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a full sun, yet, I presume from a chilliness in the air, did not revive to be able to fly.
Remarks by Mr. Collinson.-What I collect from this gentleman's relation is, that it was the practice of the boys, annually to take these birds, by their apparatus and ready method of doing it; and the frequency of it was no remarkable thing to the watermen. Next it confirmed my former sentiments, that some of this swallow-tribe go away, and some stay behind in these dormitories all the winter. If my friend had been particular as to the species, it would have settled that point.
XXV. The Properties of the Mechanic Powers Demonstrated; with some Observations on the Methods that have been commonly used for that Purpose. By Hugh Hamilton,* D.D., F.R.S. p. 103.
This paper may be read with more advantage in an improved edition of it given in this author's ingenious volume of Philosophical Essays, the 3d edition of which was published in the year 1772.
XXVI. On some Subterraneous Apartments, with Etruscan Inscriptions and Paintings, discovered at Civita Turchino in Italy. By Joseph Wilcox, Esq. F. S. A. p. 127.
Civita Turchino, about 3 miles to the north of Corneto, is a hill of an oblong form, the summit of which is almost one continued plain. From the quantities of medals, intaglios, fragments of inscriptions, &c. that are occasionally found here, this is believed to be the very spot, where the powerful and most ancient city of Tarquinii once stood; though at present it is only one continued field of corn. On the south-east side of it runs the ridge of a hill, which unites it to Corneto. This ridge is at least 3 or 4 miles in length, and almost entirely covered by several hundreds of artificial hillocks, called by the inhabitants Monti Rossi. About twelve of these hillocks have at different times been opened; and in every one of them have been found several subter
Dr. Hamilton was born in 1728, and died Dec. 1, 1805; consequently at 77 years of age. He was educated at Trinity College, Dublin, where he obtained a fellowship, and was professor of Natural Philosophy. He afterwards received promotion in the church first as dean of Armagh; then in Jan. 1796 he was elected bishop of Clonfert; and 3 years after he was translated to the see of Ossory; being preferred to those dignities, without solicitation, from his high character for piety, learning, and attention to the duties of his profession. His writings, too, in several branches of science, entitle him to rank among the highest ornaments of the university of which he was a member. The above is his only communication in the Philos. Trans. His other scientific publications, are the Philosophical Essays, above-mentioned; and a treatise on Conic Sections, in 4to. 1758; being probably the most elegant work ever produced on that subject.
ranean apartments cut out of the solid rock. These apartments are of various forms and dimensions: some consist of a large outer room, and a small one within; others of a small room at the first entrance, and a larger one within: others are supported by a column of the solid rock, left in the centre, with openings on every part, from 20 to 30 feet. The entrance to them all is by a door of about 5 feet in height, by 2 feet and a half in breadth. Some of these have no other light but from the door, while others seem to have had a small light from above, through a hole of a pyramidical form. Many of these apartments have an elevated part that runs all round the wall, being a part of the rock left for that purpose. The moveables found in these apartments consist chiefly in Etruscan vases of various forms; in some indeed have been found some plain sarcophagi of stone with bones in them. The whole of these apartments are stuccoed, and ornamented in various manners: some indeed are plain, but others, particularly 3, are richly adorned; having a double row of Etruscan inscriptions running round the upper parts of the walls, and under it a kind of freize of figures in painting: some have an ornament under the figures that seems to supply the place of an architrave. There have been no relievos in stucco hitherto discovered. The paintings seem to be in fresco, and are in general in the same stile as those usually seen on the Etruscan vases: though some of them are much superior perhaps to any thing as yet seen of the Etruscan art in painting. The paintings, though in general slight, are well conceived, and prove that the artist was capable of producing things more studied and more finished: though in such a subterranean situation, almost void of light, where the delicacy of a finished work would have been in a great measure thrown away; these artists (as the Romans did in their best ages, when employed in such sepulchral works) have in general contented themselves with slightly expressing their thoughts. But among the immense number of those subterranean apartments which are yet unopened, it is to all appearance very probable that many, and many paintings and inscriptions, may be discovered, sufficient to form a very entertaining, and perhaps a very useful work: a work which would doubtless interest all the learned and curious world, not only as it may bring to light, if success attends this undertaking, many works of art, in times of such early and remote antiquity, but as perhaps it may also be the occasion of making some considerable discoveries in the history of a nation, in itself very great, though to the regret of all the learned world at present almost unknown. This great scene of antiquities is almost entirely unknown even in Rome. Mr. Jenkins, then resident at Rome, was the first and only Englishman who ever visited it.
