perity, and had banking establishments in France, Flanders, and other countries. About the middle of the 13th century, the factions of the Guelphs and Ghibelines broke out in Asti, and distracted the citizens for many years after. Tired of these civil struggles, the people of Asti chose for their captain one of the princes of the house of Savoy. It afterwards fell into the hands of the Visconti of Milan, who transferred it in 1387 to the French. They retained it till 1529, when it was given up to the Emperor Charles V., by the peace of Cambrai. Charles gave Asti to his relation Beatrix of Portugal, who married Charles III., duke of Savoy; and it remained attached to the dominions of that house until the establishment of the modern kingdom of Italy.

ASTIG MATISM, a curious and not uncommon imperfection of the eye. The lens of the eye and the transparent outer coat, or cornea, are parts of nearly spherical surfaces; but a deviation from the spherical curvature exists to a certain extent in most eyes. It is not sufficient, usually, to cause any great effect, but where it is unequal along different lines, and at the same time excessive, it produces the inconvenience of astigmatism. Thus if a set of horizontal lines, and also a set of vertical lines, be looked at by a person whose eye is astigmatic, having a greater curvature vertically than horizontally, the set of horizontal lines will be seen with distinctness at a point nearer the eye than that required by the vertical lines so that to see both series with equal distinctness the vertical series must be held further from the eye than the horizontal. Either irregular curvature of the lens or of the cornea produces astigmatism. When the defect is not so symmetrical as that named above, but the irregularity exists in various directions (the most usual case), the result is that a bright point, such as a star, becomes not a circular but a radiate figure. It is hardly possible to find an eye which is not in some degree astigmatic. For other imperfections of the organ, see EYE.

ASTOR'GA, a musical composer of some eminence, was born at Palermo in 1681, and studied under Francesco Scarlatti. His father, the Marchese Capece da Roffrano, conspired against the Spaniards, and perished on the scaffold in the presence of the lad; who, it is said, with great likelihood, fainted at the sight. Young Roffrano was befriended by the Princess Ursini, maid of honour to Philip V. of Spain, and was brought up in the convent of Astorga in Spain. This powerful protection procured him the title of Baron d'Astorga, and a diplomatic mission to Parma in 1704. Here he fell in love with the duke's daughter, Elisabetta Farnese, to whom he was teaching music; for he was already an accomplished musician. The duke, discovering the affair, neatly extricated himself from all difficulty by recommending Astorga to the emperor, and so sending him into an honourable banishment from Parma. He remained at Vienna through three reigns, occasionally visiting other countries, high in favour with the Austrian court, and dying in the castle of Raudnitz, which Prince Lobkowitz had given up for his use.

Astorga's "Stabat Mater," composed for the "Society of Antient Musick" of London in 1713, is his best work. It is still a favourite, and was heard in London in 1880; it is considered by most crities superior even to the fine work on the same words by Pergolesi. About 100 "cantatas" by Astorga exist; these are songs, chiefly for female voices, and of great merit.

ASTOR GA, the Asturica Augusta of the Romans, once the capital of the Astures, and now a small episcopal town with about 4000 inhabitants, in the Spanish province of Leon. Pliny (iii. 3) calls it a magnificent city. It is situated in a fertile plain near the Tuerto, about 26 miles west by south of Leon. The cathedral deserves notice on account of its high altar, which is one of the best works of Gaspar Becerra.

ASTRABAD, a city of Northern Persia, and the chief town of the province of that name, is situated near the S.E. corner of the Caspian Sea. The town is surrounded by a low and dilapidated mud wall, about 3 miles in circuit; and as the houses are often intermixed with trees and gardens, it presents rather a picturesque appearance. There are a large number of half-ruined buildings, among which are the remains of the splendid castle of Shah Abbas. The noxious exhalations from the surrounding forests, during the hot weather, make it so unhealthy that it is sometimes called the "City of the Plague." The population is about 10,000.

