the Sun. He accordingly outlined a plan of work, in which the study of solar phenomena in all phases, and on a more extended scale than had been possible with the equipment of the Kenwood Observatory, formed an important part.

The great size of the telescope, its light-grasping power, and long focal length make it especially suitable for the measurement of faint and difficult objects, for the study of planetary markings, and for the spectroscopic observation of the stars. These considerations led to the inclusion in the plan of work of micrometric observation of difficult double stars, nebulæ, planets, satellites, comets, and stellar spectroscopy. Stellar and nebular photography, meridian observations, and various kinds of laboratory work of an astrophysical character were also included in the plan.

Professor HALE next considered the requirements of the various kinds of work intended to be pursued as dependent upon the quality of the seeing, the transparency of the atmosphere, the blackness of the sky, and the steadiness of the instrument used. After a study of the requirements, he wrote as follows concerning the selection of the site: "It is evident that in these various classes of work, the greater part do not require very good seeing; but on account of the importance of the double-star observations, and those of planets, satellites, the structure of the photosphere, etc., it was eminently desirable to choose a site at which the seeing would be the best attainable by night and by day. Some of the other researches demand a dark sky and great transparency of the atmosphere, while for still others the principal requisite is complete protection of the instruments from vibration of any kind. If there had been absolute freedom of choice, a site combining the excellent conditions for night work enjoyed at Mt. Hamilton with the good day seeing existing elsewhere would have been sought far and wide, without regard to geographical boundaries."

From a consideration of the plan of work, and the conditions necessary for the most successful prosecution of certain lines of it, it was at once apparent that Chicago, or any place in its immediate vicinity, would be an unsuitable location for the observatory. When this became generally known, numerous offers of land and other inducements to secure the observatory were made by individuals and by towns in various parts of the country. A practical consideration of no small weight in determining the location of the observatory was, that its value as a depart

ment of the university should not be materially affected. This required that it be located within a reasonable distance of Chicago, preferably within a hundred miles.

A committee of the Board of Trustees was appointed to select a site. After visiting the most promising places proposed, this committee reported in favor of accepting a tract of land offered by Mr. JOHN JOHNSON, Jr., of Chicago, situated on the northern shore, near the western end of Lake Geneva, in Southern Wisconsin. In speaking of this tract of land in its report, the committee says: "It is conceded by all concerned that no site thus far suggested combines in itself so many requirements, or any of the requirements, to so great a degree. The site is high and beautifully located. The atmosphere is clear, without danger of encroachments of manufactories, railroads, or electric lights." The Board of Trustees adopted the report of the committee, and the observatory has been built on the land given by Mr. JOHNSON. This tract contains 53 acres. The observatory stands in the midst of it. The center of motion of the great telescope is about 240 feet above the level of Lake Geneva, and about 1800 feet from its shore. The elevation of the site above sea level is about 1200 feet. It is 38 miles from Lake Michigan, and about 75 miles from Chicago. The nearest town is Williams Bay, about a mile distant. This is the terminus of a branch of the Chicago and Northwestern Railway. Lake Geneva, seven miles away, is the nearest town having electric lights. The country round about is woodland and cultivated fields, a beautiful region, already a favorite summer-residence place for people of Chicago.

When the lines of work to be pursued by the new observatory had been decided upon, and a site selected which, all requirements considered, promised to be the best, the next problem that confronted Professor HALE was, the plan of an observatory building suited to the scientific requirements and to its environment. To plan such a building was not an easy task. The new observatory was not to be one engaged predominantly with the astronomy of position, nor was it to be merely a spectroscopic laboratory. It was to combine both these lines of work on an extensive scale, and besides to be prepared to meet the needs of such other departments of research as might arise.

The subject was one of such importance that Professor HALE visited and studied the most important observatories and spectroscopic laboratories of the United States and Europe in search of

ideas to enable him to formulate plans embodying the results of experience and meeting the scientific requirements in the most satisfactory manner. The preliminary plans were completed in Berlin in February, 1894, and forwarded to the university architect, Mr. HENRY IVES COBB, of Chicago. During the following year, Mr. COBB worked out the details of the plan with great care, and without sacrificing architectural effect he conserved the scientific requirements. The plans were finally completed in February, 1895, and the work of construction, beginning in April of that year, has since gone on, with some interruptions, until the recent completion of the observatory.

The style of architecture adopted for the main building is Romanesque, with somewhat Saracenic details. The foundation. is concrete, and the constructive materials are brown Roman brick with terra-cotta ornaments of the same color. The partitions are of hollow tile, the floors and roof are supported by steel I-beams. The roof is of tile, the floor of the main hall is marble mosaic, and those of the offices and laboratories are maple. The doors and woodwork throughout the building are of antique oak. The form of the building is that of the Latin cross, with the longer axis (326 feet long) lying in an east and west direction, having the tower for the great dome (92 feet in diameter) at the western extremity, and the room for the meridian-circle (28 by 25 feet) at the eastern extremity. For the present, a transit instrument will be used in this room, but it is intended that this shall give place after a time to a large meridian circle. Towers also rise at the ends of the shorter axis of the cross. The northeast tower carries the dome (26 feet in diameter), which was formerly a part of the Kenwood Observatory, and the southeast tower is surmounted by a dome 30 feet in diameter. The 12.2-inch telescope of the Kenwood Observatory is now mounted in the northeast dome. A 24-inch reflecting telescope for stellar spectrographic work is being constructed for use in the southeast dome.

The main entrances to the observatory are on the north and south sides of the building. They are exactly alike, and both lead to the central rotunda. A long hall divides the building centrally lengthwise. The rooms of the main floor have their entrances into this hall or into the rotunda. The rooms on this floor are those designed for offices, computing, reception, and lecture rooms, library, chemical and spectroscopic laboratories, and those for