and his sister's method of work:--

"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 20-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,
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 deg. 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 nebulae. I went to bed about one o'clock,
and up to that time he had found that night four or five new
nebulae. The thermometer in the garden stood at 13 deg. Fahrenheit; but,
in spite of this, Herschel observes the whole night through, except
that he stops every three or four hours and goes into 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 himself attend to the preparation of the
mirrors."

[Illustration: _Painted by Abbott._

_Engraved by Ryder._

FIG. 84.--WILLIAM