As there was no science to which they devoted so much attention, there were none in which they made so many discoveries. Their Caliphs were particularly distinguished for their knowledge and patronage of this science. They soon found that Ptolemy had stated the obliquity of the ecliptic a little too great; and, after many observations, found it to be nearly what it is at present.

The Caliph Almansor the Victorious, who ascended the throne in 754, ranks among the first of their astronomers. Haroun, his grandson, who reigned from 786 to 809, sent a present to Charlemagne of a water clock, in the dial of which were twelve small doors, forming the division of the hours. Each of these doors opened at the hour it marked, and let out little balls, which, falling on a bell of brass, struck the hours. The doors continued open till 12 o'clock, when twelve little knights, mounted on horseback, came out together, paraded round the dial, and shut all the doors. This clock at that time astonished all Europe.

After Haroun, his son Al Maimon succeeded to the throne. He also cultivated the study of astronomy. In his time there lived several celebrated astronomers, among whom was Alfragan, who composed several books on astronomy; and from his facility in calculation, he was surnamed the Calculator.

Albatégni was also among the greatest of the Arabian astronomers. He found the year to contain only two minutes less then what it was found to be by Dr. Halley six hundred years after.

After the Arabs had conquered the greater part of Spain, in the year 1020, they built there many observatories to conduct their observations. Alhazen, one of their astronomers, has left a treatise on Optics, which contains the first established theory of refraction and twilight which we have.

Among the Persians, also, there have been many eminent astronomers. They made many observations to discover the real length of the solar year, which they fixed at 365 days six hours. One of their chief astronomers was the famous Ulugh Beg, grandson of Tamerlane; he not only encouraged the sciences as a sovereign, but was himself reckoned one of the most learned men of his age. To determine the latitude of Samarcand, it is said he employed a quadrant, the radius of which was one hundred and eighty feet!*

He composed a catalogue of the stars, and several astronomical tables, the most perfect then known in the east. He was assassinated by his own son.

From the year 800 till the beginning of the fourteenth century, almost all Europe was immersed in gross ignorance. The only people who paid any regard to science, was the Arabs that settled in Spain, some of whom have been mentioned above. Profiting by the books they had preserved from the wreck of the Alexandrian

* It is thought by many astronomers, that this must have been a gnomon instead of a quadrant.

library, they cultivated and improved all the sciences, and particülarly astronomy, in which they had many able professors.

From the beginning of the ninth century to the year 1423, when Purbachius appeared, there is no name that deserves to be mentioned as contributing to the improvement of astronomy. Purbachius was a man af great talents; he began an 'Epitome of Ptolemy's Almagest, but died before it was completed. This was executed by his friend and pupil, John Muller, commonly called Regiomontanus. This man made many observations, and collected the writings of many of the ancient astronomers. He published ephemerides for thirty years to come, wrote a theory of the planets and comets, and calculated a table of signs and tangents for every degree and minute of the quadrant. He died in the year 1476.

Nicolas Copernicus, born 1473, rose next, and made so great a figure in astronomy, that the true system discovered, or rather restored by him, has been ever since called the Copernican System. He revived the old system of astronomy taught by Pythagoras, which had been set aside from the time of Ptolemy. His understanding at once revolted against the explanations which that philosopher had given of the motions of our planetary system; and set about correcting his mistakes, by laying the foundation of what is at this day held to be the true system of the world. This system he gradually improved by a long series of observations, and a close attention to the writings of ancient authors. His first grand work was printed in 1543, under the care of Schoner and Osiander; and he received a copy of it only a few hours before his death, on the 23d May, 1543, at the age of seventy years.

After the death of this great man, there were several astronomers of considerable note, that greatly improved the science; but the only one that claims particular notice was Tycho Brahe, a Danish nobleman, who was the inventor of a new system, a kind of semi-Ptolemaic, which he vainly endeavoured to establish instead of the Copernican. His numerous works shew that he was a man of great abilities; and it is to be regretted that he sacrificed his talents, and perhaps his inward conviction, to superstitious considerations. He restored the earth to its fancied immobility, and made the sun and moon revolve round it; but the planets he made to revolve round the sun, which was a still more absurd hypothesis than that of Ptolemy. But we ought to forgive this error, or rather weakness, in return for the many observations and discoveries with which he enriched astronomy. No man ever made more observations than Tycho Brahe.

