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THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS
1914
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FIG. 1.-THE YERKES OBSERVATORY FROM THE SOUTHWEST
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THE YERKES OBSERVATORY
BY EDWIN BRANT FROST, Director
The establishment of a large observatory for astrophysical research in
connection with the University of Chicago was the conception of George E.
Hale, who had achieved success in his solar work with his private equipment in
Chicago known as the Kenwood Observatory. President Harper took an
active interest in the realization of the plan, which presently took shape as an
opportunity occurred for the purchase of two very perfect glass disks (crown and
flint) of 42 inches diameter, sufficient for the construction of an object-glass
of 40 inches clear aperture. These disks had been cast by the well-known
makers of optical glass, Mantois of Paris, upon order of an institution in south-
ern California, which was, however, then unable to raise the money for figuring
and mounting the telescope. The opportunity was presented by Dr. Harper
and Mr. Hale to Mr. Charles T. Yerkes, a keen business man of Chicago, of
purchasing these disks and securing the largest refracting telescope in the world.
Mr. Yerkes agreed in September, 1892, to finance the undertaking, and a con-
tract was made with the famous firm of Alvan Clark & Sons, of Cambridge-
port, Mass., for figuring the two disks, which were then in their hands, and with
Warner & Swasey, of Cleveland, Ohio, for constructing a suitable mounting.
Mr. Hale was appointed director of the new institution, and gave much
study to the plans for the instruments and building. He outlined in October,
1892, the principal lines of scientific work which would be undertaken.
The site of the observatory was selected after a careful investigation of the
available locations and after an expression of opinion had been obtained from
numerous astronomers familiar with large telescopes. On account of the
smokiness, dust, and jar, as well as the glare due to the lights of a great city, it
was at once obvious that the observatory ought not to be established within or
near the limits of Chicago. But by reason of its connection with the Uni-
versity, it was practically essential that it should not be placed more than one
hundred miles away from the other departments of the University. Tracts
of land were offered in more than twenty places in Illinois and elsewhere, but
the situation at Lake Geneva seemed to offer the advantages of freedom from
disturbance by commerce, present or prospective, and from the encroach-
ment of too numerous dwellings; together with sufficient accessibility from
the University and city. The site of 53 acres was presented by Mr. John
Johnston, Jr.; other adjacent land was later acquired by the Trustees of the
University, so that since 1907 the grounds have included about 70 acres, with
a frontage of 600 feet on the lake (where a pier for steamers is maintained in
summer).
3
1

4
THE UNIVERSITY OF CHICAGO
FIG. 2. THE 40-INCH REFRACTOR, TAKEN WITH THE RISING FLOOR NEARLY AT ITS
LOWEST POINT
The Observatory is situated about 190 feet above the level of the lake, or
1,050 feet above the sea. Its geographical position, as determined by officers of
the United States Coast and Geodetic Survey in 1900, is: Latitude, 42° 34'
12764; Longitude, 5h 54m 13 24 west of Greenwich. The building is one mile
from the post-office of the little village of Williams Bay, Wisconsin, and is a

