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in avoiding the crossing of the points； he proceeded to invent the
straight…line motion。 For this invention the Society of Arts awarded
him their gold medal in 1818。 Some years later； he submitted to the
same Society his invention of a stand for drawings of large size。 He
had experienced considerable difficulty in making such drawings； and
with his accustomed readiness to overcome obstacles； he forthwith set
to work and brought out his new drawing…table。
As with many other original…minded mechanics； invention became a
habit with him； and by study and labour he rarely failed in attaining
the object which he had bent his mind upon accomplishing。 Indeed；
nothing pleased him better than to have what he called 〃a tough job；〃
as it stimulated his inventive faculty； in the exercise of which he
took the highest pleasure。 Hence mechanical schemers of all kinds
were accustomed to resort to Clement for help when they had found an
idea which they desired to embody in a machine。 If there was any
value in their idea； none could be more ready than he to recognise
its merit； and to work it into shape； but if worthless； he spoke out
his mind at once； dissuading the projector from wasting upon it
further labour or expense。
One of the important branches of practical mechanics to which Clement
continued through life to devote himself； was the improvement of
self…acting tools； more especially of the slide…lathe。 He introduced
various improvements in its construction and arrangement； until in
his 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 capitalto 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 had been endeavoured to alter the speed of the
lathe…mandrill； according to the hardness of the metal and the
diameter of the thing to be turned； were effectually disposed of。
These； though answering very well where cylinders of equal diameter
had to be bored； and a uniform motion was all that was required； were
found very inefficient where a Plane surface had to be turned； and it
was in such cases that Mr。 Clement's lathe was found so valuable。 By
its means surfaces of unrivalled correctness were produced； and the
slide…lathe； so improved； became recognised and adopted as the most
accurate and extensively applicable of all machine…tools。
The year after Mr。 Clement brought out his improved turning…lathe； he
added to it his self…adjusting double driving centre…chuck； for which
the Society of Arts awarded him their silver medal in 1828。 In
introducing this invention to the notice of the Society； Mr。 Clement
said； 〃Although I have been in the habit of turning and making
turning…lathes and other machinery for upwards of thirty…five years；
and have examined the best turning…lathes in the principal
manufactories throughout Great Britain； I find it universally
regretted by all practical men that they cannot turn anything
perfectly true between the centres of the lathe。〃 It was found by
experience； that there was a degree of eccentricity； and consequently
of imperfection； in the figure of any long cylinder turned while
suspended between the centres of the lathe； and made to revolve by
the action of a single driver。 Under such circumstances the pressure
of the tool tended to force the work out of the right line and to
distribute the strain between the driver and the adjacent centre； so
that one end of the cylinder became eccentric with respect to the
other。 By Mr。 Clement's invention of the two…armed driver； which was
self…adjusting； the strain was taken from the centre and divided
between the two arms； which being equidistant from the centre；
effectually corrected all eccentricity in the work。 This invention
was found of great importance in ensuring the true turning of large
machinery； which before had been found a matter of considerable
difficulty。
In the same year （1828） Mr。 Clement began the making of fluted taps
and dies； and he established a mechanical practice with reference to
the pitch of the screw； which proved of the greatest importance in
the economics of manufacture。 Before his time； each mechanical
engineer adopted a thread of his own； so that when a piece of work
came under repair； the screw…hob had usually to be drilled out； and a
new thread was introduced according to the usage which prevailed in
the shop in which the work was executed。 Mr。 Clement saw a great
waste of labour in this practice； and he promulgated the idea that
every screw of a particular length ought to be furnished with its
appointed number of threads of a settled pitch。 Taking the inch as
the basis of his calculations； he determine