William de Wiveleslie Abney (1843–1920), an English scientist who made many important contributions to spectroscopy and photography, devised this level in the 1870s while working for the School of Military Engineering at Chatham. W. & L. E. Gurley described it as an English modification of the Locke hand level, noting that it gives angles of elevation "and is also divided for slopes, as 1 to 2, 2 to 1, etc."
Since the main tube of this example is square, it can be applied to any plane surface. The clinometer scale is graduated to degrees, and read by vernier to 5 minutes. The inscription on the case reads "DIETZGEN."
Ref: W. & L. E. Gurley, A Manual of the Principal Instruments Used in American Engineering and Surveying (Troy, N.Y., 1893), p. 228.
C. Jones, "Sir William de Wiveleslie Abney, K.C.B., D.C.L., D.Sc., F.R.S., Hon. F.R.P.S., etc.," The Photographic Journal 61 (1921): 296–311.
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