Jonas H. Phelps (1809-1865) and William Gurley (1821-1887) were partners in the firm of Phelps & Gurley from 1845 until 1851.  In March of 1845 the firm rented a three-story brick building, No. 319, on the west side of River Street in Troy, New York.   There they manufactured surveyor's compasses, theodolites, transits, leveling instruments, goniometers, air pumps, electrical machines and apparatus to illustrate the principles of natural philosophy.  The foundry was in the basement of the building, the office and sales rooms were on the first floor, the work rooms were on the second and third floors.  Four workmen were employed, one of which was William Gurley's brother Lewis E. Gurley.  The surveying instruments made by the firm the first year of partnership did not aggregate in value more than $1,000.00.  During the second year there was a greater demand for them, as well as the other mathematical and philosophical instruments made by the establishment.  In 1849, the business had increased so much, that to facilitate the manufacture of engineering and other instruments, the firm rented part of a building on the west side of Mechanic Street, in the rear of the establishment, and there placed a small engine to move its improved machinery.  Lewis E. Gurley continued as a workman until the fall of 1847 when he entered Union College from which he graduated in June of 1851.  That same year he was admitted to partnership with Phelps and his brother William and the firm name became Phelps and Gurleys.  In February of 1852, Jonas Phelps sold his interest in the partnership, and the firm became W. & L. E. Gurley.

Reference:  Smart, Charles E.   The Makers Of Surveying Instruments In America Since 1700  Troy, New York:  Regal Art Press.  1962