Thus let the diameter of the piston be 24 inches, and the prefiure of the atmosphere on a fquare inch be 14 pounds; the preflure on the pitton is 6333 pounds. Let the whole ftroke be 6 feet, and let the team be stopped when the pifton has deicended 18 inches, or 15 feet. The hyperbolic legarithm ofis 1.3862943. Therefore the accumulated preffure ABF DA is = 6333 X 2*3862943, 15114 pounds. As few profeflional engir cers are pofleted of a table of hyperbolic logarithms, while tables of common logarithms are or fhould be in the hands of every perion who is much engaged in mechanical calculations, let the following method be practifed. Take the

of

AD AE

1'5

AD

AE'

common logarithm of and multiply it by 23026; the product is the hyperbolic logrithm The accumulated preffure while the pif. ton moves from AB to EF is 6333 X 1, or fimply 6333 pounds. Therefore the team while it expands into the whole cylinder adds a picture of 8781 pounds. Suppofe that the team had got free admiffion during the whole defcent of the piston, the accumulated preflure would have been 6333 X 4, or 25332 pounds. Here Mr Watt obferved a remarkable refult. The fteam expended in this cafe would have been four times greater than when it was ftopped at 4th, and yet the accumulated preffure is not twice as great, being nearly 4s. One fourth of the fteam performs nearly 4ths of the work, and an equal quantity performs more than twice as much work when thus admitted during 4th of the motion. This is a curious and an important information, and the advantage of this method of working a fteam engine increases in proportion as the fteam is fooner stopped; but the increafe is not great after the team is rarefied four times. The curve approaches near to the axis, and fmall additions are made to the area. The expente of fuch great cylinders is confiderable, and may fometimes compenfate this advantage. Stop the steam at

&c.

Its performance is mult.

1'7

2'I

2.4

2.6 2.8

3'

3.2 &c.

It is very pleafing to obferve fo many unlookedfor advantages refulting from an improvement made with the fole view of leffening the wafte of fteam by condenfation. While this purpose is gained, we learn how to hufband the fteam which is not thus wafted. The engine becomes more manageable, and is more easily adapted to every variation in its talk, and all its powers are more eafily computed.

(6.) STEAM-ENGINE, MR WATT'S HIGHEST

IMPROVEMENTS ON THE. The active mind of its

ingenious inventor did not ftop here: It had always been matter of regret that one half of motion was unaccompanied by any work.

the

It

was a very obvious thing to Mr Watt, that as the fteam admitted above the pifton prefled it down," fo fteam admitted below the pifton preffed it up with the fame force, provided that a vacuum were made on its upper fide. This was eafily done, by connecting the lower end of the cylin der with the boiler and the upper end with the condenfer. Fig. 1. Plate CCCXIX. is a reprefentation of this conftruction exactly copied from Mr Watt's figure accompanying his fpecification. Here BB is a fection of the cylinder, furrounde t at a mall diftance by the cafe 1111. The fection of the pifton A, and the collar of leathers which embraces the pifton rod, gives a diftinct notion of its conftruction, of the manner in which it is connected with the piston-rod, and how the packing of the pifton and collar contributes to make all tight. From the top of the cylinder proceeds the horizontal pige. Above the letter D is obferved the feat of the fteam valve, communicating with obfervei a dark fhaded circle. This is the mouth the box above it. In the middle of this may be of the upper branch of the fteam pipe coming from the boiler. Beyond D, below the letter N, is the feat of the upper condenting valve. The bottom of the cylinder is made fpherical, fitting the piston, fo that they may come into entire cortact. Another horizontal pipe proceeds from this bottom. Above the letter E is the feat of the lower fteam valve, opening into the valve box. This box is at the extremity of another steam pipe marked C, which branches off from the upper horizontal part, and defcends obliquely, coming forward to the eye. The lower part is reprefented as cut open, to fhow its interior conformation. Beyond this fteam valve, and below the letter F, may be obferve the feat of the lower condenfing valve. A pipe defcends from hence, and at a fmall dittance below unites with another pipe GG, which comes down from the upper condenfing valve N. Thefe two eduction-pipes thus united go downwards, and open at L into a rectangular box, of which the end is feen at L. This box goes backward from the eye, and at is farther extremity communicates with the air-pump K, whofe pifton is here reprefented in fection with its butterfly valves. The pifton delivers the water and air laterally into another rectangular box M, darkly fhaded, which box communicates with the pump I. The pifton-rods of this and of the air-pump are fufpended by chains from a fmall arch head on the inner arm of the great beam. The lower part of the eduction-pipe, the horizoncating box M between it and the pump I, are all tal box L, the air-pump K, with the communiimmerfed in the cold water of the condenting ciftern. The box L is made flat, broad, and thai low, in order to increafe its furface and accelerate the condensation. But that this may be performed with the greatest expedition, a finail pipe H, open below (but occafionally stopped by a plug valve), is inferted laterally into the eductionof which reaches within a foot or two of the uppipe G, and then divides into two branches; one Per valve N, and the other approaches as near to the valve F. As it is intended by this conftruction to give the piston a ftrong impulfe in both directions, it will not be proper to fufpend its

