scientific world, says Arago, saw with astonishment the unexampled
rapidity with which Herschel's works succeeded one another for many
years, they were greatly indebted for this affluence of production to
the affectionate ardour of his sister Caroline. Her enthusiasm never
failed; her industry knew no check; and her brother's fame was dearer to
her than life.

In one of her letters she describes with graphic simplicity the
"interior" at Datchet:--

"I found that I was to be trained for an assistant-astronomer;
and by way of encouragement, a telescope adapted for 'sweeping'
(or rapidly surveying a wide extent of space), consisting of a
tube with two glasses, was given [to] me. I was to 'sweep for
comets;' and I see by my journal that I began August 22nd,
1782, to write down and describe all remarkable appearances I
saw in my 'sweeps.' But it was not till the last two months of
the same year that I felt the least encouragement to spend the
starlit nights on a grass-plot covered with dew or hoar-frost,
without a human being near enough to be within call. I knew
too little of the real heavens to be able to point out every
object so as to find it again without losing too much time
by consulting the Atlas. But all these troubles were removed
when I knew my brother to be at no great distance, making
observations with his various instruments on double stars,
planets, and the like; and I could have his assistance
immediately when I found a nebula, or cluster of stars, of
which I intended to give a catalogue. I had the comfort to
see," she continues, "that my brother was satisfied with my
endeavours to assist him when he wanted another person either
to run to the clocks, write down a memorandum, fetch and carry
instruments, or measure the ground with poles,--of which
something of the kind every moment would occur."

The conscientious care and assiduous industry with which Herschel made
his measurements of the diameter of the Georgium Sidus (now called
Uranus), and his interesting observations of other planets, of double
stars with their coloured light, of cometary and nebulous appearances,
were truly remarkable; as may be seen by the various papers which
he wrote at this time for the Royal Society. In addition to all this
labour, he perfected a twelve-inch speculum of vast magnifying power
before the spring of