Note 416 — Chapter XXIII · Closing Years of James Watt—His Death—Conclusion.

In March, 1811, he wrote Dr. P. Wilson as follows:—“For want of other news I must now say a little upon my late invention, with which Dr. Herschel seemed much pleased. It continues to succeed, and I have realised some more of my ideas on the subject. I have executed several small busts in alabaster, not being strong enough to work in marble. I had a difficulty in getting the several segments which form the surface of the bust to meet, but have now accomplished it. It requires a very accurate construction of the machine, and a very accurate adjustment of the tools, so that their axes may be always equally distant from each other, as the axes of the pattern and that of the stone to be cut are. I have also made some improvements in the tools for cutting marble and other hard stones. The things you saw were done by the tool and the guide-point, moving in parallel lines, straight or circular, and very near one another; (an illustration of Euclid’s position, that the motion of a point generates a line, and the motion of a line generates a surface). I have now contrived, though not executed, that the two points, the guide and the cutting point, may move in any line, whether straight or crooked, square or diagonal, so that an inscription might be cut in stone from a drawing on paper.”—Cited in Muirhead’s ‘Mechanical Inventions of James Watt,’ ii. 329–30.