Contemporary with Tycho flourished several eminent astronomers, among whom was the famous Kepler. To him we owe the true figure of the orbits of the planets, and the proportions of the motions and distances of the various bodies which compose the solar system. The three great Laws of Kepler may be said to be the foundation of all astronomy. Kepler was born in 1571, and died in 1631.

Galileo was the next person who rendered any very important services to astronomy. He was the first who applied the telescope

to astronomical observations, and with it made many useful and valuable discoveries. By the observations and reasoning of Galileo, the system of Copernicus acquired a probability almost equivalent to demonstration. By espousing the opinions of Copernicus, he drew on him the vengeance of the Inquisition, who decreed that he should pass his days in a dungeon; but he was liberated after the expiration of a year, on condition that he should never more teach or hold up the Copernican as the true system of astronomy. He was born in the year 1564, and died in 1642.

In spite of the Inquisition, or the passages in Scripture which were always brought forward as objections to the motion of the earth, the system of Copernicus gained ground every day.

Contemporary with Galileo were a number of astronomers, who contributed to the progress of the science. Baron Napier published his tables of logarithms in 1614. Bayer, also, obtaining great celebrity by the publication of his Uranometria, in which the stars were designated by the letters of the Greek alphabet, which is still the case on our celestial globes and planispheres.

Gassendi, a French philosopher, saw the planet Mercury on the sun's disc, which was the first observation of the kind. A little after this, in the year 1633, Mr. Horrox, an Englishman of very extraordinary talents, discovered that Venus would pass over the disc of the sun on the 24th November, 1639. This event he only mentioned to one friend, a Mr. Crabtree; and these two men were the only persons in the world who observed this transit, which was the first transit of Venus that had ever been viewed by human eyes. Mr. Horrox -made many useful observations about this time, and had even formed a new theory of the moon, so ingenious as to attract the attention of Sir Isaac Newton. But the hopes of astronomers, from the abilities of this extraordinary young man, were soon blasted, for he died in the beginning of the year 1640, aged twenty-four years.

Hevelius, burgomaster of Dantzic, also rendered himself eminent by his numerous and delicate observations. He founded an observatory at Dantzic, and furnished it with a great many excellent instruments, some of which were divided into so small divisions as 5. His observations on the spots of the sun, and on the nature of comets, were very numerous; and his catalogue of fixed stars, containing the longitude of above 1888, was remarkable for its accuracy. It is to him, also, we are indebted for the first accurate description of the spots on the moon.

The improvement of the telescope continued to lay open new sources of discovery. The celebrated Huygens constructed two excellent telescopes, one of twelve feet in length, and the other twenty-four, with which he discovered the fourth satellite of Saturn; which he said afterwards led him to discover the ring that surrounds that planet. Huygens was likewise the first person who applied pendulums to clocks. He died in 1695, aged 66 years.

About this time the Royal Society of London, and the Royal Academy of Paris, were established, each of which has produced

astronomers of the first order. The first person appointed to conduct the observations at the royal observatory at Paris, was Dominic Cassini, who soon after discovered the first, second, third, and fifth satellites of Saturn. He also discovered that the planets Jupiter, Mars, and Venus, turned round their axis in a manner similar to the earth. He died in the year 1712.

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The successive propagation of light, one of the most curious discoveries in astronomy, was about this time made by Roemer, a Danish astronomer. This has ever since been accounted a most essential element in astronomy, and must secure immortality to the name of Roemer.

England, at all times, produced astronomers of the first order; and at this period it had to boast of Hook, Flamstead, and Halley.

Hook was born in 1635, and died in 1702. He was not only a great observer in every branch of astronomy, but his inventive powers have been exhibited in almost every branch of science. He was the inventor of the Zenith Sector, an instrument which was used to determine whether or not the earth's orbit had any sensible parallax. He gave the first hint of making a quadrant for measuring angles by reflexion; and he, in some measure, anticipated the discoveries of Newton, by shewing that the motion of the planets resulted from a projectile force, combined with the attractive power of the sun.

