66 66 "which I expect will stand it." On the 30th of November he says," I saw the tilt go admirably from 16 to 24 strokes per minute, and it could have gone much faster, but our "men could not work the iron under it. Joseph said that yesterday they made it go 28 strokes per minute, which is "much more than the engine should do by my calculations; "but in the midst of our glory, the hammer helve broke it appears to have been rotten. The steel camms answer very well, and the whole will answer better when made to have a less lift and more strokes, as it will then answer for a "common tilt for steel; at present the blow is so strong, that we dare not attempt to hack a piece of iron under 1 inch square, otherwise it knocks it to pieces. 66 66 66 66 66 66 66 By the help of beam, it goes so regular that you cannot tell when the engine is going out "or when coming in." On the 12th of December,-"I went "out to Soho yesterday forenoon, hoping the engine would "be ready for trial, but it was not. In the evening they "wrought it 2 hours, 240 blows per minute, rise of hammer "8 inches." On the 13th,-" We have tried our little tilting some more weight on the outer end of the forge hammer at Soho, with success. The following are "some of the particulars :-cylinder 15 inches diameter, 4 "feet stroke, strokes per minute 20. The hammer-head, "120 lbs. weight, rises 8 inches, strikes 240 blows per minute. "The machine goes quite regular, and can be managed as easily as a water-mill. It requires a very small quantity "of steam, not above half the contents of the cylinder per "stroke. The power employed is not more than of what "would be required to raise the quantity of water which "would enable a water-wheel to work the same hammer with "the same velocity." Next month, they were "making an"other to work a hammer of 700 lbs., which will soon be at "work." This was for Mr. John Wilkinson at Bradley, and, on the 27th of April, 1783, Mr. Watt writes, "We have had a "trial of our new forge-engine at Bradley; cylinder 42 inches " diameter, 6 feet stroke. Makes from 15 to 50 (even 60 66 *To Mr. Boulton, 28 November, 1782. "strokes per minute) at pleasure, works a hammer of 73 cwt. "raised 2 feet high, which makes 6 strokes per stroke of the engine, and has struck 300 blows per minute; we are, how 66 66 ever, going to make it strike only 4 blows per stroke of "the engine, because we want the latter to go 20 strokes per "minute, and they want only 90 blows of the hammer in "that time; but will increase the weight of the hammer to "10 cwt. N.B. The engine is to work two hammers, but is capable of working four hammers, of 7 cwt. each.” 66 In a letter written on the previous day, he had said, with excusable pride, "I believe it is a thing never done before, "to make a hammer of that weight make 300 blows per “minute; and, in fact, it is more a matter to brag of than "for any other use, as the rate wanted is from 90 to 100 "blows, being as quick as the workmen can manage the iron "under it." This most valuable application of steam-power was, accordingly, reserved for insertion in yet another patent, which Mr. Watt took out on the 28th of April, 1784. The relative specification, enrolled on the 25th of August in that year, may probably be viewed as second in importance to none of those prepared by Mr. Watt subsequent to that of the Separate Condenser in 1769; as, besides many improvements now of minor consequence, such as steam-wheels, balancing of pumprods, communication of motion from the same engine to two separate primary axes, and apparatus for opening the regulating-valves with rapidity, it contains various methods of converting a circular or angular motion into a perpendicular or rectilineal motion,-one of those methods being the wellknown and much-admired Parallel Motion;-a method of working a tilt-hammer for forging iron, making steel, &c., by steam; and the application of the steam-engine to give motion to wheel carriages for carrying persons or goods. Of the last-mentioned invention, and of its inventor's views of the subject of locomotion by steam, in general, we shall presently treat. Of the invention of the Parallel Motion,-a beautiful mechanical puzzle which different philosophers have attempted to explain in various ways, but which has uniformly commanded the admiration of all who either comprehend the principles on which it acts, or behold the smoothness, orderly power, and "sweet simplicity" of its movements, we find the following account in a letter from Mr. Watt to his son, already cited; (Mr. Watt to Mr. James Watt, 10th November, 1808): 66 "The idea originated in this manner. On finding double chains, or racks and sectors, very inconvenient for communicating the motion of the piston-rod to the angular motion "of the working-beam, I set to work to try if I could not "contrive some means of performing the same from motions "turning upon centres, and after some time it occurred to me that AB, CD, being two equal radii revolving on the "centres B and C, and connected together by a rod AD, in 66 A B दू SE "moving through arches of certain lengths, the variations "from the straight line would be nearly equal and opposite, "and