THE YERKES OBSERVATORY
10
5
mile and a quarter from the station, at the terminus of a branch of the Chicago
& Northwestern Railway, 76 miles from Chicago.¹
In the summers of 1907 and 1908 a beginning was made in grading the
grounds of the Observatory after a plan designed by Olmsted Bros., of Brook-
line, Massachusetts. Further work in grading and planting was done in 1913.
When the original plan is completed and the planting has been carried out
as proposed, an appropriate setting will be secured for the architecturally
impressive building.
The Observatory was designed by Henry Ives Cobb, who carried out the
plans drawn up by Professor Hale in a way that successfully combined archi-
tectural effect with scientific utility. The large observatories of America and
Europe were visited by Mr. Hale before the plans were begun; the most useful
suggestions being received from the designs of the Lick Observatory and the
Astrophysical Observatory at Potsdam, Prussia. The style of the building is
Romanesque with rather elaborate details. It is constructed of brown Roman
brick, with terra-cotta ornaments to match. The shape is that of a Latin
cross, with the three towers and the meridian room at the extremities. The
long axis lies east and west, with the great tower at the west, 92 feet in diameter.
The entire length of the building in this direction is 326 feet. The two smaller
domes are on the north-and-south axis, with their centers 144 feet apart.
The basement floor contains the instrument shop, the machine shop, a car-
penter shop, a large physical laboratory adjoining a room fitted with a Rowland
concave grating, and several dark rooms for photographic work. The main
floor contains seven offices for the staff, a laboratory, computing-room, and
lecture-room, a reception room for women, a library 40X 20 feet, besides dark
rooms, chemical laboratory, and cabinets for instruments. The low attic along
the east-and-west axis is available only for storage, but an important room is
provided on the second floor between the smaller towers, called the heliostat
room, nearly 100 feet long. At the north end the roof can be slid back so that
a good view of the sky is obtained, and a heliostat can be mounted on the pier
at that point. The horizontal beam of light can then be studied in the par-
ticular manner desired in the long room, which is provided with numerous
piers. The most important piece of work thus far done in this laboratory was
the first successful measurement of the heat of the stars by Professor Ernest F.
Nichols (of Dartmouth College) in the summers of 1898 and 1900.
THE GREAT REFRACTOR
The forty-inch telescope is mounted upon a massive brick pier, which rests
upon a solid concrete foundation set in the prevalent gravel formation. The
column is of cast iron in four heavy sections. The center of motion of the
telescope is 62 feet above the ground. The length of the telescope is 63½ feet,
I
¹ Additional railway facilities are obtained by the trolley line terminating at the head of the lake
(Fontana), two miles from the Observatory, which connects with the Chicago, Milwaukee & St. Paul
Railway (Chicago and Madison line) at Walworth, Wisconsin, and with the Chicago & Northwestern
Railway (main line to Minneapolis) at Harvard, Illinois, twelve miles distant.
THE UNIVERSITY OF CHICAGO
and spectroscopic attachments can be added which increase the length by
nearly 10 feet. The instrument can be readily moved by hand, in spite of
the weight, 6 tons, of the tube, and that (total 20 tons) of all moving parts.
Electric motors are available, however, by which the instrument can be quickly
pointed toward any part of the sky. For spectroscopic and photographic work
it is necessary to correct the position of the telescope by very slight motions,
for which additional motors, controlled by the observer's hand, are provided.
With these the eye-end can be moved by an amount as small as T inch, and
to
stopped at the position desired. The driving-clock, by which the telescope is
made to follow the stars, occupies a small room in the top of the pier. Its
performance has been remarkably satisfactory during the seventeen years it has
now been in use, at temperatures ranging from -25° F. to +90° F., and under
great variations as to humidity. When the driving-weight reaches the end of
its descent within the pier, it touches a button, turning on a switch, and the
clock is wound up by a motor. By shifting a gear, the rate of the clock may
be changed to make the telescope follow either the sun, or moon, or stars.
Finely graduated circles were provided for reading off the position of the
telescope, but in practice the two coarse circles, five and eight feet in diameter,
with large graduations visible from the floor, have been found sufficient and
quicker in operation. For sighting the instrument a finder of 4 inches aper-
ture is provided, and for the spectrograph a small finder of 60 feet focus,
without tube, is used.
6
