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 of Tarvin in Cheshire, and shortly afterwards entered the workshop of Maudslay & Co. in the Westminster Bridge Road, London [see ]. Maudslay soon recognised his exceptional talent, and placed him next to John Hampson, a Yorkshireman, the best workman in the establishment. Here Whitworth made his first great discovery, that of a truly plane surface, by means of which for all kinds of sliding tools frictional resistance might be reduced to a minimum. After intense and protracted labour at the problem Whitworth ended by completely solving it. The most accurate planes hitherto had been obtained by first planing and then grinding the surface. ‘My first step,’ he says, ‘was to abandon grinding for scraping. Taking two surfaces as accurate as the planing tool could make them, I coated one of them thinly with colouring matter and rubbed the other over it. Had the two surfaces been true the colouring matter would have spread itself uniformly over the upper one. It never did so, but appeared in spots and patches. These marked the eminences, which I removed with a scraping tool till the surfaces became gradually more coincident. But the coincidence of two surfaces would not prove them to be planes. If the one were concave and the other convex they might still coincide. I got over this difficulty by taking a third surface and adjusting it to both of the others. Were one of the latter concave and the other convex, the third plane could not coincide with both of them. By a series of comparisons and adjustments I made all three surfaces coincide, and then, and not before, knew that I had true planes’ (Brit. Assoc. Proc. 1840; Inst. Mechan. Engineers Proc. 1856; Presidential Address at Glasgow). The importance of this discovery can hardly be overestimated, for it laid the foundation of an entirely new standard of accuracy in mechanical construction.

On leaving Maudslay's Whitworth worked at Holtzapffel's, and afterwards at the workshop of Joseph Clement, where Babbage's calculating machine was at that time in process of construction [see ]. In 1833 he returned to Manchester, where he rented a room with steam power in Chorlton Street, and put up a sign, ‘Joseph Whitworth, tool-maker, from London,’ thus founding a workshop which soon became a model of a mechanical manufacturing establishment. The next twenty years were devoted mainly to the improvement of machine tools, including the duplex lathe, planing, drilling, slotting, shaping, and other machines. These were all displayed and highly commended at the Great Exhibition of 1851. A natural sequel to the discovery of the true plane was the introduction of a system of measurement of ideal exactness. This was effected between 1840 and 1850 by the conception and development of Whitworth's famous measuring machine. A system of planes was so arranged that of two parallel surfaces the one can be moved nearer to or further from the other by means of a screw, the turns of which measure the distance over which the moving plane has advanced or retired. Experience showed that a steel bar held between the two planes would fall if the distance between the surfaces were increased by an incredibly small amount. For moving the planes Whitworth used a screw with twenty threads to an inch, forming the axle of a large wheel divided along its circumference into five hundred parts. By this means if the wheel were turned one division, the movable surface was advanced or retired 1/500 of a turn of the screw—that is by 1/10000 of an inch. This slight difference was found successfully to make the difference between the steel bar being firmly held and dropping. A more delicate machine, subsequently made and described to the Institution of Mechanical Engineers in 1859, made perceptible a difference of one two-millionth of an inch.

By means of this gradually perfected device was elaborated Whitworth's system of standard measures and gauges, which soon proved of such enormous utility to engineers. But of all the standards introduced by Whitworth, that of the greatest immediate practical utility was doubtless his uniform system of screw threads, first definitely suggested in 1841 (cf. Minutes of Proc. Inst. Civil Engineers, 1841, i. 157). Hitherto the screws used in fitting machinery had been manufactured upon no recognised principle or system: each workshop had a type of its own. By collecting an extensive assortment of screw bolts from the different English workshops, Whitworth deduced as a compromise an average pitch of thread for different diameters, and also a mean angle of 55°, which he adopted all through the scale of sizes. The advantages of uniformity could not be resisted, and by 1860 the Whitworth system was in general use. The beauty of Whitworth's inventions was first generally recognised at the exhibition of 1851, where his exhibit of patented tools and inventions gained him the reputation of being the first mechanical constructor of the time.

In 1853 Whitworth was appointed a member of the royal commission to the New York Industrial Exhibition. The incomplete state of the machinery department prevented his