_ ring to be rough,
owing to luminous points like mountains seen on it, till one of
these was kind enough to venture off the edge of the ring and appear
as a satellite."

In 1782 he replies with a certain concealed sharpness to the idea that
he used magnifying powers which were too high. There is a tone almost of
impatience, as if he were conscious he was replying to a criticism based
on ignorance:

"We are told that we gain nothing by magnifying too much. I grant
it; but shall never believe I magnify too much till by experience I
find that I can see better with a lower power." (1782.)

By 1786, when he returns to this subject, in answer to a formal request
to explain his use of high magnifiers, he is quite over any irritation,
and treats the subject almost with playfulness:

"Soon after my first essay of using high powers with the Newtonian
telescope, I began to doubt whether an opinion which has been
entertained by several eminent authors, 'that vision will grow
indistinct when the optic pencils are less than the fiftieth part of
an inch,' would hold good in all cases. I perceived that according
to this criterion I was not entitled to see distinctly with a power
of much more than about 320 in a seven-foot telescope of an aperture
of six and four-tenths inches, whereas in many experiments I found
myself very well pleased with magnifiers which far exceeded such
narrow limits. This induced me, as it were, by way of apology to
myself for seeing well where I ought to have seen less distinctly,
to make a few experiments."

It is needless to say that these experiments proved that from the point
of view taken by HERSCHEL, he was quite right, and that his high powers
had numerous valuable applications. He goes on to say:

"Had it not been for a late conversation with some of my highly
esteemed and learned friends, I might probably have left the papers
on which these experiments were recorded, among the rest of those
that are laid aside, when they have afforded me the information I
want."

The last sentence seems to be a kind of notice to his learned friends
that there is yet more unsaid. As a warning to those to whose criticisms
he had replied, he gives them this picture of the kind of assiduity
which will be required, if some of his observations on double stars are
to be repeated:

"It is in vain to look for these stars i