ASTRÆ A, the goddess of right dealing amongst the Greeks. She was the daughter of Zeus and Themis (goddess of justice), and lived amongst men in the golden age. When that blessed time had passed away with the rule of Kronos, and to the silver and bronze ages had succeeded the iron age, Astræa, who of all the immortals had remained longest on the earth, was forced by the greed of gain, and the toil and trouble of mankind, to retire into Olympus. She forms the constellation Virgo. With her, her sister Aidos (Modesty) forsook the close companionship of mortals; and Zeus, determined to destroy the wretched god-forsaken race, overwhelmed the earth with a flood. All Greece was submerged, no living soul escaping but Pyrrha and, her husband DEUCALION.

AS TRAGAL or Bead, a moulding used in architecture, and applied principally to the upper ends of the shafts of columns and to their bases. It is also used in the entablatures of the Roman Doric, the Ionic, Corinthian, and Composite orders. The term is derived from the Greek astragalos, which signifies the bone on which the tibia rests, and sometimes a vertebra. The form of this moulding is semicircular, projecting from a vertical diameter. In Egyptian architecture, bands curved after the manner of astragals seem to bind the reeds of which the shaft of the column often appears to be formed.

The apparent use of the astragal is to bind the parts of columns and entablatures together, for which purpose it is employed both at the top of the shaft where the capital commences, and at the bottom where the base terminates.

ASTRA'GALUS, an extensive genus of leguminous plants, the most remarkable species of which is the Astragalus gummifer, from which the substance called gum tragacanth is obtained. Although the principal part of the tragacanth of commerce is furnished by this species, it is also procured from several others. It belongs to the order LEGUMINOSÆ, suborder Papilionaceæ.

ASTRAKHAN, a government of European Russia, bounded on the S.E. by the Caspian Sea, on the W. by the country of the Don Cossacks and the Caucasus, and on the N. by the governments of Saratoff and Orenburg. It is comprised between 45° and 50° N. lat., and 44° and 51° E. lon., and has an area of about 85,000 square miles. The land is, with little exception, an enormous plain, lying below the level of the ocean and the Black Sea. It is divided into two parts or steppes, by the Volga. The soil is saturated in almost every direction with salt; the very atmosphere, the rain, and dew are charged with it; and briny lakes are of frequent occurrence. Rocks, either of limestone or sandstone, rarely occur; but the province is full of extensive moors, the soil of which consists of a deep spongy saline loam, which bears no vegetation whatever on its surface; its edges only are skirted with saline plants. It is supposed that the Caspian once covered this province, and hence the abundant beds of salt and saltpetre. There are only a few fertile spots, situated near the rivers, where fruit, vegetables, grain, and vines are reared; as well as a little tobacco and cotton.

The climate of Astrakhan is one of extremes; a dry and parching heat prevails in summer, when the thermometer frequently stands, even in the shade, at 100°

Fahr.; yet the nights are in general nipping, and the winds deposit the saline particles with which the air is charged in such profusion, that every object appears veiled in the morning with hoar-frost.

The river Volga flows through the province with a winding course; and before its fall into the Caspian, about 30 miles below Astrakhan, it branches into eight principal arms and sixty-five subsidiary outlets, forming a delta of seventy islands. This river is scarcely equalled by any other stream in the world for abundance of fish-the most important of which is the sturgeon. In the spring of the year its fishing grounds, particularly between the sea and the capital, are so abundantly stocked with fish as to employ upwards of 5000 vessels, coming to the fisheries from remote places.

The river Ural forms the eastern boundary of Astrakhan, and between it and the Volga is a dreary expanse of sand and swamps. There is a winter fishery on the Ural, which gives

employment to the poor Cossack inhabitants of the neighbouring shores.