XXVII. Of a new Peruvian Plant,* lately introduced into the English Gardens; the several Characters of which differ from all the Genera hitherto described. By George Dionysius Ehret, F. R. S. p. 130.
This plant blowed in the Physic Garden at Chelsea, and flourished there in great perfection in the year 1761. It produced abundance of branches, which spread themselves on the surface of the ground: these branches were greatly multiplied by side ones, which grow alternately; and are smooth towards the ground, and streaked towards the top. Each joint is furnished with many ovate-shaped leaves, having membranous ciliated footstalks. This plant was also richly ornamented with abundance of buds and flowers: the flowers being of a sky-blue, with a dark embroidered purple bottom, made a beautiful
Mr. Philip Miller proposed to honour this plant with the name of Walkeria, in gratitude to Dr. Richard Walker, who, by his indefatigable pains, and at a large expence of his own, had founded a Physic Garden in the University of Cambridge, to incite and extend the study of Botany there.
XXVIII. Observations on two Ancient Roman Inscriptions discovered at Netherby in Cumberland. By the Rev. John Taylor, LL.D. p. 133. The inscriptions were discovered at Netherby in Cumberland, the former in the year 1762, the other early in the present century: they both make mention of Marcus Aurelius Salvius, tribune of the cohors prima ælia Hispanorum milliaria equitata. The former also points out the particular emperor, M. Aurelius Severus Alexander, in whose reign it was engraved: and almost directs us to the very year; which must have been either the 226th or 229th of the Christian æra, for in those two years was that emperor consul: and one of those consulates this stone alludes to, in the last words of it; which Dr. T. reads thus:
IMPERATORE DOMINO NOSTRO
SEVERO ALEXANDRO PIO
FELICE, AVGVSTO, CONSVLE.
The purport of the inscription now under consideration is this, viz. In the reign of Severus Alexander, Pius, Felix, &c. the cohors prima ælia Hispanorum milliaria equitata put the finishing hand to a building, termed here Basilica equestris exercitatoria, the foundations of which had been laid some time before. This was conducted under the care and direction of Valerianus, the emperor's lieutenant and pro-prætor, at the instance of M. Aurel. Salvius, tribune of the aforesaid company. Basilica is a word of large extent, and commonly signifies. what is built for public use, or by public authority. It is therefore frequently
* This plant is the Nolana prostrata of Linnæus..
applied to a burse or exchange. The public roads are termed basilica: and the Christian writers took this word for their churches. Though this be the common use of the word, it is not the primary. It signifies originally and principally as it does in this inscription, a portico or colonnade, which being very large and considerable in places built for courts of justice, for public auditories and meetings of merchants, it came to pass that the name of the principal was sunk in the adjunct; and all these places called alike basilicæ, from the colonnade, which attended, and perhaps sometimes encompassed them,
