Evocati. Were a class of soldiers among the Romans, who, after having served their full time in the army, entered as volunteers to accompany some favorite general. Hence they were likewise called emereti and beneficiarii.
Evocation. A religious ceremony which was observed among the Romans at the commencement of a siege, wherein they solemnly called upon the gods and goddesses of the place to forsake it and come over to them. When any place surrendered they always took it for granted that their prayer had been heard.
Evolutions. Are the movements of troops in order to change position. The object may be to maintain or sustain a post, to occupy a new post, to improve an attack, or to improve a defense. All such movements as marching, countermarching, changing front, forming line, facing, wheeling, making column or line, defiling, deploying, etc., come under the general heading of evolutions.
Evreux (anc. Mediolanum). A city of France, capital of the department of Eure. It has sustained several sieges, and was burned by Henry I. of England in 1119.
Examination, Boards of. See Boards of Examination.
Exarchs. Were appointed by the Byzantine emperors of the East, to govern Central Italy after its conquest by Belisarius and Narses, 548. They ruled from 568 to 752, when Eutychus, the last, was overcome by Astolphus the Lombard.
Exauctoratio. In the Roman military discipline, differed from the missio, which was a full discharge, and took place after soldiers had served in the army twenty years; whereas the exauctoratio was only a partial discharge; they lost their pay, indeed, but still kept under their colors or vexilla, though not under the aquila or eagle, which was the standard of the legion; whence instead of legionarii, they were called subsignani, and were retained till they had either served their full time, or had lands assigned them. The exauctoratio took place after they had served seventeen years.
Excavation. The art of cutting or otherwise making hollows in the earth; also the cavity formed.
Exchange. The act of two officers changing regiments, battalions, or batteries. The mutual giving up of an equal number of prisoners by hostile states or armies. In this sort of exchange an officer, according to his rank, is reckoned as equal to a certain number of men or of officers of a lower grade than his own.
Excubiæ. In ancient warfare, the watches and guards kept in the day by the Roman soldiers. They differed from the vigiliæ, which were kept in the night.
Execution, Military. Is the pillaging or plundering of a country by the enemy’s army. Military execution also means every kind of punishment inflicted in the army by the sentence of a court-martial; which is of various kinds, including putting a soldier to death by shooting him, which is the ordinary punishment of deserters to the enemy, mutineers, etc. This form of death is considered less disgraceful than hanging by the neck.
Exempt. Not subject, not liable to. Men of certain age are exempt from serving in the militia. An aide-de-camp and brigade-major are exempt from all regimental duties while serving in those capacities. Officers on courts-martial are sometimes exempt from all other duties until the court is dissolved.
Exercise. The practice of all those motions and actions, together with the whole management of arms, which are essential to the perfection of a soldier, and the rendering him fit for service.
Exercise, Artillery. Is the method of teaching the regiments of artillery the use and practice of all the various machines of war belonging to that particular arm of the service.
Exon. In England, an officer of the Yeomen of the Royal Guard; an exempt.
Exostre (Fr.). Bridge of the Helepole or movable tower of the ancients, by which they passed upon a wall during a siege.
Expanding System of Projectiles. See Projectiles, Rifle.
Expedient. A stratagem in warfare.
Expedition. Is an enterprise taken by sea or by land against an enemy, the fortunate termination of which depends on the rapidity and unexpected nature of its movements. It is usually intrusted to a commander of acknowledged talents and experience.
Expense Magazines. Are small powder-magazines containing ammunition, etc., made up for present use. There is usually one in each bastion.
Experiments. The trials or applications of any kind of military machines in order to ascertain their practical qualities and uses.
Expiration of Service. The termination of a soldier’s contract of enlistment.
Explode. To burst with a loud report; to detonate, as gunpowder, or a shell filled with powder or the like material.
Explosion. The sudden enlargement of the volume of a body by its conversion into gas or vapor. (See Explosives.) The explosion of powder may be divided into three distinct parts, viz.: ignition, inflammation, and combustion, all of which see under their proper headings.
Explosives. Substances the elements of which under certain conditions suddenly undergo a chemical rearrangement into gases, giving rise to great pressures on surrounding bodies. Modern writers recognize two different kinds of explosions—explosions of the 1st order, or detonations, and explosions of the 2d order, or rapid combustions. Detonating explosions are practically instantaneous. The explosion is supposed to be propagated by a vibration throughout the mass. Ordinary explosions are propagated by inflammation. Gunpowder, which may be taken as a type of explosives of the 2d order, burns at a certain rate, depending upon the density. When a charge is fired the inflammation spreads from the point of ignition to all parts of the charge—each grain is successively enveloped and burned from surface to centre. The velocity of inflammation is the greater in proportion to the degree of confinement from the increased tension of the gases. The velocity of combustion is the rate at which the solid grains are burned. It is measured by the distance passed over by the burning surface (the line being taken perpendicular to the surface) in the unit of time. Time thus enters into the explosion of gunpowder and gives it its peculiar value as a ballistic agent.
In the detonating explosives, the case is very different. These bodies may be supposed to be made up of molecules containing so many atoms of carbon, oxygen, nitrogen, etc., so placed as to be held in a state of equilibrium by their mutual attractions and repulsions, but this equilibrium is unstable; that is to say, each atom has only a very small arc of vibration in which the molecule is stable. If by any cause an atom is forced beyond this limit the equilibrium of the whole mass is destroyed, and the elements instantly rearrange themselves under the influence of the chemical affinities which obtain under the particular conditions of the explosion. This kind of explosion is brought about in various ways—by percussion, concussion, heat, etc.—some bodies being susceptible to one mode of firing more than another. The theory which offers the best explanation of the various phenomena is that the molecular balance is peculiarly susceptible to overturn by certain vibrations. The vibrations given out by the explosion of the fulminates seem to have the widest range in bringing about the detonation of different substances. For this reason the fulminate of mercury is the universal detonating agent. Its own susceptibility to explosion by heat, percussion, and the electric spark especially fits it for this work. Wet gun-cotton requires in addition to the fulminate a “primer” of dry gun-cotton.
Explosives, Composition of. Ordinary explosives of which gunpowder is the type are mechanical mixtures of two essential ingredients—one a combustible, the other an oxidizing agent. The combustible is usually