The animals found in Astrakhan include the wild ass, camel, and antelope-saiga, whose horns are semitransparent; there are also the bustard, kite, falcon, pheasant, and snipe. The natives are herdsmen and graziers as well as fishers; droves of horned cattle are kept wherever there is pasture, and are turned out half-starved from their wretched winter quarters as soon as the snow has disappeared. Goats are also reared, not so much for the sake of their milk or flesh, as of their hides, with which the Russians prepare morocco leather. There is a fine species of hair too, which either falls from the animal's back, or is combed from it, out of which a stuff of beautiful texture is occasionally woven. But the greatest resource possessed by the rural population and nomadic tribes of the province is their flocks of sheep, which are valuable both for their wool and for their fat. The horses of the province are diminutive and ill-conditioned;

but they are suited to the climate, and are very valuable to the Kalmucks, who, when the services of the living animal are over, use the flesh for food, the skin for clothing, the sinews for ropes and tackle.

The population of Astrakhan is composed of a motley group of Russians, Cossacks, Tartars, Kalmucks, Armenians, Hindus, and other settlers. A considerable portion is composed of the Cossacks of the Ural, who are esteemed the finest, the wealthiest, and the bravest Cossack corps in the Russian service, whence they have acquired the appellation of "the Eye of the Army," and garrison the small forts along the line of their native river. The Tartars and other inhabitants are fewer in number.

To the principal branches of industry already enumerated may be added the manufacture of magnesia, tallow, and soap in considerable quantities, and distilleries of brandy and spirits. Astrakhan soap is in much request among the Russians on account of its firm substance and fragrant scent.

ASTRAKHAN, the capital of the above government, which has become the principal seat of Russian intercourse with Asia and the storehouse of fish for the whole empire, stands

VOL. II.

on the island of Zaietchy Bugor, or "the Hare's Mound," which lies between the small river Kutum and the Volga, about 30 miles from the mouth of the Volga, and 820 south-east of Moscow. It has a navigable communication also with St. Petersburg, from which it is upwards of 1200 miles distant. The town is irregularly built, and although it contains many respectable streets and squares, most of the thoroughfares are unpaved, so that they are alternately deep sand and liquid mud. The houses present a singular medley of European and Asiatic taste; they are constructed principally of wood, brick, or mud, with only a few of stone. The ordinary population of the town is about 50,000. The uneven ground on which it stands, its half-decayed battlements, and a multitude of steeples, minarets, and cupolas, give it a handsome appearance at a distance; and the effect is heightened by contrast with the flat marshy ground which surrounds it. The climate of such a site cannot rank among the healthiest; and it is liable, moreover, to very sudden changes of temperature. Astrakhan is the seat of an Armenian as well as Greek archbishopric, and has a large number of churches. The Roman Catholics, Lutherans,

2

Mohammedans, and Hindus also have each their separate places of worship. There are numerous schools, missions, and printing houses in the town. The chief architectural ornaments of Astrakhan are-the "Kreml" or citadel, which contains the cathedral and barracks; the "new" or "white" town, so called from its being embellished with the principal government buildings and the three factory halls, one for the use of the Russian, another for the Asiatic, and a third for the Hindu dealers; the beautiful street inhabited by the Persian merchants, on each side of which runs an arcade, supported by handsome columns; and the cathedral, which was erected in 1696, and, like most ecclesiastical edifices in Russia, consists of a massive parallelogram with four small cupolas on the roof, and a large one in the centre, from which the building receives its light.

The fisheries of the Volga centre principally at Astrakhan, or rather on the branches of the river some distance below it. Every weir has its group of huts, with a little church attached to it, in which from two to three score fishermen reside; they are divided into divers, catchers, salting-men, and makers of caviar and isinglass. Each little colony is provided with spacious ice-cellars, which contain compartments for storing away the fish when salted, with intervals between the compartments which are filled with ice.

It has been calculated that, in the fishing season, the population of Astrakhan is increased by at least 30,000; a motley concourse, collected from almost every quarter of Asia and Europe, of whom nearly one-third are Russians. Astrakhan carries on a considerable trade with Persia and the countries east of the Caspian. There are several establishments for weaving silk and cotton; and some of the inhabitants are also employed in manufacturing considerable quantities of leather-particularly a superior description of morocco and shagreen-as well as tallow and soap. There are some large saltworks near the town. Living at Astrakhan is so cheap that £20 per annum is a fair income for the maintenance of an ordinary family.

