Part 112

DISPOSITION, in a general sense, is the just placing an army or body of men upon the most advantageous ground, and in the strongest situation for a vigorous attack or defence.

DISPOSITION de guerre, Fr. warlike arrangement, or disposition. Under this head may be considered the mode of establishing, combining, conducting, and finally terminating a war, so as to produce success and victory.

Wisdom and discretion in council point out the form necessary for the first establishment of a warlike enterprise, or disposition, afford the means of bringing it to a conclusion, and assimilate all the various parts so as to unite the whole.

The following maxims are in the memoirs of general Montecuculli.

1. Deliberate leisurely, execute promptly.

2. Let the safety of your army be your first object.

3. Leave something to chance.

4. Take advantage of circumstances.

5. Use all the means in your power to secure a good reputation.

The disposition or arrangement of a warlike enterprise may be universal, or particular.

An universal disposition or arrangement of war implies every thing which relates to that system upon an extensive scale; such as the combination of many parts for the ultimate benefit of the whole, &c.

A particular disposition or arrangement of war signifies the detail of minute objects, and the appropriation of various parts, one with another, for the purpose of effecting a general combination. This disposition, (without which the other must prove abortive,) consists in an observance of the strictest discipline by every individual that belongs to a troop or company. To this end, general officers should be scrupulously exact in attending to the inspection of particular corps; specific instructions for regimental œconomy and discipline should be given, and the strictest regard be paid to the execution of orders.

DISTANCE, in military formation, signifies the relative space which is left between men standing under arms in rank, or the intervals which appear between those ranks, &c.

DISTANCES. Inaccessible distances may be found several ways; the most correct of which of course is by means of proper mathematical instruments; which, however, are not always to be had in the field.

The following different methods are laid down by several authors, where instruments cannot be had.

1. Wishing to know the distance of the object A from B (fig. 1.) place a picket at B and another at C, at a few fathoms distance, making A B C a right angle, and divide B C into 4, 5, or any number of equal parts: make another similar angle at C, in a direction from the object, and walk along the line C D till you bring yourself in a line with the object A, and any of the divisions, (say o) of the line B C. Then, as Co : C D ∷ Bo : B A.

VAUBAN.

2. To gain the distance between two objects C and D (fig. 2.) from any point A, taken in the line C D, erect the perpendicular A E: on which set off from A to E, 1 or 200 feet, more or less, according to the distance between the points C and D; set off from E to G in the prolongation A E, one eighth or one tenth of A E; at G raise the perpendicular G F, and produce it towards I; plant pickets at E and G, then move with another picket on G F till it becomes in a line with E and D: and on the prolongation of the perpendicular F G place another picket at I in the line with E and C; measure F I, and it will be as G E : A E ∷ F I : C D.

3. To gain the inaccessible length A B, (fig. 3.) of the front of a fortification; plant a picket at C, from whence both points may be seen: find the lengths C A and C B by the method just given (No. 1.) make C E ¹⁄₄, or any part of C B, and make C D bear the same proportion to C A: measure D E, then it will be as C D : D E ∷ C A : A B.

See Am. Mil. Lib. Article FIELD FORTIFICATION.

Nearly after the same manner may be ascertained the distance from B to A when the point B is accessible; for having measured the line C B, and made the angle C E D equal to C B A, it will be, as C E : D E ∷ C B : B A.

4. The distance of a battery, or other object, may be ascertained by the tangent scale on the breech of a gun. It is however necessary in this case to know the height of the object, the distance of which is required. Lay the gun by the upper line of metal for the top of the object, then raise the tangent scale till the top of the scale and the notch at the muzzle are in a line with the bottom of the object, and note what height of the tangent scale is required: then say, as the length of the scale above the base ring of the gun is to the length from the base ring to the swell of the muzzle, so is the height of the object to its distance from the muzzle of the gun.