The optical quality of the telescope is of the highest order; under favorable
atmospheric conditions very faint objects have been seen with it, and close stars
separated. A German authority who has investigated the quality of many
objectives, by means of photographs taken inside and outside of the focus,
placed this at the head of the great lenses he had studied. A great telescope,
of long focal length, makes very exacting demands upon the atmosphere, far
more than is the case with a smaller instrument. Consequently a casual
visitor would very probably be disappointed not to find a higher magnification
employed on an average night. In a more favorable climate, such as that of
California, the performance would undoubtedly be much better than here.¹
In the work done with the spectrograph the steadiness of the air is not of as
much consequence, as unfavorable conditions merely protract the exposure
without injuring the quality of the plate. For visual observations of objects
which are sufficiently bright, a large iris diaphragm has recently been con-
structed in the shop, by which any desired part of the whole aperture may be
used.
The operation of the large telescope is greatly facilitated by the admirable
arrangements of the dome and rising floor, designed and constructed by Warner
& Swasey. In order to have ample room for attaching spectroscopes and other
¹ Weather at Lake Geneva.-A record is kept of the number of hours during which the 40-inch tele-
scope is in use at night. It should be understood that except for cloudy skies it is employed throughout
every night of the year. In 1908, a very clear year, it was in use during over 1880 hours, or about 52 per
cent of the total night hours. It is doubtful if many European observatories could give as good a record
of clearness.
THE YERKES OBSERVATORY
7
apparatus, it was necessary that the dome should be large, and its diameter is
90 feet. It is turned on 36 wheels by an electric motor which actuates an end-
less wire rope extending around the whole dome. The controller is on the
rising floor just at the north side of the pier. Six minutes are required for
turning the dome completely around. The rising floor is 75 feet in diameter,
and is supported by four cables running over four sheaves just under the upper
balcony and connecting with heavy counterpoises which balance a large part
of the weight of the floor (37 tons). A powerful motor, with its controller
conveniently near to that for turning the dome, supplies the power. The
floor moves through a range of 23 feet from the lower to the upper balcony.
It has to be nearly at its lowest point when an observer is looking at a star near
the zenith. In intermediate positions the floor can be quickly adapted to
the height of the eyepiece of the telescope. The opening in the dome through
which the sky is observed is 11 feet wide, and it is closed by shutters 85 feet
long. These are so well constructed that they can be very easily moved by
hand. Canvas screens, which may be raised over part of the opening, serve
to break the force of the wind.
ACCESSORIES AND LINES OF RESEARCH
The principal accessories of the telescope and the lines of work done with
each may now be mentioned. The filar micrometer is attached at the eye-end
for nearly all visual observations. It was presented by Mr. Yerkes, and con-
structed by Warner & Swasey. It enables the observer to determine very
exactly the angular separation of two objects (or points) both of which are
visible in the eyepiece at the same time, and to fix the angle made by the line
joining the points with the north-and-south direction. The micrometer has
during the past fourteen years been in use for a little more than one-half the time,
generally on three or four nights per week. With it Mr. Burnham has made a
great number of observations, most of which were utilized in his monumental
catalogue of double stars published in 1906. Mr. Barnard has similarly meas-
ured with great skill and persistence the positions of many stars in a number of
the star clusters, of the fainter satellites of our system, of nebulae and faint
comets, and has observed the most important objects suitable for visual
examination.
A very important method of using the telescope as a camera was successfully
applied by Mr. G. W. Ritchey, principally in 1900 and 1901. The photographs
obtained by him of the moon, star clusters, and some nebulae were at once
recognized as among the very best thus far secured. For this service there is
substituted, in place of the eyepiece, a plate-holder, which can be very delicately
moved either north and south or east and west, and can thus follow the slight
oscillations of the object due to the unsteadiness of our atmosphere during the
exposure. The crown and flint lenses of the 40-inch objective were of course
so figured as to be achromatic for the rays to which the eye is most sensitive,
the yellow and the green. By the interposition of a color-filter cutting down

