fore it was separated: for the polarity of every fragment is usually, if not always, before they are separated, parallel to that of the whole stone, and, consequently, to that of each other and if ever it is found otherwise, Mr. S. thinks that loadstone wants of perfection. So that the parts of any magnet, when cut in two transversely, or perpendicular to its axis, become complete magnets, having each their poles and axis parallel to the whole magnet; and that, whether the two parts are equal or unequal. And the sum of the weights of iron, lifted by the two parts separately, is greater than the single weight lifted by the whole magnet.

That all magnetical attraction (as also repulsion) is mutual; for iron or steel attracts the loadstone, as that does iron or steel, and they also each other.

That every loadstone communicates virtue to iron or steel, not only by contact, but even by their approach within its attractive sphere, more or less as nearer to, or farther from, its body; and likewise its poles, also according to the shape, size, and specific virtue, and figure of the iron or steel, and their proportion of magnitude to each other; and that a small magnet communicates nearly as much virtue as a large one. Some authors write, that the loadstone loses none of its virtue by communicating of it to iron or steel, which Mr. S. doubts the truth of, especially if the stone is small in proportion to the steel, in which case he has known touched steel to lose considerable virtue.

That steel is not only more receptive, but more retentive of magnetism, than common iron; and iron or steel hammered hard, than the same while soft; but steel hardened by quenching, than either of them.

That such iron or steel as has magnetic virtue communicated to it, also communicates it to other iron or steel after the same manner as a loadstone does. Which virtue, after ever so many communications, is, as to its nature, perfectly the same with that of the stone itself, having both poles, and will touch other steel, and that a compass, as well as the loadstone itself, and as vigorous, if properly used.

That every loadstone, within its attractive sphere, has a power to keep one piece of iron suspended to another, especially if that to which it is suspended is the larger, and their ends be bright and clean, where they touch each other; and if the suspended iron is not too heavy, the other will draw it up from either pole of the naked loadstone actually touching it, and will also keep it suspended, till at a considerable distance; but will not draw it off in such manner from the

armour of unarmed stone, if the armour and iron are both of them bright and clean at their contact. Hence it must follow,

any

That an armed loadstone can lift more with either of its poles, used singly, than the same can lift naked: that not only steel or iron, regularly touched, but also oblong iron void of permanent virtue, will perform all that loadstone can, though not with the same degree of power: for either of them will attract, keep one piece of iron suspended to another, and communicate some degree of permanent polarity to steel well hardened, as Mr. S. has experienced, and also to an iron wire.

That, of a soft iron bar void of fixed polarity, as soon as it is in an erect position, the higher part from the middle upward becomes a north pole in north, or a south pole in south magnetic latitude. And, e contra, the lower part from the middle downward becomes a south pole in north, and a north pole in south latitude: but as soon as the bar is inverted, the polarity is shifted in it, and in north latitude the end newly placed upward becomes the north pole, though it was a south one immediately before, and the other end the south pole, though it was its north one just before. The case is the same, if such a bar is placed horizontally in or near the magnetical meridian; for the end directed toward the north will constanly be a south pole, and that which is directed toward the south a north one; and as soon as the ends of the bar are shifted, the polarity, in respect of the bar, is shifted also, but not in respect of the earth, for which reason this virtue is called transient, and is communicated by the earth's central magnet in such manner as other loadstones are said to do.

That if a bar of iron or steel, not having the least degree of fixed virtues, be placed in any position, except at or near to a right angle with the magnetical line, it will not only for the present receive a transient polarity, but if it remain so long, the said polarity will gradually become fixed or permanent, more or less, according to the hardness or softness of the bar, and the time it has remained in that position, and the angle its length makes with the magnetical line, and the proportion of the length to its magnitude, the longest, cæteris paribus, usually receiving most virtue; and sometimes when all these advantages concur, the polarity will be sensibly permanent in a little time, and not require a very long time to be rendered pretty strong.

That by placing the said bar afterwards in the same position,

only with its ends shifted, it will gradually lose its gained magnetism, and at length have its polarity changed.

That magnetism not only in touched iron and steel, but also in the loadstone itself, is soon destroyed by fire.

That though fire destroys fixed magnetism in steel or iron, yet if they are set to cool in an erect position, or rather in the direction of the magnetical line, they will gain more or less fixed virtue by the time they are cold; but especially steel heated to a seasoning height, and in that position cooled suddenly under water.

That while a piece of iron of some magnitude is held at one pole of a loadstone, it will increase the attraction of the other pole thereof, and enable it to lift somewhat more.

That if either pole of a magnet, large enough, touch one end of an oblong piece of steel, not too large and long for the magnet easily to act on, it will transmit its own virtue to the other end of the steel which is farthest off, and make it a pole. of its own kind; while the end that touches the stone has virtue of the contrary pole: but the virtue usually is not so strong in the end which is untouched as in that which is.

