Part 253

First.--To find the height of the apparent level above the true, at any distance.--If the given distance be contained in the table, the correction of level is found in the same line with it; but if the exact distance be not found in the table, then multiply the square of the distance in yards, by 2.57, and divide by 1,000,000, or cut off 6 places on the right for decimals; the rest are inches: or multiply the square of the distance in miles, by 66 feet 4 inches, and divide by 100.

Second.--To find the extent of the visible horizon, or how far can be seen from any given height, on a horizontal plane, at sea, &c.--The height of the observer’s eye above the horizon being known, the extent of his visible horizon is found in the column opposite, under the word Distances.

Third.--To find the distance of any object when it first comes in sight, its height being known.--For the distance of any object will be the extent of the visible horizon of the observer, added to the visible horizon of the point he observes. It is necessary in this case for the observer to know only the height of that part of the object which is kept from his view, by the curvilinear figure of the globe.--Knowing the distance of an object, its height may be found in the same manner.

If the height or distance exceed the limits in the table; then, first, if the distance be given, divide it by 2, 3, or 4, till the quotient comes within the distances in the table; then take out the height answering to the quotient, and multiply it by the square of the divisor for the height required. But when the height is given, divide it by one of these square numbers, 4, 9, 16, 25, &c. till the quotient come within the limits of the table, and multiply the quotient by the square root of the divisor.

LEVELLING staves, instruments used in levelling, that carry the marks to be observed, and at the same time measure the heights of those marks from the ground. These usually consist of two wooden square rulers, that slide over one another, and are divided into feet, inches, &c.

LEVELLING has two distinct applications in the art of war, in the one case it implies the reduction of an uneven surface to that of a plane, so that the works of a fortification may be of a correspondent height or figure throughout. The other is the art of conveying water from one place to another; in this process, it is found necessary to make an allowance between the true and apparent level, or in other words, for the figure of the earth, for the true level is not a straight line, but a curve which falls below the straight line about 8 inches in a mile, 4 times 8 in 2 miles, 9 times 8 in 3 miles, 16 times 8 in 4 miles, always increasing with the square of the distance.

LEVELLING System, a term which since the commencement of the French revolution has been grossly misinterpreted, and cannot be found in any civilized country to answer any other purpose than that of delusion; such was the calumny raised by the patricians of Rome, when they having plundered the soldiers of their lands and appropriated to themselves; when the people complained they were thus reproached; the agrarian law which proposed only to restore the lands to the owners, was called a levelling system; but the people were robbed and the consequence was the ultimate ruin of Roman liberty, and Rome itself; the word Jacobin in modern times has superseded leveller.

LEVER, a balance which rests upon a certain determinate point called a fulcrum.

LEVER in mechanics, an inflective line, rod, or beam, moveable about, or upon a fixed point, called the prop or fulcrum, upon one end of which is the weight to be raised, at the other end is the power applied to raise it; as the hand, &c.

Since the momentum of the weight and power are as the quantities of matter in each, multiplied by their respective celerities; and the celerities are as the distances from the centre of motion, and also as the spaces passed through in a perpendicular direction in the same time, it must follow, that there will be an equilibrium between the weight and power, when they are to each other reciprocally as the distances from the centre, or as the celerities of the motions, or as the perpendicular ascent or descent in the same time; and this universally in all mechanical powers whatsoever, and which is therefore the fundamental principle of all mechanics. See MECHANICAL POWERS.

LEVET, the blast of a trumpet.

LEVIER, Fr. Lever. The French writers having been more explicit on this head than any of our lexicographers, we shall extract the following passages as conducive to general information. The levier or lever is an instrument made of wood or iron, by whose means the heaviest weights may be raised with few hands. When the lever is made of iron, it is called pince or crow. The lever may be considered as the first of all machines. Wheels, pullies, capstans, &c. act only by the power it possesses. The lever must be looked upon as a straight line, which has three principal points, namely, the one on which the load is placed, and which is to be raised, the appui or rest which is the centre round which it turns, and which the French mechanics call orgueil, and lastly the human arm, which is the power that puts the lever into motion. The different arrangements or disposition which is given to these three points, or rather the unequal distances at which they are placed, occasion the force that is collectively displayed.

Belidor makes the following remarks on this useful machine. It is an inflexible bar which must be considered as having no weight in itself, upon which three powers are made to act in three different points in such a manner, that the action of two powers must be directly opposed to the one that resists them. The point where the opposing power acts is called the point d’appui.

LEVIER, in artillery, a wedge.

LEVIER de pointage, Fr. a wedge to assist in pointing pieces of ordnance.

LEVIERS de support, Fr. a wedge by which cannon is raised to a certain line of direction.

To LEVY, has three distinct military acceptations, as to levy or raise an army, to levy or make war; and, to levy contributions.

LEVY, the levying, or raising troops, by enregistering the names of men capable of bearing arms, for the common defence and safety of a country, has from time immemorial been a leading principle among men.

There are indeed some people still existing, who indiscriminately go to war, leaving, for the immediate security of their huts or habitations, only their old men, their wives and children.

Among the Romans, however, and in some other civilized countries, it was a prevailing maxim never to employ above a certain proportion of matured population, and that proportion consisted uniformly of men who were expert at arms.

National assemblies were called together whenever the situation of the country required, that the senate’s decree should be published and put into effect.

The levying or raising of troops for service was regulated in the following manner under two specific heads, called ordinary and extraordinary levy. The ordinary levy took place in consequence of a decree from the senate by which all males of a certain age were called out to do military service: the extraordinary levy was enforced when a deficiency was found in the ordinary levy to answer the immediate exigencies of the state.

The extraordinary levy, which was further distinguished by the word evocation, (See Evocati) was performed as follows. A public orator mounted the rostrum, and after having expatiated upon the urgency of the case, and paid a handsome tribute of commendation to all who should voluntarily step forward to defend their country, he entrusted the conclusion of the business to two superior officers who were to command the new levies.

These officers instantly unfurled two flags, and emphatically exclaimed, let all those brave men who have the safety of the Republic at heart flock to our standards! A red flag was the rallying mark for all who were to serve on foot, and a blue flag pointed out the rendezvous for cavalry. Every one was at liberty to chuse the service he liked best.

With respect to the ordinary levy by which every citizen was liable to be called upon for personal service, it was conducted in the following manner.

All the different tribes into which the inhabitants of the country were divided, assembled in places marked out for that purpose, and as soon as a whole tribe, consisting of males only, had entered, the public crier called over, in a distinct and audible manner, the names of four persons, after which the first military tribune, from among those of that rank who were to command the intended legion, selected one out of the four, and had him enrolled.

The crier then called over the names of four others belonging to the same class, and the second tribune selected one from the four in the same manner as the first had done. This selection went on through the different classes, until the whole tribe was drafted, and another tribe was then subjected to the same rotation. Legions were formed out of these levies, and completed to so effective a strength, that three of them generally composed a Roman army. The Romans readily submitted to these calls of the state; and they did so the more cheerfully, because it was a fundamental rule amongst them, that no man could be provided for in a military or civil way, unless he had served a prescribed number of years.

Kennett, in his antiquities of Rome, gives the following account, which the reader will perceive differs in some particulars from the former.