The scope of the lathe, slide-rest and operating tool, by its adaptation to cut out from a vast roll of steel a ponderous gun, or by a change in the size of parts to operate in cutting or drilling the most delicate portions of that most delicate of all mechanisms, a watch, reminds one of that other marvel of mechanical adaptation, the steam hammer, which makes the earth tremble with its mighty blows upon a heated mass of iron, or lightly taps and cracks the soft-shelled nut without the slightest touch of violence upon its enclosed and fragile fruit. The adaptation of the lathe and slide to wood-working tools will be referred to in the chapter relating to wood-working. Following the invention of the lathe and the slide-rest, came the _metal-planing_ machines. It is stated in Buchanan’s _Practical Essays_, published in 1841, that a French engineer in 1751, in constructing the Marly Water Works on the Seine in France, employed a machine for planing out the wrought iron pump-barrels used in that work, and this is thought to be the first instance in which iron was reduced to a plane surface without chipping or filing. But it needed the invention of the slide-rest and its application to metal-turning lathes to suggest and render successful metal-planing machines. These were supplied in England from 1811 to 1840 by the genius of Bramah, Clement, Fox, Roberts, Rennie, Whitworth, Fletcher, and a few others. When it is considered how many different forms are essential to the completion of metal machines of every description, the usefulness of machinery that will produce them with the greatest accuracy and despatch can be imagined. The many modifications of the planing machine have names that indicate to the workman the purpose for which they are adapted--as the _jack_, a small portable machine, quick and handy; the _jim crow_, a machine for planing both ways by reversal of the movement of the bed, and it gets its name because it can “wheel about and turn about and do just so”; the key groove machine, the milling machine with a serrated-faced cutter bar, shaping machine and shaping bar, slotting machine, crank planer, screw cutting, car-wheel turning, bolt and nut screwing, etc. As to the mutual evolution and important results of these combined inventions, the slide-rest and the planer, we again quote Nasmyth:--