rod

the eye and the box E of the lower fteam valve, and the box F of the lower eduction valve.

rod by a chain from the great beam; for it must not only pull down that end of the beam, but alfo push it upwards. It may indeed be fufpended by double chains like the piftons of the engines for extinguishing fires; and Mr Watt has accordingly done fo in fome of his engines. But in his drawing from which this figure is copied, he has communicated the force of the pifton to the beam by means of a toothed rack OÔ, which engages or works in the toothed sector QQ on the end of the beam. The reader will understand, without any farther explanation, how the impuife given to the pifton in either direction is thus tranfmitted to the beam without diminution. The fly XX, with its pinion Y, which also works in the toothed arch QQ, may be supposed to be removed for the prefent, and will be confidered afterwards. We fhall now describe Mr Watt's method of communicating the force of the fteam-engine to any machine of the rotatory kind. VV reprefents the rim and arms of a very large and heavy metalline fly. On its axis is the concentric toothed wheel U. There is attached to the end of the great beam a strong and stiff rod TT, to the lower end of which a toothed wheel W is firmly fixed by two bolts, fo that it cannot turn round. This wheel is of the fame fize and in the fame vertical plane with the wheel U; and an irou link or ftrap (which cannot be feen here, because it is on the other fide of the two wheels) connects the centres of the two whecis, fo that the one cannot quit the other. The engine being in the pofition reprefented in the figure, fuppofe the fly to be turned once round by any external force in the direction of the darts. It is plain, that fince the toothed wheels cannot quit each other, being kept to gether by the link, the inner half (that is, the half next the cylinder) of the wheel U will work on the inner half of the wheel W, so that at the end of the revolution of the fly the wheel W must have got to the top of the wheel U, and the outer end of the bean must be raised to its higheft pofition. The next revolution of the fly will bring the wheel W and the beam connected with it to their firft pofitions; and thus every two revolutions of the fly will make a complete period of the beam's reciprocating movements. Now, inftead of fuppofing the fly to drive the beam, let the beam drive the fly. The motions must be perfectly the fame, and the afcent or defcent of the pifton will produce one revolution of the fly. A fide view of this apparatus is given in fig. 4. pl. 319. marked by the fame letters of reference. This hows the fituation of parts which were fore hortened in fig. 1. particularly the defcending branch C of the fteam pipe, and the fituation and Communications of the two pumps K and I. 8, 8 is the horizontal part of the fteam pipe. 9 is a Bt of it whofe box is reprefented by the dark circle of fig. 1. D is the box of the fteam clack, and the little circle at its corner represents the end of the axis which turns it, as will be deferibed afterwards. N is the place of the upper eduction valve. A part only of the upper eduction-pipe Gis reprefented, the rest being cut off, because I would have covered the defcending fteam pipe GC. When continued down, it comes between

