Evening star., 1900-09-25
DIR. PEATE's coNcAvE MIRROR.
1t is Larger Even Than the Famous
YerkeS Lens.
From the Philadelphia Ledger.


From the Philadelphia Ledger.
While on his way to the late conference
of astronomers and astrophysicists at Will
liams bay, Wis, the Ledger's astronomical
correspondent was privileged to spend a
day at Greenville, Pa, with the Rev. DR..
John Peate. the creator of the huge specu-
lum designed for the rejecting telescope of
the American University at Washington.
His ministerial career for upward of
forty-five years-the doctor is now in his
seventy eighth year-has been exceedingly
fruitful, and he has held the most impor-
tant position within the bounds of the Erie
conference of the Methodist Episcopal
Church 1t was during the session of this
body, under the presidency of Bishop John
F. Hurst that DIR. Peate's crowning optical
work had its inception. The bishop was
securing subscriptions to the fund for the
endowment of the projected American Uni
versity, when he was startled by the an
nouncement of one of the ministers that
Dr. Peate, who was seated by his side,
would contribute his skill toward the con-
struction "of the greatest silver-on-glass
rejecting telescope in the world"
The doctor had devoted his spare time
for many years to the study of the difficult
process of grinding and polishing concaye
mirrors, and. entirely unaided by extrane-
Gus suggestions, had completed a number
of specula, ranging in diameter from six
to thirty inches. One of his twelve-inch
mirrors is mounted in an observatory in the
rear of his house.
The extraordinary offer was entertained
for a year before 1t was accepted; but on
July 15, 1895, the critical work was COM
menced upon a rough disk sixty-two inches
in diameter and seven inches thick. furnish
ed by the Butler glass works. Heretofore all
such costly molds had been imported; but,
both because of patriotic and economic rea-
sons, the Butler people We're induced to
make the attempt to produce the largest
glass disk ever designed for telescope pur-
poses. Other parties had refused to under
take it. or else required an installment of
several thousand dollars. Four separate
pourings were made into a mod with an
iron bottom and a wrought iron rim, and
all proved unsuccessful, the disk break
ing during the anneaiing; but the fifth
was triumphant owing to luminous sug-
gestion of the doctor, and at the end of
two weeks 1t was found to be properly an
nealed and without fracture. When trans
ported to Greenville and carried to the shop
prepared for 1t dozen men carried 1t to
the turntable upon which 1t was to receive
the treatment necessary to transform it
into a vast concave mirror.
A piece of ground had been purchased in
the suburbs of Greenvills and shop erect
ed with testing gallery some eighty feetin
length. The concrete foundation and the
brick chimney were the work of the doc
tors own hands. AT one side of the shop.
facing the testing gallery, was the turn
table, pierced with many auger holes for
purposes of ventilation On this lay car
petite bed of the great disk. A gas en-
gine of four horsepower revolved the ta-
BILE and crane supported the cast iron con-.
vex grinding tool, weighing 800 pounds,
made in Greenvilie. which the doctor In
cessantly plowed across the surface of the
mirror as he moved around It.
An hour or two of such treatment 50 dis
turbed tho equilibrium of the glass that 1t
was usually suffered to remain at rest until
the next morning. when. by means of q