XXIX. A Method of Lessening the Quantity of Friction in Engines. By Keane. Fitzgerald, Esq., F. R. S. p. 139.
Mechanics, or that branch of mathematics which considers motions and moving. powers, their nature and laws, is properly distinguished into rational and practical.. Aknowledge in rational mechanics, which comprehends the whole theory of motion, on which natural philosophy so greatly depends, is chiefly confined to the learned; and the proper construction of engines and machines, which is the principal object of practical mechanics, though so very necessary to carry on the several branches of husbandry, manufacture, and commerce, on which the riches and power of a nation in a great measure depend, is seldom attended to, but by the mere handicraftsman; who is little acquainted with the principles he works on, and from whom no great improvements can well be expected; yet it has sometimes happened, that excellent contrivances have been invented, for raising heavy weights, and overcoming their resistances, by persons who never took the trouble of examining into the cause of gravity. It often happens that mechanical powers, seemingly demonstrable in theory, are found very deficient in operation, from unexpected obstructions; which, with the expence and trouble that generally attend the reducing speculations of this nature into practice, have probably been. the greatest obstacles to improvements in it. One of the greatest obstructions to the mechanical powers of engines proceeds from the friction, or resistance of the parts rubbing on each other; which in general is greater or less, as the rubbing parts bear the greater or less pressure; and yet this obstruction is but little attended to. The theorist makes no allowance on account of friction; and the practical mechanician, who feels the effects, yet, as if unavoidable, seldom takes the trouble of searching for a remedy. Among the few who have endeavoured to ascertain the quantity of friction proceeding from weight, some have deemed it equal to others to, and others more or less, according to their different methods, or accuracy in making experiments. Doctor Desaguliers gives an account of some experiments, which show the quantity of friction in a cylinder, to be equal to of the power required to move it, when the surface of the cylinder moves as fast as the power.
In order to examine the quantities of friction proceeding from different weights, Mr. F. had an exact balance made, which weighed 27 oz.; the pivots of the axis were inch diameter, and turned in brass sockets, fixed in a frame for the purpose. At each end of the beam he suspended several pairs of equal weights, and then tried how much added at one end would just move the beam, and also how much would depress the end 2 inches. Whence he infers, that the least power required was equal to the weight on the pivots; and that it required a power nearly equal to the whole weight, to overcome the resistance from friction with but a small degree of velocity.
It is not imagined that these experiments should determine the exact quantity of friction proceeding generally from weight or pressure: which probably can never be ascertained by any experiments, however accurate; for even in engines of equal dimensions, and loaded with equal weights, the quantities of friction may be very unequal, from circumstances differing, which are sometimes imperceptible; such as the firmness, elasticity, roundness and smoothness of the parts rubbing on each other; particularly the roundness, and smoothness of the gudgeons or pivots, which in large engines are seldom turned true, or polished. But it appears from these experiments, that the quantity of friction in large engines may reasonably be estimated at the weight, or pressure, on the rubbing parts; though in such as are small, and finished with exactness, the quantity may probably be about 4.
Mr. F. then endeavours to determine how much friction will be lessened by placing the axis of a wheel on the circumferences of two other, or friction wheels; and also the pivots of these two each on two others, &c.; calculating the dimi nution of the friction on the ratio of the decrease of velocity in each wheel or axis; hence he says, thus it is evident that by the application of additional wheels, or by enlarging the diameters of these, the resistance from friction may be reduced to less than the resistance of the medium the wheel passes through.
In order to form some estimate of the quantity of weight with which the axis of the lever of a fire-engine is loaded, Mr. F. took the dimensions of the several parts of that at the York-buildings water-works; the lever of which is 27 feet long, 2 feet 6 inches by 2 feet 2 inches in the middle, and 2 feet by 22 inches at the ends. The weight of which, with the archeads, chain, rods, and working frame hanging at one end, and the piston and chain at the other, may be computed at 6 tons, or 12,000 lb. The cylinder is 45 inches diameter, about 1591 square inches; which at 15 lb. per inch pressure of the atmosphere, is 22,274 lb. The column of water to be raised is 10,060 lb., which is not 6 lb. per inch; so that the remainder of the power is employed in overcoming the resistance from friction in the several parts of the engine, and giving the lever a degree of velocity equal to 120 feet per minute, which it moved in common work.