At

On the other hand the water is continually wearing away the brims of its channel, and this with the more force, as by the direction of its stream it impinges more directly against them. By this means it has a continual tendency to render them parallel to its own course. the same time that it has thus rectified its edges, it has widened its own bed, and thence becoming less deep, it loses part of its force and pressure: this it continues to do till there is an equilibrium between the force of the water and the resistance of its banks, and then they will remain without further change. And it appears, by experience, that these equilibriums are all real, as we find that rivers only deepen and widen to a certain pitch.

The union of two rivers into one makes the whole flow the swifter, because, in stead of the friction of four shores, they have only two to overcome, and one bot tom instead of two; also the stream being further distant from the banks, goes on with the less interruption; besides, that a greater quantity of water, moving with a greater velocity, digs deeper in the bed, and of course retrenches of its former width. Hence also it is, that rivers by being united, take up less space on the surface of the earth, and are more advantageous to low grounds, which dran their superfluous moisture into them, and have also less occasion for dykes to prevent their overflowing.

A very good and simple method of measuring the velocity of the current of a river, or canal, is the following.

Take

a cylindrical piece of dry light wood, and of a length something less than the depth of the water in the river; about one end of it l there be suspended as many small weights as may keep the cylinder in a vertical or upright position, with its head just above water. To the centre of this end fix a small straight rod, precisely in the direction of the cylinder's axis; to the end that, when the instrument is suspended in the water the deviations of the rod from a perpendicularity to the surface of it may indicate which end of the cylinder goes foremost, by which may be discovered the different velocities of the water at different depths; for when the rod inclines forward, according to the direction of the current, it is a proof that the surface of the water has the greatest velocity: but when it reclines backward, it shows that the swiftest current is at the bottom; and when it remains perpendicular, it is a sign that the

velocities at the top and bottom are equal. This instrument, being placed in the cur rent of a river or canal, receives all the percussions of the water throughout the whole depth, and will have an equal velocity with that of the whole current from the surface to the bottom at the place where it is put in, and by that means may be found, both with exactness and ease, the mean velocity of that part of the river for any determinate distance and time. But to obtain the mean velocity of the whole section of the river, the instrument must be put successively both in the middle and towards the sides, because the velocities at those places are often very different from each other. Having by this means found the several velocities, from the spaces run over in certain times, the arithmetical mean proportional of all these trials, which is found by dividing the common sum of them all by the number of the trials, will be the mean velocity of the river or canal. And if this medium velocity be multiplied by the area of the transverse section of the waters at any place, the product will be the quantity running through that place in a second of time.

If it be required to find the velocity of the current only at the surface, or at the middle, or at the bottom, a sphere of wood loaded, or a common bottle corked with a little water in it, of such a weight as will remain suspended in equilibrium with the water at the surface or depth which we want to measure, will be better for the purpose than the cylinder, because it is only affected by the water of that sole part of the current where it remains suspended.

It follows from what has been said in the former part of this article, that the deeper the waters are in their bed in proportion to its breadth, the more their motion is accelerated; so that their velocity increases is the inverse ratio of the breadth of the bed, and also of the magnitude of the section; whence, in order to augment the velocity of water in a river or canal, without augmenting the declivity of the bed, we must increase the depth of the channel, and diminish its breadth. And these principles are agreeable to observation; as it is well known, that the velocity of flowing waters depends much more on the quantity and depth of the water, and on the compression of the upper parts on the lower, than on the declivity of the bed; and therefore the declivity of a river must be

made much greater in the beginning than toward the end of its course, where it should be almost insensible.

RIVINA, in botany, a genus of the Tetrandria Monogynia class and order. Natural order of Holoracex. Atriplices, Jussieu. Essential character: calyx fourleaved, permanent; berry containing one lens-shaped seed. There are four species. ROAD, an open way, or public passage, forming a communication between one place and another. The Romans took the most pains in forming roads, and the labour and expenses they were at in rendering them spacious, firm, straight, and smooth, is incredible. They usually strengthened the ground by ramming it, laying it with flints, pebbles, or sand, and sometimes with a lining of masonry, rubbish, bricks, &c. bound together with mortar. In some places in the Lionois, F. Menestrier observes that he has found huge clusters of flints cemented with lime, reaching ten or twelve feet deep, and making a mass as hard and compact as marble, and which, after resisting the injuries of time for 1600 years, is still scarce penetrable by all the force of hammers, mattocks, &c. and yet the flints it consists of are not bigger than eggs. The most noble of the Roman roads was the Via Appia, which was carried to such at vast length, that Procopius reckons it five days journey to the end of it, and Leipsius computes it at 350 miles it is 12 feet broad, and made of square free-stone, generally a foot and a half on each side; and though this has lasted for above 1800 years, yet in many places it is for several miles together as entire as when it was first made.

