MANUFACTURES.

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Manu-

factures

XI. THE IDENTITY OP THE WORK WHEN IT IS OF THE SAME KIND.

Nothing is more remarkable, and yet less unexpected, than the perfect identity ofthings manufactured by the same Tool. If the top of a box is to be made to fit over thelower part, it may be done by gradually advancing the tool of the sliding rest; theproper degree of tightness between the box and its lid being found by trial. After thisadjustment, if a thousand boxes are made, no additional care is required; the tool isalways carried up to the stop, and each box will be equally adapted to every lid.

The same identity pervades all the arts of Printing; the impressions from the sameblock, or the same copper plate, have a similarity which no labour could produce byhand. The minutest traces are transferred to all the impressions, and no omission canarise from the inattention or unskilfulness of the operator. The steel punch, with whichthe card wadding for a fowling-piece is cut, if it once perform its office with accuracy,constantly reproduces the same exact circle.

XII. accuracy of the work when of different kinds.

The accuracy with which Machinery executes its work is, perhaps, one of its mostimportant advantages: it may, however, be contended that a considerable portion ofthis advantage may be resolved into a saving of time.

It generally happens, that any improvement in tools increases the quantity of workdone in a given time. Without tools, that is, by the mere efforts of the human hand,there are, undoubtedly, multitudes of things which it would be impossible to make.Add to the human hand the rudest cutting instrument, and its powers are enlarged:the fabrication of many things then becomes easy, and that of some possible with greatlabour. Add the saw to the knife or the hatchet, and other works become possible,and a new course of difficult operations is brought into view, whilst many of the formerdifficulties are removed. This observation is applicable even to the most perfect toolsor machines. It would be 'possible for a very skilful workman with files and polishingsubstances to form a cylinder out of a piece of steel, but the time which this wouldrequire would be so considerable, and the number of failures would probably be solarge, that for all practical purposes such a mode of producing a steel cylinder might besaid to be impossible.

The same process by the aid of the lathe and the sliding rest is the every-dayemployment of hundreds of workmen.

It is more easy to make a good circle than to produce a straight line. Of all theoperations of art, that of turning is the most perfect. If two surfaces are workedagainst each other, whatever may have been their figure at the commencement, thereexists a tendency in them to become portions of spheres. Either of them may becomeconvex, and the other concave, with various degrees of curvature. A plain surface is

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