CHARGE

, in Electricity, in a strict sense, imports the accumulation of the electric matter on one surface of an electric, as the Leyden phial, a pane of glass, &c, whilst an equal quantity passes off from the opposite surface. Or, more generally, electrics are said to be charged, when the equilibrium of the electric matter on the opposite surface is destroyed, by communicating one kind of electricity to one side, and the contrary kind to the opposite side: nor can the equilibrium be restored till a communication be made by means of conducting substances between the two opposite surfaces: and when this is done, the electric is said to be discharged. The charge properly refers to one side, in contradistinction from the other; since the whole quantity in the electric is the same before and after the operation of charging; and the operation cannot succeed, unless what is gained on one side is lost by the other, by means of conductors applied to it, and communicating either with the earth, or with a sufficient number of non-electrics. To facilitate the communication of electricity to an electric plate &c, the opposite surfaces are coated with some conducting substance, usually with tin-foil, within some distance of the edge; in consequence of which the electricity communicated to one part of the coating, is readily diffused through all parts of the surface of the electric in contact with it; and a discharge is easily made by forming a communication with any conductor from one coating to the other. If the opposite coatings approach too near each other, the electric matter forces a passage from one surface to the other before the charge is complete. And some kinds of glass have the property of conducting the electricity over the surface, so that they are altogether unsit for the operation of charging and discharging. If indeed the charge be too high, and the glass plate or phial too thin, the attraction between the two opposite electricities forces a passage through the glass, making a spontaneous discharge, and the glass becomes unfit for farther use. See Conductors, Electrics, Leyden Phial, &c.

, in Gunnery, the load of a piece of ordnance, or the quantity of powder and ball, or shot, with which it is prepared for execution.

The charge of powder, for proving guns, is equal to the weight of the ball; but forservice, the charge is 1/2 or 1/3 the weight of the ball, or still less; and indeed in most cases of service, the quantity of powder used is too great for the intended execution. In the British navy, the allowance for 32 pounders is but 7/16 of the weight of the ball. But it is probable that, if the powder in all ship guns was reduced to 1/3 the weight of the ball, or even less, it would be a considerable advantage, not only by saving ammunition, but by keeping the guns cooler and quieter, and at the same time more effectually injuring the vessels of the enemy. With the present allowance of powder, the guns are heated, and their tackle and furniture strained, and all this only to render the ball less efficacious: for a ball which can but just pass through a piece of timber, and in the passage loses almost all its motion, is found to rend and fracture it much more, than when it passes through with a much greater velocity. See Robins's Tracts, vol. 1. pa. 290, 291.

Again, the same author observes, that the charge is not to be determined by the greatest velocity that may be produced; but that it should be such a quantity of powder as will produce the least velocity necessary for the purpose in view; and if the windage be moderate, no field-piece should ever be loaded with more than 1/6, or at the utmost 1/5 of the weight of its ball in powder; nor should the charge of any battering piece exceed 1/3 of the weight of its bullet. Ib. pa. 266.

Different charges of powder, with the same weight of ball, produce different velocities in the ball, which are in the subduplicate ratio of the weights of powder; and when the weight of powder is the same, and the ball varied, the velocity produced is in the reciprocal subduplicate ratio of the weight of the ball: which is agreeable both to theory and practice. See my paper on Gunpowder in the Philos. Trans. 1778, pa. 50; and my Tracts, vol. 1. pa. 266.

But this is on a supposition that the gun is of an indefinite length; whereas, on account of the limited length of guns, there is some variation from this law in practice, as well as in theory; in consequence of which it appears that the velocity of the ball increases with the charge only to a certain point, which is peculiar to each gun, where the velocity is the greatest; and that by farther increasing the charge, the velocity gradually diminishes, till the bore is quite full of powder. By an easy sluxionary process it appears that, calling the length of the bore of the gun b, the length of the charge producing the greatest velocity, ought to be b/2.718281828, or about 3/8 of the length of the bore; where 2.718281828 is the number whose hyp. log. is 1. But, for several reasons, in practice the length of the charge producing the greatest velocity, falls short of that above mentioned, and the more so as the gun is longer. From many experments I have found the length of the chgre producing the greatest velocity, in guns of various lengths of bore, from 15 to 40 calibres, as follows.

CHARLES's WAIN, a name by which some of the astronomical writers, in our own language, have called Ursa Major, or the great bear; though some writers say the lesser bear. Indeed both of the two bears have been called waggons or wains, and by the Latins, who have followed the Arabians, two biers, Feretrum majus & minus.