Flamstead was born 1646, and died in 1720. After the Royal Observatory at Greenwich was finished, he was appointed by King Charles II. to the management of it, with the title of Astronomer Royal. He made a very great number of observations, which he has recorded in his Historia Celestis, and in the Philosophical Transactions. But the principal service he rendered astronomy, was by forming a catalogue of 3000 fixed stars.

Flamstead was succeeded, in 1719, by Dr. Halley, the greatest astronomer, says M. de la Lande, in England; and Dr. Long adds, "I believe he might have said the whole world." He was sent by King Charles II. to St. Helena, in order to form a catalogue of the stars in the southern hemisphere, which was published in 1679. While he was in the island of St. Helena, making this catalogue, he had an opportunity of observing a transit of Mercury across the sun's disc, by which he was enabled to point out the method of determining the parallax of the sun.

On his way between Calais and Paris, he obtained a sight of the famous comet that appeared in 1680, which suggested to him the idea of writing a treatise on the subject of comets, in which he investigates the orbits of these wandering bodies, and predicted the return of the one that appeared in 1759, which is the only prediction of the kind that ever was verified. It is said that during the nine years he was at Greenwich, he made 1600 observations. Halley was acquainted, either personally or by letter, with every astronomer of note in Europe then living. He died in the year 1742, aged eighty-six years; and was succeeded by Dr. Bradley, to whom we are indebted for two of the most beautiful discoveries of which the science can boast-the

aberration of light, and the nutation of the earth's axis. He also made a great many observations, in order to discover if the fixed stars had any sensible parallax. These observations are partly published, and the remainder of them are in the hands of a Mr. Abraham Robertson, to whom their publication was entrusted. Bradley died in the year 1762.

But to no individual is the science of astronomy more indebted than to the celebrated Sir Isaac Newton. This great man was born on the 25th December, 1642, at Woolstrope in Lincolnshire. His discoveries were not confined to astronomy alone; for in mathematics and natural philosophy he was equally great. His chief discovery in astronomy was the law of gravitation, by which he was enabled to account for some of the greatest phenomena in nature. His great work the Principia, appeared in 1686. This work is one of the most valuable books on physical astronomy that ever was published. His discoveries are so numerous and important in this science, that the, solar system, or that restored by Copernicus, has received the appellation of the Newtonian system.

In this country there have been several distinguished astronomers since the time of Newton, among whom may be mentioned Dr. Long, Dr. Keil, Dr. Bliss, Mr. Ferguson, Mr. Hadley, and Dr. Herschel; the latter of whom, for his many accurate observations, deserves to, be ranked among the first class of astronomers of any age or nation. In the year 1781, on the 13th of September, he discovered the planet Georgium Sidus. In the year 1787, he discovered two satellites revolving round that planet; and in 1790 and 1794, he discovered other two satellites. These discoveries of Herschel form a new era in Astronomy.

Dr. Maskelyne, the late Astronomer Royal, has likewise rendered very important service to the science. He was the first who proposed to the Board of Longitude the publishing of an Ephemeris or Nautical Almanack, which was begun in the year 1767. This almanack is still continued annually, and has been of the utmost service to navigation.

Dr. Maskelyne died a few years ago, and was succeeded by the present Astronomer Royal, Mr. Pond, who is also a man of genius, and promises to be of great service to astronomy.

On the continent also there have been many astronomers of great talents since the time of Newton, particularly in France. Among these, La Caille deserves to be mentioned with credit. He was born in 1713, and in the year 1751 he undertook a voyage to the Cape of Good Hope, for the purpose of perfecting the catalogue of the stars in the southern hemisphere. After incredible labour and exertion, he returned to Europe with a catalogue of 9800 stars, which were comprehended between the south pole and the tropic of Capricorn. In addition to these labours, La Caille calculated new tables of the Sun, made observations on the parallax of Mars and Venus, on atmospherical refraction, on the length of pendulums, and measured a degree of the meridian during his stay at the Cape: he died in the