The graceful sandstone Washburn Observatory was a gift to the University of Wisconsin from former governor and wealthy businessman Cadwallader Washburn. The exact specifications of the telescope appear to have been determined by competitive gamesmanship between the upstart land grant university and the much older, far more august Harvard University. Apparently the president of the UW wanted to be able to look the president of Harvard in the eye and say, "Mine is bigger than yours."
The short summary of Washburn's history on the observatory's website puts it a bit more discreetly. (There's also a long summary, written for the Washburn's 100th birthday.)
On Sept 19, 1877, John Bascom, the president of UW at the time, announced that the observatory would be built and that it should be larger than the 15-inch refractor at Harvard. The observatory was started in May of 1878 with a contract with the famous Alvan Clark family to build the telescope. It was decided that the telescope would have a diameter of 15.6 inches, which would make it the third largest in the United States. James C. Watson was appointed to be the first director of the Observatory, but he died before its completion in 1881.Volunteers open Washburn Observatory for informal public viewing every summer Wednesday that the sky is 75% free of clouds, from June through August. The rest of the year, it's open the first and third Wednesdays of the month. Why not check it out tonight? The price is right, and the skies are supposed to be clear.
The telescope was used heavily from the 1880's until 1958 when the new Pine Bluff Observatory, about 15 miles from Madison, was dedicated. Today, the Washburn is primarily used for public viewing and some of the Introductory Astronomy classes.