Evening star., 1900-09-25
Infants Department ssOpemimg.

hinged device, it was placed upon edge to
be tested by the Foucau.t method in the
adjoining gallery. Boxes of steel and nat
ural emeries, and bottles used in successive
triturations, filled several shelves of the
grinding room, while here and there a keg
of pitch was visible.
Exactly two years from the time of COM
mencing his arduous task the doctor de-
clared his work of figuring and polishing
complete, and disposed of the engine and
the bulky tools employed. The correspond
ent found the mammoth disk beautlfui
piece Of glass, with scarcely a scratch upon
it's polished surface, supported in tenn
porary cell by iron straps, and capable OF
being swung like a toilet mirror in its
frame. Its diameter is trifie above sixty
one inches and its thickness five and hVe-
SiXteenthS inches.
To try its power-although yet unsil-
vered-upon distant objects part of the
side of the shop had to be cut away, ana
this was afterward made into door for
convenient use. When in position facing
the testing gallery the opening or a door
at the farther end placed the mirror In line
with certain test objects. To move 1t to
this point from a distance of ten feet was
the work of the doctor and his visitor. who.
with block and tackle and levers and with
much perspiring shifted the cell and its
tenant of crystal weighing more than a
ton.
at a distance Of sixty-six feet, twice the
focal length of the mirror, and upon this
stood a lamp the flame of which was used
to illuminate the surface of the mirror, in
which no zones could be detected. fine
hole in metallic shield furnished an arti-
fetal star. the image Of which was thus ex-
am;ned, and the cutting off by knife edge
of the light rays and the coming on of the
gray shadow was the really critical test.
Afterward the image OF watch dial 5oO
feet away was magnified by the use OF an
eyepece, and at the distance of 1000 feet
a pin carrying hair was plainly seen. The
speculum a 40-inch pasteboard disk TO rep
resent the Yerkes lens. and the latter
seemed pigmy in comparison, and frame
house half mile distant was viewed with
such disturbances without an eyepiece that
even nailholes We're visible.
OF course the speculum is to be silvered
upon its concave surface before being placed
in it's tube, and this will have to be accom-
plished by. building a rim around its edge
to hold the silvering solution poured upon
it until precipitation has occurred 1t is
customary to partially immerse mirrors of
ordinary size face downward in the silver
ing bath, but this is impossible In the case
of large ones.
When silvered and FURNISHED this mighty
specuium will certainly gather twice as
much light as the Yerkes lens. making full
allowance for loss by reflection. 1t will be
particularly available for stellar spectre
scopy and for the photography of nebulae.
To use 1T visually plane mirror will be
placed In the center of the tube near the
sky end, and the rays reflected from the
great glass at the bottom Of the tube win
be caught by. the diagonal and elbowed out
at the side where the eyepiece viii be
placed.
The American University Is very willing
to receive funds for mounting its prize, for
which a large sum will be necessary and
would doubtless perpetuate in its observa-
tory the name Of any generous donor who
would assume the cost Of housing it ready
for astronomical work.
The famous Lord Rosse reflector has a
speculum six feet in diameter, but 1t Is
metallic, being made of an alloy Of copper
and tin, and weighs some four tons. besides
being exceedingly brittle. Visitors to the