Cohesion culty we can overcome; and having got within one fphere of repulfion, we fancy that we are now impeded by the folid matter itfelf. But the very fame is the opinion of the generality of mankind with refpect to the firft obftruction. Why, therefore, may not the next be only another fphere of repulfion, which may only require a greater force than we can apply to overcome it, without difordering the arrangement of the conftituent particles; but which may be overcome by a body moving with the amazing velocity of light.

"This fcheme of the immateriality of matter, as it may be called, or rather the mutual penetration of matIO ter, firft occurred to Mr Michell on reading Baxter on MrBaxter's the immateriality of the Soul. He found that this auopinion. thor's idea of matter was, that it confifted as it were of bricks cemented together with immaterial mortar. These bricks, if he would be confiftent with his own reafoning, were again compofed of lefs bricks, cemented likewife by an immaterial mortar; and fo on ad infinitum. This putting Mr Michell upon the confideration of the feveral appearances of nature, he began to perceive that the bricks were fo covered with this immaterial mortar, that if they had any existence at all, it could not poffibly be perceived; every effect being produced, in nine inftances of ten certainly, and probably in the tenth alfo, by this immaterial, fpiritual, and penetrable mortar. Inftead therefore of placing the world upon the giant, the giant upon the tortoife, and the tortoife upon he could not tell what, he placed the world at once upon itself."

II Cohesion

Other philofophers have fuppofed the powers both fuppofed of gravitation and cohefion to be material; and to be owing to only different actions of the etherial fluid, or elemenelementary tary fire. In fupport of this it hath been urged, that fire. before we have recourse to a spiritual and immaterial power as the cause of any natural phenomenon, we ought to be well affured that there is no material fubftance with which we are acquainted, that is capable of producing fuch effects. In the prefent cafe, we are fo far from having fuch affurance, that the contrary is manifeft to our fenfes. One inftance of this is in the experiment with the Magdeburg hemifpheres, as they are called. Thefe are two hollow hemifpheres of brafs, exactly fitted to one another, fo as to form one globe when joined together, without admitting any air at the joining. In this fate, if the air within them is exhaufted by means of a pump, they will cohere with such force, if they are five or fix inches diameter, as to require a weight of fome hundreds of pounds to feparate them. The preflure of the atmofphere, we fee, is in this cafe capable of producing a very strong cohesion; and if there is in nature any fluid more penetrating, as well as more powerful in its effects, than the air we breathe, it is poffible that what is called the attraction of cohefion may fome how or other be an effect of the action of that fluid. Such a fluid as this is the element of fire. Its activity is fuch as to penetrate all bodies whatever; and in the ftate in which it is commonly called fire, it acts according to the quantity of folid matter contained in the body. In this ftate, it is capable of diffolving the ftrongest cohesions obferved in nature: but whatever is capable of diffolving any.cohefion, muft neceflarily be endued with greater power than that by which the

The

Cohoba. tion.

cohefion is caufed. Fire, therefore, being able to Cohefion, diffolve cohefions, muft alfo be capable of caufing them, provided its power is exerted for that purpose. Nor will it feem at all ftrange that this fluid fhould act in two fuch oppofite ways, when we confider the different appearances which it affumes. Thefe are three, viz. fire or heat, in which it confumes, deftroys, and diffolves: light, in which it seems deprived of all deftructive or diffolvent power, and to be the moft mild, quiet, and placid being in nature. third ftate of this element is, when it becomes what is called the electric fluid; and then it attracts, repels, and moves bodies, in a vast variety of ways, without either burning or rendering them vifible by its light. In this ftate it is not lefs powerful than in either of the other two; for a violent fhock of electricity will difplace and tear in pieces the molt heavy and folid bodies. The feeming capricious nature of this fluid, however, probably renders it lefs fufpectedas the cause of cohesion, than it otherwife would be, were the attractions regular and permanent, which we obferve it to occafion. But here we must observe, that the fluid has an existence in all bodies before the experiments are tried which make its effects visible to us, and was acting in them according to its fettled. and established laws. While acting in this manner it was perfectly invifible; and all we can do is, to produce fome little infringement of thefe regular laws according to which it commonly acts. In fome cafes, however, the electrical attractions produced by art are found to be pretty permanent and strong. Thus, Mr Symmer, in fome experiments with filk ftockings, found their attraction fo ftrong, that it required upwards of 15 pounds weight to feparate them from each other; and this attraction would continue for more than an hour. In plates of glass, too, be obferved a remarkable cohesion when electrified. the Philofophical Tranfactions for 1777, we find this hypothefis taken notice of, and in fome measure adopted, by Mr Henly. "Some gentlemen (fays he) have fuppofed that the electric matter is the cause of the cohefion of the particles of bodies. If the electric matter be, as I fufpect, a real elementary fire inherent in all bodies, that opinion may probably be well founded; and perhaps the foldering of metals, and the cementation of iron, by fire, may be confidered as trong proofs of the truth of their hypothefis."

