The great idea of using a single lead screw for various pitches, by means of change gears, was Maudslay’s own. Fig. 16 shows how rapidly the idea was developed.[38] This machine, built about 1800, is distinctly modern in appearance. It has a substantial, well-designed, cast-iron bed, a lead screw with 30 threads to the inch, a back rest for steadying the work, and was fitted with 28 change wheels with teeth varying in number from 15 to 50. The intermediate wheel had a wide face and was carried on the swinging, adjustable arm in order to mesh with wheels of various diameters on the fixed centers. Sample screws having from 16 to 100 threads per inch are shown on the rack in front. Both of these lathes are now in the South Kensington Museum in London. With lathes of this design, Maudslay cut the best screws which had been made up to that time. One of these was 5 feet long, 2 inches in diameter, with 50 threads to the inch, and the nut fitted to it was 12 inches long, thus engaging 600 threads. “This screw was principally used for dividing scales for astronomical and other metrical purposes of the highest class. By its means divisions were produced with such minuteness that they could only be made visual by a microscope.”[39] [38] No. 1602 in South Kensington Museum, London. Cat. M. E. Collection, Part II, pp. 266-267. [39] “Autobiography of James Nasmyth,” p. 140. London, 1883. Some idea of how far Maudslay was in advance of his time is shown by the fact that the wooden pole-lathes in Fig. 2 represent fairly the state of the art at that time. This form had been in use in many countries for centuries. One of these wooden lathes, built in 1800, the same year as Maudslay’s lathe, Fig. 16, is also in the South Kensington Museum, and was in use as late as 1879. Similar lathes are said to be still used by chair makers in certain portions of England.[40] [40] No. 1596 in South Kensington. Museum, London. Cat. M. E. Collection, Part II, p. 264. About 1830, shortly before his death, Maudslay designed and constructed a lathe with a face-plate 9 feet in diameter operating over a pit 20 feet deep. This lathe had a massive bed and was used to turn flywheel rims. It was fitted with a boring bar and was capable of boring steam cylinders up to 10 feet in diameter. We regret that no picture of this lathe is available. It would be interesting as it would show in a striking way the development of the slide-rest and lathe in the hands of this great mechanic.