hands it became as nearly perfect as it was possible to be. In 1818,
he furnished the lathe with a slide rest twenty-two inches long, for
the purpose of cutting screws, provided with the means of
self-correction; and some years later, in 1827, the Society of Arts
awarded him their gold Isis medal for his improved turning-lathe, which
embodied many ingenious contrivances calculated to increase its
precision and accuracy in large surface-turning.

The beautiful arrangements embodied in Mr. Clement's improved lathe can
with difficulty be described in words; but its ingenuity may be
inferred from a brief statement of the defects which it was invented to
remedy, and which it successfully overcame. When the mandrill of a
lathe, having a metal plate fixed to it, turns round with a uniform
motion, and the slide rest which carries the cutter is moving from the
circumference of the work to the centre, it will be obvious that the
quantity of metal passing over the edge of the cutter at each
revolution, and therefore at equal intervals of time, is continually
diminishing, in exact proportion to the spiral line described by the
cutter on the face of the work. But in turning metal plates it is
found very in expedient to increase the speed of the work beyond a
certain quantity; for when this happens, and the tool passes the work
at too great a velocity, it heats, softens, and is ground away, the
edge of the cutter becomes dull, and the surface of the plate is
indented and burnished, instead of being turned. Hence loss of time on
the part of the workman, and diminished work on the part of the tool,
results which, considering the wages of the one and the capital
expended on the construction of the other, are of no small importance;
for the prime objects of all improvement of tools are, economy of time
and economy of capital--to minimize labour and cost, and maximize
result.

The defect to which we have referred was almost the only remaining
imperfection in the lathe, and Mr. Clement overcame it by making the
machine self-regulating; so that, whatever might be the situation of
the cutter, equal quantities of metal should pass over it in equal
times,--the speed at the centre not exceeding that suited to the work
at the circumference,--while the workman was enabled to convert the
varying rate of the mandrill into a uniform one whenever he chose.
Thus the expedients of wheels, riggers, and drums, of different
diameters, by which it ha