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. Ihave 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 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, Ishall 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, Ishall 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 consultation with you, but have been prevented by sundry matters among others by that plaguey stove, which is now in your hands."Watt was most grateful to Murdock for his unvarying assistance.
In January, 1813, when Watt was in his seventy-seventh year, he wrote to Murdock, asking him to accept a present of a lathe "Ihave not heard from you," he says, "in reply to my letter about the lathe; and, presuming you are not otherwise provided, I have bought it, and request your acceptance of it. At present, an alteration for the better is making in the oval chuck, and a few additional chucks, rest, etc., are making to the lathe. When these are finished, I shall have it at Billinger's until you return, or as you otherwise direct. I am going on with my drawings for a complete machine, and shall be glad to see you here to judge of them."The drawings were made, but the machine was never finished.
"Invention," said Watt, "goes on very slowly with me now." Four years later, he was still at work; but death put a stop to his "diminishing-machine." It is a remarkable testimony to the skill and perseverance of a man who had already accomplished so much, that it is almost his only unfinished work. Watt died in 1819, in the eighty-third year of his age, to the great grief of Murdock, his oldest and most attached friend and correspondent.
Meanwhile, the firm of Boulton and Watt continued. The sons of the two partners carried it on, with Murdock as their Mentor. He was still full of work and inventive power. In 1802, he applied the compressed air of the Blast Engine employed to blow the cupolas of the Soho Foundry, for the purpose of driving the lathe in the pattern shop. It worked a small engine, with a l2-inch cylinder and 18-inch stroke, connected with the lathe, the speed being regulated as required by varying the admission of the blast. This engine continued in use for about thirty-five years.
In 1803 Murdock experimented on the power of high-pressure steam in propelling shot, and contrived a steam-engine with which he made many trials at Soho, thereby anticipating the apparatus contrived by Mr. Perkins many years later.
In 1810 Murdock took out a patent for boring steam-pipes for water, and cutting columns out of solid blocks of stone, by means of a cylindrical crown saw. The first machine was used at Soho, and afterwards at Mr. Rennie's Works in London, and proved quite successful. Among his other inventions were a lift worked by compressed air, which raised and lowered the castings from the boring-mill to the level of the foundry and the canal bank. He used the same kind of power to ring the bells in his house at Sycamore Hill, and the contrivance was afterwards adopted by Sir Walter Scott in his house at Abbotsford.
