"
At last Watt seems to have become satisfied: "The lathe," he
says, "is very much improved, and you seem to have given the
finishing blow to the roofed frame, which appears perfectly
stiff. I had some hours' intense thinking upon the machine last
night, and have made up my mind on it at last. The great
difficulty was about the application of the band, but I have
settled it to be much as at present."
Watt's letters to Murdock are most particular in details,
especially as to screws, nuts, and tubes, with strengths and
dimensions, always illustrated with pen-and-ink drawings. And
yet all this was done merely for mechanical amusement, and not
for any personal pecuniary advantage. While Watt was making
experiments as to the proper substances to be carved and drilled,
he also desired Murdock to make similar experiments. "The
nitre," he said in one note, "seems to do harm; the fluor
composition seems the best and hardest. Query, what would some
calcined pipe-clay do? If you will calcine some fire-clay by a
red heat and pound it,--about a pound,--and send it to me, I
shall try to make you a mould or two in Henning's manner to cast
this and the sulphur acid iron in. I have made a screwing tool
for wood that seems to answer; also one of a one-tenth diameter
for marble, which does very well." In another note, Watt says:
"I find my drill readily makes 2400 turns per minute, even with
the large drill you sent last; if I bear lightly, a three-quarter
ferril would run about 3000, and by an engine that might be
doubled.
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