Von Magellan writes to Bode concerning a visit to Herschel:[20]
"I spent the night of the 6th of January at Herschel's, in Datchet, near Windsor, and had the good luck to hit on a fine evening. He has his twenty-foot Newtonian telescope in the open air and mounted in his garden very simply and conveniently. It is moved by an assistant, who stands below it. . . . Near the instrument is a clock regulated to sidereal time. . . . In the room near it sits Herschel's sister, and she has Flamsteed's Atlas open before her. As he gives her the word, she writes down the declination and right ascension [Pg 79] and the other circumstances of the observation. In this way Herschel examines the whole sky without omitting the least part. He commonly observes with a magnifying power of one hundred and fifty, and is sure that after four or five years he will have passed in review every object above our horizon. He showed me the book in which his observations up to this time are written, and I am astonished at the great number of them. Each sweep covers 2° 15′ in declination, and he lets each star pass at least three times through the field of his telescope, so that it is impossible that anything can escape him. He has already found about 900 double stars and almost as many nebulæ. I went to bed about one o'clock, and up to that time, he had found that night four or five new nebulæ. The thermometer in the garden stood at 13° Fahrenheit; but, in spite of this, Herschel observes the whole night through, except that he stops every three or four hours and goes in the room for a few moments. For some years Herschel has observed the heavens every hour when the weather is clear, and this always in the open air, because he says that the telescope only performs well when it is at the same temperature as the air. He protects himself against the weather by putting on more clothing. He has an excellent constitution, and thinks about nothing else in the world but the celestial bodies. He has promised me in the most cordial way, entirely in the service of astronomy, and without thinking of his own interest, to see to the telescopes I have ordered for European observatories, and he will [Pg 80] himself attend to the preparation of the mirrors."
It was at this time, 1783, May 8, that Herschel married. His wife was the daughter of Mr. James Baldwin, a merchant of the city of London, and the widow of John Pitt, Esq. She is described as a lady of singular amiability and gentleness of character. She was entirely interested in his scientific pursuits, and the jointure which she brought removed all further anxiety about money affairs. They had but one child, John Frederick William, born March 7, 1792.[21]
The house at Datchet became more and more unfit for the needs of the family, and in June, 1785, a move was made to Clay Hall, in Old Windsor. The residence here was but short, and finally a last change was made to Slough on April, 3d, 1786.
The ardor of the work during these years can be judged of by a single sentence from Carolina Herschel's diary:
"The last night at Clay Hall was spent in sweeping till daylight, and by the next evening the telescope stood ready for observation at Slough."
From 1786 until his death, Herschel remained at Slough; his life, truly speaking, was in his observatory.
It is indeed true, as Arago has said in his eloquent tribute to him: "On peut dire hardiment du jardin et de la petite maison de Slough, que c'est le lieu du monde où il a été fait le plus de découvertes. Le nom de ce village ne périra pas; les sciences le transmettront religieusement à nos derniers neveux."
Herschel's first contribution to the Philosophical Transactions was printed in the volume for 1780, his last in that for 1818. Of these thirty-nine volumes, there are only two (1813 and 1817) which contain no paper from his hand, and many volumes contain more than one, as he published no less than sixty-eight memoirs in this place.
And yet it must not be thought that his was an austere and grave existence. Music, which he loved to enthusiasm, was still a delight to him. All the more that his devotion was free. The glimpses which we get of his life with his friends show him always cheerful, ardent, and devoted. Even in his later years, he had not lost a "boyish earnestness to explain;" his simplicity and the charm of his manner struck every one.