In

On this laft hypothefis we must observe, that if the electric, or any other fluid, is fuppofed to be the cause of the attraction of cohefion univerfally, the particles of that fluid must be deftitute of all cohesion between themfelves; otherwife we fhould be at as great a lofs to account for the cohesion of thefe particles, as for that of terreftrial matter. Philofophers, indeed, do not fuppofe any cohefion between the particles of the electric fluid themselves; it is generally believed that the particles of this fluid are repulfive of one another, though attracted by all other matter. If this is a fact, we cannot fuppofe the electric fluid to be the caufe of cohefion. The probability or improbability of the hypothefis juft mentioned, muft greatly depend: on its being afcertained whether the particles of the electric fluid do really repel one another, and attract all other kinds of matter, or not; but for this we must refer to the article ELECTRICITY.

COHOBATION, in chemistry, an operation by

Coin.

which have currency as a medium in COMMERCE. Coin is a particular fpecies, always made of metal, and ftruck according to a certain procefs called COINING.

The precife epo ha of the invention of money is too ancient for our artals; and, if we might argue from the neceffity and obvioufnefs of the thing, muit be nearly coeval with the world.

Cohorn which the fame liquor is frequently diftilled from the fame body, either with an intention to diffolve this body, or to produce fome change upon it. This is, one of thofe operations which the ancient chemists practifed with great patience and zeal, and which are now neglected. To make this operation eafier, and to prevent the trouble of frequently changing the veffels, a particular kind of alembic, called a pelican, 'was invented. This veffel was made in the form of a cucurbit with an alembic-head, but had two spouts communicating with the body. As the vapour role up into the head, it was gradually condenfed, and ran down the fpouts into the body of the pelican, from whence it was again diftilled; and fo on. This veffel is reprefented Plate CXXXIV. fig. 6.

COLORN (N.) the greateft engineer Holland has produced. Among his other works, which are elteemed mafler-pieces of fkill, he fortified Bergen-op-zoom; which, to the furprise of all Europe, was taken by the French in 1747. He wrote a treatife on fortification; and died in 1704.

COHORT, in Roman antiquity, the name of part of the Roman legion, comprehending about 600 men. There were ten cohorts in a legion, the firit of which exceeded all the reft both in dignity and number of

men.

When the army was ranged in order of battle, the first cohort took up the right of the firft line; the reft followed in their natural order: fo that the third was in the centre of the first line of the legion, and the fifth on the left; the fecond between the bit and third; and the fourth between the third and fifth: the five remaining cohorts formed a fecond line in their natural order.

COIF, the badge of a fergeant at law, who is called fergeant of the coif, from the lawn coif they wear under their caps, when they are created fergeants.

The chief use of the coif was to cover the clerical tonfure. See TONSURE.

COILING, on flipboard, implies a fort of ferpentine winding of a cable or other rope, that it may occupy a finall space in the fhip. Each of the windings of this fort is called a fale; and one range of fakes upon the fame line is called a tier. There are generally from five to feven fakes in a tier; and three or four tiers in the whole length of a cable. This, however, depends on the extent of the fakes. The fmaller ropes employed about the fails are coiled upon cleats at fea, to prevent their being entangled amongst one another in traverfing, contracting, or extending the fails.

COÏLON, in the ancient Grecian theatres, the fame with the cavea of the Romans.

COIMBRA, a handfome, large, and celebrated town of Portugal, capital of the province of Beira, with a bishop's fee, and a famous univerfity. The cathedral and the fountains are very magnificent. It is feated in a very pleafant country abounding in vineyards, olive-trees, and fruits. It stands on a mountain, by the fide of the river Mondego. W. Long. 8. 57. N. Lat. 40. 10.

COIN, a piece of metal converted into money by the in preffing of certain marks or figures thereon.

CoN differs from MONEY as the fpecies from the genus. Moneys any matter, whether metal, wood, leather, glafs, horn, paper, fruits, fhells, or kernels,

Whether coins be of equal antiquity, may admit of fome doubt; efpecially as most of the ancient writers are fo frequent and exprefs in their mention of leathen-moneys, paper-moneys, wooden-moneys, &c. Some, however, notwithflanding this, are of opinion, that the firit moneys were of metal: the reasons they give, are the firmness, neatnefs, cleanlinefs, durableneís, and univerfality of metals; which, however, do rather conclude they ought to have been fo, than that they actually were fo.

In effect, the very commodities themselves were the firft moneys, i. & were current for one another by way of exchange; and it was the difficulty of cute › ting or dividing certain commodities, and the impoffibility of doing it without great lofs, that first put men on the expedient of a general inedium. See Ex

CHANGE.

