Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/313

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   N its early days this science might have been simply defined as the art of determining the motions of projectiles discharged from pieces of ordnance; in its present stats it includes also the employment of projectiles specially adapted to the purpose in view, and the manipulation of artillery so as to enable the projectiles to produce the maximum effect.

Theory of Gunnery.—Instruments of great precision, mechanical construction of much accuracy, and a consider able knowledge of the higher mathematics are necessary to obtain and make use of trustworthy data for the establish ment of sound principles on which to base the theory of gunnery. It is therefore not surprising that, owing to the early discovery of gunpowder, the art was long practised in a rude manner, without any attempt being made to reduce it to a science. Thus, though firearms appear to have been in use from the, little of value was understood of the laws regulating the flight of projectiles till the time of Nicholas Tartaglia, who published a treatise on the subject at Venice in. About sixty years before that date, Leonardo da Vinci had enunciated some of the mathematical principles of trajec tories in a manner which shows him to have possessed far arly more insight than any of his contemporaries ; but he did Lews. no t p ursue the inquiry, and Tartaglia may be regarded as the father of ballistics. He was a man of great talent and ingenuity, but unfortunately had no opportunities of observ- arta- ing artillery practice ; he was unable, therefore, to bring lia&amp;gt; his calculations and speculations to the test of fact, and failed to carry conviction to the minds of the philosophers of the age. Before his time it had been generally believed that a ball on leaving the bore of a gun proceeded for some distance in a straight path, a fallacy which lurks in the phrase &quot;point-blank,&quot; riot yet expunged from popular speech. He saw, however, that &quot; a piece of artillery cannot shoot one pace in a right line,&quot; and propounded the axiom that &quot; the more swifter a pellet doth flie, the lesse crooked is his range,&quot; a truth expressed at the present day by the statement that a high velocity gives a flat trajectory. This eminent philosopher claimed the invention of the gunner s quadrant ; he took into account in his calculations the resistance of the air, but placed the angle of elevation at which the maximum range would be obtained at 45, which would only be the case in vacuo. Galileo was the next mathematician of note who investigated the subject. In his Dialogues on Motion, published in 1638, he recognized fully the resistance of the air, and pushed on the inquiry in the direction indicated by Tartaglia. It was not, however, wtcm. till Newton s time that a substantial basis was laid down for a true theory of gunnery. The grand discovery of the law of gravitation revealed the hitherto nnguessed secret of the projectile s fall to earth. The great improvements in mathematical methods of analysis invented by him rendered possible solutions of previously impracticable problems ; while the splendour of his achievements in natural science stimulated philosophers of all countries. Towards the end of the 17th century he investigated the trnj jctory of a pro jectile on the supposition that the resistance of the air varied as the first power of the velocity. Bernoulli in 1718 gave a solution of the problem, on the supposition that the resistance varied as any given power of the velocity. This solution was, however, left in such a complicated state that no practical use can be made of it. No further tobins. progress was made till Benjamin Robins in 1742 published his New Principles of Gunnery, in which he furnishes a notable example of the manner in which theory should be wedded to practice, and hypothesis to experiment. Had Robins been in the possession of accurate instruments he would probably have arrived at results of considerable correctness. He invented the ballistic pendulum, and was the first to ascertain experimentally with any degree of correctness the velocities of projectiles on leaving a gun. A &quot; triangle &quot; or gyn supported a pendulum of iron having a massive wooden bob ; to the bob was fixed a steel ribbon which passed through a steel clamp set to the desired pressure. A bullet fired into the wooden bob caused the pendulum to swing ; the length of the arc described was recorded by the steel ribbon ; the weight of the bullet and the conditions of oscillation of the pendulum being known, the velocity of the bullet could be calculated from the length of the arc. The weight of Robins s first pendulum was 56 ft&amp;gt;, and it was therefore only suited for small arms. It could measure the velocity at only one point each round, and therefore, to ascertain the velocity lost by a ball in passing through the air, it was necessary to fire a series of rounds at one distance, and afterwards a similar series of rounds at another distance, Velocities of 1700 feet per second were measured, and the loss of velocity due to the resistance of the air, up to a distance of 250 feet from the muz/la, was approximately ascertained. Robins discovered that the resistance of the air was greatly increased as soon as the ball travelled faster than sound, and attributed it to the creation of a vacuum behind the shot, into which the air could not rush with speed greater than that of sound. Count Rumford in 1751 made use of the recoil to measure the velocities of bullets, on the principle that the momentum of the bullet forward was equal to the momentum of the gun backward. To carry this out, the gun was suspended as a pendulum, and the length of the arc it described on firing measured. By firing a bullet from a gun thus suspended into the ballistic pendulum, two independent records were obtained, and it would have been easy to calculate the loss of velocity, from the muzzle to any range at which the pendulum could be hit, by the combination. The roughness of the methods unfortunately did not permit completely satisfactory results. Dr Hutton next took up the inquiry, and increased the weight of the pendulum and the bullets. No very great advance, however, seems to have been made till 1840, when experiments on the resist ance of the air to the motion of spherical shot were carried on at &quot;Metz by the French Government. MM. Piobert, Didion Morin, and Didion were the chief experimenters. They raised the weight of the receiving pendulum to nearly 6 tons, and fired into it 50-pound balls at a range of 330 feet. The information now obtained spread over a much wider field than that traversed by Robins. It was even found possible to construct the trajectories of projectiles with some approach to truth, and empirical formulae were laid down by whic i ranges and times of flight could be approxi mately calculated. It was not, however, till the introduc tion of electricity as a means of determining the velocities of projectiles that accurate knowledge of the resistance of the air was obtained. In 1840 Professor Wheatstono invented an instrument for this purpose, called the electro magnetic chronoscope. He has had many successors, whose productions exhibit a great amount of ingenuity ; those Electri from which the most valuable results have been obtained, y elocit and which are in use at the present moment, are the Bash- &quot; forth chronograph, the Noble chronoscope, the Le Boulenge chronograph, and the Watkin chronograph. The general principle on which these four instruments are designed is that a projectile after leaving the gun shall 