Jesse Ramsden, an English instrument maker, died Nov. 5, 1800. Ramsden was one of the finest scientific instrument makers in Britain in the last half of the 18th century. Two of his instruments are especially noteworthy. The first was a dividing engine, used to inscribe the measuring scales on instruments such as quadrants. Ramsden made his in the 1770s and it brought unprecedented precision to the task of dividing a circle. It was considered such an important contribution to navigation that when the Longitude Board gave out its awards for developments that helped solve the longitude problem, £615 went to Ramsden for his dividing engine. The Smithsonian Institution has one of Ramsden’s dividing engines, reportedly the very one that won a share of the Longitude Prize (see first image above).

Ramsden’s other famous instrument is a five-foot vertical transit circle, made for the astronomical observatory at Palermo, Sicily, and commissioned by the future director at Palermo, Giuseppe Piazzi.  Piazzi used this telescope to discover Ceres, the first asteroid, in 1801. We have several of Piazzi’s star catalogs in our collection, and one (Praecipuarum stellarum, 1814), has a headpiece that depicts the circle (see second image above). Piazzi’s task was no doubt made easier by his light-footed, winged assistants. The vertical circle measures altitude, and the horizontal circle at the bottom measures azimuth. Both circles were fashioned using Ramsden’s dividing engine. The circle is still there at Palermo, although now it serves mainly as an attraction for astro-tourists (see third image above).

Dr. William B. Ashworth, Jr., Consultant for the History of Science, Linda Hall Library and Associate Professor, Department of History, University of Missouri-Kansas City