The Hickman courier. [volume] (Hickman, Ky.) 1859-current, 1877-08-10

Richard :. Floyd, one Of the trustees
OF the Lick Trust, has Just returned from
an extended European tour. During his
absence he has talked with many scien-
tific men OF this and other countries but
almost invariably found them afraid TO
commit themselves TO an opinion as to
whether n greater Success can be obtained
with a rejecting or retracting telescope.
Prof Newcombe, of the observatory in
Washington, after his visit to Europe to
look into this matter for Mr. Lick, re-
ported warmly in favor of a gigantic re-
tractor, and forwarded complete kesti-
mates as to thecosu. He has since Changed
his opinion, however, and now recon-
mends a silver On-glass reflector OF about
seven feet diameter. Ross, HerscEels
and other celebrated telescopes have
speculum-metal refectoTs, which have
until lately been considered the best.
Now the palm is claimed for an iuven-
tion Of Leon Foucault's by which silver
in solution is deposited on glass Fou-
cault made a reflector upon this system
about thirty-one and one-hith inches in
diameter, and excellent work has been
accomplished with it. After his death,
a reflector upon this plan about four feet
in diameter was constructed for tie OBJ
servatory. Owing to s0me not thor
/ oughly explained cause tvis has not
/ proved a success, and anoti or OF the same
/ dimensions Is being constructed 70 re
/ place it. Great interest is manifested III
/ the result OF this second experiment,
which cannot be proven f5r year yet.
/ DR.. Higgins, the well known astronomer,
/ also favOrs large reflector, rs II Is better
! for spectroscopic analysis, his favorite
study. 1t is natural that he should pre-
fer a reflector as he desires to have the
! field of physical astronomy enlarged.
Theoretically a reflector of four feet in
diameter is about equal to refractor OF
twentv-six inches. The Ross reflector is
six feet in diameter, only four feet OF
which are effective, and so far 1t has not
been proven that more than four feet OF
n reflector can be made effective. The
great trouble with the reflector is that it
is very sensitive TO atmospheric changes,
while with the refractOr the difficulty
lies in the secondary spectrum The ob-
J iect-glass of the refractor Is composed OF
two glasses Joined, the outer being OF
Icrown glass, the inner OF flint. Rays
-! -5sing through the crown glass are re-
I fracted, and entering the flint glass, are
refracted. The consequence Is that per
feet achromatism is impossible, and the
difficulty of compromising these refrac.
tions increases with the size OF the object
glass. The largest refractor in the world
is that in the Washington observatory
it is twenty-six inches in diameter.
Mr.. Floyd said that after as careful al
examination as he could make, he is in
clined to believe that the best interests
of the fund vii be served, to have con
structed larger re ractor than any yet
made. This ought not TO cost, complete
more than S15O,002 Then there will be
a subsidiary reflector, about four feet in
diameter, supplied with both siIver-on'
glass and speculum metal mirrors. Such
an instrument has been offered, or rather
parties have agreed to construct one, tol
about $4,000 Tell, of Paris, will under
take to make crown and flint glass disc:
for the object glasses of a forty-inch re-
tractor for $50, 000-stipulating that he
shall he allowed two years for their con
struction. After they have lett hi
hands the optician will require about
three years more to figure these disc
mathematically,