DeLisle's Reflecting Clinometer. The clinometer was used for initial surveying & layout of roadways (military) in difficult terrain. Marked: "Troughton & Simms / London / 1915 / No. 1578" This Clinometer (ca. 1915) by Troughton & Simms is a variation of the Burel Reflecting Hand-held Level & may be used as such by the appropriate setting of the index arm. The Burel Level was modified by Alfred Cooke (Thomas Cooke & Sons) in the late 1860's at the suggestion of General A.De Lisle by the addition of a graduated counterweight to the lower limb. Different gradients (1:5 to 1:50) could be set by an index on the arc with its own counterweight. The small pocket device is suspended from a ring by the fingers or suspended from the thumb of one hand or from a hook on a pole. The instrument comes to rest vertically by the pendulum motion of the counterpoise weight. A triangular mirror reflects the observer's eye & the reflected image is used as a height index against which a distant target plate is elevated on a graduated rod to eye level. The height is read off the rod. Troughton & Simms was a British instrument-making firm, formed when Edward Troughton in his old age took on William Simms as a partner in 1826. It became a limited company in 1915 and in 1922 it merged with T. Cooke & Sons to form Cooke, Troughton & Simms. The firm produced hundreds of astronomical instruments such as mural circles, transit circles, sextants, and other astronomical instruments for observatories around the world.