The number of these grooves differ according to the size of the barrel, and fancy of the workman; and their depth and width are not regulated by any invariable rule. The method of loading them is as follows: when the proper quantity of powder (one drachm avoirdupois) is put down at the muzzle, and a piece of calico or linen is gently rammed down 'over it as a wad, a circular piece of strong calico is greased on one side, and laid on the mouth of the piece, with the greased side downwards; and a bullet of the same size as the bore of the piece before the grooves were cut, being placed upon it is then forced gently down the barrel with it; by which means, the calico incloses the lower half of the bullet; and, by its interposition between the bullet and the grooves, prevents the lead from being cut by them, and, by means of the grease slides down, without its being necessary to use any violent efforts, which would destroy the circular shape of the bullet. In order to understand the cause of the superiority of a rifle-barrel gun over one with a smooth barrel, it will be necessary to refer to Mr. Robins's discovery of the cause of the irregularities which occur in the flight of projectiles from smooth barrels, which we shall give in his own words "Tracts on Gunnery." p. 196, &c. "Almost every projectile, besides the forces we have hitherto considered, namely, its gravitation, and that resistance of the air which directly opposes its motion, is affected by a third force, which acts obliquely to its motion, and in a variable direction; and which, consequently, deflects the projectile from its regular track, and from the verticle plane in which it began to move; impelling it sometimes to one side, and sometimes to the other, occasioning thereby very great inequalities in the repeated ranges of the same piece, though each time loaded and pointed in the same manner; and this force, operating thus irregularly, I conceive to be the principal source of all that uncertainty and confusion in the art of gunnery which has hitherto been usually ascribed to the difference of powder. The reality of this force, and the cause which produces it, will, I hope, appear from the following considerations: It will easily be granted, I suppose, that no bullet can be discharged from the pieces generally in use, without rubbing against their sides, and thereby acquiring a whirl. ling motion, as well as a progressive one; and as this whirl will, in one part of its revolution, conspire in some degree with the progressive motion, and in another part be equally opposed to it, the resisttance of the air on the fore-part of the bullet will be hereby affected, and will be increased in that part where the whirling motion conspires with the progressive, and diminished where it is opposed to it. And by this means the whole effort of the resistance, instead of being in a direction opposite to the direction of the body, will become oblique thereto, and will produce those effects already mentioned. If it were possible to predict the position of the axis, round which the bullet should whirl, and if that axis were unchangeable during the whole flight of the bullet, then the aberration of the bullet, by this oblique force, would be in a given direction, and the incurvation produced thereby would regularly extend the same way, from one end of its track to the other. For instance, if the axis of the whirl were perpendicular to the horizon, then the deflection would be to the right or left; if that axis were horizontal, and perpendicular to the direction of the bullet, then the deflection would be upwards or downwards. But as the first position of this axis is uncertain, and as it may perpetually shift in the course of the bullet's flight, the deviation of the bullet is not necessarily in one certain direction, nor tending to the same side in one part of its track that it does in another; but it more usually is continually changing the tendency of its deflection, as the axis round which it whirls must frequently shift its position to the progressive motion by many inevitable accidents." RIGGING of a ship, is all her cordage and ropes, belonging to her masts, yards, &c. A ship is said to be well rigged, when all her ropes are of a fit size and proportion and she is said to be over-rigged, when her ropes are too large, which is of great prejudice to her sailing, and is apt to make her heel. RIGHT, in geometry, signifies the same with straight; thus, a straight line is called a right one. RIGHT, in general signification, includes not only right, for which a writ of right lies, but also any claim or title, either by virtue of a condition, mortgage, or the like, for which no action is given by law, but only an entry. A writ of right is the most ancient remedy, in the law, for the recovery of lands, and is not barred till sixty years have elapsed since the claimant or his ancestor was disseised, or ousted of possession. RING, in astronomy and navigation, an RING instrument used for taking the sun's altitude, &c. It is usually of brass, about nine inches diameter, suspended by a little swivel, at the distance of 45° from the point of which is a perforation, which is the centre of a quadrant of 90°, divided in the inner concave surface. To use it, let it be held up by the swivel, and turned round to the sun, till its rays, falling through the hole, make a spot among the degrees, which marks the altitude required. This instrument is preferred before the astrolabe, because the divisions are See here larger than on that instrument. ASTROLABE. RING of Saturn, is a thin, broad, opaque, circular arch, encompassing the body of that planet, like the wooden horizon of an artifical globe, without touching it, and appearing double when seen through a good telescope. See SATURN. RINGS of colours, in optics, a phenomenon first observed in thin plates of various substances, by Boyle, and Hooke, but afterwards more fully explained by Sir Isaac Newton. Mr. Boyle having exhi bited a variety of colours in colourless liquors, by shaking them till they rose in bubbles, as well as in