on; but at the seventh time the
polish came up beautifully, with scarcely a scratch upon the surface.
Stopping my work one night, and it being starlight, I thought I would
try the mirror on a star. I had a wooden frame ready for the purpose,
which the carpenter had made for me. Judge of my surprise and delight
when I found that the star disc enlarged nearly in the same manner from
each side of the focal point, thus making it extremely probable that I
had accidentally hit on a near approach to the parabola in the curve of
my mirror. And such proved to be the case. I have the mirror still,
and its performance is very good indeed.

"I went no further with this mirror, for fear or spoiling it. It is
very slightly grey in the centre, but not sufficiently so as to
materially injure its performance. I mounted it in a wooden tube,
placed it on a wooden stand, and used it for a time thus mounted; but
getting disgusted with the tremor and inconvenience I had to put up
with, I resolved to construct for it an iron equatorial stand. I made
my patterns, got them cast, turned and fitted them myself, grinding all
the working parts together with emery and oil, and fitted a
tangent-screw motion to drive the instrument in right ascension. Now I
found the instrument a pleasure to use; and I determined to add to it
divided circles, and to accurately adjust it to the meridian. I made
my circles of well-seasoned mahogany, with slips of paper on their
edges, dividing them with my drawing instruments, and varnishing them
to keep out the wet. I shall never forget that sunny afternoon upon
which I computed the hour-angle for Jupiter, and set the instrument so
that by calculation Jupiter should pass through the field of the
instrument at 1h. 25m. 15s. With my watch in my hand, and my eye to
the eye-piece, I waited for the orb. When his glorious face appeared,
almost in a direct line for the centre of the field, I could not
contain my joy, but shouted out as loudly as I could,--greatly to the
astonishment of old George Johnson, the miller, who happened to be in
the field where I had planted my stand!

"Now, though I had obtained what I wanted--a fairly good
instrument,--still I was not quite satisfied; as I had produced it by a
fortunate chance, and not by skill alone. I therefore set to work
again on the other disc of glass, to try if I could finish it in such a
way as to excel the first one. After nearly a year's work I found that
I