efracting telescope
in existence the object-glass being of thirty inches diameter. Even
this, however, is to be surpassed by the lens which Mr. Clark has in
hand for the Lick Observatory (California), which is to have a clear
aperture of three feet in diameter.

[11] Since the above passage was written and in type, I have seen (in
September 1884) the reflecting telescope referred to at pp. 357-8. It
was mounted on its cast-iron equatorial stand, and at work in the field
adjoining the village green at Bainbridge, Yorkshire. The mirror of
the telescope is 8 inches in diameter; its focal length, 5 feet; and
the tube in which it is mounted, about 6 feet long. The instrument
seemed to me to have an excellent defining power.

But Mr. Lancaster, like every eager astronomer, is anxious for further
improvements. He considers the achromatic telescope the king of
instruments, and is now engaged in testing convex optical surfaces,
with a view to achieving a telescope of that description. The chief
difficulty is the heavy charge for the circular blocks of flint glass
requisite for the work which he meditates. "That," he says, "is the
great difficulty with amateurs of my class." He has, however, already
contrived and constructed a machine for grinding and polishing the
lenses in an accurate convex form, and it works quite satisfactorily.
Mr. Lancaster makes his own tools. From the raw material, whether of
glass or steel, he produces the work required. As to tools, all that
he requires is a bar of steel and fire; his fertile brain and busy
hands do the rest. I looked into the little workshop behind his
sitting-room, and found it full of ingenious adaptations. The turning
lathe occupies a considerable part of it; but when he requires more
space, the village smith with his stithy, and the miller with his
water-power, are always ready to help him. His tools, though not
showy, are effective. His best lenses are made by himself: those
which he buys are not to be depended upon. The best flint glass is
obtained from Paris in blocks, which he divides, grinds, and polishes
to perfect form.

I was attracted by a newly made machine, placed on a table in the
sitting-room; and on inquiry found that its object was to grind and
polish lenses. Mr. Lancaster explained that the difficulty to be
overcome in a good machine, is to make the emery cut the surface
equally from centre to edge of the lens, so that the lens will neither
len