bubbles of soap and water, and also in turpentine, procured glass blown so thin as to exhibit similar colours; and he observes, that a feather of a proper shape and size, and also a distance black ribband, held at a proper between his eye and the sun, showed a variety of little rainbows, as he calls them, with very vivid colours. Dr. Hook, about nine years after the publication of Mr. Boyle's Treatise on Colours, exhibited the coloured bubbles of soap and water, and observed, that though at first it appeared white and clear, yet, as the film of water became thinner, there appeared upon it all the colours of the rainbow. He also described the beautiful colours that appear in thin plates of Muscovy glass; which appeared, through the microscope, to be ranged in rings surrounding the white specks or flaws in them, and with the same order of colours as those of the rainbow, and which were often repeated ten times. He likewise took two thin pieces of glass, ground plane and polished, and putting them one upon another, pressed them till there began to appear a red coloured spot in the middle; and pressing them closer, he observed several rings of colours encompassing the first place, till at last all the colours disappeared out of the middle of the circles, and the central spot appeared white. The first colour that appear ed was red, then yellow, then green, then blue, then purple; then again red, yellow, green, blue, and purple; and again in the same order; so that he sometimes counted nine or ten of these circles, the red immediately next to the purple; and the last colour that appeared before the white was blue; so that it began with red, and ended with purple. These rings, he says, would change their places, by changing the position of the eye, so that the glasses remaining the same, that part which was red, in one position of the eye, was blue in a second, green in the third &c. Sir Isaac Newton, having demonstrated that every different colour consists of rays which have a different and specific degree of refrangibility, and that natural bodies appear of this or that colour, according to their disposition to reflect this or that species of rays, pursued the hint suggested by the experiments of Dr. Hook, with regard to thin transparent substances. Upon compressing two prisms hard together, in order to make their sides touch one another, he observed, that in the place of contact they were perfectly transparent, which appeared like a dark spot, and when it was looked through, it seemed like a hole in that air, which was formed into a thin plate, by being impressed between the glasses. When this plate of air, by turning the prisms about their common axis, became so little inclined to the incident rays, that some of them began to be transmitted, there arose in it many slender arcs of colours, which increased, as the motion of the prisms was continued, and bended more and more about the transparent spot, till they were completed into circles, or rings, surrounding it; and after. wards they became continually more and more contracted. He then took two object-glasses of a telescope, the one planoconvex, the other a little convex on both sides; he placed one of the faces of this upon the plane face of the former, and pressed the two glasses at first gently, and then, by degrees, more closely against one another. The effect of this gradual pressure was an appearance in the plate of air between the glasses of different coloured circles, which had the point of contact for the common centre, and which increased in number according to the greater degree of pressure, in such a manner, that the circle which appeared last always surrounded the point of contact, and on a still further pressure extended its circumference, while it con tracted itself breadthwise, to form a kind of ring round a new circle that arose near its middle. The pressure having been carried to a certain term, Newton stopped, and observed as follows. At the point of contact was a black spot that was encompassed by several series of colours. The order of the colours from the centre to the borders of the two glasses was this: in the first series, blue, white, yellow, and red; in the second, violet, blue, green, yellow, and red; in the third, purple, blue, green, yellow, and red; in the fourth, green and red; in the fifth, greenish blue, and red; in the sixth, greenish blue, and pale red; in the seventh, greenish blue, and reddish white. Beyond this number, the tints of which were regularly paler, the colour became white. Newton measured the diameters of the annular bands, formed of these different colours, by taking the points where they had most lustre; and he found that the squares of those diameters were to one another as the terms of the ascending progression, 1, 3, 5, 7, 9, 11, &c.; from which it results, that the intervals between the two glasses, relatively to the corresponding points, followed the same progression. From these proportions, it was merely necessary to ascertain the absolute length of a single diameter, to know the lengths of all the others, as well as the different thicknesses of the plates of air at the points where the dif ferent colours were seen. He drew up a table of these degrees of thickness, by which it appears, that the most intense blue, for example, that of the first series, is expressed by a thickness of 0.000024 of an inch, supposing the visual ray to be nearly perpendicular to the two glasses. Sir Isaac Newton having measured also the diameters of the rings, at the intermediate places where the colours were obscure, found that their squares were to one another as the even numbers 2, 4, 6, 8, 10, 12, &c.; and hence the intervals between the glasses, at the corresponding points, observed a similar progression. The diameters of the rings increased or diminished, as the visual ray was more or less inclined to the surface of the two glasses, so that the greatest contraction took place when the eye was situated perpendicularly above the glasses. The diameters also retained the same proportions to one another. From other curious