flanking or enfilade rifle-fire, and to localize the burst of shell. (3) A parapet on the rear side (parados), to shield the defenders from the back-blast of shell which burst beyond the trench. (4) Wide trenches (6 feet at the top), to minimize the risk of men getting buried during bombardment. (5) Accommodation, in dug-outs and other refuges, for a proportion of the troops.
Arms of precision have, during the past twenty years, compelled careful attention to the concealment of entrenchments. Although systems of trenches cannot now be hidden from the eye of the aeroplane-camera, yet the enemy can be kept in doubt, by correct design and careful siting of trenches, as to the strength in which the various portions of a position are held. It is for this reason that the deep fire-trench, with a low parapet in front, has been universally adopted, despite the obvious objection that minor undulations restrict the field of fire because the rifle is brought nearer to the ground. Earthworks on a sky-line, or those seen by the enemy against a distant background, violate the first principles of siting.
Modern entrenchments are arranged in depth. The 'lines' of Wellington's time have given place to a broad belt of mutually supporting defences, organized in three zones. These merge imperceptibly into one another, and each zone extends upwards of a mile from front to rear. The foremost fringe of the outpost zone is in contact with the enemy; it is the high-water mark on which the troops advancing during the last action have come to a standstill and dug themselves in. Very lightly manned, as befits an area where heavy shelling is rife, this zone, nevertheless, plays an important rôle. It harbours the forward artillery observation posts, which control and direct the fire of the guns in rear. It furnishes a 'jumping-off' place for attacks. It takes the first shock of a hostile attack, and, although not strong enough to repulse a serious offensive, contributes to the enemy's ultimate defeat by depriving his onslaught of momentum. The battle zone is more elaborately organized, and capable of being very heavily manned. Within this area the defence intend to bring to a standstill the most determined offensive. It lies sufficiently far back from the fringe of the outpost zone to be reasonably immune from destructive bombardment. Lying still farther back is the third zone, which serves for the accommodation of reserves of troops, and is also prepared for defence, as a last resort, in case the enemy should penetrate the battle zone.
Entrepôt (a˙n˙-tr-pō; Fr.), a port where foreign merchandise which cannot enter the interior of a country is deposited in magazines under the surveillance of the custom-house officers till it is re-exported; also, any place where goods are sent to be distributed wherever customers are found.
Entre Rios (en´tre rē´os; 'between rivers'), a province of the Argentine Republic, lying between the Uruguay and the Paraná; area estimated at 29,240 sq. miles; pop. 425,370. The province is largely pastoral. Capital, Paraná, with a pop. of 25,000
Entro´pion is the inversion or turning in of the eyelid. It may be congenital, or arise as the result of some inflammatory process or burn of the conjunctiva. Entropion affecting the lower lid appears also as the result of extreme photophobia (intolerance to light).
Entropy, a term introduced into physics by Clausius as the name of one of the two important thermodynamical properties of a substance which depend on its 'state'. Suppose we have 1 lb. of water at atmospheric pressure and 212° F., say, and suppose we apply heat to the water and change it into 1 lb. of steam at 212° F. The temperature does not change during this process, while the heat which must be added is the latent heat of the steam, namely, about 960 British Thermal Units. The increase of entropy from the first state to the second state is got by dividing the heat given to the substance, namely, 960 B.Th.U., by the absolute temperature at which that heat was given to the substance, namely, 461 + 212 = 673 degrees absolute, i.e. the increase of entropy is 960/673 = 1.43 units. If the temperature changes with the addition of heat, as it would usually do, we have to imagine the heat to be supplied in small quantities, and to take the average temperature of the body at which these tiny quantities of heat are supplied. The quotient heat ÷ temperature is taken for each small quantity of heat, and the results are added together. The summation is defined as the increase in entropy between the initial and the final states.
In mathematical language the increase in entropy between state A and state B is given by (φB - φA) =
