were made at a time, so that by the mutual rubbing of each on each the projecting surfaces were effaced. When the surfaces approached very near to the true plane, the still projecting minute points were carefully reduced by hard steel scrapers, until at last the standard plane surface was secured. When placed over each other they would float upon the thin stratum of air between them until dislodged by time and pressure. When they adhered closely to each other, they could only be separated by sliding each off each. This art of producing absolutely plane surfaces is, I believe, a very old mechanical "dodge." But, as employed by Maudslay's men, it greatly contributed to the improvement of the work turned out. It was used for the surfaces of slide valves, or wherever absolute true plane surfaces were essential to the attainment of the best results, not only in the machinery turned out, but in educating the taste of his men towards first-class workmanship.

Maudslay's love of accuracy also led him to distrust the verdicts given by the employment of the ordinary callipers and compasses in determining the absolute or relative dimensions of the refined mechanism which he delighted to construct with his own hands. So much depended upon the manner in which the ordinary measuring instruments were handled and applied that they sometimes failed to give the required verdict as to accuracy. In order, therefore, to get rid of all difficulties in this respect, he designed and constructed a very compact and handy instrument which he always had on his bench beside his vice. He could thus, in a most accurate and rapid manner, obtain the most reliable evidence as to the relative dimensions, in length, width, or diameter, of any work which he had in hand. In consequence of the absolute truth of the verdicts of the instrument, he considered it as a Court of Final Appeal, and humorously called it "The Lord Chancellor."

Maudslay's "Lord Chancellor"

This trustworthy "Companion of the Bench" consisted of a very substantial and inflexible bed or base of hard brass. At one end of it was a perfectly hardened steel surface plate, having an absolutely true flat or plane face, against which one end or side of the object to be measured was placed; whilst a similar absolutely true plane surface of hardened steel was advanced by means of a suitable fine thread screw, until the object to be measured was just delicately in contact with it. The object was, as it were, between the jaws of a vice, but without any squeeze -- being just free, which could be easily ascertained by feeling. These two absolutely plane surfaces, between which the object lay, had their distances apart easily read off from the scale engraved on the bed of the instrument, in inches and tenth parts of an inch, while the disk-head or handle of the screw was divided on its edge rim into hundredth or thousandth parts, as these bore an exact metrical relation to the pitch of the screw that moved the parallel steel faces of the measuring vice (as I may term it) nearer or farther apart.

Not only absolute measure could be obtained by this means, but also the amount of minute differences could be ascertained with a degree of exactness that went quite beyond all the requirements of engineering mechanism; such, for instance, as the thousandth part of an inch! It might also have been divided so far as a millionth part of an inch, but these infinitesimal fractions have really nothing to do with the effective machinery[note: I may mention another saying of Mr. Maudslay's. Besides his observation that "in going from London to Greenwich we must not go round by Inverness," he said, "We must not become too complicated with our machinery. Remember the get-at-ability of parts. If we go on as some mechanics are doing, we shall soon be boiling our eggs with a chronometer!"]

that comes forth from our workshops, and merely show the mastery we possess over materials and mechanical forms. The original of this measuring machine of Maudslay's was exhibited at the Loan Collection at South Kensington in 1878. It is now treasured up, with other relics of his handiwork, in a cabinet at the Lambeth works. While writing upon this subject it may be worthy of remark, that the employment of a screw as the means of adjusting the points or reference marks of a measuring instrument, for the ascertainment of minute distances between objects, was first effected by William Gascoigne, about the year 1648. There can be no doubt that he was the inventor of the Micrometer -- an instrument that, when applied (as he first did so) to the eye-piece of the Telescope, has been the means of advancing the science of astronomy to its present high position (See Grant's History of Astronomy, p. 453)