8
THE UNIVERSITY OF CHICAGO
FIG. 3.-LUNAR CRATER THEOPHILUS AND SURROUNDING REGION
Photographed with the 40-inch refractor in less than one-half second (Ritchey).
The diameter of the large crater is 64 miles; its walls rise to a height of 18,000 feet,
and the central peaks (notice their shadows cast toward the left) are about 6,000
feet high.
the blue and the violet rays, which are not simultaneously in focus with the
visual rays, and by the use of isochromatic plates, which are sensitized for the
visual rays, a sharp photograph is obtained. A negative of a star cluster, or
other object, secured in this way when atmospheric conditions are particularly
good, is then measured under a microscope in the laboratory, and even weeks
of work can be profitably spent upon a single fine negative.
During 1904 and 1905 a large number of stellar photographs were thus
obtained by Mr. Schlesinger, who measured them most carefully in order to
determine from the plates the distances from the sun of certain selected stars.
The results were published in 1911, and are probably the most accurate thus
far attained. This work has been continued by Mr. Slocum and others.

THE YERKES OBSERVATORY
9

FIG. 4.-MARS
Photographs made on September 28, 1909, with 40-inch telescope (Barnard).
A small lens takes the place of the eyepiece and enlarges the image about three
times. Numerous exposures of 3 or 4 seconds' duration are made in quick succession
in order to catch a moment when the atmosphere permits good definition.
Note the bright spot at the left of the top of the pictures: this is the south polar
"cap," probably due to snow in the planet's polar regions; it diminishes rapidly as the
planet's summer comes on for that hemisphere.
It is not known what the large dark regions represent. They were formerly
supposed to be oceans, but this idea is now abandoned. It is thought that there are
no large bodies of water on the planet. The lighter regions are possibly deserts, and
the dark ones are possibly due to vegetation.
IO
THE UNIVERSITY OF CHICAGO
Another attachment of the telescope is a stellar photometer with which the
brightness of the stars is measured. Observations of many faint stars have
thus been made by Mr. Parkhurst.
About one-third of the nocturnal hours of the telescope, generally two nights
per week, are devoted to stellar spectroscopy. The instrument, which was
largely constructed in the shops of the Observatory, is designated as the Bruce
spectrograph, the funds for its construction and early operation having been
contributed by the late Miss Catherine W. Bruce, of New York. A photo-
graph of the spectrum of a star, accompanied by a comparison spectrum on the
same plate from metallic terminals vaporized by the passage of sparks from an
induction coil in the dome, can be measured under a microscope, and the
speed of the star in the line of sight (on the average about 10 miles per second)
can be inferred from the displacements of the star's lines from the position of
the lines due to the spark. About 5,500 photographs, or spectrograms, have
been obtained with the instrument, chiefly by Messrs. Frost, Ellerman, Adams,
Barrett, and Lee. Interesting results have come from the measurements of
the spectrograms, and some 150 spectroscopic binaries, or double stars so
close to each other that they can be separated only in this spectroscopic
manner, have been detected.
An especially important use of the great refractor has been in the study of
the sun.
The attachment generally used is the spectroheliograph, so named by
Mr. Hale, its inventor, when he brought it into successful operation at the Ken-
wood Observatory.
The instrument regularly in use here since 1903 is known as the Rumford
spectroheliograph. It is a heavy spectrograph (700 lbs.) with which, by the
motion of the plate while the sun's image is passing across the slit, pictures of
the sun's surface and surrounding prominences may be secured in monochro-
matic light, from some one line of calcium, or hydrogen, or other element which
may be particularly active on the sun. Adjustments can be so made that the
photograph will depict either the lower, the intermediate, or the upper levels
of the incandescent vapors that lie above the surface. The scarlet radiation of
hydrogen shows in a marked degree the vortices forming around a sun-spot
(which may be regarded as a storm in the sun's atmosphere), as was first found
by Mr. Hale with his fine apparatus installed on Mt. Wilson, California. Vis-
ual and photographic studies of the sun are made with other spectroscopes,
and direct photographs are also taken with the great telescope. This work
was carried on by Messrs. Hale and Ellerman, in 1903-4, then by Mr. Fox,
and from September, 1909, to July, 1914, by Mr. Slocum.
OTHER TELESCOPES AND APPARATUS
The southeast dome, 30 feet in diameter, contains the two-foot reflector, an
instrument quite as powerful for some purposes as the 40-inch telescope itself.
The silvered concave mirror was made in the optical shop by Mr. Ritchey, who
also supervised the construction of the mounting in the Observatory machine
THE YERKES OBSERVATORY
II


Ti
Star
Ti
Ti
Star
Ti
4300
4300
4400
4500
4400
4600
7 Leonis. Star and earth were separating at speed of 18 miles per second.
4500
4600
4700
4700
a Boötis (Arcturus). Star and earth were approaching at speed of 11 miles per second.
FIG. 5.-STELLAR SPECTRA PHOTOGRAPHED WITH THE BRUCE SPECTROGRAPH (Frost and Adams)
The white lines are due to titanium vaporized by an electric spark in front of the spectrograph. They furnish reference points on
every plate. The dark lines on a light background are in the spectrum of the star. From the lack of perfect coincidence of the titanium
lines in spark and star, the velocity of the star may be inferred, after positions of lines have been measured to one twenty-five-thousandth
of an inch. After correcting for the earth's velocity (in its orbit around the sun), the above stars are found to have speeds of 2 miles
per sec. (recession) and 3 miles per sec. (approach), respectively.

12
THE UNIVERSITY OF CHICAGO
FIG. 6. THE SUN, PHOTOGRAPHED WITH THE SPECTROHELIOGRAPH ON
AUGUST 12, 1903 (Hale and Ellerman)
The white blotches are areas of intensely brilliant calcium vapor, which would
be invisible on an ordinary photograph.
shop. The figure of the mirror is very perfect, and remarkably fine photo-
graphs of nebulae have been obtained with it, principally by Mr. Ritchey.
It has the great advantage over a refractor that the rays of all colors are united
in the same focus, here 8 feet from the surface of the mirror. A star of the
ninth magnitude (having less than one-thousandth of the brightness of a first-
magnitude star) can be photographed with it in one second, and the instru-
ment is exclusively used photographically. With an exposure of three hours,
vast numbers of stars will impress their images on the plate, many of which
cannot be seen at all with the 40-inch refractor. Some work on stellar spectra
has also been done with the instrument.
The northeast dome contains the Kenwood equatorial refractor of 12 inches
aperture, which, together with much valuable equipment, was given to the
University by Mr. William E. Hale, and moved here from its former location at