The ancient roads are distinguished into military roads, double roads, subterraneous roads, &c. The military roads were grand roads, formed by the Romans for marching their armies into the provinces of the empire; the principal of these Roman roads in England are, Watlingstreet, Ikenild-street, Foss-way, and Erminage-street.-Double roads, among the Romans, were roads for carriages with two pavements, the one for those going one way, and the other for those return ing the other: these were separated from each other by a causeway raised in the middle, paved with bricks, for the conveniency of foot passengers; with borders and mounting stones from space to space, and military columns to mark the distance. Subterraneous roads are those dug through a rock, and left vaulted; as that of Puzzoli near Naples,

which is nearly half a league long, and is 15 feet broad, and as many high.

ROAD, in navigation, is a place of anchorage at some distance from shore, where vessels usually moor, to wait for a wind or tide proper to carry them into harbour, or to set sail. When the bottom is firm, clear of rocks, and sheltered from the wind, it is called a good road; and when there is but little land on any side, it is termed an open road

The roads in his Majesty's dominions, are free to all merchant vessels belonging to his subjects and allies Captains and masters of ships, who are forced by storms, &c. to cut their cables, and leave their anchors in the roads, are obliged to fix marks, or buoys, on pain of forfeiting their anchors, &c. Masters of ships coming to moor in a road must anchor at such a distance, as that the cables, &c. do not mix, on pain of answering the damages; and when there are several vessels in the same road, the outermost to the sea-ward is obliged to keep a light in his lanthorn in the nighttime, to apprise vessels coming in from

sea.

cast

ROASTING, in metallurgy, the separation of volatile bodies from those which are more fixed, by the combined action of air and fire; and is generally the first process in the separation of metals from their ores it differs from sublimation only in this, that in this operation the volatile parts are dissipated, when resolved into vapours, whereas in that they are preserved.

ROBBERY, is a felonious taking away of another man's goods from his person, or presence, against his will, putting him in fear, on purpose to steal the same. The value is immaterial.

If a man force another to part with his property, for the sake of preserving his character from the imputation of having been guilty of an unnatural crime, it will amount to a robbery, even though the party was under no apprehension of personal danger. If any thing is snatched suddenly from the head, hand, or person, of any one, without any struggle on the part of the owner, or without any evidence of force or violence being exerted by the thief, it does not amount to robbery. But if any thing be broken or torn in consequence of the sudden seizure, it would be evidence of such force as would constitute a robbery; as where a part of a lady's hair was torn away by snatching a diamond pin from her head, and an ear was torn by pulling off an ear-ring; each

of these cases was determined to be orbbery.

By 7 George II. c. 21. if any person shall, with any offensive weapon, assault, or by menaces, or in any forcible or violent manner, demand any money or goods, with a felonious intent to rob another, he shall be guilty of felony, and be transported for seven years.

If any person, being out of prison, shall commit any robbery, and afterwards discover two or more persons who shall commit any robbery, so as two or more be convicted, he shall have the King's pardon for all robberies he shall have committed before such discovery.

High-way robbery differs from robbery only in this, that there is a reward of 401. for the apprehending of the offender, and the horse which the robber rides is forfeited.

ROBERGIA, in botany, so named in honour of Laurentius Roberg, a genus of the Decandria Pentagynia class and order. Natural order of Terebintaceæ, Jussieu. Essential character: calyx fiveparted: petals five; drupe with a oneseeded nut, and a two-valved shell. There is but one species, viz. R. frutescens, a native of the woods of Guiana.

ROBINIA, in botany, a genus of the Diadelphia Decandria class and order. Natural order of Papilionacea, or Leguminosa. Essential character: calyx fourcleft; legume gibbous, elongated. There are seventeen species.

ROBINS, (BENJAMIN,) in biography, an English mathematician and philosopher, of great genius and eminence, was born at Bath, in Somersetshire, 1707. His parents were of low condition, and quakers; and consequently, neither able from their circumstances, nor willing from their religious profession, to have him much instructed in that kind of learning which they are taught to despise as human. Nevertheless he made an early and surprising progress in various branches of science and literature, particularly in the mathematics; and his friends being desirous that he might continue his pursuits, and that his merit might not be buried in obscurity, wished that he could be properly recoinmended to teach that science in London. Accordingly, a specimen of his abilities, in this way, was sent up thither, and shown to Dr. Pemberton, the author of the "View of Sir Isaac Newton's Philosophy;" who thence conceiving a good opinion of the writer, for a further trial of his skill, sent him some problems, which Robins re

solved very much to his satisfaction. He then came to London, where he confirmed the opinion which had been preconceived of his abilities and knowledge.

