The second of the linear dividing engines, built in 1854, had a graduated silver ring set into the dividing wheel. This ring was graduated at the office of the Coast Survey in Washington by William Wurdeman on a machine having an index wheel with 4320 graduations copied from the plate of the Troughton & Simms machine in London. Mr. Brown went to Washington to see the work done and was so well satisfied with it that he arranged with Mr. Wurdeman to graduate the copper ring used in the precision gear cutter which was built in 1855. Patrick Harlow, who operated this machine from about 1860 to 1910, says that it was Mr. Brown’s special pride, that it was given the honor and care due a precision machine, was located in a room by itself and carefully covered every night to protect it from injury. Long after it was supplanted by automatic gear cutters, it was used for index drilling. The formed milling cutter, which retains accurately the contour of its cutting edge through successive sharpenings, was invented in 1864 by J. R. Brown with special reference to the cutting of gear teeth. In fact, the oldest milling cutter known was used for cutting gear teeth. This cutter was made some time prior to 1782 by the French mechanic Jacques de Vaucanson and came into the possession of the Brown & Sharpe Manufacturing Company about 1895. The teeth are very fine and apparently were cut with chisels. The hole in the center is octagonal and seems to have been broached. The formed cutters came as one of the important elements in the system of interchangeable involute gears, introduced by Brown & Sharpe, based on the principles of Professor Willis. While they used both the involute and cycloidal systems, they threw the weight of their influence toward the former and were a strong factor in the general adoption of the involute form for cut gearing, as well as for the use of diametral pitch, which, as we have seen, was suggested by Bodmer in Manchester, England.