ASTRIN'GENTS (from Lat. astringo, to constringe or bring closer together) are agents which contract the fibres of muscles and bloodvessels. They produce this effect generally by a vital, but sometimes by a chemical action. Their power is manifested first, and often solely, on the part to which they are applied; yet in many instances it is extended by sympathy very rapidly over the whole body, as is observed when the austere juice of the sloe is brought in contact with the tongue. The sensation then experienced may be considered the best general test of the presence of astringency, which cannot be ascribed to any one principle, but is owing to tannin, gallic acid, and hæmatin, in vegetable astringents, and is possessed by acids and many metallic salts among mineral agents; it is also one of the effects of the application of cold to the body.

uterus.

The effect of astringents, which is due to their chemical action, is nearly the same in dead as in living animal matter; their long-continued application to the skin will produce a condition similar to that of a tanned hide. They are therefore sometimes employed to effect this, when internal parts are exposed, to change them from a secreting to a non-secreting surface-such as an irreducible prolapsed Their use in this way, however, is very limited; while their vital action is extensive and important. The chief effects of astringents are to contract the muscular and vascular tissues, to diminish secretion and lessen irritability, and in many instances to impart strength or increased tone to an organ or part. Their action is always greatest on the part to which they are applied. When a drop of diluted acetic or sulphuric acid is placed on the skin, whiteness of the part is observed, which soon disappears, and the natural colour, or even a more intensely red one, follows. If this is frequently repeated, the structure of the part is changed, it ceases to secrete, is no longer

pliant, but becomes stiff and inflexible. The loss of colour is owing to the diminished calibre of the blood vessels, which no longer admit the red globules. During the absence of these, the sensibility of the part is less than natural, just as cold and torpid fingers lose their finenessof touch. Nearly similar effects follow the internal administration of astringents. Some astringents which lessen the action of the heart are called sedatives; while others, which combine with and neutralize the unhealthy or excessive secretions, as lime and its carbonate with the secreted fluids of the intestinal canal, are more properly termed absorbents. When astringents are applied directly to the bleeding vessels, such as to external wounds, or to the nostrils or gums, they are termed styptics, and in such cases they often act chemically as well as vitally.

Of vegetable astringents the chief are barks, as of oak and willow, the best kind of the former of which is obtained from the Quercus robur of Linnæus (the true British oak), which is synonymous with the Quercus pedunculata of Willdenow, while the inferior sort is obtained fom the Quercus sessiflora of Salisbury, which is synonymous with the Quercus robur of Willdenow; the best willow-bark is procured from the Salix pentandra, or sweet bay-leaved willow, though very excellent bark is yielded by the Salix Russeliana, or Bedford willow; roots, as of tormentil' (Potentilla tormentilla); bistort (Polygonum bistorta); common avens (Geum urbanum), which are British plants; and rhatany (Krameria triandra); rhubarb (Rheum palmatum); pomegranate (Punica granatum), which are exotic plants; leaves of arctostaphylos (Uva ursi), petals of the Rosa gallica, fruits of Prunus spinosa, or sloe-thorn (Punica granatum), and secreted juices of many plants, as kino, from Pterocarpus Senegalensis, and several others; and catechu, from Acacia catechu, and galls, from Quercus infectoria-in all of which the astringent principle is tannin, with more or less of gallic acid; and lastly logwood (Hæmatoxylon Campechianum), in which hæmatin as well as tannin possesses an astringent property. Acetic acid must also be classed among the vegetable astringents.

The mineral astringents are-diluted sulphuric acid, and salts of iron, zinc, copper, silver, and the salts of lead. Cold, in whatever way applied, is also a valuable astringent.

The ancient Egyptians would appear to have been acquainted with the power of astringents in preserving vegetable as well as animal substances, and they seem to have dipped the coarse cloths in which the mummies wereenveloped in some astringent liquid, which tanned the skin, and rendered it less subject to change, as well as excluded the air from the interior of the body.

ASTROCA RYUM, a genus of PALMS found in small groups or in single specimens in the tropical parts of South America, of middling stature, and of a very singular appearance on account of the spines with which they are armed. Their stems are covered all over, except at the places where the leaves are attached, with stiff and very numerous spines, which also cover the foliage, fruit-stalks, and sometimes even the fruit. The leaves are feathershaped, and form a dense crown at the top of the stem. The fruits hang down from among the leaves; they arefleshy, of a yellow or orange colour, and have a hard stone in the middle.

Astrocaryum Murumuru is a common inhabitant of swampy places in the neighbourhood of Para, where it is called Murumuru; the flesh of the fruit resembles the melon in flavour and the musk in odour, and is considered a great delicacy by the Americans. Another species, Astrocaryum Ayri, has very hard wood, which is much used for bows and similar purposes, where hardness and toughness are required. The fibres of the leaves of Astrocaryum vulgare are much valued for fishing nets. These are known as Tucum palm nets.

ASTROLABE, from two Greek words signifying "to take the stars." It has an earlier and a later meaning. As used by Ptolemy, it may stand for any circular instrument used for observations of the stars; but in the sixteenth and seventeenth centuries it signified a projection of the sphere upon a plane, being used in the same sense as the word planisphere. To this small projection, which had a graduated rim, sights were added for the purpose of taking altitudes; and in this state it was the constant companion and badge of office of the astrologer. In later times, before the invention of Hadley's quadrant, a graduated circular rim with sights attached, called an astrolabe, was used for taking altitudes at sea.

ASTROLOGY. If this word were used in a sense analogous with that of geology or theology, it would mean simply the science of the stars; while astronomy might mean the science of their order and arrangement. But the term long signified the discovery of future events by means of the position of the heavenly bodies.

It has fortunately long been unnecessary to produce any arguments against this pretended science to educated persons, but it may be useful to show a few of its details. Works seriously professing to inculcate and defend the principles of astrology are not only sold but bought with avidity. One or two popular almanacks still give astrological predictions. This may be a mere matter of amusement with the more enlightened, but it is to be feared that there are some who play with edge-tools in reading these fooleries.

Our old English writers, particularly the dramatists, cannot be well understood without some information upon the leading terms and principles of this art; which, therefore, may be as lawfully studied as the mythological history of Jupiter and the "Metamorphoses" of Ovid.

The science which, under the name of astrology or some term of equivalent meaning, found universal belief among all the nations of antiquity except the Greeks, and also prevailed through the whole world of the middle ages, is based upon the supposition that the heavenly bodies are the instruments by which the Creator regulates the course of events in this world, giving them different powers according to their different positions. This is the description of the more learned astrologers; for we need hardly say that the ignorant have made the stars themselves the agents, just as the image of any deity has generally come in time to be regarded by the vulgar as the deity himself. The arguments against astrology are, first, that it is selfcontradictory; secondly, that its predictions are not borne out by facts. To see the first of these we must describe the leading principles of the art.

In the following globes the circle projected horizontally represents the horizon, the double circle the meridian, and the other four circles are drawn at equal distances from the meridian and horizon, through the north and south points of the latter, thus dividing the whole heavens, visible and invisible, into twelve equal parts. Let these circles remain immovable, while the diurnal revolution of the globe takes place under them. The twelve divisions are called the twelve houses of heaven, and are numbered in the order in which they would rise, if the circles accompanied the diurnal revolution. Every heavenly body passes through the twelve houses in twenty-four hours, but is not always in the same house with the same stars, except at the equator. For it is evident that, in order to have two bodies always in the same house, the revolution must take place round the north and south poles of the heavens, which poles are in the horizon only to a spectator on the equator itself. The principal point attended to in each house is the part of the zodiac which occupies it; and the place of any planet in the house is the distance of the body from the cusp, or boundary circle, measured on the zodiac. The houses have different powers. The strongest of all

marriage; the eighth, of death; the ninth, of religion; the tenth, of dignities; the eleventh, of friends; the twelfth, of enemies. Each house has one of the heavenly bodies as its lord, who is stronger in his own house than in any other, as is but fit; and of two planets, equally strong in other respects, he who is in the strongest house is the stronger. Now conceive all plants, animals, minerals, countries, &c., parcelled out under the different planets, which exercise their influence in abundance of different ways, according to the houses they may happen to be in for the time, and their positions relatively to each other, the result will be as good an idea of the mysteries of astrology as it is worth anybody's while to obtain.

That the ancient system of astrology contained the most contradictory assertions may be made evident in very few words. The position of the heavens at the time of birth settled every man's character of body and mind, the various fortunes he would meet with, and his relative positions with regard to friends and enemies. Thus, every one who was born at or very near the same time as Alexander the Great, in the same country, would have a right to expect a somewhat similar career; and twin brothers could never fail to have the same horoscope, and therefore the same success in life. To take a case that might have occurred: Suppose two men had engaged to throw dice against each other for their whole fortunes, and that they went the night before to consult different astrologers in the same town. To them it would not be necessary to tell their names or exhibit their horoscopes; the present position of the heavens would be sufficient for pointing out a favourable hour, and if both astrologers worked by the same rules, as they ought to do, they would both arrive at the same result-that is, the same would be recommended to both inquirers, though one of them must certainly lose.

The astrologers never made any allowance for the precession of the equinoxes. Thus, though the constellation Aries is now in the sign Taurus, and the influences of its stars ought to have moved with them, we find that the astronomical Aries, or the first thirty degrees of the ecliptic, is used for the constellation. For astrology this or any other error is of little consequence, but such a practice would be fatal to astronomy.

The art is at present under the ban of the law, in order

that designing persons may have at least one access stopped to the pockets of the credulous. By the 1 James I. c. 12, sorcery of all species was prohibited, though it does not appear certain that this term included astrology; but by the vagrant act, 5 Geo. IV. c. 8, s. 4, all "persons pretending to tell fortunes, or using any subtle craft, means, or device, by palmistry or otherwise, to deceive and impose upon any of his Majesty's subjects," are rogues and vagabonds-that is, punishable by any magistrate with three months' imprisonment and hard labour.

The history of astrology, at least up to the middle of the fifteenth century, is very nearly that of astronomy, since the latter branch of the science, except among the Greeks, was mostly cultivated for the sake of the former. Hence to astrology, as to alchemy, we owe many really useful discoveries. There is no question that the necessity which the astrologer lay under, of being ready, at any moment, to lay down the positions of the heavenly bodies, produced great numbers of useful tables and observations; and the Greek works which have been preserved by the Arabs were valued principally for the use to which their mathematics could be turned in astrology. The origin of the science is beyond the reach of history, nor is it much worth while to collect all that is known on this point. It certainly came into Europe from the East, where it is mentioned in the earliest records of every nation. The Chinese are said to have placed it on the same footing with agriculture and medicine; the Chaldeans cultivated it sedulously, and the invention is attributed to them by Suidas; and the Hindus have long regulated the most important actions of their lives by the stars. Among the Egyptians it was of great antiquity; but it is not mentioned in the books of Moses, unless included in "magic" or sorcery, which probably it was. The books of Isaiah and Jeremiah allude directly to it in several places, as does also that of Daniel. During the Captivity the Jews appear to have learned the art, and from that time probably, but certainly in the earlier centuries of the Christian era, became much addicted to it.

In Greece, at least during the classical ages, astrology found no reception; nor do we trace any marks of it even in the earlier astronomical writers of that country. The system was little in harmony with the allegorical mythology which prevailed there, and the oracles afforded perhaps sufficient nourishment to the appetite for the marvellous. But among the Romans astrology was cultivated with avidity from the time of the conquest of Egypt, in spite of several edicts of the senate; and in the second century the whole world was astrological.