But though Robins was possessed of much more skill than is usually required in a common teacher; yet, being very young, it was thought proper that he should employ some time in perusing the best writers upon the sublimer parts of the mathematics, before he should undertake publicly the instruction of others. In this interval, besides improving himself in the modern languages, he had opportunities in reading, in particular, the works of Archimedes, Apollonius, Fermat, Huygens, De Witt, Slusius, Gregory, Barrow, Newton, Taylor and Cotes. These authors he readily understood, without any assistance, of which he gave frequent proofs to his friends: one was, a demonstration of the last proposition of "Newton's Treatise on Quadratures," which was thought not undeserving a place in the Philos. Trans. for 1727.

Not long after, an opportunity offered him of exhibiting to the public a specimen also of his knowledge in natural philosophy. The Royal Academy of Sciences at Paris had proposed among their prize questions in 1724 and 1726, to demonstrate the laws of motion in bodies impinging on one another. John Bernoulli here consented to be a candidate; and as his dissertation lost the reward, he appealed to the learned world by printing it in 1727. In this piece he endeavoured to establish Leibnitz's opinion of the force of bodies in motion, from the effects of their striking against springy materials: as Poleni had before attempted to evince the same thing, from experiments of bodies falling on soft and yielding substances. But as the insufficiency of Poleni's arguments had been demonstrated in the Phi

los. Trans. for 1722; so Robins published in the "Present State of the Republic of Letters," for May, 1728, a confutation of Bernoulli's performance, which was allowed to be unanswerable.

Robins now began to take scholars. About this time he quitted the dress and profession of a quaker; and, probably, without reflecting very much upon the subject of religion, he soon shook off the prejudices of his early habits. But though he professed to teach the mathematics only, he would frequently assist particular friends in other matters; for he was a man of universal knowledge; and the confinement of this way of life not

suiting his disposition, which was active, he gradually declined it, and went into other courses that required more exercise. Hence he tried many laborious experiments in gunnery; believing that the resistance of the air had a much greater effect on swift projectiles than was generally supposed. And hence he was led to consider those mechanic arts that depend upon mathematical principles, in which he might employ his invention; as the constructing of mills, the building of bridges, draining of fens, rendering of rivers navigable, and making of harbours. Among other arts of this kind, fortification very much engaged his attention; in which he met with opportunities of perfecting himself, by a view of the principal strong places of Flanders, in some journies he made abroad with persons of distinction.

On his return home from one of these excursions he found the learned here amused with Dr. Berkeley's treatise, printed in 1734, entitled "The Analyst," in which an examination was made into the grounds of the Doctrine of Fluxions, and occasion thence taken to explode that method. Robins was, therefore, advised to clear up this affair, by giving a full and distinct account of Newton's doctrines, in such a manner as to obviate all the objections, without naming them, which had been advanced by Berkeley, and accordingly he published, in 1735, a Discourse concerning the nature and certainty of Sir Isaac Newton's Method of Fluxions, and of Prime and Ultimate Ratios. This is a very clear, neat, and elegant performance; nevertheless some persons, even among those who had written against the Analyst,taking exception at Robins's manner of defending Newton's doctrine, he afterwards wrote two or three additional discourses.

In 1738, he defended Newton against an objection contained in a note at the end of a Latin piece, called "Matho, sive Cosmotheoria puerilis," written by Baxter, author of the "Inquiry into the Nature of the Human Soul:" and the year after he printed Remarks on Euler's Treatise of Motion, on Smith's System of Optics, and on Jurin's Discourse of Distinct and Indistinct Vision, annexed to Dr. Smith's work.