THE YERKES OBSERVATORY
13

FIG. 7.-COMPOSITE OF TWO PLATES MADE ON AUGUST 14, 1907 (Fox)
Showing calcium vapor as prominences at sun's edge and on the disk
Mr. Hale's residence on Drexel Boulevard, Chicago. The instrument has two
objectives, one for visual work, the other for photography, both made by Mr.
J. A. Brashear. The mounting is by Warner & Swasey. An excellent filar
micrometer, by the last-named firm, was purchased for this telescope in 1906.
The old stellar spectrograph, provided by Mr. Yerkes in the original equipment
for the 40-inch telescope, has recently been adapted for use in solar spectroscopy
with the 12-inch telescope. The telescope has been used for observations of
comets, double stars, variable stars, for direct photographs of the sun, stellar
photometry, etc.
On the main roof, between the two small domes, is housed the Brashear
comet-seeker, of six inches aperture. In the meridian room at the east end of
the building is located the broken-tube transit of 3 inches aperture, made in the
machine shop. It is used for determining the time.
At the north window of the short corridor leading to the meridian room are
the barometer, maximum and minimum thermometers, and the thermograph.
Observations are made twice a day, solely for the purposes of the Observatory,
and not for publication. A thermograph has also lately been installed on the
north side of the great dome on the outside balcony, to give a record of tempera-
ture for correction for the atmospheric refraction. No seismographs for
recording earthquakes, nor instruments for determining the state of the earth's
magnetism, are maintained at the Observatory.
THE UNIVERSITY OF CHICAGO
In an upper room has been set up an apparatus devised by Professor Hale
by which the photographs of the sun taken with the spectroheliograph can be
optically projected upon a steel globe ruled with parallels and meridians, so
that the positions of significant markings on the sun can be easily read off
without trigonometrical computation.
An important adjunct of an astrophysical observatory is its spectroscopic
laboratory, where experiments may be made to match in some degree the con-
ditions found in celestial objects, in running to earth unknown elements in their
spectra, and in various researches calculated to assist in the interpretation of the
phenomena of the heavenly bodies. Unfortunately it has not been possible to
obtain funds for keeping a physicist steadily employed. During two or three
years, principally from a gift of about $4,000 made by Mr. Yerkes, such work
was in progress. Extensive studies were made by Mr. N. A. Kent, in collabora-
tion with Mr. Hale, on the effect of heavy pressure upon the spectrum of the
spark; by Mr. Kent on the comparison of wave-length in the spectrum of the
same element when rendered luminous in the spark and in the arc; and by
Mr. H. M. Reese on the enhanced lines in spark spectra. A large spectro-
meter by Fuess has recently been added to the equipment of this laboratory.
14
In view of the very general use of photography in modern astronomy, a
laboratory for photographic research is important for an institution like this.
In the years from 1903 to the end of 1908 such a laboratory was in successful
operation under the charge of Mr. R. J. Wallace. Particularly during the
years 1905-8, under a grant to the Observatory from Mr. George Eastman, of
Rochester, New York, Mr. Wallace was able to devote his time to research on
various problems in photography, including the adaptation and sensitization
of plates for particular purposes. Aside from the improvement of the photo-
graphic routine in the different departments of the Observatory, these investi-
gations resulted in important papers published in the Astrophysical Journal
and elsewhere.
The great optical works at Jena, having the firm-name Carl Zeiss, have
rendered great service in the development of microscopes and apparatus for
measuring photographs. Several are owned by the Observatory, the most
important being known as the "Stereo-comparator" and "Blink-mikroskop,"
purchased in 1907. This is a massive instrument in which two different nega-
tives can be examined, either at the same time or in instantaneous succession,
so that any change in position, size, or intensity of the images is at once notice-
able to the eye, and discoveries are greatly facilitated. Accurate measure-
ments of various kinds can also be made with this apparatus. Another valu-
able accessory is the Hartmann spectro-comparator, acquired at the same time,
with which two negatives of spectra can be simultaneously compared and
measured against each other. Several other measuring machines, some of
them made in the Observatory shop, are in use for the precise study of plates.
In the computing-room, calculating machines made in Europe, capable of
handling 18 figures, are principally employed for multiplication and division.
THE YERKES OBSERVATORY
15

FIG. 8.-THE 24-INCH REFLECTOR, OCCUPYING THE SOUTHEASTERN DOME
The silvered glass mirror was made by Mr. Ritchey in the optical shop, the
mounting in the machine shop of the Observatory. It will photograph stars which
cannot be seen with the great refractor.

