ntion of
automatic machine-tools by the mechanical engineers about to be
mentioned, that the manufacture of the steam-engine became a matter of
comparative ease and certainty. Watt was compelled to rest satisfied
with imperfect results, arising from imperfect workmanship. Thus,
writing to Dr. Small respecting a cylinder 18 inches in diameter, he
said, "at the worst place the long diameter exceeded the short by only
three-eighths of an inch." How different from the state of things at
this day, when a cylinder five feet wide will be rejected as a piece of
imperfect workmanship if it be found to vary in any part more than the
80th part of an inch in diameter!

Not fifty years since it was a matter of the utmost difficulty to set
an engine to work, and sometimes of equal difficulty to keep it going.
Though fitted by competent workmen, it often would not go at all. Then
the foreman of the factory at which it was made was sent for, and he
would almost live beside the engine for a month or more; and after
easing her here and screwing her up there, putting in a new part and
altering an old one, packing the piston and tightening the valves, the
machine would at length begot to work.[17] Now the case is altogether
different. The perfection of modern machine-tools is such that the
utmost possible precision is secured, and the mechanical engineer can
calculate on a degree of exactitude that does not admit of a deviation
beyond the thousandth part of an inch. When the powerful oscillating
engines of the 'Warrior' were put on board that ship, the parts,
consisting of some five thousand separate pieces, were brought from the
different workshops of the Messrs. Penn and Sons, where they had been
made by workmen who knew not the places they were to occupy, and fitted
together with such precision that so soon as the steam was raised and
let into the cylinders, the immense machine began as if to breathe and
move like a living creature, stretching its huge arms like a new-born
giant, and then, after practising its strength a little and proving its
soundness in body and limb, it started off with the power of above a
thousand horses to try its strength in breasting the billows of the
North Sea.

Such are among the triumphs of modern mechanical engineering, due in a
great measure to the perfection of the tools by means of which all
works in metal are now fashioned. These tools are themselves among the
most striking results of the mec