In the mean time Robins's performances were not confined to mathematical subjects; for, in 1739, there came out three pamphlets upon political affairs, which did him great honour. The first was entitled "Observations on the pre

sent Convention with Spain:" the second, "A Narrative of what passed in the Common-Hall of the Citizens of London, assembled for the Election of a Lord Mayor;" the third, " An Address to the Elec. tors and other Free Subjects of Great Britain, occasioned by the late Succession; in which is contained a particular account of all our negociations with Spain, and their treatment of us for above ten years past." These were all published without our author's name; and the first and last were so universally esteemed, that they were generally reputed to have been the production of the great man himself, who was at the head of the opposition to Sir Robert Walpole. They prov ed of such consequence to Mr. Robins, as to occasion his being employed in a very honourable post; for the patriots at length gained ground against Sir Robert, and a Committee of the House of Commons being appointed to examine into his past conduct, Robins was chosen their Secretary. But after the Committee had presented two reports of their proceedings, a sudden stop was put to their further progress, by a compromise between the contending parties.

In 1742, being again at leisure, he published a small treatise, entitled "New Principles of Gunnery;" containing the result of many experiments he had made, by which are discovered the force of gunpowder, and the difference in the resisting power of the air to swift and slow motions. To this treatise was prefixed a full and learned account of the progress which modern fortification had made from its first rise; as also of the invention of gunpowder, and of what had already been performed in the theory of gunnery. It seems that the occasion of this publication was the disappointment of a situation at the Royal Military Academy at Woolwich. On the new modelling and establishing of that Academy, in 1741, our author and the late Mr. Muller were competitors for the place of Professor of Fortification and Gunnery. Mr. Muller held then some post in the Tower of London, under the Board of Ordnance, so that, notwithstanding the great knowledge and abilities of our author, the interest which Mr. Muller had with the Board of Ordnance carried the election in his favour. Upon this disappointment Mr. Robins, indignant at the affront, determined to show them, and the world, by his military publications, what sort of a man he was that they had rejected.

Upon a discourse containing certain ex

periments being published in the Philos. Trans. with a view to invalidate some of Robins's opinions, be thought proper,in an account he gave of his book in the same Transactions, to take notice of those experiments and in consequence of this, several dissertations of his, on the resistance of the air were read, and the experiments exhibited before the Royal Society in 1746 and 1747; for which he was presented with the annual gold medal by that society.

In 1748, came out "Anson's Voyage round the World;" which, though it bears Walter's name, in the title page, was, in reality, written by Robins. Of this voyage the public had for some time been in expectation of seeing an account, composed under that commander's own inpection for which purpose the Rev. Richard Walter was employed, as having been Chaplain on board the Centurion the greatest part of the expedition. Walter had accordingly almost finished his task, having brought it down to his own departure from Macao for England, when he proposed to print his work by subscription. It was thought proper, however, that an able judge should first review and correct it, and Robins was appointed; when, upon examination, it was resolved that the whole should be written entirely by Robins, and that what Walter had done, being mostly taken, verbatim, from the journals, should serve as materials only. Hence it was that the whole of the introduction, and many dissertations in the body of the work, were composed by Robins, without receiving the least hint from Walter's manuscripts, and what he had transcribed from it regarded chiefly the wind and weather, the currents, courses, bearings, distances, offings, soundings, moorings, the qualities of the ground they anchored on, and such particulars as usually fill up a seaman's account. No production of this kind ever met with a more favourable reception, four large impressions having been sold off within a year: it was also translated into most of the European languages; and it still supports its reputation, having been repeatedly reprinted in various sizes. The fifth edition, at London, in 1749, was revised and corrected by Robins himself; and the ninth edition was printed there

in 1761.

Thus becoming famous for his elegant talents in writing, he was requested to compose an apology for the unfortunate affair at Preston-Pans in Scotland. This was added as a preface to the report of the

proceedings and opinions of the board of general officers, on their examination into the conduct of Lieutenant General Sir John Cope, &c. printed at London in 1749; and this preface was esteemed a master-piece of its kind.

Robins had afterwards, by the favour of Lord Anson, opportunities of making further experiments in gunnery; which have been published since his death, in the edition of his works by his friend, Dr. Wilson. He also not a little contributed to the improvements made in the Royal Observatory at Greenwich, by procuring for it, through the interest of the same noble person, a second mural quadrant, and other instruments; by which it became perhaps the completest observatory of any in the world.

His reputation being now arrived at its full height, he was offered the choice of two very considerable employments. The first was, to go to Paris as one of the commissaries for adjusting the limits in Acadia; the other to be engineer general to the East India Company, whose forts being in a most ruinous condition, wanted an able person to put them into a proper state of defence. He accepted the latter, as it was suitable to his genius, and as the Company's terms were both advantage. ous and honourable.

He designed, if he had remained in England, to have written a second part of the voyage round the world, as ap pears by a letter from Lord Anson, to him, dated Bath, October 22, 1749, as follows.