All the followers of Mohammed are and have been astrologers. The predestinarian doctrines of their system render the transition easy and natural; for, as we have seen, the science of astrology is based upon the notion of the necessity of human actions. The establishment of the Moors in Spain, and the crusades, caused the introduction or the increased cultivation of the art among the descendants of the Gothic barbarians who destroyed the Roman empire. But the predestinarian principle assumed a modified form, more consistent with the belief of the Roman Catholic Church. It was said that the stars only incline, but cannot compel; which position, while it left the will free, was a convenient explanation of any failure in the predictions. The Greek and Roman Christians of the earlier centuries had in many instances received the whole of astrology; in others, the modified belief above mentioned. St. Augustine argues against astrology altogether. The church, in its public capacity, condemned the art in the first councils of Braga and Toledo, and in the Decretals. The doctrine of astrology was among the errors imputed to the Priscillianists. But many Roman Catholics in later times adopted the same opinions, and among them churchmen of the highest rank, such as Cardinal d'Ailly (died in 1425), who calculated the horoscope of Jesus Christ. The

astrology of comets, which is hardly yet out of date, has even been recognized by a pope. In the fifteenth century Calixtus III. directed prayers and anathemas against a comet which had either assisted in or predicted the success of the Turks against the Christians.

The establishment of the Copernican system was the death of astrology, which survives now as a mere toy, or as a tool ready to the hands of unscrupulous knaves wherewith to juggle the foolish.

ASTRONOMY signifies "the laws of the stars," and is applied generally to all that relates to the motions and theory of the heavenly bodies, as well as of the earth. If we except general terms, such as science, there is perhaps no single word which implies so many and different employments of the human intellect.

The work of the astronomer begins in the observatory, where means are provided for noting the positions of the stars. We shall therefore confine ourselves here to a slight sketch of the annals of astronomy, and a few general considerations. There are two classes of observations. The first is that of known bodies, of which the places are so nearly determined that no question remains except about quantities less than a second of time, or its corresponding quantity, fifteen seconds of space; and for this class the consideration what phenomena shall be observed is made to rest entirely upon the instruments-those phenomena being preferred, for the observation of which the steadiest instruments can be made. These move only in the meridian, and the star is waited for. The second class of observations, such as those of comets, double stars, and all mere appearances, which require an instrument that can be pointed to any part of the heavens, or can be made to follow a star, is performed by telescopes which are made to revolve with the heavens.

The second division of astronomical labour is the department of the mathematician only. The observations as they come from the instruments are subject to all the errors of the latter; and no perfect instruments can be constructed. The best circle that can be made is slightly oval; the best pivot that can be turned will not be truly cylindrical. The question now comes, in what manner to compare different species or sets of observations, so that the discordances themselves shall point out the quantity and quality of the instrumental errors; and how from thence to derive the corrections necessary for future observations; also, how to choose the time and manner of observation, so that any particular error, whether of instruments or theory, shall be least if the observer be desirous of avoiding it, or greatest if he wish to detect and measure it. Every-day experience shows that there is no better test of the progress of observation than the discovery of new instrumental errors, provided only the quantities in question become less and less. The angular error which now sets an observer to work to correct his result is less than the six-hundredth part of that which would have been required to annoy Ptolemy or Hipparchus. And in speaking of an instrument we may consider the observer himself as a most material part, on the combined power of whose eye, ear, and judgment the correctness of the observation depends. It is hardly to be expected that, even under precisely the same circumstances, two observers should note the same phenomenon so as to agree within a small fraction of a second; and recent experiments on phenomena noted with both the eye and hand have demonstrated the existence of small differences between different observers, attributable only to their different habits of perception or physical constitution.

When observations have been as nearly as possible freed from instrumental errors, the next step would be, if we could imagine a system of astronomy only in its infancy, with instruments as near perfection as our own, to deduce, by combination of mathematical reasoning and calculation,