"Troughton & Simms LONDON"
height 13.5 inches; horizontal circle 7 inches diameter; vertical arc 3.5 inches radius; needle 3 inches long; telescope 13.25 inches long; hanging level 5.25 inches
The Proprietors of the Locks & Canals in Lowell, Massachusetts, used this theodolite to lay out the canals that provided transportation and power for the textile mills in that city. It was probably made soon after 1826, when John Troughton took William Simms into partnership and began trading as Troughton & Simms. But for its lack of magnifiers, it is identical to the theodolite described in F. W. Simms, A Treatise on the Principal Mathematical Instruments (London, 1836). The horizontal circle and vertical arc are silvered, and read by verniers to 20 seconds. The scale for "Diff. of Hypo. & Base" on the back of the vertical arc is used to correlate the angle of elevation or depression with horizontal distances when surveying sloping ground.
Troughton & Simms