Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1890-07-16

observer In consequence Of this change,
the trustees. In 1857, invited 8. j. Langley
to assume the Office OF direotorj but II was
not until 1860 that the equipment was In
such state OF iorwardness as TO permit sys-
tematic observation, such as has since been
uninterruptedly maintained.
The Observatory 10 situated on the high
ground just north OF the most populous part
Of the city Of Allegheny, about 400 Ieet
above the Ohio river and 1,150 feet above
sea level. The original building was ~
feet In length and consisted Of o principal
story and basement, the facade looking
toward the south, and being divided into
central dome with two wings. Additions
have been made from time to time, and the
newer part. which adjoins the eastern wing,
extends in northerly direction SS feet. The
material is brick, excepting the dark
room." physical laboratory, for investiga-
tions in light and heat, which is of wood.
The revolving dome (having an internal d.
ameter OF 20 feeD is OF wood and iron.
FIRsT-oLAss EQUIPMENTS.
Beneath the dome is the principal instru-
ment, the equatorial, of Is inches aperture
(with an excellent objective by Clarke, the
mounting being by Fitz, of New York;,
with hour circle, reading to seconds of time,
declination circle reading to ten seconds OF
arc, and clock movement controlled by
Bonds system. The instrument has also a
position filar micrometer, polarizing solar
eye piece, star spectroscope with two prisms
OF Higgins pattern, large and small
grating spectroscope, and accessories for at
taching rejecting telescope (employing no
lenses whatever) for special heat researches
for attaching an optically plane mirror to
the polar axis (thus forming Fahrenheit
heliostat), and for converting the inverted
telescope into great equatorially mounted
spectroscope.
In the western wing is the transit-r room,
containing an instrument OF four-inch aper-
ture by Simms, a standard barometer by
Green, the sidereal clock by Frodsham, and
the principal meantime clock BY Howard.
Both clocks, as we'll as the observer at the
meridian instrument, or the equatorial, can
be placed in electric connection with the
rest Of the building, and also With the lines
oftelegraph connecting the Observatory with
the city, 50 that beats of the clock can at
few moments notice be transmitted to any
part of the country-those OF the sidereal
clock for the determination Of longitude,
and those OF the meantime clock for sup
plying time to near or distant cities and to
railroads.
In the small hall connecting this room
with the dome is o stand for the galvano.
meter when this 10 used In connection with
thermo- electric apparatus, attached to the
equatorial IN diffcrential measurements of
the heat from different parts of the sun.
From this hall access Is also had to the
self-registering and other Thermometers. In
the east wing 10 the room containing the
ohronograph, various pieces Of electric ap.
paratus, q third clock, and chronometers. II
10 occupied by the assistant In charge Of the
time service.
THE SUN STUDIED.
The north wing contains the private study
Of the director, the library (Which has also
been used ~ workroom and study for one
OF the assistants), and, In an extension (eon.
strpeted In 1881, VI the cost Of Mr.. William
Thaw, with the exception Of $500 contributed
by Dr. q. q. Hussy), q sleeping room, O
small workshop, al aleeve fitted up with O
cabinet Of shelves and drawers Of instru-
ments, and the dark ROOM" or physical
laboratory. The latter 10 provided with two
stone tables, on which are mounted galyan-
emeters OF great delieaey, and three stone
piers In line with each other, on which are
placed various instruments for researches
In solar physics, which do not form part of
the equipment proper Of the Observatory,
The principal OF these, the spectrobolomete
Constructed from designs OF the director tor
the study Of invisible radiations) stands In
the center Of the room, and receives sunlight
through an aperture In the north wall from
the mirror of large Fouoault siderostat.
This last important instrument Is placed
upon a pier OF masonry outside the building,
but connected with 1t by platform, and
protected from the weather by "rolling
house." 1t carries 12-inch optically
plane silvered glass mirror, by Clarke, and
was made by Hilger, Of London. 1t Is in
constant use.
The equatorial Is mainly used in the
study OF the suns surface, of which daily
drawings on a scale OF eight inches to the
solar diameter have been made for several
years. Beside these drawings, others on q
much larger scale have been made, on IA
vorAble occasions, by the aid of the polar
izing eye-piece. The larger part have never
been published, but some of them have fur
nished valuable information in regard to
the minute structure of the solar photo
sphere. Researches upon the relative
thermal, luminous and actinic intensities of
different parts OF the suns disk, have been
carried on with thermopiles and special op-
tical devices; and these are now being
greatly extended by the use of the new bolo-
metric and spectroscopic apparatus.
TIME DISTRIBUTION.
A mention OF the Observatory's work
would be incomplete without some account
of its system Of time-distribution introduced I
by Prof Langley in 1859. Previous to that
date, time had been sent in occasional in
stances from American obserYatories tor