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Men of Invention and Industry-Part22_Samuel Smiles(1812-1904)_English Literature(文学名著)-第2页

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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 cut will remain at rest

fixed upon a lath of cast iron or stout steel." Watt is very



particular in all his details: "I am sorry," he says in one note,

"to trouble you with so many things; but the alterations on this



spindle and socket [he annexes a drawing] may wait your

convenience." In a further note, Watt says. "The drawing for



the parallel lathe is ready; but I have been sadly puzzled about

the application of the leading screws to the cranes in the other.



I think, however, I have now got the better of the difficulties,

and made it more certain, as well as more simple, than it was. I



have done an excellent head of John Hunter in hard white in

shorter time than usual. I want to show it you before I repair



it."

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 mechanicalamusement, 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."

The materials to be drilled into medallions also required much



consideration. "I am much obliged to you," said Watt, "for the

balls, etc., which answer as well as can be expected. They make



great progress in cutting the crust (Ridgways) or alabaster, and

also cut marble, but the harder sorts soon blunt them. At any



rate, marble does not do for the medallions, as its grain

prevents its being cut smooth, and its semi-transparence hurts



the effect. I think Bristol lime, or shell lime, pressed in your

manner, would have a good effect. When you are at leisure, I



shall thank you for a few pieces, and if some of them are made

pink or flesh colour, they will look well. I used the ball quite



perpendicular, and it cut well, as most of the cutting is

sideways. I tried a fine whirling point, but it made little



progress; another with a chisel edge did almost as well as the

balls, but did not work so pleasantly. I find a triangular



scraping point the best, and I think from some trials it should

be quite a sharp point. The wheel runs easier than it did, but



has still too much friction. I wished to have had an hour's




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