Scientist of the Day - Great Refractor at Harvard
The 15-inch “Great Refractor” at Harvard College Observatory, Cambridge, Mass., photogravure, 1870s, courtesy of Tom Fine (hea-www.harvard.edu/~fine)
The Great Refractor, a telescope at Harvard College Observatory (HCO) saw its "first light" on June 24, 1847, meaning it was ready to view and/or photograph astronomical objects on that day. The observatory at Harvard, located on Garden St. in Cambridge, had been founded in 1839; its first director was William Cranch Bond.
The buildings of Harvard College Observatory, Cambridge, Mass., with the large dome for the Great Refractor, woodcut, 1851, courtesy of Tom Fine (hea-www.harvard.edu/~fine)
When a prominent comet appeared in 1843, and it was realized that only one American observatory had a telescope suitable for observing such an object, and that was in, of all places, Cincinnati, there was a fund-raising campaign in Cambridge that raised $25,000 to be used to acquire a large refractor from Germany.
Portrait of William Cranch Bond, painting by Cephas Thompson, 1849, Smithsonian Astrophysical Observatory, Harvard (https://timeandnavigation.si.edu)
"Great Refractor" is a loose and relative term, but it is usually considered that the first such instruments were built by Joseph Fraunhofer in Munich in the 1820s and 1830s. Two 9-inch Fraunhofer refractors were installed at Dorpat Observatory in Estonia and at Berlin Observatory (the latter used to discover Neptune in 1846); they are often considered in hindsight as being the first modern great refractors, although they did not acquire that label until later. These were achromatic telescopes, meaning the resolved images were not marred by colored fringes. Fraunhofer's achromatic refractors used two objective lenses, made of two different kinds of optical glass, each separately ground, figured, and spaced to produce sharp images that were free of chromatic aberration.
Photograph of the moon, taken with the 15-inch Merz & Mahler refractor at Harvard College Observatory, by John Adams Whipple, Feb. 26, 1852, Harvard College Observatory Stacks (Wikimedia commons)
By the time Harvard got around to ordering its own refractor, there was another German firm producing large, high-quality, achromatic refractors, Merz & Mahler, also in Munich, the heirs of the Fraunhofer firm. Merz & Mahler had built an 11-inch refractor for the Cincinnati Observatory, and were building a 15-inch achromat for the new Pulkovo Observatory near Saint Petersburg, and Bond chose to order a duplicate of the 15-inch Pulkovo refractor for Harvard. You can see images of Georg Merz, and the Cincinnati and Pulkovo refractors, at our post on Merz and our post on Friedrich G. W. von Struve, the director at Pulkovo.
The inner or “crepe” ring of Saturn (labeled x/y), newly discovered by W.C. Bond and G.P. Bond in 1850, wood engraving illustrating article by W.C. Bond, Annals of Harvard College Observatory, vol. 2, fig. 57, 1857 (Linda Hall Library)
The Harvard Merz & Mahler 15-inch refractor was called the Great Refractor from the very beginning, and it was installed on a specially built concrete pier on Observatory Hill at Harvard; the pier was called the Sears tower after its donor, which was soon graced by a dome, which as far as I know, has no name. You can see the new dome in a wood engraving of the Hill published in 1851 (second image).
Observing chair for 15-inch refractor at Harvard College Observatory, line-drawing, Annals of Harvard College Observatory, vol. 1, p. xlii, 1856 (Linda Hall Library)
The Harvard 15-inch refractor was not only the largest and finest instrument in the United States, but it was quickly adapted to photography, which had only been invented in 1839. Bond, with John Adams Whipple, used the Great Refractor to take the first photographs of the Moon (fourth image), and the first photographs of a star. Bond also used it to discover the inner ring (the "crepe" ring) of Saturn in 1850. Bond published a long article on his observations of Saturn in the second volume of the Annals of Harvard College Observatory in 1857, with many wood engravings of Saturn, its moons, and its rings, and one of them shows the discovery of the new dusky ring, which lies inside the two prominent outer rings, the A and B rings, and looks very much like a shadow. We show here a close-up view of the observation of Nov. 11, 1850 (fifth image).
“Great Refractor” at Harvard College Observatory, with observing chair in use, line-drawing, Annals of Harvard College Observatory, vol. 1, p. xxxiv, 1856 (Linda Hall Library)
Because the Harvard 15-inch refractor was so lengthy and had such a range of movement, special arrangements were needed so that the observer could keep up with the moving eyepiece. Bond designed a special observation chair which could travel in a full circle on a rail and could also move up and down. There is a line drawing in an article Bond published in the first volume of the Annals (sixth image), and you can see the chair in use in another drawing of the telescope in operation in the same issue (seventh image). I sat in that chair once, courtesy of the late and dearly missed Owen Gingrich.
The 15-inch refractor at Harvard College Observatory, Cambridge, Mass., recent photograph (hco.cfa.harvard.edu)
The Great Refractor was in use for a century, but it was soon eclipsed by the much larger refractors built by Alvin Clark and Sons right there in Cambridge (see our post on Clark and a post on the 36-inch Lick refractor). Now the 15-inch refractor is used for outreach programs for the public. It is a true historic astronomical landmark. Be sure to visit if the opportunity ever comes up, or, should we say, if the stars are ever properly aligned.
William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor emeritus, Department of History, University of Missouri-Kansas City. Comments or corrections are welcome; please direct to ashworthw@umkc.edu.
