people. This vaft work appears to have been founded on enormous piles, driven clofely together: on their tops were laid long planks, ten inches thick, ftrongly bolted; and on them was placed the bafe of the pier, the lowermoft ftones of which are bedded in pitch, to prevent the water from damaging the work; around the whole were the piles which are called the fterlings, defigned to strengthen and preferve the foundation: thefe contracted the space between the piers in fuch a manner, as to occafion, at the return of every tide, a fall of five feet, or a number of cataracts full of danger, and, as they have proved, of deftruction. This ftructure has been ftyled, by ancient writers, the wonder of the world, the bridge of the world, and the bridge of wonders; and how well it deferved this pompous character will be feen from the defcription of its form and condition, previous to that alteration to which it owes its prefent appear

ance.

The Thames, in this part of it, is 915 feet broad, which is the length of the bridge. The street that covered it confifted, before the houses fell to decay, of lofty edifices, built with fome attention to exterior regularity: it was 20 feet wide, and the buildings on either fide about 26 feet in depth. Across the middle of the street ran feveral lofty arches, extending from fide to fide, the bottom part of each arch terminating at the firft ftory, and the upper part reaching near the tops of the houses; the work over the arches extending in a ftraight line from fide to fide. They were defigned to prevent the buildings from giving way; and were therefore formed of ftrong timbers,

bolted in the correfponding woodwork of the houses that flanked them. Thus the ftreet on the bridge had nothing to diftinguifh it from any narrow ftreet in the city but the high arches just described, and three openings, guarded with iron rails, which afforded a view of the river. But the appearance from the water baffles all defcription, and difplayed a ftrange example of curious deformity. Nineteen unequilateral arches, of different heights and breadths, with fterlings increafed to a monftrous fize by frequent repairs, ferved to fupport a range of houfes as irregular as themselves; the back part of which, broken by hanging clofets and irregular projections, offered a very difgufting object; while many of the buildings overhung the arches, fo as to hide the upper part of them, and feemed to lean in fuch a manner as to fill the beholder with equal amazement and horror. In one part of this extraordinary ftructure, there had formerly been a drawbridge, which was useful by way of defence, as well as to admit fhips to the upper part of the river, and it was guarded by a tower. It pre vented Fauconbridge, the bastard, from entering the city in 1471 with his armed followers, on the pretenc of liberating the unfortunate Henry from his imprisonment in the Tower. It also checked, and indeed feemed to annihilate, the illconducted infurrection of Sir Thomas Wiatt, in the reign of Queen Mary. In the times of civil diffention, which rendered this kingdom a continual fcene of turbulence and bloodthed, this tower was em ployed to expofe the heads of trai tors: and an old map of the city, in 1597, reprefents this building as decorated

exhibition of them. But though the paffage over the bridge is very much enlarged and improved, and forms a very handfome communication between the city of London and borough of Southwark, we cannot but lament, as if the miferable. contrivance of the bridge itself were not a fufficient impediment to the navigation, that the four arches, which have been fo long occupied by an engine to fupply the neighbourhood with water, ftill continue to be incumbered with it.

Account of the Pyramid of Caius Ceftius. From Lumifden's Remarks on the Antiquities of Rome.

LMOST joining to the gate of St. Paul, there is an elegant pyramid, which is built up in and ferves for part of the city wall. It had certainly stood without the city before Aurelian extended the walls. This is the only pyramid remaining about Rome: but which conveys to us, though in miniature, an idea of thofe in Egypt! * It was built to perpetuate the name of Caius Ceftius, one of the feptemvir Epulonum. one of But who this Ceftius was, other than the title given him on this monument, is uncertain. The Epulones were a college of priests, of great dignity, who prepared thofe feafts to the gods, called Lectifternia, where their ftatues, laid on rich beds, were placed at table as the principal guests. One of thofe beds (of bronze curiously wrought)

Thefe fumptuous entertainments were devoured by the feven noble gormandizing priefts. It was to appeafe the gods, in time of a plague, that the Romans firft inftituted thefe feafts, in the year of Rome 356 †. As the ground about the pyramid. is much raifed, we have not fo advantageous a fight of it as formerly. It is 1613 palms high, all incrufted, with white marble, and rests on a bafe of Tiburtine ftones, whofe height is 3 palms. The breadth of the fquare, on which it ftands, is 130 palms. Agreeable to the teftament of Ceftius, this vaft monument was built in 330 days. The fepulchral chamber had been finely painted; it is now much defaced; more perhaps from the fmoke of the torches ufed in flowing it, than from the humidity of the place. Thefe figures and ornaments feem all to relate to the facred ceremo nies of the Epulones. The monu ment was judiciously repaired, without altering its form, by Pope Alex

ander VII.

+ Livius, 1. 5. c. 13.

mans regulated their time by it for the fpace of ninety-nine years, when Q. Marcus Philippus, who was cenfor with L. Paulus, caufed another dial, conftructed for the latitude of Rome, to be erected near the old one. But as a fun-dial did not ferve in cloudy weather, Scipio Nafica, five years after, remedied this defect, by introducing a method of dividing the night as well as the day into hours, by means of a water machine, a clefidra, which Pliny calls an horologium.