(7.) STEAM ENGINE, OPERATION OF MR WATTS. Let us now trace the operation of this machine through all its fteps. Recurring to fig. 1. let us fuppofe that the lower part of the cyander BB is exhaufted of all claftic fluids; that the upper fteam vaive D and the lower eduction valve F are open, and that the lower fteam valve E and upper eduction valve N are fhut. It is evident that the piston must be pressed toward the bot tom of the cylinder, and muft pull down the end of the working beam by means of the toothed rack 00 and fector QQ, cauling the other end of the beam to urge forward the machinery with which it is connected. When the piston arrives at the bottom cylinder, the valves D and F are shut by the plug frame, and E and N are opened. By this laft paffage the fteam gets into the eduction pipe, where it meets with the injection wa ter, and is rapidly condenfed. The team from the boiler enters at the fame time by E, and preffing on the lower fide of the piston, forces it upwards, and by means of the toothed rack OO and toothed sector QQ forces up that end of the working beam, and caufes the other end to urge forward the machinery with which it is connected; and in this manner the operation of the engine may be continued for ever. The injection water is continually running into the eduction-pipe, becaufe condenfation is continually going on, and therefore there is a continual atmospheric preffure to produce a jet. The air which is difengaged from the water, or enters by leaks, is evacuated only during the rife of the pifton of the air-pump K. When this is very copious, it renders a very large air-pump neceflary; and in fome Gituations Mr Watt has been obliged to employ two air-pumps, one worked by each arm of the beam. This in every cafe expends a very confiderable portion of the power, for the air-pump is always working against the whole preffure of the atmosphere. It is evident that this form of the engine, by maintaining an almost constant and uninterrupted impulfion, is much fitter for driving any machinery or continued motion than any of the former engines, which were inactive during half of their motion. It does not, however, feem to have this fuperiority when employed to draw water: But it is equally fitted for this task. Let the engine be loaded with twice as much as would be proper for it if a fingle ftroke engine, and let a fly be connected with it. Then it is plain that the power of the engine during the rife of the team pifton will be accumulated in the fly; and this, in conjunction with the power of the engine during the defcent of the steam piston, will be equal to the whole load of water. In fpeaking of the fteam and eduction valves, we faid that they were all puppet vaives. Mr Watt employed cocks, and also sliding valves, such as the regulator or fteam vaive in the old engines. But he found them always lofe their tightness after a fhort time. This is not furprising, when we confider that they are always perfectly dry, and aloft burning hot. He was therefore obliged to change them ad for puppet clacks, which, when

truly

ployers felect the beft engine of the ordinary kind in the kingdom, compare the quantities of fuel expended by each, and pay to Meffrs Watt and Boulton one 3d of the annual favings for a certain term of years. By this the patentees are excited to do their utmost to make the engine perfect; and the employer pays in proportion to the advantage he detives from it.