16
THE UNIVERSITY OF CHICAGO
FIG. 9.-THE GREAT NEBULA IN ORION, PHOTOGRAPHED WITH THE 24-INCH
REFLECTOR (Ritchey)
This inconceivably large mass of gas, chiefly hydrogen, helium, and nebulum
(not yet found in the earth), is a feature of the constellation Orion.
As the original equipment of the Observatory was chiefly limited to the
40-inch and 12-inch telescopes, much remained to be done in fitting out the
institution for its best efficiency. The Trustees of the University appreciated
the wisdom of the recommendation of the Director, and provided from the
start for maintaining an instrument-maker and machine shop, the machines of
which were chiefly donated from the Kenwood Observatory. In this way the
equipment has been gradually increased, kept in repair, and perfected. At
times, when special gifts were available, three men have been employed in the
shop. The principal apparatus constructed have been these: the two-foot
reflector, the Snow horizontal telescope, the Bruce spectrograph, the transit
instrument, a spectroheliograph, a coelostat for eclipse use, a quartz spectro-
graph for the two-foot reflector, and many smaller instruments and attach-

THE YERKES OBSERVATORY
17

FIG. 10. NEBULA IN TRIANGULUM (Messier 33), PHOTOGRAPHED WITH THE 24-INCH
REFLECTOR (Ritchey)
The spiral structure can readily be seen. Its distance from the earth is not
less than that of the surrounding stars, which, it should be recalled, are all suns, pre-
sumably not smaller and perhaps much larger than our own sun.
THE UNIVERSITY OF CHICAGO
ments. In the carpenter shop a great number of patterns have been made, and
special cabinets of various kinds have been constructed for negatives, charts,
and other valuables.
18
The optical shop was a particular feature of the early operation of the
Observatory. This was in charge of Mr. Ritchey, and by himself, or under his
direction, a great number of mirrors of the highest optical quality, flat and con-
cave, including the two-foot reflector, were made. During the first two years
the work was chiefly on the great five-foot mirror, under a gift from Mr.
William E. Hale. As the University was finally unable to accept the terms of
gift and to provide a mounting and building for this instrument, it later became
a part of the equipment of the Mt. Wilson Solar Observatory of the Carnegie
Institution at Pasadena. After being finished at the Pasadena optical shop,
and being provided with a fine mounting and dome on Mt. Wilson, one of the
best sites for astronomical work yet found, it came into operation at the
beginning of 1910 and is undoubtedly the most perfect instrument of its kind
in the world.
HORIZONTAL TELESCOPE
Owing to the great convenience of operation of a horizontal coelostat tele-
scope for solar work where massive spectroheliographs must be attached and
removed, Mr. Hale early began the construction of such an instrument. The
first one had barely been completed, in a temporary wooden and paper struc-
ture outside of the Observatory, when it was burned (December 22, 1902) from
the sparks of the high-potential apparatus used for the comparison spectrum.
A 30-inch plane mirror and a 24-inch concave mirror, made in the optical shop,
were destroyed, together with the driving-clock and all but the heavy castings
of the coelostat. A few months later Miss Helen M. Snow, of Chicago, made a
gift of $10,000 in honor of her father, the late George W. Snow, for reconstruct-
ing the instrument. A wooden building was erected 600 feet north of the
Observatory, and by great activity in the optical and machine shops it was
possible formally to open the Snow telescope in October, 1903.
Having been interested in the possibilities of solar research under the more
perfect atmospheric conditions of southern California, Mr. Hale, in the next
year, obtained a grant of $10,000 from the Carnegie Institution of Washington