5. The breadth of a river, or other short distance, may be taken thus: take two pickets of different lengths, drive the shortest into the ground close to the edge of the bank; measure some paces back from it, and drive in the other till you find, by looking over the tops of both, that your sight cuts the opposite side--Then pull up the first picket, measure the same distance from the second, in any direction the most horizontal, and drive it as deep in the ground as before. Consequently, if you look over them again, and observe where the line of sight falls, you will have the distance required.

6. The following simple method of ascertaining the breadth of a river may be sufficiently correct for some cases: Place yourself at the edge of one bank, and lower one corner of your hat till you find the edge of it cuts the other bank; then steady your head, by placing your hand under your chin, and turn gently round to some level spot of ground, and observe where your eyes and the edge of the hat again meet the ground: your distance from that point will be nearly the breadth of the river.

7. DISTANCES ascertained by the difference between the true and apparent level. See LEVELLING.

8. DISTANCES measured by sound. See SOUND.

9. The following simple micrometer may be so usefully applied to military purposes, that we shall extract it verbatim from the Philosophical Transactions for 1791, where it is described by Cavallo. This micrometer consists of a thin and narrow slip of mother of pearl, finely divided, and placed in the focus of the eyeglass of a telescope, just where the image is formed. It is immaterial whether the telescope be a reflector, or a refractor, provided the eye glass be a convex lens and not a concave one, as in the Galilean construction. The simplest way to fix it, is to stick it on the diaphragm, which generally stands within the tube, and in the locus of the eye glass. When thus fixed, if you look through the eye glass, the divisions on the scale will appear very distinct, unless the diaphragm is not exactly in the focus: in which case the scale must be placed exactly in the focus, by pushing the diaphragm, backwards or forwards, when this is practicable; or else the scale may be easily removed from one surface of the diaphragm to the other, by the interposition of a circular bit of paper or card, or a piece of sealing wax. This construction is fully sufficient when the telescope is always to be used by the same person; but when different persons are to use it, then the diaphragm, which supports the micrometer, must be so constructed as to be easily moved backwards or forwards, though that motion need not be greater than about the tenth or eighth of an inch. This is necessary, because the distance of the focus of the same lens appears different to the eyes of different persons; and therefore whoever is going to use the telescope for the mensuration of an angle, must first unscrew the tube which contains the eye glass and micrometer, from the rest of the telescope, and, looking through the eye glass, place the micrometer where the divisions of it may appear most distinct to his eye. The mother of pearl scale may be about the 24th part of an inch broad; its length is determined by the aperture of the diaphragm; its thickness that of writing paper. The divisions on it maybe the 200th of an inch, which may reach from one edge of the scale to about the middle; and every fifth and tenth division may be a little longer, the tenths going quite across. When the telescope does not magnify above 30 times, the divisions need not be so minute. For the sake of those not conversant in trigonometry, the following is an easy method of determining the value of the divisions on the scale. Mark upon a wall or other place, the length of 6 inches; then place the telescope before it so that the 6 inches be at right angles to it, and exactly 57 feet 3¹⁄₂ inches distant from the object glass of the telescope. This done, look through the telescope, and observe how many divisions of the micrometer are equal to it, and that same number of divisions will be equal to half a degree, or 30′; and this is all that need be done to ascertain the value of the scale. The reason on which it is founded is, that an extension of six inches at the distance of 57 feet, 3¹⁄₂ inches, subtends an angle of 30′, as is easily calculated by trigonometry. To save the trouble of calculation, a scale may be made requiring only inspection. Thus, draw a line equal to the diameter of the field of the telescope, and divide its under side into the same number of parts as are on your micrometric scale, and, by the above operation on the wall, having determined the value of 30′, which we will suppose to correspond with 16 divisions on the scale, mark 30′ on the opposite side of the line, opposite 16 on the lower; 15 opposite 8, and so on.

By the following table the results may be ascertained by inspection only: thus, suppose an extension of 1 foot is found by the table to subtend an angle of 22′, the distance will be 156.2: and suppose at the distance of 171.8 an object subtends an angle of 20′, its height will be found to be 1 foot; or, suppose an object of 6 feet high to subtend an angle of 20′, the distance is 1030.8, by multiplying 171.8 by 6.