stood in a class by themselves. Their preëminence lay not so much in novelty of design as in the standard of accuracy and quality of workmanship which they embodied. With unerring judgment, Whitworth had turned his attention first, to use his own words, “to the vast importance of attending to the two great elements in constructive mechanics,--namely, _a true plane_ and _power of measurement_. The latter cannot be attained without the former, which is, therefore, of primary importance.... All excellence in workmanship depends upon it.”[102] [102] Presidential Address. Institution of Mechanical Engineers, 1856, p. 125. The first step, the production of true plane surfaces, made while he was at Maudslay’s, was, we are told, a self-imposed task. The method of producing these, three at a time, is generally credited to Whitworth. We have already quoted Nasmyth’s statement that the method was in use at Maudslay’s and that it was “a very old mechanical dodge.” While this is probably true, Whitworth contributed something to the method, which very greatly increased the accuracy of the product. The writer is inclined to believe that that element was the substitution of _hand scraping_ for grinding in the final finishing operations. Whitworth’s paper, read before the British Association for the Advancement of Science at Glasgow in 1840, indicates this, although it does not say so directly. In this paper he specifically points out the reason why planes should _not_ be finished by grinding them together with abrasive powder in between; namely, that the action of the grinding powder was under no control, that there was no means of securing its equal diffusion or modifying its application and localizing its action to the _particular spot_ which needed it. Holtzapffel confirms this view, saying, in 1847: “The entire process of grinding, although apparently good, is so fraught with uncertainty, that accurate mechanicians have long agreed that the _less grinding_ that is employed on rectilinear works the better, and Mr. Whitworth has recently shown in the most satisfactory manner,[103] that in such works grinding is _entirely unnecessary_, and may, with the greatest advantage be dispensed with, as the further prosecution of the scraping process is quite sufficient to lead to the limit of attainable accuracy.... The author’s previous experience had so fully prepared him for admission of the soundness of these views, that in his own workshop he immediately adopted the suggestion of accomplishing all accurate rectilinear works by the continuance of scraping, to the entire exclusion of grinding.”[104] [103] Referring to the paper before the British Association, 1840. [104] “Turning and Mechanical Manipulation,” Vol. II, p. 872.