observations on these rings, made by different kinds of light thrown upon them, he inferred, that the thicknesses of the air between 8 5 3 2 3 9 the glasses, where the rings are succes sively made, by the limits of the seven colours, red, orange, yellow, green, blue, indigo, and violet, in order, are one to another as the cube roots of the squares of the eight lengths of a chord, which sound the notes in an octave, sol, la, fa, sol, la, mi, fa, sol; that is, as the cube roots of the squares of the numbers 1, 1 1 1 1 1. These rings appeared of that prismatic colour with which they were illuminated, and by projecting the prismatic colours immediately upon the glasses, he found that the light, which fell on the dark spaces between the coloured rings, was transmitted through the glasses without any change of colour. From this circumstance he thought that the origin of these rings is manifest; because the air between the glasses is dis posed according to its various thickness, in some places to reflect, and in others to transmit, the light of any particular colour, and in the same place to reflect that of one colour, where it transmits that of another. In examining the phenomena of colours made by a denser medium surrounded by a rarer, such as those which appear in plates of Muscovy glass, bubbles of soap and water, &c. the colours were found to be much more vivid than the others, which were made with a rarer medium surrounded by a denser. From the preceding phenomena, it is an obvious deduction, that the transparent parts of bodies, according to their several series, reflect rays of one colour, and transmit those of another; on the same account that thin plates, or bubbles, reflect or transmit those rays; and this Sir Isaac Newton supposed to be the reason of all their colours. Another inference is, that the particles, even of those bodies which we call opaque, are in reality transparent, which persons who are in the habit of using the microscope must conSee NEWTON'S OPtinually perceive. TICS see also COLOUR, &c. RIOT, rout, and unlawful assembly. When three persons, or more, assemble themselves together, with an intent mutually to assist one another, against any who shall oppose them in the execution of some enterprise of a private nature, with force or violence, against the peace, or to the manifest terror of the people, whether the act intended were of itself lawful or unlawful, if they only meet for such a purpose or intent, though they shall after depart of their own accord without doing any thing, this is an unlawful assembly. By 34 Edward III c 1. it is enacted, that if a justice find persons riotously assembled, he alone has not only power to arrest the offenders, and bind them to their good behaviour, or imprison them, if they do not offer good bail; but he may also authorize others to arrest them, by a bare verbal command, without other warrant; and by force thereof, the persons so commanded may pursue and arrest the offenders in his absence, as well as presence. It is also said that, after any riot is over, any one justice may send his warrant to arrest any person who was concerned in it, and that he may send him to gaol till he shall find sureties for his good behaviour. The punishment of unlawful assemblies, if to the number of twelve, may be capital, according to the circumstances which attend them; but from the number of three to eleven, it is by fine and imprisonment only. The same is the case in riots and routs by the common law, to which the pillory, in very enormous cases, has been sometimes superadded. By the act 1 George II. st. 2. c. 5. every justice, mayor, sheriff, &c. shall, upon notice of a riot, or unlawful, tumultuous assembly of twelve persons, proceed to the place, and make proclamation for them to depart, upon the pains of that act commonly called the riot-act. If any person shall wilfully oppose or hurt any person going to make proclamation, and prevent the same, he shall be guilty of felony, without benefit of clergy. If twelve continue together, after proclamation, for one hour, it is felony, in like manner. And every justice, &c. shall apprehend persons, and if the rioters are killed, the justice, &c. shall not answer for it. A riot, though of fewer persons than twelve, to destroy any church, chapel, meeting, or dwellinghouse, out-house, &c. is a capital felony and the hundred shall answer the damages, as in case of robbery. If two justices go out to quell a riot, they may assemble the posse comitatus, and every person capable of travelling is, upon being warned, to join them, on pain of imprisonment. 13 Henry IV. c. 7. s. 1, 2, 11, 5. c. 8. s. 2. RISBAN, in fortification, a flat piece of ground upon which a fort is constructed for the defence and security of a port or harbour. It likewise means the fort itself. The famous Risban of Dunkirk, was built entirely of brick and stone; having within its walls excellent barracks, a large cistern well supplied with water, maga zines for stores, provisions, and ammunition. A ready communication was kept up with the town by means of the jettée, which corresponded with the wooden bridge that joined the entrance into the fort. The rampart was capable of receiving forty-six pieces of ordnance, which were disposed in three different alignements or tiers, owing to the triangular figure of the fort; so that a fire could be kept up on all sides. RITTERA, in botany, a genus of the Polyandria Monogynia class and order. Natural order of Leguminose. Essential character: calyx four-leaved; petals one, lateral; legume one-celled, two-valved. There are five species. RIVER, a current, or stream of fresh water, flowing in a bed or channel, from its source, into the sea. When a stream is not large enough to bear boats, or small vessels laden, it is called a rivulet or brook. The great, as well as the middle-sized rivers proceed either from a confluence of brooks and rivulets, or from lakes; but no river of considerable magnitude Aows from one spring, or one lake, but is augmented by the accession of others. Thus the Wolga receives above two hundred rivers