We learn from M. Lalande* that "each time that Herschel undertakes to polish a mirror (of a telescope) he condems himself to ten, or twelve, or even fourteen hours of constant work. He does not quit his workshop for a minute, not even to eat, but receives from the hands of his sister that nourishment without which no one could undergo such prolonged fatigue. Nothing could induce Herschel to leave his work; for, according to him, if he did so it would be spoiled."

Herschel's labors in constructing telescopes were not vainly expended on useless apparatus which could exhibit no practically valuable results, for on the 13th of March, 1781, he discovered a new planet which proved to be on the confines of our system of that time. He had been engaged for more than a year in making a regular survey of the heavens, when on the evening of the day above mentioned, between ten and eleven o'clock, he saw a star which, by its apparent magnitude, attracted his particular attention. This star was the planet Uranus. The discovery was made with one of his seven-foot telescopes. This discovery was at first thought to be that of a new comet, but subsequent observations and calculations proved it to be a planet.

Dating from this important discovery, Herschel's reputation as a constructor of telescopes and as an astronomer spread throughout the world. George III., king of England, a friend to science, and much inclined to protect and patronise both men and things of Hanoverian origin, caused Herschel to be presented to him. He was charmed with the simple yet lucid and modest account which the astronomer gave of his repeated endeavors; he caught a glimpse of the glory that such an observer might reflect on his reign, and granted him a pension of three hundred guineas a year, and furnished him a residence near Windsor Castle, first at Clay Hall, and afterwards at Slough. We need hardly mention that the anticipations of George III. were most completely realized. "We

* In a memoir printed in 1783, which forms a part of the preface to tome viii des Ephémérides des mouvements célestes.

† Annuaire for 1849, p. 255.

may confidently assert," says Arago, "with respect to the garden of the little house at Slough, that it is the place, in all the world, where the greatest number of discoveries in astronomy have been made. The name of that village will never perish. Science will transmit it religiously to our latest posterity."

We have now traced the career of Herschel from his early youth to that period in his life when his pecuniary trial may be said to be ended, and he is settled in a place where, under the patronage of the king, he can devote his whole time and energy to the prosecution of his studies and observations in astronomy and kindred sciences, to which he was destined to add numerous and important discoveries. The powerful telescopes which he employed enabled him to extend the boundaries of astronomical science vastly beyond what had been accomplished before him, so that for many years he was the principal authority in that department of astronomy which is dependent on observation. Henceforth we have little else to record than the numerous discoveries which he made. But the history of science can only possess a deep interest for those who have made science their special study, and we shall, therefore, not detain the reader with any details in relation to this part of William Herschel's career. He was thirty-six years of age when he finished his first telescope, and he reached the mature age of forty-three before he made his great discovery of the planet Uranus, which brought him into general notice as an astronomer among scientific men, and procured him the patronage of the king, which enabled him to devote his time wholly to his favorite science.

We thus see that Herschel may be said to have just begun his career as a scientific man and a discoverer at a period in life when most men have completed their discoveries. But he lived to a great age, and was able for a period of forty years to devote the energies of his great mind to the advancement of science. His life thus offers us a proof of the deduction from the observation of nature, that a thing which is slow in maturing retains its strength and vigor for a correspondingly long period.

The account of Herschel's observations and discoveries is found in his memoirs, presented to the Royal Society of London, and printed in that important collection known as the Philosophical Transactions. His contributions are contained in seventy-one memoirs, which are found in thirty-seven volumes of that series-from 1780 to 1818, inclusive, excepting the years 1813 and 1816. The memoirs of Herschel form some of the principal riches contained in the publications of the Royal Society. In the year 1822, a paper of his on the position of one hundred and forty-six double stars was published in the memoirs of the Royal Astronomical Society of London.

