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THE ANN ARBOR TELESCOPE 195 ern sky; therefore the observer decides to work on a star to the south. He starts a one-hour exposure. Within ten minutes the smoke has shifted and is crossing directly in front of the telescope, making necessary an increase of exposure time by perhaps 50 per cent. When at last the exposure is finished, the observer starts work on a northern star. Yes, you guessed it! In ten minutes or so the smoke is crossing the northern field. A less obvious but very real type of interference is due to the inevitable smog that hangs over any city. This was almost nonexistent when the 37-inch was new and Ann Arbor a small town. With the growth of the city and increased industrial activity, the smog has become appreciable. N SPITE OF the many handicaps, the efficiency of our recording of star spectra has increased considerably over the years. The gains are due to three main improvements. 1. In 1936 an evaporated coat of aluminum was substituted for the former chemically deposited silver coating of the 37-inch mirror. Silver is as good as aluminum when fresh, but it tarnishes rapidly and renewal twice a year was necessary. An aluminum coat is still fairly good after two years, but we usually renew it every year. This change alone has gained us a factor of about two in efficiency. 2. In 1949 the surfaces of prisms and lenses in the spectrograph were given a coating that greatly reduces losses of light transmission due to reflections from the surfaces. This gained us a factor of about two and a half. 3. The sensitivity of photographic plates has been increased by a factor of about two since twenty years ago. Taken all together, these gains mean a factor of about ten in efficiency of recording. But over against this we must set the deterioration of observing conditions due to smoke-both the power plant and the general city smog. These are estimated to cut the efficiency in half. The result is a net gain of five over the observing in 1911. Still, this means that the 37-inch is now able to do what it would have taken an 80-inch to accomplish fifty years ago. F OR MANY YEARS the 37-inch was the Observatory's only major instrument. When it was new, stellar spectroscopy was still a burgeoning field of research, and many interesting discoveries were yet to be made. even among the brightest stars. It is very fortunate that the study of spectra was chosen as the main area of research. Had a program requiring direct photography been started, the increase of sky brightness would have put us out of business more than twenty years ago. But such a single-purpose program as stellar spectra is too narrow for a major observatory today. We have branched out into several other fields. In 1927 the Lamont-Hussey Observatory was established at Bloemfontein, South Africa, for the discovery and measurement of southern double stars. Professor Hussey had planned this program but did not live to see the observatory become a reality. The observing with the 27-inch refractor was carried on for many years by R. A. Rossiter until his retirement in 1953. After several years of alternating idleness and occasional use by visiting astronomers, this distant station has recently been reactivated, and work on double stars is again going forward. The 1930's saw the development of the McMath-Hulbert Observatory for solar research, making the University of Michigan a leader in that field. After an interruption due to World War II, theoretical astrophysics was strongly emphasized under the direction of Leo Goldberg (Director from 1946 to 1960). During his administration the Schmidt camera, 24 inches aperture, was installed at the so-called Portage Lake site (on Peach Mountain, about a mile from the WUOM station). This instrument can be used not only for direct photography, but for low-dispersion spectroscopy when a large prism is mounted in front of it. Thus it can supplement the work of the 37-inch when necessary or desirable. Finally, the radio telescopes were installed on Peach Mountain, further broadening the astronomical work of the University. However, the
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