The McMath-Hulbert Observatory of the University of Michigan is near Lake Angelus, about five miles north of Pontiac and fifty miles northeast of Ann Arbor. The buildings reflect the purpose and spirit of the Observatory as well as its history. The administration and office building and the three units in which the observational work is centered are functional in design and unified in purpose. They were constructed in the 1930's as the program of the Observatory expanded and as the various donors made possible new construction and equipment. The Observatory is concerned entirely with solar research, and its program is based on a battery of varied but unified solar observations, studied and analyzed by a team of experienced astronomers. The buildings and the instruments that they house have been designed and constructed to carry out this program.
The oldest building in the group is the dome that now houses the 24-inch reflecting telescope. It was in this dome, in July, 1930, that the McMath-Hulbert Observatory began operations (see Part III: The McMath-Hulbert Observatory). The development of the Observatory and its evolution from smaller equipment preceded this date. The first building and its original 10 ½-inch reflector, both of which were designed and constructed by the three men who established the Observatory — Robert R. McMath, Francis McMath, and Judge Henry S. Hulbert — were given by deed to the University on December 15, 1931. The original building, of concrete block, is octagonal and is surmounted by a dome 16 feet in diameter. The dome frame is of steel construction with an inner and an outer skin of wood separated by a 3-inch air space. The outer skin is covered with a treated waterproof canvas laid in white lead, which gives excellent temperature control. The base of the instrument pier is a concrete monolith, 4 by 6 feet, completely isolated from surface tremors. Although the original 10 ½-inch reflector has been replaced by a telescope with a mirror 24 inches in diameter, the building is essentially the same as when first constructed.
The widespread scientific interest in the Page 1676early motion pictures and in continuous records of solar activity led to plans for the construction of a second building, a solar tower, where the techniques and methods which had been used in the initial studies of the sun could be further developed and put into practice on every clear day. With the help of President Ruthven, $20,000 was secured from the Rackham Fund as an initial grant for this new project. After inspection of other solar installations and consultations with astronomers at the Mount Wilson Observatory and with H. D. Curtis, of the University of Michigan, it was deemed wise to try to build a truly major solar instrument. The cost of such a project greatly overran the initial grant, but a very substantial gift from McGregor Fund of Detroit and generous contributions from a number of individuals made the building of the 50-foot tower and its spectroheliographs possible. This extension of the Lake Angelus plant was begun in 1935. The tower was completed and in operation June 30, 1936.
The 50-foot solar tower consists of an observing room surmounted by two concentric towers and a spectrograph well dropping 31 feet into the earth beneath. A small office and an underground photographic darkroom complete the installation. The octagonal observing room at the foot of the tower proper is built of cement blocks and is approximately 28 feet in diameter. The outer tower, which serves as a windbreak and sunshade for the inner tower, and as the mechanical support of the dome, is 16 ½ feet in diameter. It is made of onequarter-inch steel plates with all joints riveted. The inner tower is 6 feet in diameter and is made of one-quarter-inch steel plates welded together. Since the two towers are structurally separate, the outer tower shields the instrumentbearing inner tower from shock and vibration. Both towers are surmounted by a single steel dome 17 ½ feet in diameter, actually the hemispherical bottom of a standard water-tower tank turned upside down.
For three years the instruments installed in the dome and in the 50-foot tower were in continuous use. Their success in the simultaneous recording of prominence motions in three dimensions and in the light of different elements showed the great desirability of adding still another simultaneous record, that of the energy changes in prominences and other solar features. In order to provide these new observations and to care for the rapidly expanding program of solar research, plans were drawn up for a new 70-foot tower telescope and for an office building. The latter was to include office space for the staff, a library, darkrooms, laboratory facilities, and a suitably equipped instrument shop. In September, 1939, McGregor Fund of Detroit made a grant of $100,000 to the University, and Dr. and Mrs. Robert R. McMath deeded the necessary land, so that the above plans could become a reality. The new installations were dedicated on May 25, 1940. They are known as the McGregor Tower and Building in memory of Tracy W. McGregor, the founder of McGregor Fund, who had a lifelong interest in astronomy.
The new building and tower are to the north of the two earlier structures. The McGregor Building, constructed of cement block, is two stories in height and covers an area of 5,600 square feet. It includes all of the facilities envisaged in the original plans. The McGregor Tower rises some 70 feet from the ground on a site at the southeastern corner of the McGregor Building. This tower follows the general plan of the 50-foot tower, with two separate, concentric steel towers. The lateral dimensions Page 1677were adjusted to be compatible with the increased height of the new tower. There is no well beneath the 70-foot tower. Instead, the light is sent horizontally through openings in the towers to spectrographs inside the McGregor Building.
In January, 1954, construction of a 50-foot focal length vacuum spectrograph was begun. The need for this special instrument, which had been demonstrated over the years, arises from the fact that a spectrograph with a long light path suffers from seeing difficulties as does a telescope when used in a dome. The spectrograph has an outer steel shell of ¼-inch steel plates 4 feet in diameter and 53 feet long. It utilizes to the fullest possible extent the superb diffraction gratings now made under the supervision of Dr. Horace W. Babcock, of Mount Wilson, and the great improvements in photoelectric detection tubes which were primarily the result of World War II. Substantial grants in aid were made by McGregor Fund, the Detroit Edison Company, and the Arthur Curtis James Foundation of New York.
Throughout this extensive building program it was unnecessary to secure the services of an architect. All of the buildings were designed and the construction supervised by Robert R. McMath, Director of the Observatory. From the time the Observatory was deeded to the University until the present, the buildings have been occupied exclusively by the regular and auxiliary members of the Observatory staff. The property has been cared for by a local caretaker now in the employ of the University of Michigan Plant Department.
From the preceding description of the manner of growth of the Observatory it is clear that the cost of the buildings cannot be determined accurately. Much of the material and many of the services were donated. It is therefore impossible to give even an estimate of the cost.
The equipment of the McMath-Hulbert Observatory is extensive and varied. The principal instruments are: 24-inch Reflecting Telescope; 50-foot Tower Telescope (Telescope focal lengths of 50, 40, 20, or 6 feet and spectrograph with focal lengths of 15 and 30 feet; Stone Radial-Velocity Spectrograph); McGregor Tower Telescope (spectrographs of Littrow and Pfund type, echelle grating, infrared spectrograph with lead sulfide cell as sensitive element); vacuum spectrograph; densitometers for intensity measurement of films and plates; instruments for the measurement of position on motion picture films; Lyot and Baird type monochromatic filters; Perkin-Elmer Infrared Spectrometer; shop equipment; fundamental machine tools of rather large size.