method of finding the longitude, and proposed that tables for facilitating that method should be calculated and published in the Nautical Almanac. This recommendation was adopted, and the Nautical Almanac continued to be published under his superintendence during forty-eight
successive years.
Sir William Herschel, born in Hanover in 1738, has rendered his name immortal by the discovery of a new planet beyond the orbit of Saturn, and thereby doubling the ancient boundaries of the solar system. Having settled in England at Bath, he began to devote his leisure to the construction of telescopes and the polishing of reflecting mirrors. Endowed with equal skill and patience, he soon obtained instruments superior to any that had been known before, by means of which he was led to the most brilliant discoveries that have been made in the heavens since the time of Galileo. Being employed in making a review of the sky with a powerful telescope, he perceived, on the 13th of March 1781, near the feet of Gemini, a star of the fifth magnitude, having a disk perfectly well defined, and differing in appearance from other stars which afforded the same quantity of light. On observing it with a telescope whose magnifying power was 932, he perceived its diameter was enlarged while that of the stars underwent no change. These circumstances were sufficient to draw his attention to the star, and nothing more was requisite to enable him speedily to discover that it had a slow motion. He at first supposed it was a comet, and acquainted Dr Maskelyne with the discovery. The circumstance was soon made known at Paris ; and it was gradually perceived, that as the distance of the star did not sensibly vary, it was necessary to regard it as a seventh planet. Herschel, in honour of his patron George III., gave it the name of the Georgium Sidus ; but the mythological appellation of Uranus has prevailed. On the llth of January 1787 he discovered two satellites revolving round the new planet, and subsequently found that it was accompanied by four others. It was soon noticed that Uranus had been observed by Flamsteed, Mayer, and Lemonnier, who had each supposed it to be one of the fixed stars. Their observa tions enabled Delambre to correct the elements of the orbit, and calculate tables of its motion. By means of his powerful telescopes Herschel determined the figure and rotation of Saturn, discovered the parallel belts on his surface, and perceived that the ring is double. In 1789 he discovered two new satellites belonging to this planet, revolving near the ring. From some appearances in dicated by the fixed stars, Herschel was led to conclude that the whole solar system is in motion about some distant centre, and that its direction is at present, towards the constellation Hercules, a conclusion which recent investi gations have verified. His observations on nebulae and double stars opened up a new field of research, bound less in extent, and interesting by reason of the variety of the objects it presents to the attention of the observer. The extraordinary activity with which he pursued his favourite occupations is attested by 67 memoirs communicated by him from time to time to the Royal Society.
Few individuals have contributed so much to the perfection of modern astronomy as Delambre, for many years perpetual secretary of the Academy of Sciences. Associated with Mechain, he was employed during the troubles of the French Revolution in measuring the meridian from Dunkirk to Barcelona, a labour which was prosecuted with admir able zeal in the face of innumerable difficulties, and even dangers of the most formidable kind. By an immense number of excellent observations he determined the con stants which enter into the formula deduced from theory by the profound researches of Lagrange and Laplace, and also formed a set of tables much more exact than any that had appeared before them. His Astronomic Theorique et Pratique, in three quarto volumes, contains the best rules and methods which have yet been devised for the guidance of the practical astronomer; and his llistoire, in six large quarto volumes, gives an account of every successive improvement which has been made in the science, and a full abstract of every work of celebrity which has been written respecting it, from the first rude observations of the Greeks to the end of the last century. It is invaluable to the historian, and will always attest the profound learning and laborious research of its author.
The observatory which was established at Palermo about the year 1790, under the active superintendence of Piazzi, holds a distinguished rank among the similar institutions of Europe. Piazzi, born in 1746, took the habit of the religious order of the Theatins at Milan, and finished his noviciate in the convent of St Anthony. Among his pre ceptors he had the advantage of counting Tiraboschi, Beccaria, Le Soeur, and Jacquier ; and from these illus trious masters he speedily acquired a taste for mathematics and astronomy. After holding several professorships in the colleges of the Jesuits at Rome and Ravenna, he was appointed, in 1780, professor of the higher mathematics in the Academy of Palermo. A few years after his appointment he obtained from the prince of Caramanico, viceroy of the island, permission to found an observatory, and undertook a voyage to France and England in order to provide the instruments necessary for the new estab lishment. Having procured a vertical circle, a transit, and some other instruments from Ramsden, he returned to Palermo and commenced his observations. His first care was to prepare a new catalogue of stars, the exact positions of which he justly considered as the basis of all true astronomy. In prosecuting this object he did not content himself with a single observation, but before he fixed the position of any star, observed it several times successively ; and, by this laborious but accurate method, he constructed his first great catalogue of 6748 stars, which was crowned by the Academy of Sciences of France, and received with admiration by the astronomers of all countries. His con stant practice of repeating his observations led to another brilliant result, the discovery of an eighth planet. On tho 1st of January 1801, Piazzi, searching for the star 87 of the catalogue of Mayer, cursorily observed a small star of the eighth magnitude between Aries and Taurus. On the following day he remarked that the star had changed its position, and accordingly supposed it to be a comet. He communicated his observations to Oriani, who, seeing that this luminous point had no nebulosity like the comets, and that it had been stationary and retrograded within comparatively small limits like the planets, computed its elements on the hypothesis of a circular orbit. He found that this hypothesis agreed with the observations, and other astronomers soon confirmed its accuracy. He gave the planet the name of Ceres Ferdinandea, in honour of Ferdi nand, king of Naples, in whose dominions he had made the discovery, and who proposed to commemorate the event by a gold medal, struck with the effigy of the astronomer; but Piazzi, preferring the interests of science to vain honours which could add nothing to his glory, requested that the money destined for this purpose should be employed in the purchase of an equatorial, which was still wanting to his observatory. In 1814 he published a new catalogue, extended to 7G46 stars, a splendid monument of inde fatigable zeal and activity. He made an uninterrupted series of solstitial observations from 1791 to 1816, for tho purpose of determining the obliquity of the ecliptic, which, compared with those of Bradley, Mayer, and Lacaille, in 1 750, give a diminution of 44" in a year.
