Introduction
Francis Gladheim Pease was one of the original staff members of the Mount Wilson Solar Observatory when it was formed in 1904. His most important contribution to the Observatory was his expertise in the design and use of astronomical instruments. Together with George W. Ritchey, Pease designed most of the equipment for the new Observatory. His most significant work was in the design of the 100-inch Hooker Telescope, the 20-foot and 50-foot Interferometers, and the 200-inch Hale Telescope. In the field of astronomical observations, Pease is best remembered for his collaborations with Albert A. Michelson, the Nobel Laureate physicist at the University of Chicago. Together, they developed new experiments for determining the diameters of stars, the velocity of light, and the non-existence of the "ether." Nevertheless, Pease will be noted for having been a major twentieth-century figure in the field of astronomical instrument design.
Pease was born on January 14, 1881, in Cambridge, Massachusetts, to Daniel and Katherine Bangs Pease. He did not reside long in Cambridge, however, for shortly after his birth the family moved to Highland Park, Illinois. There his father was a businessman and justice of the peace. One of five children, Pease attended high school at Highland Park and matriculated at the Armour Institute of Technology in Chicago. While in school Pease would work evenings at Petitdidier's optical shop. Here he received his training in the field of instrument design and construction. Pease's skills soon surfaced and before long Petitdidier could recommend the young man to G. W. Ritchey, the optician at Yerkes Observatory. Ritchey could use Pease in his shop and employed him upon the latter's graduation from Armour with a B.S. in mechanical engineering in 1901. At Yerkes, Pease learned the trade of optical work and engineering but also took part in astronomical observations, skills which would be needed during the early years at Mt. Wilson. Pease also met his future wife, Caroline T. Furness, during his last year at Yerkes. They were married in 1905, one year later.
The director of Yerkes, George Ellery Hale had planned to establish a solar observatory on Mt. Wilson, and in 1904 he obtained funding from the Carnegie Institution of Washington to move the Snow Telescope from Yerkes to the California mountain. Pease was one of the men (along with Ritchey, Walter S. Adams, and Ferdinand Ellerman) called from Yerkes to assist in this task. When Mt. Wilson Observatory was created as a separate institution in December, he stayed on to work there, leaving his position at Yerkes.
Pease's early work at Mt. Wilson dealt with engineering and construction tasks. As a result, he does not appear very much in the early Annual Reports of the Director. Nevertheless, he was an important figure at the Observatory, designing, with Ritchey, most of the early telescopes and structures on the mountain. He was mainly, if not totally, responsible for the design of portions of the Snow Telescope, the 60-foot and 150-foot Solar Tower Telescopes, the 60-inch and 100-inch Telescopes, the 50-foot Interferometer, as well as Hale's Solar Laboratory in Pasadena. Pease also designed a hypothetical 300-inch telescope in 1926, much of which was incorporated in the early planning of the 200-inch Hale Telescope on Palomar. Indeed, after 1930 until his death, Pease spent half his time on the design of the Hale Telescope. Astronomically, Pease is best remembered for his collaborations with A. A. Michelson. Michelson was often a Research Associate at Mt. Wilson where he would prosecute his researches on the velocity of light and stellar diameters. The latter experiment was one of the first uses of the 100-inch Hooker Telescope. Michelson and Pease attached a 20-foot long interferometer beam onto the telescope tube. By pointing the telescope at a nearby star and adjusting the distance between mirrors on the beam, they could interferometrically determine the physical diameter of the star. The success of this method in 1920 prompted Pease to construct a dedicated 50-foot interferometer on Mt. Wilson in 1928 to extend the scope of the stellar diameter research. Unfortunately, the device proved to be not sensitive enough to succeed with more distant stars.
As mentioned above, Michelson was also interested in redetermining the velocity of light. Using the distance from equipment on Mt. Wilson to a mirror on Mt. San Jacinto and back, as well as other locations, Michelson and Pease began their attempts in the mid-1920s. Unsatisfied with the results, they turned their efforts to constructing a mile-long tube at the Irvine Ranch in Santa Ana, California. Evacuating the tube, they used it as their light path in the velocity of light experiment. This work began in 1930, but Michelson died shortly thereafter. Pease, with the assistance of Fred Pearson of Chicago, continued the experiment to its successful conclusion in 1934. In a related matter, Pease in 1929 recreated the Michelson-Morley ether drift experiment using a light path 85 feet long, once again obtaining the famous negative result. Pease's papers contain a great deal of data on the velocity of light and ether drift experiments.
Other astronomical tasks that occupied Pease's research time were in taking direct photographs of the Moon, star clusters, and nebulae. He was also involved in the determination of the rotation of a spiral nebula [galaxy] by spectrographic means. In the 1920s, Pease was on the Committee for Study of the Surface Features of the Moon, established by the Carnegie Institution of Washington. After 1904, he spent almost all of his life at Mt. Wilson and Pasadena, passing away in the latter city on February 7, 1938. Only two weeks later his friend and director, George Ellery Hale, also died.
Although Pease was involved with the astronomical research of the Mt. Wilson Observatory, his most significant contribution, as noted above, was to the design and construction of the telescopes that dot the summit of the mountain. The 100-inch Hooker Telescope, the largest in the world from 1917 to 1948, was largely his design. As Walter Adams (second Director of Mt. Wilson) said, "The 100-inch telescope in particular remains as an illustration of a simple and efficient type of instrument constructed almost wholly in accordance with his design." Pease's status in the history of astronomy is best summed up by Berendzen and Hart: "In astronomical research, Pease made important, although not pioneering, contributions; in instrument design, however, he was a leading figure of the twentieth century."
From the guide to the Francis Gladheim Pease Papers, 1901-1938, (The Huntington Library)
