move such carriages
"on a hard smooth plane," and there is no evidence to show that he
ever anticipated the union of the rail and wheel.

Among Watt's mechanical recreations, soon after the date of the last
of his steam-engine patents, were four plans of making lamps, which
he describes in a letter to Argand; and for a long time lamps were
made at Soho upon his principles, which gave a light surpassing,
both in steadiness and brilliancy, anything of the kind that had
appeared. About a year after, in 1788, he made "a pretty instrument
for determining the specific gravities of liquids," having, he says
to Dr. Black, improved on a hint he had taken.

Watt also turned his "idle thoughts" toward the construction of an
_arithmetical machine_, but he does not appear ever to have
prosecuted this design further than by mentally considering the
manner in which he could make it perform the processes of
multiplication and division.

Early in the present century Watt devised, for the Glasgow
water-works, to bring pure spring-water across the Clyde, an
articulated suction-pipe, with joints formed on the principle of
those in a lobster's tail, and so made capable of accommodating
itself to all the actual and possible bendings at the bottom of the
river. This pipe was, moreover, executed at Soho from his plans, and
was found to succeed perfectly.

Watt describes, as his hobby, a _machine to copy sculpture_,
suggested to him by an implement he had seen and admired in Paris in
1802, where it was used for tracing and multiplying the dies of
medals. He foresaw the possibility of enlarging its powers so as to
make it capable of working even on wood and marble, to do for solid
masses and in hard materials what his copying machine of 1782 had
already done for drawings and writings impressed upon flat surfaces
of paper--to produce, in fact, a perfect fac-simile of the original
model. He worked at this machine most assiduously, and his "likeness
lathe," as he termed it, was set up in a garret, which, with all its
mysterious contents, its tools, and models included, have been
carefully preserved as he left them.

It is gratifying to find that the charm of Watt's presence was not
dimmed by age. "His friends," says Lord Jeffrey, speaking of a visit
which he paid to Scotland when upward of eighty, "in that part of
the country never saw him more full of intellectual vigor and
colloquial animation, never more delightful or more instructive." I