That a needle first equally poised, then touched and put to oscillate on its pivots in the magnetical meridian, will in north latitude have its north end (i. e. its south pole) depressed until it directs to the north-attracting point of the central magnet; where, after several oscillations, it will at last rest: and in south latitude the south end will be depressed after the same

manner.

An Account of the different Sorts of Paper of the Ancients. By the Hon. Sir JOHN CLERK, F.R.S.— [1731.] Or the several sorts of charta used for writing, the most ancient were made of barks of trees, or skins, or were such as are called pugillares. The oldest were of the inner bark of trees, called liber in Latin, whence a book had the name of liber; but very little of this sort is now in being, except the Egyptian papyrus may be accounted one species of it.

The papyrus was made of a plant having many pelliceous tunicles, as Pliny informs us, which were separated from one another by a needle, and then glued again together, to give them a strength and firmness sufficient to retain what might be written on them. Alexandria was the place most eminent for this manufacture. There are some fragrants of this sort still extant in libraries, particularly the famous manuscript of St. Mark's Gospel at Venice,

The chartæ membranacea are made of the skins of animals, dressed either like our glove-leather, or modern parchment. The first sort was commonly used by the Jews for writing the law of Moses on it, and from the rolling up of these skins comes the word volumen. But the skins which Varro and Pliny say were first made by Eumenes king of Pergamus, were in more common use: however, Eumenes, who is related by these authors to have made them in opposition to Ptolemy king of Egypt, who had forbidden the exportation of the papyrus from his dominions, does not seem to be the inventor of the chartæ membranacea; since Herodotus, who lived long before his time, informs us, that the Ionians and other nations used to write on goat and sheep skins. Josephus also tells us, that the Jews sent their laws written on skins in letters of gold to Ptolemy; by which it seems as if the writing on skins was no new thing at that time among the Jews.

The use of the pugillares was also very ancient, being mentioned by Homer, and among the Latins by Plautus. They were made of all sorts of wood, ivory, and skins, covered over with wax. They were likewise of several colours, as red, yellow, green, saffron, white, and others. Being waxed over, any thing was easily written on them by the point of the stylus, and as easily rubbed out, and altered by the flat part of it. Sometimes these pugillares were made of gold, silver, brass, or lead, and then there was a necessity of an iron stylus to write or cut the letters on them.

The diptychs and triptychs that were covered with wax served only for common occurrences; the other sorts received every thing else that was written on chartæ or membranæ, and were sometimes called by the Greeks palimpsestæ, from the rubbing out of the letters on them.

The chartæ linteæ, and bombycineæ, which were made of linen or cotton, were of much later date; and from these we learned to make the paper now in use of linen rags, an invention probably of about 600 years standing.

Writing was practised on all these charte with a reed, and afterwards with a pen, except on the pugillares. These reeds grew on the banks of the Nile; the Greeks also used reeds imported from Persia for the same purpose. Calami argentei are also mentioned for writing.

Their letters were formed with liquors of various colours, but chiefly black, thence called atramentum. It was sometimes made of the blood of the cuttle-fish, sometimes of soot. Apelles composed a black of burnt ivory, which was called

elephantinum. They had ink also from India, of an improved composition, as Pliny says.

The titles of their chapters and sections were written in red or purple: hence the titles of the Roman laws are called rubrica. Their purpura was an exceedingly bright red, or crimson, much in vogue with the Byzantine writers; which was a liquor made of the murex boiled, and its shell very finely powdered; or, as Pliny relates, of the blood of that fish. Almost all the ancient emperors wore this colour; their names were painted in it on their banners; and they frequently wrote with it, and wore it. This colour was often the distinction of a Roman magistrate, and to put on the. purple, was the same thing as to assume the government.

The children of the emperors, and such as had a prospect of rising to the throne, and their guardians, sometimes wrote with green; gold also was employed for the like purpose.

Conjectures concerning Stars which sometimes appear and disappear; and on Saturn's Ring. By PETER LEWIS DE MAUPERTUIS.

[1731.]

}

THE consideration of the figures which fluids may take, according to the different ratio of gravity to the centrifugal force, suggested to M. Maupertuis, that probably the planets have such forms; since for this there is only necessary a swifter motion round the axis, or a less density of matter: for, though few planets, that we know of, come sufficiently near a spheroidal figure, why may we not admit of other forms, either about other suns, or even our own? these lentiform planets would never be seen by us, either by reason of their distance, or because they would be in the plane of the ecliptic, or in a plane somewhat inclined to it, to which plane their axis of revolution would be perpendicular, or nearly so; for in this situation they could not be seen from the earth.

And why might not such a variety of forms obtain among the fixed stars? especially, since it is very probable that they revolve round their axis, like our sun. There are, probably, lentiform fixed stars in the heavens; and probably they are surrounded with very eccentric planets or comets, which, since they are not fixed in the plane of the equator, when they approach the perihelion, disturb the direction of the star's axis; and then the star, which by reason of its situation now disappears, appeared; or that which appeared before, now disappears. And so a reason might be assigned, why some stars seem to appear and disappear alternately.