for an expedition for solar research from the Yerkes Observatory to Mt. Wilson,
California. The Snow telescope was safely transported thither and mounted
in a steel and canvas building, which experience showed to be more suitable
than the wooden structure. The results obtained were so satisfactory and so
promising for the future, that the Carnegie Institution decided to establish
its own observatory there. An arrangement satisfactory to the donor and all
others interested was later made whereby the Snow telescope was purchased
by the Solar Observatory, the money thus returned to the University of Chicago
being used to buy the stereo-comparator, and $5,000 being established as the
Snow fund, from the interest of which instrumental equipment can be pur-
THE YERKES OBSERVATORY
19
chased. This was the first endowment fund provided specifically for the use
of the Observatory. In this connection it may be stated that in his will Mr.
Yerkes made a bequest for the maintenance of the Observatory of $100,000,
a first portion of which was received from his estate in 1913.
In 1908 the eclipse coelostat was mounted in the Snow building in con-
nection with an autocollimating spectrograph, and a powerful instrument for
research in the solar spectrum was secured at small additional cost.
BRUCE PHOTOGRAPHIC TELESCOPE
In 1897 in response to a presentation of the advantages of such an instru-
ment by Mr. Barnard, Miss Catherine W. Bruce, of New York, placed in his
hands, as a gift to the University of Chicago, the sum of $7,000 for the con-
struction of a telescope especially designed for the photography of the large
areas and extended objects in the sky, particularly the Milky Way and comets—
a field in which Mr. Barnard has been a particularly successful pioneer. A
number of years were spent in the endeavor to secure a lens which should fully
meet the ideal requirements. A fine 10-inch doublet, constructed by Brashear,
was finally accepted, in 1900, and a special mounting was designed and built
by Warner & Swasey. The instrument was set up in April, 1904, in a neat
wooden building (erected from interest on the Bruce fund), 350 feet southwest
of the great dome of the Observatory. In addition to the 10-inch (focal
length 50 inches), the mounting also carries a 61-inch Voigtländer doublet, a
5-inch visual guiding telescope, and generally a 31-inch portrait lens. Many
photographs of the Milky Way, showing good definition over a field of 50
square degrees, have been obtained by Mr. Barnard. In 1905 he spent nine
months at Mt. Wilson (altitude nearly 6,000 feet) in photographing the Milky
Way, particularly those southern portions not to be reached at Lake Geneva.
This trip was made possible by a grant from Mr. J. D. Hooker, of Los Angeles.
The Carnegie Institution of Washington has lately made a grant for the purpose
of publishing an atlas of reproductions of these pictures of the Milky Way,
and the work is now in progress. Of the comet Morehouse, discovered on
plates taken with the Bruce telescope by Mr. Morehouse on September 1,
1908, Mr. Barnard secured no less than 350 negatives.
Another photographic lens of special value is the Zeiss doublet, made of
glass particularly transparent to ultra-violet rays, of 5.7 inches aperture and
32 inches focal length. The stellar images it produced when slightly out of
focus were found to be disks of remarkably uniform intensity. By measuring
the intensity of these disks under the Hartmann "surface photometer" Mr.
Parkhurst has attained an exceedingly high degree of accuracy in stellar pho-
tometry. An objective-prism of the same transparent glass and of the same
aperture as the lens is provided for the doublet and makes possible the study
of the spectra of the stars which are within the field of view. It has also been
useful for photographing the spectra of comets. The Zeiss doublet is used on