Herschel's memoirs are, for the most part, extracts from his journals of observations at Slough, accompanied by brief remarks. These memoirs succeeded each other with great rapidity; and without the necessary explanation it may seem strange that Herschel was able to devote so much time to observation and experiment, and yet find time to write so extensively. He was enabled to do this, however, only by the help of his sister, Miss Caroline Lucretia Herschel, who went to England as soon as her brother became special astronomer to the king. She was appointed assistant astronomer, with a moderate salary. From that time she devoted her whole attention to the assistance of her brother and added through her labors not a little to his rapidly increasing scientific reputation. "Miss Caroline shared in all the night-watches of her brother with her eye constantly on the clock and the pencil in her hand; she, without exception, recorded all the observations; she afterwards made three or four copies, in separate registers; coördinated, classed, and analyzed them." Caroline Herschel, besides, had some reputation of her own as a discoverer, by the detection of several new comets, among them that of 1795, which has since been proved to be a return of Encke's comet. After the death of her illustrious brother, she retired to Hanover to the house of Johann Dietrich Herschel, a musician of great celebrity, and the last of William Herschel's brothers. She died at an advanced age (we believe about ninety-eight)

in 1848.

Alexander Herschel, William's brother, was also his assistant. Alexander possessed unusual mechanical skill, that was ever at his brother's command, which enabled him to realize, without delay, any new idea which he conceived requiring the aid of a mechanic. When age and infirmities obliged Alexander Herschel to give up his profession as a musician, he retired from Bath, his place of residence, to Hanover, where his brother William very generously provided for him a comfortable subsistence during the remainder of his days.

So celebrated a person as Herschel could not fail to attract the attention of the various learned societies of Europe, and he was accordingly elected a member of the principal academies. In the year 1786, the honorary degree of doctor of laws was conferred on him by the University of Oxford. This dignity was conferred on him without any of the usual formalities or pecuniary contributions which were customary in that learned body. In 1816, he was named a Knight of the Guelphic Order of Hanover. According to the English custom, he was henceforth called Sir William Herschel.

Sir William married Mary Pitt, the widow of John Pitt, Esq., a lady of considerable fortune, and with her he lived to the end of his days, blessed with the happiness of a congenial companion who added greatly to his domestic felicity. They had one child only, the late distinguished philosopher, Sir John Frederick William Herschel, who was born at Slough in the year 1792.

Herschel is best known to the general reader, perhaps, as the constructor of a giant reflecting-telescope forty feet in length, and four feet in diameter. This was begun in 1785, at the suggestion of the king, who provided the means for making it, and it was finished in 1789. With this great instrument he made some important discoveries, though it was rarely that the state of the atmosphere in England permitted him to use it.

Herschel introduced a very important improvement into the construction of large reflecting telescopes, known as the front view. The Gregorian reflecting-telescope contains two

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mirrors, the large one which collects the rays of light from the object, and a small one, near the upper end of the tube, which re-reflects the rays through a small hole in the centre of the large mirror, or speculum, where the eye-piece receives them before they enter the eye of the observer. In the Newtonian reflector, the small mirror is placed at an angle of forty-five degrees to the axis of the tube, and thus throws the rays through a hole in the side of the tube, where the eye-piece receives them. Herschel proposed to incline the axis of the speculum a little to the axis of the tube, so that the eye-piece can receive the rays of light at one side of the tube, and that the head of the observer will obstruct but a small portion of the light which enters the tube. This Herschel called the front view. It distorts the image somewhat, but the light lost by the second reflection in the other focus was saved by Herschel's method, and he found it very advantageous in some cases where the amount of light was small, as when making observations on the satellites of the more distant planets. In studying the solar spectrum with a thermometer, Herschel ascertained that it is prolonged on the red side far beyond the visible limits. This fact thus made known by Herschel has led to very important discoveries in our day.† He made experiments on the illuminating power of the prismatic rays, and found the greatest power for illumination to exist between the brightest yellow and the palest green. We have thus attempted to give the reader a general idea of the life and labors of Sir William Herschel. "William Herschel died, without pain, on the 23d of August, 1822, aged eightythree years. Fortune and fame never changed in him that depth of child-like candor, inexhaustible good will, and sweetness of character, with which nature had endowed him. He preserved up to his last moments all his lucidness of mind and vigor of intellect. For several years before he died he enjoyed with delight the distinguished success of his only son. At his last hour he sunk to rest with the pleasing conviction that this beloved son, the inheritor of a great name, would

*Phil. Trans. for 1800.

See Tyndal On Radiation, Smithsonian Report for 1868, p. 292.