Indeed, thus much may be faid in behalf of coins, that, on this view, it was natural for men to have their first recourse to metals; as being almoft the only things whofe goodness, and as it were integrity, is not diminished by partition; befides the advantages above expreffed, and the conveniences of melting and returning them into a mass of any fize or weight.

It was probably, then, this property of metals which first accuftomed people, who trafficked toge ther, to account them in lieu of quantities of other merchandizes in their exchanges, and at length to fubititute them wholly in their ftead; and thus arote money: as it was their other property to preferve any mark or impreffion a long time, which confirmed them in the right; and thus was the first rise of coins.

In the firft ages, each perfon cut his metal into pieces of different fizes and forms, according to the quantity to be given for any merchandize, or according to the demand of the feiler, or the quantity stipu lated between them. To this end they went to mar ket loaden with metal in proportion to the purchase to be made, and furnished with inftruments for portioning it, and fcakes for dealing it out, according as occation required. By degrees, it was found more commodious to have pieces ready weighed; and as there were different weights required according to the value of the different wares, all thofe of the fame weight began to be diftinguished with the fanie mark or figure thus were coins carried one #tep further. At length the growing commerce of money begin. ning to be disturbed with frauds, both in the weights and the matter, the public authority interpofed; and hence the first itamps or impreflions of money; tɔ which fucceeded the names of the moniers; and at length the figy of the prince, the date, legend, and other precautions to prevent the alterations of the fpccies; and thus were coins completed.

Modern Coins. In England the current fpecies of gold are the guinea, half-guinea, Jacobus, laureat, angel, and rofe-noble: the four laft of which are now feldom to be met with; having been moft of them

con

GRECIAN.

converted into guineas, chiefly during the reign of Charles II. and James II. The filver coins are the crown, half-crown, filling, and fixpence. Copper coins are the half-penny and farthing.

In Scotland, by the articles of the Union, it is appointed that all the coins be reduced to the English, and the fame accounts obferved throughout. Till then the Scots had their pounds, fhillings, and pence, as in England; but their pound was but 20 pence English, and the others in proportion: accordingly, their merk was 13s. Scots, current in England at 13 d. their noble in proportion. Befides thefe they had their turnorer-pence and half-pence; their penny of that of England: befides bafe money of achifons, babees, and placks. The bodle of the penny, of the achifon, of the babee, and of the plack.

In Ireland, the coins are as in England, viz. fhillings, pence, &c. with this difference, that their fhilling is but equal to 11d. Sterling: whence their pound is only 18s. 54d.

But, for a view of all the coins prefently current in the four quarters of the globe, with their values and proportions, fee the table fubjoined to the article Mo

NEY.

In many places fhells are current for coins; particularly a fmall white kind dug out of the ground in the Maldives, and fome parts of America, called in the Indies cowries, or coris, on the coaft of Africa bonges, and in America porcelaines; of which it takes a vaft number to be equivalent in value to a penny. Of zimbis, another kind of fhell current, particularly in the kingdoms of Angola and Congo, two thousand make what the negroes call a macoute; which is no real money; for of this there is none in this part of Africa but a manner of reckoning: thus, two Flemish knives they eftcem a macoute; a copper-bafon two pounds weight, and 12 inches diameter, they reckon three

macoutes; a fufee 10, &c.

Diobolum

Tetrobolum 14Drachma

2

1 2 6

2

12

Note: Of these the drachma, didrachm, &c. were of filver,, the reft for the most part of brass. The other parts, as tridrachm, triobolus, &c. were fometimes coined.

Note alfo: The drachma is here, with the generality of authors, fuppofed equal to the denarius; though

there is reafon to believe that the drachma was fomewhat the weightier. See DRACHMA and DENARIUS. d. Sterl.

The Grecian gold coin was the ftater aureus, weighing two attic drachms, or half of the ftater argenteus; and exchanging ufually for 25 attic drachms of filver; in our money

According to our proportion of gold to filver

There were likewife the ftater' cycizenus, exchanging for 28 attic drachms, or

alexandrinus, of the fame value. Stater philippicus, and ftater

fephus, worth 50 attic drachms, Stater daricus, according to Jo-1

or

}

Stater cræfius, of the fame value.

ROMAN.

}

Quinarius Victoriatus 2 Denarius

}

R

S. d. Sterl.

I

4 3

I

1 09

Ac

VOL. V. Part I.

COIN, in architecture, a kind of dye cut diagonalwife, after the manner of a flight of a ftair-cafe, ferving at bottom to fupport columns in a level, and at top to correct the inclination of an entablature fupporting a vault.

COIN is alfo ufed for a folid angle compofed of two furfaces inclined towards each other, whether that angle be exterior, as the coin of a wall, a tree, &c. or interior, as the coin of a chamber or chimney. See QUOIN.

