Ballis´ta, a machine used in military operations by the ancients for hurling heavy missiles, thus serving in some degree the purpose of the modern cannon. The motive power appears to have been obtained by the torsion of ropes, fibres, catgut, or hair. They are said to have sometimes had an effective range of a quarter of a mile, and to have thrown stones weighing as much as 300 lb. The ballistæ differed from the catapultæ, in that the latter were used for throwing darts.
Ballis´tic Pendulum, an apparatus for ascertaining the velocity of military projectiles, and consequently the force of fired gunpowder. A piece of ordnance is fired against bags of sand supported in a strong case or frame suspended so as to swing like a pendulum. The arc through which it vibrates is shown by an index, and the amount of vibration forms a measure of the force or velocity of the ball.
Ballistics, the science of the motion of projectiles. Interior ballistics deals with the motion of the shot while inside the gun, and with the results of the explosion of the charge. Exterior ballistics comprises a study of the trajectory or path of the projectile in the air, and the causes which affect the shape of this path, such as the density of the air, shape and weight of the shot, rifling of the barrel, angle of fire and speed of the projectile. If the air-resistance be neglected, it can be shown that the trajectory is a parabola. This result, given by Galileo, is of little use in gunnery except when taken along with a knowledge of air-resistance. Robins, in 1742, first measured the muzzle-speed of the shot by firing into a ballistic pendulum and noting the swing of the pendulum. Wheatstone, in 1840, suggested measuring the speed by causing the shot to cut successive wire screens, each of which formed part of an electric circuit. The Boulangé chronograph is a modern development of this idea. Rev. F. Bashforth's experiments, carried out between 1865 and 1880, form the basis of
our knowledge of air-resistance. He found that the latter was proportional to the square of the diameter of the shot, and that, although the resistance is expressible in terms of a power of the speed, this power changes with the speed. The air-resistance is a maximum at about the speed at which sound travels, viz. 1100 feet per second. Artillerists employ ballistic tables based on the results obtained by Bashforth and others, by means of which, given the kind of projectile, its initial velocity, and angle of fire, they can calculate the range and time of flight of the projectile. See Gunnery.—Bibliography: F. Bashforth, The Motion of Projectiles; J. M. Ingalls, Interior Ballistics; P. Charbonnier, Balistique Extérieure.
Balloon-fish (Tetraŏdon lineātus), ord. Plectognathi, a curious tropical fish that can inflate itself so as to resemble a balloon.
Balloons, the most elementary form of lighter-than-air air-craft, unprovided with any means of propulsion or steering. Deriving its power of sustentation from the gas contained in the gas-bag, the free balloon is spherical in form. It is usually filled with coal-gas, which has a lifting-force of 35 lb. per 1000 cu. feet. Varying in size from 5000 to 20,000 cu. foot capacity, the gas-bag is covered with a 'net', from which is hung the 'basket' for the accommodation of the aeronaut, or pilot, and passengers. The spherical gas-bag has at the bottom an elongation, known as the 'neck', which is open to the air in order that the gas may escape as it expands during the rise into the rarefied atmosphere of the upper air. A 'valve' is fitted at the top, which may be opened by a cord from the basket when it is desired to allow gas to escape in order to descend. Bags containing sand are carried in order that ballast may be dropped when it is desired to rise. A free balloon is completely at the mercy of the wind, and simply drifts where the wind takes it. Balloons are usually constructed of cotton fabric, though occasionally of gold-beater's skin, in which case they are commonly filled with hydrogen in place of coal-gas. A 'trail-rope' is usually carried, with which the practice of 'trailing' may be effected over open country or the sea. This consists in allowing the end of the trail-rope to drag on the ground. As the balloon rises it raises more of the rope off the ground, the additional weight bringing it down again. Per contra, as it falls the weight of the trail-rope is taken by the ground and so lightens the balloon. This tends to maintain the balloon at a uniform height. The greatest height ever attained by a balloon is 37,000 feet, reached by Glaisher and Coxwell in Sept., 1862. Both aeronauts nearly perished from the effects of the cold and rarefaction of the atmosphere. In 1895 Parseval and Siegsfield, two officers of the Prussian army, invented the 'Drachen-ballon' or 'Kite-balloon' (Fr. Saucisse). This consists of a captive balloon comprising an elongated gas-bag fitted with an automatic air-chamber, or 'ballonet', for maintaining the pressure, and automatic stabilizers to prevent yawing off the wind, rolling from side to side, and pitching horizontally. This was improved upon by Captain Caquot of the French army, who in 1916 produced an improved type, offering many advantages, which was used in large numbers by the British, French, and American armies and navies during the Great European War of 1914-8. See also Aeronautics, Air-ships.—Bibliography: British Military Manual of Ballooning; Rev. J. M. Bacon, The Dominion of the Air; H. Coxwell, My Life and Balloon Experiences; J. Glaisher, Travels in the Air; G. Tissandier, Histoire de mes Ascensions.
Bal´lot, Voting by, signifies literally voting by means of little balls (called by the French ballottes), usually of different colours, which are put into a box in such a manner as to enable the voter, if he chooses, to conceal for whom or for what he gives his suffrage. The method is adopted by most clubs in the election of their members—a white ball indicating assent, a black ball dissent. Hence, when an applicant is rejected, he is said to be blackballed. The term voting by ballot is also applied in a general way to any method of secret voting, as, for instance, when a person gives his vote by means of a ticket bearing the name of the candidate whom he wishes to support. In this sense vote by ballot is the mode adopted in electing the members of legislative assemblies in most countries, as well as the members of various other bodies. In ancient Greece and Rome the ballot was in common use. In Britain it had long been advocated in the election of members of Parliament and of municipal corporations, but it was only introduced by an Act passed in 1872.
Ballyme´na, a town of Ireland, County Antrim, 22 miles from Belfast, with a considerable trade in linens and linen yarns, the manufacture of which is carried on to a great extent. Pop. 11,380.
Ballymo´ney, a town of Ireland, County Antrim, 38 miles N.W. of Belfast; linen, chemicals, tanning, and brewing. Pop. 3100.
Ballyshan´non, a small seaport of Ireland, County Donegal, on the Erne, about 1 mile from the S.E. shore of Donegal Bay. Pop. 2471.