and brooks, before it discharges itself into the Caspian Sea; and the Danube receives no less, before it enters the Euxine Sea. Some rivers are much augmented by frequent rains, or melted snow. In the country of Peru and Chili, there are small rivers that only flow in the day; because they are only fed by the snow upon the mountains of the Andes, which is then melted by the heat of the sun. There are also several rivers upon both sides the extreme parts of Africa, and in India, which, for the same reason, are greater by day than by night. The rivers also in these places are almost dried up in summer, but swell and overflow their banks in winter, or in the wet season. Thus the Wolga in May and June is filled with water, and overflows its shelves and islands, though at other times of the year it is so shallow as scarcely to af ford a passage for loaded ships. The Nile, the Ganges, the Indus, &c. are so much swelled with rain or melted snow, that they overflow their banks, and these deluges happen at different times of the year because they proceed from various causes. Those that are swelled with rain are generally highest in winter, because it is usually then more frequent than at other times of the year; but if the pre ceed from snow, which, in some places, is melted in the spring, in others, in summer, or, between both, the deluges of the rivers happen accordingly. Again, some rivers hide themselves under ground, and rise up in other places, as if they were new rivers. Thus the Tigris, meeting with mount Taurus, runs under it, and flows out at the other side of the mountain: also, after it has run through the lake Tospia, it again immerges, and being carried about eighteen miles under ground, breaks out again, &c. The channels of rivers, except such as were formed at the creation, Varenius thinks, are artificial. His reasons are, that, when a new spring breaks out, the water does not make itself a channel, but spreads over the adjacent land; so that men were necessitated to cut a channel for it, to secure their grounds. He adds, that a great number of channels of rivers are certainly known from history to have been dug by men. The water of most rivers flow impregnated with particles of metals, minerals, &c. Thus some rivers bring sands intermixed with grains of gold: as in Japan, Peru, and Mexico, Africa, Cuba, &c. particularly in Guinea is a river, where the negroes separate the gold-dust from the sand, and sell it to the Europeans, who traffic thither for that very purpose. The Rhine in many places is said to bring a gold mud. As to rivers that bring grains of silver, iron, copper, lead, &c. we find no mention of them in authors, though, doubtless, there are many, and it may be to them that mineral waters owe many of their medicinal virtues. Modern philosophers endeavour to reduce the motion and flux of rivers to precise laws; and with this view they have applied geometry and mechanics to the subject; so that the doctrine of rivers is become a part of the new philosophy. The authors, who have most distinguished themselves in this branch, are the Italians, and among them more especially Gulielmini and Ximenes. Rivers, says Gulielmini, usually have their sources in mountains or elevated grounds; in the descent from which it is mostly that they acquire the velocity, or acceleration, which maintains their future current. In proportion as they advance further, this velocity diminishes, on account of the continual friction of the water against the bottom and sides of the channel, as well as from the various obstacles they meet with in their progress, and from their arriving at length in plains, where the descent is less, and conseVOL. X. quently their inclination to the horizon greater. When the acquired velocity is quite spent through the many obstacles, so that the current becomes horizontal,there will then nothing remain to propagate the motion, and continue the stream, but the depth or the perpendicular pressure of the water, which is always proportional to the depth. And this resource increases, as the occasion for it increases; for in proportion as the water loses of the velocity acquired by the descent, it rises and increases in its depth. It appears from the laws of motion, pertaining to bodies moved on inclined planes, that when water flows freely upon an inclined bed, it acquires a velocity, which is always as the square root of the quantity of descent of the bed. But in an horizontal bed, opened by sluices or otherwise, at one or both ends, the water flows out by its gravity alone. The greatest velocity of a river is about the middle of its depth and breadth, or that point which is the furthest possible from the surface of the water, and from the bottom and sides of the bed or channel. Whereas, on the contrary, the least velocity of the water is at the bottom and sides of the bed, because there the resistance arising from friction is the greatest, which is communicated to the other parts of the section of the river inversely as the distances from the bottom and sides. To find whether the water of a river almost horizontal flows by means of the velocity acquired in its descent, or by the pressure of its depth, set up an obstacle perpendicular to it; then if the water rise and swell immediately against the obstacle, it runs by virtue of its fall; but if it first stop a little while, in virtue of its pressure. Rivers, according to this author, almost always make their own beds. If the bottom have originally been a large declivity, the water, hence falling with a great force, will have swept away the most elevated parts of the soil, and carrying them lower down, will gradually render the bottom more nearly horizontal. The water, having made its bed hori zontal, becomes so itself, and consequently rakes with the less force against the bottom, till at length that force becomes only equal to the resistance of the bottom, which is now arrived at a state of permanency, at least for a considerable time; and the longer, according to the quality of the soil, clay and chalk resist ing longer than sand or mud. Nn |