In 1836 Samuel Colt invented his revolver, and the first lot contracted for by the Government was made at the Whitney works in 1847. Mr. Colt determined about 1850 to establish his own factory, moved to Hartford, and in 1854-1855 built the present Colt’s Armory, in which the principles of interchangeable manufacture were adopted in a most advanced form. Hand work was practically eliminated and automatic and semi-automatic machinery substituted. A type of manufacturing miller, built for this work by George S. Lincoln & Company, is still known as the Lincoln miller. E. K. Root, superintendent under Colt, had a profound influence in the development of manufacturing at this time. He put the art of die forging on its present basis. At first he used a type of hammer in which four impressions were arranged in four different sets of dies. The hammers were lifted, first by a set of dogs, later by a central screw, and the operator walked around the machine, using the impressions successively. A few years later the present form of board drop was developed. Two of George S. Lincoln & Company’s men were Francis A. Pratt, superintendent, and Amos Whitney, contractor, who later founded the firm of Pratt & Whitney. In 1857 Smith & Wesson began manufacturing revolvers at Springfield along similar lines. Mr. Smith had worked in the old Whitney shops. Another firm of great influence was that of Robbins & Lawrence, later the Windsor Machine Company, in Windsor, Vt. Frederick W. Howe built there a number of machines for profile milling, rifling, barrel drilling, and is said to have designed the first “universal” miller in 1852.[163] The Ames Manufacturing Company in Chicopee, which had been founded in 1829, was also engaged in this work. By 1850 the interchangeable system began to extend its influence abroad. Robbins & Lawrence had an exhibit of interchangeable guns in the exposition at London in 1851, which attracted much attention. In 1853 a British Commission came to this country and visited the government and private armories, the Ames Manufacturing Company and Robbins & Lawrence. During the visit of this Commission at Springfield, Major Ripley, superintendent of the armory, ordered ten guns, which had been manufactured in ten successive years, from 1843 to 1853, to be stripped, and the parts to be reassembled at random. [163] Not to be confused with the Brown & Sharpe universal milling machine, which was invented by Joseph R. Brown in 1871. [Illustration: