This instrument was made by Troughton & Simms of London, belonged to Columbia College (now University), and dates from around 1837. The horizontal and vertical circles are
silvered, graduated to 10 minutes, and read by verniers to 10 seconds. There is a trough for a
magnetic needle. Ref: Frederick W. Simms, A Treatise on the Principal Mathematical Instruments Employed in
Surveying, Levelling, & Astronomy (Baltimore, 1844), pp. 89-109, describes a similar
instrument, but with two vertical circles.
