at the warmest part of that day, observe and set down the degree of the thermometer at which the spirit stands, and likewise the degree of the water in the barometer at D; then screw on the cape at A, pour out the water, and carry the instrument to the place whose level you would know; then pour in your water, and when the thermometer is come to the same degree as before, open the screw at top, and observe the liquor in the barometer.

The doctor's scale for the barometer is ten inches long, and divided into tenths; so that such an instrument will serve for any heights not exceeding ten feet, each tenth of an inch answering to a foot in height.

The doctor made no allowance for the decrease of density in the air, because he did not propose this machine for measuring mountains (though, with a proper allowance for the decreasing density of the air, it will do very well), but for heights that want to be known in gardens, plantations, and the conveyance of water, where an experiment that answers two or three feet in a distance of 20 miles, will render this a very useful instrument.

Artillery Foot-Level is in form of a square, having its two legs or branches of an equal length; at a junc-foot-levelture, whereof is a little hole, whence hangs a thread