722 
man brick, with terra cotta trimmings, is 
in the form of a Latin cross, having a 
longer axis of one hundred meters, with 
the great tower and dome at its western 
end, and with two smaller (ten-meter) 
domes at the northern and southern ex- 
tremities of the shorter axis. A meridian 
room, with double sheet-iron walls, is at the 
eastern end of the building. The space of 
thirty-two meters in the attic between the 
small towers serves as a heliostat room. 
The main floor of the building contains 
offices, computing rooms, spectroscopic 
laboratories, an instrument and a photo- 
graphic room, a chemical laboratory, a lec- 
ture room, library and reception room. 
The lower story, or basement, contains a 
concave grating room, an emulsion, an en- 
larging and a photographic dark room, 
and a constant temperature room. Very 
important features of this floor are the op- 
tical and the instrument shops, well sup- 
plied with machines and tools. Here large 
instruments are being constructed, and a 
sixty-inch glass reflector is now being 
ground by the optician. 
The great dome, twenty-seven meters in 
diameter and eighteen meters in height, is 
provided with a rising floor having a verti- 
cal range of seven meters and operated by 
electric motors. This floor is a very essen- 
tial feature in working with a telescope of 
sixty-two feet focal length and successfully 
overcomes what would otherwise be almost 
insurmountable (acrobatic) difficulties in 
observing. The massive iron and steel 
mounting of the forty-inch telescope (con- 
structed, as were the dome and rising floor, 
by Warner and Swazey), is operated by 
electric motors regulated at the eye-end. 
The driving clock controls the motion of a 
mass of twenty tons. 
The tests of the optical efficiency of the 
telescope have been thoroughly satisfactory. 
It has also been already demonstrated that 
the ‘seeing’ by day is excellent at Williams 
SCIENCE. 
[N.S. Von. VI. No. 150. 
Bay, a fortunate condition in view of the 
disturbed day atmosphere at the Lick Ob- 
servatory, but it is not to be expected that 
the night seeing can equal that at Mt. 
Hamilton. 
The northeastern dome, nine meters in 
diameter, shelters the telescope formerly at 
the Kenwood Observatory, having two 12- 
inch objectives, visual and photographic. 
The southeast tower will for the present be 
occupied by a reflecting telescope. The 
equipment of the Yerkes Observatory in 
solar and stellar spectroscopes, gratings and 
kindred apparatus is already large. The 
gifts of Mr. Yerkes have included: For the 
objective, $66,000; for the equatorial mount- 
ing, $55,000; for the dome and rising floor, 
$45,000; for the building and smaller 
domes, stellar spectrograph, steam heating 
plant and power house, engine, dynamo 
and motors, over $145,000. The fifty-five 
acres of land, valued at $50,000, was given 
by Mr. John Johnston, Jr.; the instruments 
of the Kenwood Observatory by Mr. W. E. 
Hale; and $7,000 for a 10-inch photographic 
telescope, with building and dome, by Miss 
Catherine Bruce, of New York, to whose 
liberality astronomy owes much. 
The address at the formal exercises of 
dedication was delivered in the ninety-foot 
dome, before a company of six hundred of 
the officers and guests of the University, 
by Professor J. HK. Keeler on ‘The Impor- 
tance of Astrophysical research and the 
relation of Astrophysics to other physical 
sciences.’ In a few well chosen words Mr. 
Charles T. Yerkes presented the deed of 
the institution to the President of the Trus- 
tees of the University, who responded in 
their behalf, as did President Harper for the 
Faculty. After a luncheon and inspection 
of the Observatory a special train conveyed 
the visitors to Chicago. 
On the following day, October 22d, striking 
demonstrations were given, at the Ryerson 
Physical Laboratory by Professors Michel- 