that the point E would describe a line nearly straight, "and that if for convenience the radius CD was only half of "AB, by moving the point E nearer to D, the same would "take place; and from this the construction, afterwards called "the parallel motion, was derived. Though I am not "over anxious after fame, yet I am more proud of the parallel "motion than of any other mechanical invention I have ever "made." See also on this subject Mr. Watt's Appendix to 'Robison on 'Steam and Steam-engines,' pp. 152, 153 ;where he mentions that "the invention was made in the latter end of 1783." The manner in which we find the contrivance of this admirable piece of mechanism first recorded in his correspondence, although six months later than the date thus 66 66 66 assigned to it by Mr. Watt, is interesting:-"I have started "a new hare. I have got a glimpse of a method of causing "a piston-rod to move up and down perpendicularly, by only fixing it to a piece of iron upon the beam, without chains, or perpendicular guides, or untowardly frictions, arch-heads, "or other pieces of clumsiness; by which contrivance, if it "answers fully to expectation, about five feet in the height "of the [engine-] house may be saved in 8-feet strokes, which "I look upon as a capital saving; and it will answer for "double engines as well as for single ones. I have only tried "it in a slight model yet, so cannot build upon it, though I "think it a very probable thing to succeed, and one of the "most ingenious simple pieces of mechanism I have contrived, but I beg nothing may be said on it till I specify." And again, on the 11th of July:-" I have made a very large "model of the new substitute for racks and sectors, which 66 seems to bid fair to answer. The rod goes up and down, quite in a perpendicular line, without racks, chains, or guides. It is a perpendicular motion derived from a com"bination of motions about centres, very simple, has very "little friction, has nothing standing higher than the back "of the beam, and requires the centre of the beam to be 66 66 66 66 only half the stroke of the engine higher than the top of "the piston-rod when at lowest, and has no inclination to pull "the piston-rod either one way or another except straight up "and down. It has rather more power at beginning and end "of the stroke than in the middle,-I think about one-sixth; "which I believe will do no hurt in rotative motions, and "little in any case. Beams mounted in this way need no "arches; and the whole iron-work will not, I think, be more "than chains, martingales, and their appendages, if quite so "much. However, don't pride yourself on it; it is not fairly "tried yet, and may have unknown faults. Where it is "used, the beams will be best above the centre of motion, "which will answer double engines very well, and may in "most cases be dispensed with in the others." On the 21st *To Mr. Boulton, 30 June, 1784. of October, 1784, he writes:-"The new central perpen"dicular motion answers beyond expectation, and does not "make the shadow of a noise." The manufacturing profits which Boulton and Watt stipulated to receive from the Cornish miners who used their engines, were at first one-third of the savings of fuel made by each engine, when compared with a common one burning the same kind of coal, to be paid annually or half-yearly, with an option of redemption at ten years' purchase. In point of fact, they did not receive nearly that proportion; but still, such was the agreement made, and such, had it been honestly adhered to on the side of the miners, would have been the amount paid. It therefore became essential to ascertain the exact number of strokes made by each engine during any given time, and that in a way that should be independent of all possibility of deception or interference by those employed about the engine. This object was fully attained by Mr. Watt's invention of his "Counter;" a neat piece of clockwork containing a pendulum, a train of wheels with an escapement, and several dials like those of watches graduated with numbers, and each with its index: the first index marking, on its own dial, tens; the next, hundreds; the next, thousands; and so on in the same ratio up to any required amount. Eight dials, with their respective indices, were found sufficient to count the strokes of an engine going constantly, day and night, for a year. The pendulum was fixed horizontally and transversely across the width of the beam, with the axes of the wheels vertical, while the beam was horizontal, and the piston at the middle of a stroke: thus at every inclination of the beam either downwards or upwards, the pendulum moved across the width of the box, and, by the vibratory movement of the pendulum and pallets, the escapement wheel was turned one tooth for each complete stroke of the piston. And the whole work of the counter being enclosed in a box which was fastened by screws from within on The specification of the patent of April 28th, 1784, is printed in the Mechanical Inventions of James 'Watt,' 1854, vol. iii., pp. 88 to 114; and the relative drawings are engraved on Plates XX., XXI., XXII., XXIII., XXIV., XXV., XXVI., XXVII., and XXVIII. |