THOMAS FREDERICK COLBY (1784-1852), British majorgeneral and director of ordnance survey, was born at St Margaret's, Rochester, on the 1st of September 1784, a member of a South Wales family. Entering the Royal Engineers he began in 1802 a life-long connexion with the Ordnance Survey department. His most important work was the survey of Ireland. This he planned in 1824, and was engaged upon it until 1846. The last sheets of this survey were almost ready for issue in that year when he reached the rank of major-general, and according to the rules of the service had to vacate his survey appointment. He was the inventor of the compensation bar, an apparatus used in base-measurements. He died at New Brighton on the 9th of October 1852.