I got a rough disc of glass, from St. Helens, of ten
inches diameter. It took me from nine to ten days to grind and
polish it ready for parabolising and silvering. I did this by
hand labour with the aid of emery, but without a lathe. I
finally used rouge instead of emery in grinding down the glass,
until I could see my face in the mirror quite plain. I then sent
the 8 3/16 inch disc to Mr. George Calver, of Chelmsford, to turn
my spherical curve to a parabolic curve, and to silver the
mirror, for which I paid him 5L. I mounted this in my timber
tube; the focus was ten feet. When everything was complete I
tried my instrument on the sky, and found it to have good
defining power. The diameter of the other glass I have made is a
little under six inches.
"You ask me if their performance satisfies me? Well; I have
compared my six-inch reflector with a 4 1/4 inch refractor,
through my window, with a power of 100 and 140. I can't say
which was the best. But if out on a clear night I think my
reflector would take more power than the refractor. However that
may be, I saw the snowcap on the planet Mars quite plain; and it
is satisfactory to me so far. With respect to the 8 3/16 inch
glass, I am not quite satisfied with it yet; but I am making
improvements, and I believe it will reward my labour in the end."
Besides these instruments John Jones has an equatorial which is
mounted on a tripod stand, made by himself.
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