66 "Watt derived most valuable assistance from that able "mechanician and engineer, Mr. John Rennie, then just entering into business, who assisted in planning them, and "under whose direction they were executed. The engines "and mill-work were contained in a commodious and elegant building, designed and executed under the direction of the "late Mr. Samuel Wyatt, architect.” * We may add, that Mr. Peter Ewart was then Rennie's apprentice, was sent for from Scotland expressly to assist in the erection of those mills, and was employed for four years upon them as a millwright; when his great mechanical talents and industry sufficiently recommended him to his future employers, patrons, and friends, Messrs. Boulton and Watt.t We have here spoken of the "double-acting" engine, (a name sometimes applied to it on its first introduction), to distinguish it from the next of the new improvements included in the specification of 1782, viz. :— 66 66 3. The double, or compound engine; the nature and advantages of which are thus shortly described by Mr. Watt:-" A new compound engine, or method of connecting together the " cylinders and condensers of two or more distinct engines, so "as to make the steam which has been employed to press on "the piston of the first, act expansively upon the piston of "the second, &c., and thus derive an additional power to "act either alternately or conjointly with that of the first " cylinder."+ 4. Toothed rack and sector, instead of chains, for guiding the piston-rod. In consequence of Mr. Watt's beautiful invention of the Parallel Motion, made at no distant date from that of this specification, the rack and sector may be looked on as having been only a temporary expedient to avoid the inconveniences which had been found to result from the old system of chains connecting the piston-rod with the beam. 5. Rotative engine, or steam-wheel. For the reason already mentioned when treating of the patent of 1781, viz. that "self"acting rotative engines, not derived from the rectilinear "motion of a piston in a cylinder, instead of being more simple in their construction, are more complex than those "derived from reciprocating motions, and more difficult in execution," it seems unnecessary to enlarge on this article, which is fully described in the specification.* 66 66 CHAPTER XIX. - LOCO MOST STEAM TILT-HAMMER -PATENT OF 1784. PARALLEL MOTION A FAVOURITE employment of Mr. Watt in the workshops at Soho in the latter months of 1783 and earlier ones of 1784, was to teach his steam-engine, now become nearly as docile as it was powerful, to work a tilt-hammer for forging iron and making steel. So far back as 3 May, 1777, he had informed Mr. Boulton that "[John] Wilkinson is going to work "in the forge way, and wants an engine to raise a stamp of "15 cwt. thirty or forty times in a minute. I have set Webb "to work to try it with the little engine and a stamp-hammer " of 60 lbs. weight. Many of these battering rams will be "wanted if they answer.' During his long absence, and constant occupation in Cornwall, this labour seems to have been intermitted; and we do not find it resumed in earnest till November, 1782. Then "the rotative motion and mill "part answered to every expectation, but the hammer-frame and anvil-block were not sufficiently secured, which, how"ever, I have given orders for doing. And as the engine has a great overplus of power, I mean to increase the weight of "the hammer to about 1 cwt., and to cause it to make 250 or 300 strokes per minute, by diminishing the height it "rises to 9 or 10 inches. The present facts are, cylinder, 15 "inches diameter, and 4 feet stroke, 25 strokes per minute; "hammer makes 6 blows per stroke of the engine; fly under "5 cwt., and 7 feet diameter; hammer 120 lbs., and 18 inches wide; it strikes a good blow, and forges iron very well. “The camms were wood, and were cut all to pieces by the "anvil-block sinking. I have ordered steel ones to be made, 66 66 66 66 mentioned when treating of the patent of 1781, viz. that “selfacting rotative engines, not derived from the rectilinear "motion of a piston in a cylinder, instead of being more simple in their construction, are more complex than those "derived from reciprocating motions, and more difficult in execution," it seems unnecessary to enlarge on this article, which is fully described in the specification.* 66 66 * See the specification of this third steam-engine patent, printed in vol. iii. of the Mechanical Inventions of James Watt,' 1854, pp. 55 to 87; and the relative drawings, engraved in the same volume, Plates VIII., IX., X., XI., XII., XIII., XIV., XV., XVI., XVII., XVIII., and XIX. CHAPTER XIX. STEAM TILT-HAMMER — PATENT OF 1784- PARALLEL MOTION - LOCO- A FAVOURITE employment of Mr. Watt in the workshops at Soho in the latter months of 1783 and earlier ones of 1784, was to teach his steam-engine, now become nearly as docile as it was powerful, to work a tilt-hammer for forging iron and making steel. So far back as 3 May, 1777, he had informed Mr. Boulton that "[John] Wilkinson is going to work "in the forge way, and wants an engine to raise a stamp of "15 cwt. thirty or forty times in a minute. I have set Webb "to work to try it with the little engine and a stamp-hammer " of 60 lbs. weight. Many of these battering rams will be "wanted if they answer." During his long absence, and constant occupation in Cornwall, this labour seems to have been intermitted; and we do not find it resumed in earnest till November, 1782. Then " the rotative motion and mill part answered to every expectation, but the hammer-frame " and anvil-block were not sufficiently secured, which, how"ever, I have given orders for doing. And as the engine has "a great overplus of power, I mean to increase the weight of "the hammer to about 14 cwt., and to cause it to make 250 or 300 strokes per minute, by diminishing the height it "rises to 9 or 10 inches. The present facts are, cylinder, 15 " inches diameter, and 4 feet stroke, 25 strokes per minute; "hammer makes 6 blows per stroke of the engine; fly under "5 cwt., and 7 feet diameter; hammer 120 lbs., and 18 inches "wide; it strikes a good blow, and forges iron very well. "The camms were wood, and were cut all to pieces by the "anvil-block sinking. I have ordered steel ones to be made, 66 66 |