I do not indeed conceive how a fun-dial, or any other inftrument, could point out the various hours, as time was computed by the ancient Romans. The time the earth takes to revolve once round its axis, or the space between the rifing of the fun till its next rifing, which makes a day and a night, divided into twenty-four equal parts, we call hours. Now, the Romans divided the day and the night into twenty-four hours. Twelve of thefe, from the rifing of the fun to its fetting, conftituted their day; and the other twelve, from the fetting of the fun to its rifing, conftituted their night. Thus as the feafons changed, the length of their hours must have varied. In winter the twelve hours of the day were fhort, and thofe of the night long: in fummer they were the reverfe. How then could these hours, of an

unequal length, and which daily varied, be measured by an inftrument? I have not been able to discover any method by which this could be done. However, they had two fixed points, viz. mid-day and mid-night, which they called the fixth hour: fo that a meridian line would always point out the fixth hour, or mid-day.

But

Neither have I been able to difcover when the modern Romans changed this method of computing time. In the courfe of the day and night they reckon twenty-four hours, which are all of an equal length in every feafon of the year. Noinconvenience can arife in reckoning twenty-four hours in place of twelve and twelve, as we do. Perhaps to far the modern Roman method is preferable to ours. the difficulty is, that they do not begin to reckon their hours from a fixed point, viz. from mid-day, when the fun croffes the fame meridian line every day in the year. Thus they call half an hour after fun-fet the twenty-fourth hour; and an hour and a half after fun fet the first hour, or one o'clock.. Hence the nominal hour of mid-day conftantly changes with them: in June it is called fixteen, and in December nineteen o'clock. To regulate, therefore, a time - piece by this method of computing, it must be daily altered.

MISCELLANEOUS,

directing its Operations. From Count Rumford's Eays, vol. 2, chap. 3.

HAT heat paffes more freely through fome bodies than others, is a fact very well known; but the caufe of this difference in the conducting powers of bodies, with refpect to heat, has not yet been difcovered.

The utility of giving a wooden handle to a tea-pot or coffee-pot of metal, or of covering its metallic handle with leather, or with wood, is well known: but the difference in the conducting powers of various bodies with regard to heat, may be fhown by a great number of very fimple experiments;-fuch as are in the power of every one to make at all tiines and in all places, and almoft without either trouble or expence.

If an iron nail and a pin of wood, of the fame form and dimenfions, be held fucceffively in the flame of a candle, the difference in the conducting powers.

ner in which there will be no room left for doubt, As foon as the end of the nail, which is expofed in the flame of the candle, begins to be heated, the other end of it will grow fo hot as to render it impoffible to hold it in the hand without being burnt; but the wood may be held any length of time in the fame fituation without the leaft inconvenience; and, even after it has taken fire, it may be held till it is almost entirely confumed; for the uninflamed wood will not grow hot, and, till the flame actually comes in contact with the fingers, they will not be burnt. If a fmail flip or tube of glafs be held in the flame of the candle in the fame manner, the end of the glafs by which it is held will be found to be more heated than the wood, but incomparably lefs fo than the pin. or nail of metal ;-and among all the various bodies that can be tried in this manner, no two of them will be found to give paffage to heat through their fubftances with exann. id fame doge of facility *.

To confine heat is nothing more than to prevent its efcape out of the hot body in which it exifts, and in which it is required to be retained; and this can only be done by furrounding the hot body by fome covering compofed of a fubftance through which heat cannot pafs, or through which it paffes with great difficulty. If a covering could be found perfectly impervious to heat, there is reafon to believe that a hot body, completely furrounded by it, would remain hot for ever; but we are acquainted with no fuch fubfrance; nor is it probable that any fuch exifts.

Thofe bodies in which heat paffes freely or rapidly, are called conductors of heat; thofe in which it 'makes its way with great difficulty, or very flowly, non-conductors, or bad conductors of heat. The epithets, good, bad, indifferent, excellent, &c. are applied indifferently to conductors and to non-conduc'tors. A good conductor, for inftance, is one in which heat paffes very freely; a good non-conductor is one in which it paffes with great difficulty; and an indifferent conductor may likewife be called, without any impropriety, an indifferent non-conductor.

Thofe bodies which are the worst conductors, or rather the 'beft nonconductors of heat, are beft adapted for forming coverings to confine it.

Some experiments which I have lately made, and which have not yet been publifhed, have induced me to fufpect that water, mercury, and all other non-elastic fluids, do not permit heat to pafs through them from particle to particle, as it undoubtedly paffes through folid bodies, but that their apparent conducting powers depend effentially upon the extreme mobility of their parts. In fhort, that they rather tranfport heat than allow it a paffage. But I will not anticipate a fubject which I propose to treat more fully at fome future period.

The conducting power of any folid body in one folid mafs, is much greater than that of the fame body reduced to a powder, or divided into many fmaller pieces. An iron bar, or an iron plate, for instance, is a much better conductor of heat than iron filings; and faw-duft is a better non-conductor than wood. Dry wood-afhes is a better non conductor than either; and very dry charcoal, reduced to a fine powder, is one of the beft non-conductors known; and as charcoal is perfectly incombuftible when confined in a fpace where fresh air can have no accefs, it is admirably well calculated for forming a barrier for confining heat where the heat to be confined is intense.

But among all the various fubftances of which coverings may be formed for confining heat, none can be employed with greater advantage than common atmospheric air. It is what Nature employs for that purpofe; and we cannot do better than to imitate her.

ftrongly