COINAGE, or COINING, the art of making money, as performed either by the hammer or mill.

Formerly the fabric of coins was different from what it is at prefent. They cut a large plate of metal into feveral little fquares, the corners of which were cut off with fheers.. After having fhaped thefe pieces, fo as to render them perfectly conformable, in point of weight, to the standard piece, they took each piece in hand again, to make it exactly round by a gentle hammering. This was called a planchet, and was fit for immediate coining. Then engravers prepared, as they still do, a couple of fteel maffes in form of dyes, cut and terminated by a flat furface, rounded off at the edges. They engraved or ftamped on it the hollow of a head, a crofs, a fcutcheon, or any other figure, according to the cuftom of the times, with a fhort legend. As one of thefe dyes was to remain dormant, and the other moveable, the former ended in a fquare prifm, that it might be introduced into the fquare hole of the block, which, being fixed very fait, kept the dye as fteady as any vice could have done. The planchet of metal was horizontally laid upon this inferior mass, to receive the ftamp of it on one fide, and that of the upper dye, wherewith it was covered, on the other. This moveable dye, having its round engraved furface refting upon the planchet, had at its oppofite extremity a flat fquare, and larger furface, upon which they gave feveral heavy blows, with a hammer of an enormous fize, till the double stamp was fufficiently, in relievo, impreffed on each fide of the planchet. This being finished, was immediately fucceeded by another, and they thus became a ftandard coin, which had the degree of fineness of the weight and mark determined by the judgment of the infpectors, to make it good current money. The ftrong tempering which was and is ftill given to the two dyes, rendering them capable of bearing thofe repeated blows. Coining has been confiderably improved and rendered expeditious, by feveral ingenious machines, and by a wife application of the fureft phyfical experiments to the methods of fining, dyeing, and ftamping the different metals.

The three fineft inftruments the mint-man uses, are the laminating engine; the machine for making the impreffions on the edges of coins; and the mill.

After they have taken the laminæ, or plates of me

tal, out of the mould into which they are caft, they Coinage. do not beat them on the anvil, as was formerly done, but they make them pafs and repafs between the feveral rollers of the laminating engine, which being gradually brought clofer and clofer to each other, prefently give the lamina its uniform and exact thickness.. Inftead of dividing the lamina into fmall fquares, they at once cut clean out of it as many planchets as it can contain, by means of a fharp fteel trepan, of a roundith figure, hollow within, and of a proportionable diameter, to shape and cut off the piece at one and the fame time. After thefe planchets have been prepared and weighed with ftandard pieces, filed or fcraped to get off the fuperfluous part of the metal, and then boiled and made clean, they arrive, at last, at the machine (fig. 1.), which marks them upon the edge; and finally, the mill (fig. 2), which, fqueezing each Pla of them fingly between the two dyes, brought near CXLIK each other with one blow, forces the two furfaces or fields of the piece to fill exactly all the vacancies of the two figures engraved hollow. The engine which ferves to laminate lead, gives a fufficient notion of that which ferves to flaten gold and filver lamine between rollers of a leffer fize.

The principal pieces of the machine (fig. 1.), to ftamp coins on the edge, are two steel laminæ, about a line thick. One half of the legend, or of the ring, is engraved on the thickness of one of the laminæ, and the other half on the thickness of the other; and these two lamine are straight, although the planchet marked with them be circular.

When they ftamp a planchet, they first put it between the laminæ in fuch a manner, as that these being each of them laid flat upon a copper-plate, which is faftened upon a very thick wooden table, and the planchet being likewife laid flat upon the fame plate, the edge of the planchet may touch the two lamina on each fide, and in their thick part.

One of thefe lamina is immoveable, and fastened with feveral fcrews; the other flides by means of a dented wheel, which takes into the teeth that are on the furface of the lamina. This fliding lamina makes the planchet turn in fuch a manner, that it remains ftamped on the edge, when it has made one turn. Only crown and half-crown pieces can bear the impreffion of letters ou the thickness of their edges.

The coining engine or mill is fo handy (fig. 2.), that a fingle man may ftamp twenty thousand planchets in one day: gold, filver, and copper planchets, are all of them coined with a mill, to which the coining fquares (fig. 3.), commonly called dyes, are fastened; that of the face under, in a fquare box garnished with male and female fcrews, to fix and keep it steady; and the other above, in a little box garnished with the fame fcrews, to fasten the coining fquare. The plan chet is laid flat on the fquare of the effigy, which is dormant; and they immediately pull the bar of the mill by its cords, which caufes the fcrew fet within it to turn. This enters into the female fcrew, which is in the body of the mill, and turns with so much strength, that by pushing the upper fquare upon that of the effigy, the planchet, violently preffed between both fquares, receives the impreffion of both at one pull, and in the twinkling of an eye.

The