unfinished work.

The principle of the machine was to carry a guide-point at one side
over the bust or alto-relievo to be copied, and at the other side to
carry a corresponding cutting-tool or drill over the alabaster, ivory,
jet, or plaster of Paris to be executed. The machine worked, as it
were, with two hands, the one feeling the pattern, the other cutting
the material into the required form. Many new alterations were
necessary for carrying out this ingenious apparatus, and Murdock was
always at hand to give his old friend and master his best assistance.
We have seen many original letters from Watt to Murdock, asking for
counsel and help. In one of these, written in 1808, Watt says: "I have
revived an idea which, if it answers, will supersede the frame and
upright spindle of the reducing machine, but more of this when we meet.
Meanwhile it will be proper to adhere to the frame, etc., at present,
until we see how the other alterations answer." In another he says: "I
have done a Cicero without any plaits--the different segments meeting
exactly. The fitting the drills into the spindle by a taper of 1 in 6
will do. They are perfectly stiff and will not unscrew easily. Four
guide-pullies answer, but there must be a pair for the other end, and
to work with a single hand, for the returning part is always cut upon
some part or other of the frame."

These letters are written sometimes in the morning, sometimes at noon,
sometimes at night. There was a great deal of correspondence about
"pullies," which did not seem to answer at first. "I have made the
tablets," said Watt on one occasion, "slide more easily, and can
counterbalance any part of their weight which may be necessary; but the
first thing to try is the solidity of the machine, which cannot be done
till the pullies are mounted." Then again: "The bust-making must be
given up until we get a more solid frame. I have worked two days at
one and spoiled it, principally from the want of steadiness." For
Watt, it must be remembered, was now a very old man.

He then proceeded to send Murdock the drawing of a "parallel motion for
the machine," to be executed by the workmen at Soho. The truss braces
and the crosses were to be executed of steel, according to the details
he enclosed. "I have warmed up," he concludes, "an old idea, and can
make a machine in which the pentagraph and the leading screw will all
be contained in the beam, and the pattern and piece to be cu