and increafing; and brought into view a very interefting propofition in the mechanical theory of the engine, viz. that the whole performance of a given quantity of team may be augmented by admitting it into the cylinder only during a part of the pifton's motion. Mr Watt has varied the application of this propofition in a thousand ways; and there is nothing about the machine which gives more employment to the fagacity and judg ment of the engineer. The third improvement of the double impulfe may be confidered as the finishing touch given to the engine, and rend rs it as uniform in its action as any water-wheel. In the engine in its molt perfect form there does not feem to be above one 4th of the steam wafted by warning the apparatus; fo that it is not poffible to make it one 4th part more powerful than it is a prefent. The only thing that feems fufciptible of confiderable improvement is the great beam, The enormous ftrains exerted on its arms require a proportional ftrength. This requires a vaft mafs of matter, not lefs indeed in an engine with a cylinder of 34 inches than three tons and a half, moving with the velocity of three feet in a second, which must be communicated in about half a fe cond. This mats must be brought into motion from a state of reft, mult again be brought to rest, again into motion, and again to reft, to complete the period of a stroke. This confumes much power; and Mr Watt has not been able to load an engine with more than 10 or 11 pounds on the inch and preferve a futficient quantity of motion, fo as to make 12 or 15 fix-feet ftrokes in a fecond. Many attempts have been made to leffen this mafs by using a light framed wheel, or a light frame of carpentry, in place of a folid beam. Thefe have generally been constructed by perfons ignorant of the true fcientific principles of car pentry, and have fared accordingly. Mr Watt has made fimilar attempts; but found, that aithough at firit they were abundantly strong, yet after a short time's employment the ftraps and bolts with which the wooden parts were connected cut their way into the wood, and the framing grew loofe in the joints, and, without giving any warning, went to pieces in an inftant. A folid maffy fimple beam, of fufficient strength, bends, and fenfibly complams as the carpenters exprefs it.) before it breaks. In all great engines, there fore, such only are employed, and in smaller en gines he fometimes utes caft-iron wheels or pulleys: nay, he frequently uses no beam or equivalent whatever, but employs the fteam pifton-rod to drive the machinery to which the engine is applied. Such is the interefting hiftory of the progrefs of this engine in the hands of its ingenious and worthy inventor. He has now been long af fociated with the no leis celebrated mechanic and philofopher, M: Boulton of Soho, near Birmingham. (See Soно.) They have fhared the royal patent from the beginning; and the alliance is equally honourable to both. The advantages de rived from the patent-right thow both the fuperiority of the engine and the liberal minds of the proprietors. They erect the engines at the expence of the employers, or give working drafts of all the parts, with inftructions, by which any refident engineer may execute the work. The em

(9) STEAM-ENGINES, ACTUAL PERFORMANCE OF MR WATT'S. The actual performance of fome of thefe ergines has been afcertained by experiment. An engine having a cylinder of 31 inches in diameter, and making 17 double ftrokes per minute, performs the work of 40 horfes working night and day (for which three relays or 120 horfes muft be kept,) and burns 11,000 pounds of Staffordinire coal per day. A cylinder of 19 inches, making 25 ftrokes of 4 feet each per minute, performs the work of 12 horses working conftantly, and burns 3700 pounds of coals per day. A cylinder of 24 inches, making 22 strokes of 5 feet, burns 5500 pounds of coals, and is equi valent to the conftant work of 20 horses. And the patentees think themselves authorized by experience to fay in general, that thefe engines will raife more than 20,000 cubic feet of water 24 feet high for every hundred weight of good pit. coal confumed by them. In confequence of the great fuperiority of Mr Watt's engines, both with refpect to economy and manageablenefs, they have become of most extenfive ufe; and in every demand of manufacture on a great feale they offer us an indefatigable fervant, whofe ftrength has no bounds. The greatest mechanical project that ever engaged the attention of man was on the point of being executed by this machine. The States of Holland were treating with Meffrs Watt and Boulton for draining the Haerlem Meer, and even reducing the Zuyder-Zee: and we doubt not but that it will be accomplished whenever that unhappy nation fhall get rid of the French yoke. Indeed fuch unlimited powers are afforded by this engine, that the engeneer now thinks that no talk can be propofed to him, which he cannot execute with profit to his employers. Mr Watt's form alfo fuggefts the construction of an excellent air-pump. A large veffel may be made to communicate with a boiler at one fide, and with the pump-receiver on the other, and also with a condenser. Suppose this vessel of ten times the capacity of the receiver: fill it with fteam from the boiler, and drive out the air from it; then open its communication with the receiver and the condenfer. This will rarefy the air of the receiver 10 times. Repeating the operation will rarefy it 100 times; the third operation wil rarefy it 1000 times; the fourth 10,000 times, &c. All this may be done in half a minute.

(10.) STEAM ENGINES, FRUITLESS ATTEMPTS TO IMPROVE AND RIVAL Mr WATT's. All claffes of engineers have turned much of their attention to this engine; and fecing that it has done fo much, that they try to make it do still more. Numberless attemps have been made to improve Mr Watt's engine; and it would occupy a volume to give an account of them, whilft that account would do no more than indulge curiofity

Our