20
THE UNIVERSITY OF CHICAGO
100
Oxy
FIG. 11. THE BRUCE PHOTOGRAPHIC TELESCOPE AS TEMPORARILY SET UP IN THE
CORRIDOR OF THE YERKES OBSERVATORY
It is now located in the small dome to the southwest of the Observatory.
With this Professor Barnard has obtained many unsurpassed photographs of the
Milky Way and of comets.

THE YERKES OBSERVATORY
21

FIG. 12.-A SMALL PORTION OF THE MILKY WAY IN CEPHEUS, PHOTOGRAPHED WITH
THE BRUCE TELESCOPE ON SEPTEMBER II, 1904 (Barnard)
EXPOSURE 6 HOURS AND 40 MINUTES
As will be seen in this picture, the Milky Way consists of innumerable faint stars
(in reality distant suns) separately indistinguishable with the naked eye, which are
distributed irregularly in the sky. Only three or four of the stars on this plate can
be seen with the naked eye.
22
THE UNIVERSITY OF CHICAGO
a mounting and in a small building belonging to Mr. Parkhurst, located 1,000
feet north of the Observatory.
The power-house, which also furnishes the steam heat (largely exhaust)
for the main building, is situated about 750 feet northeast from the center of
the large dome. It was included in the original gift of Mr. Yerkes. Its equip-
ment is in duplicate, consisting of 8X10 Ideal engines, directly connected with
Siemens & Halske dynamos, of capacity 200 amperes at 125 volts, which fur-
nish current for the motors in the shops, for the great dome and rising floor,
for the 30-foot dome, and for all the general lighting and dark-room lamps of
the Observatory. The water for all purposes of the institution is obtained from
the lake by an electric pump at the shore operated by current from the power-
house, and is stored in a 30,000 gallon tank near the power-house.
Questions are so often raised as to the cost of the equipment that a brief
statement may be given here. The land originally given was valued at $30,000.
The cost of the completed object-glass of the great refractor was $66,000; of
the telescope mounting itself, $55,000; of the dome and rising floor, $45,000;
and of the remainder of the Observatory building, including the southeast
dome and the power-house and its equipment, about $150,000. The instru
ments and equipment of the Kenwood Observatory, with its dome, the gift
of Mr. William E. Hale and his son, were valued at $30,000. The Bruce
telescope and building cost about $9,000; the Snow telescope and building,
$10,000. About $15,000 have thus far been spent on grading and planting.
In response to the numerous calls for lantern slides, transparencies, and
prints from astronomical negatives made at this Observatory, it became
necessary several years ago to arrange for supplying them to teachers, lecturers,
and others interested. A young man is employed in preparing these repro-
ductions, which are sold at a price to cover their cost, through the medium
of the University of Chicago Press. A catalogue of such slides, etc., including
a total of about 600 subjects, has been printed, and is sent on request by the
University of Chicago Press.
PUBLICATIONS
Current results of investigations at the Observatory are published in various
journals, American and foreign. Those of an astrophysical character gener-
ally appear in the Astrophysical Journal, of which the director of the Observ-
atory is an editor, published ten times a year by the University of Chicago
Press. The Carnegie Institution of Washington has published several separate
volumes by members of the staff, two of which have been already referred to.
Others are: Researches in Stellar Photometry by J. A. Parkhurst; The Rotation
Period of the Sun by George E. Hale and Philip Fox; Measures of Proper
Motion Stars by S. W. Burnham. The University authorities have not yet
been able to provide a regular fund for the issue of the formal quarto Publica-
tions of the Yerkes Observatory, and these are therefore much in arrears. Only
two volumes have so far been issued: I (1900), pp. 296, A General Catalogue

THE YERKES OBSERVATORY
23
FIG. 13.-HALLEY'S COMET AS PHOTOGRAPHED WITH BRUCE TELESCOPE
ON MAY 29, 1910 (Barnard)
The plate was exposed for two hours. The observer kept the telescope constantly
pointed on the comet, following its motion among the stars, which caused the elonga-
tion of the star images. The tail of the comet, as shown on this plate, was about
7 million miles long. It was composed of luminous vapors, chiefly hydrocarbons.
THE UNIVERSITY OF CHICAGO
of 1290 Double Stars Discovered from 1871 to 1899, by S. W. Burnhan.; II (1904),
pp. 413, papers by Messrs. Burnham; Barnard; F. R. Moulton; Frost and
Adams; Hale, Ellerman, and Parkhurst; Ritchey; and Laves.
A valuable work by Professor Hale entitled The Study of Stellar Evolution
was published by the University of Chicago Press in 1908. It describes in
particular the methods and results of research at the Yerkes and Mt. Wilson
observatories in their relation to the general investigation of the problem of
stellar evolution.
24
INSTRUCTION
Undergraduate instruction in astronomy is not given at the Observatory.
This is provided at the University, together with thorough courses in theoretical
astronomy and celestial mechanics taught by Professors Moulton, Laves, and
MacMillan. Graduate students mpetent in observational work in astron-
omy and astrophysics are welcom
University regulations. All candi-
ment are required to work at 1
omers from other institutions fre
assistants.
may become Fellows under the usual
Doctor's degree in the depart-
the Observatory. Astron-
ere as volunteer research
The Observatory library contair
pamphlets. About 30 sentif
principally in exchs.
The pressure fo
mit visitors to see thr
for them to inspect the
from June to September,
of the year, between so and
operation of the large telesc
Several thousand visitors and
The saf
Olgervot
EDWIN B
SHERBURN
EDWARD E
JOHN A. PA
STORRS B. B..
OLIVER J. LEE,
EUDORA MAGILL,
MARY R. CALVER
CHARLES A. MANE
FLORES
FRANK
OSCA
TIFR
puter.
Computer.
LEZ, Office Secret
F

OETJEN, Day F gineer.
Y. Night Engi ser.
ENDELL, Janitor.
:
}
volumes and 4,000
regularly received,
: impossible to per-
is given, however,
ctor, on Saturdays:
luring the remander
aff demonstrate the
of the Observatory.
this opportunity.
follows (July 1, 1914):
i Director.
of Practical Astronomy.
Astronomy.
↑ Practical Astronomy.
Secretary and Librarian.
tronomy.
LIVAN, Engineer charge of 40-inch telescope.
MARF, Instrume Jaker.
OOTE, Carpenter n Supervisor of Building.
T, Photographer

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