Thomas S. Negus was an immigrant from England who began making and selling chronometers in New York in 1848. The firm was trading as Thos. S. Negus & Co. in 1864 and T. S. & J. D. Negus in 1869, and was described as "probably the most prolific American chronometer manufacturer" up through the first quarter of the 20th century. Negus was still a going concern in 1961. In addition to chronometers, Negus offered a wide range of instruments for nautical use.
Ref: Marvin Whitney, The Ship’s Chronometer (Cincinnati, 1985), pp. 341-343.
T. S. & J. D. Negus, Illustrated Catalogue and Price List of Nautical & Optical Instruments, Manufactured and Imported (New York, 1892 and 1899).
T. S. & J. D. Negus, Illustrated Catalogue of Nautical Instruments (New York, ca. 1938).