Unidad documental simple 139 - Letter from George Airy

4 pp.

Royal Observatory Greenwich - Sheepshanks Exhibition [see GA to WW, 30 Sept. 1856] can be divided into three parts: 1. Gravitational, 2. Geometrical Astronomy and 3. Theory and Practice of Observations. GA could do number 3, Mathison [William C. Mathison] number 2 and if Adams [John C. Adams] is around, he could do number 1. A Transit-Circle was first introduced in Greenwich, because 'a Mural Circle cannot carry a large object-glass. - But there are many distinct advantages. As a Transit, it is no better than a detached Transit, but as a Circle it holds its position much better than a Mural Circle: the same object is infallibly observed in both elements; and (probably for that reason) one observer with the Transit-Circle observes a greater number of objects than two with Transit and Mural Circle: and it saves the salary of one observer'.