Slide valve control mechanism
I have represented this Mechanism infigs. 5 and 6,Plate 31:whereA Bshew the crank-shaft of a steam-engine, working by means of slide-valves, the place of theexcentricbeing ata b, in a line with the pulling-bare f. Instead, then, of the usual connectingframebetween the excentric ata b, and the valve-lever atg, I use for the above purpose, a levere fterminated by an arco, furnished (in the present instance) withfiveteeth, and connected by the jointewith the valve-leverg, in the usual manner. In the arc, which terminates this leverto the right, are the five teeth above-mentioned; and, they geer in thetenteeth of the wheelc d, which will be seen (infig. 6) to be on the same shaft with the spur-wheelm, itself driven by the spur-wheeln, of twice the diameter. This wheelc d, therefore, makes two revolutions for one of the crank-shaft: and, supposing it to turn in the direction of the arrow, it will first of all drawupwardthe arco, producing no effect on the valve-lever atg; but, when the toothris arrived atp(the toothpbeing then arrived at the entrance of the curveq), the wheelc dwill begin to draw the arcoalong with it, round it’s own centre; and, the teeth of the arc being kept in it’s teeth by the similar curveq, the valve-bar will be drawn fromgtoh, in the course ofone quarterof a revolution of the crank-shaftA B. But, now, the toothrof the arcowill be found ats: and, therefore, the further revolution of the wheelc dwill carry the arcodownward towardt, until the toothrhas reached the pointt; that is, until the wheelc dhas made another half-revolution, and the shaftA Banother quarter; when, as before, the arco, conducted by the curvet r, willagain drive back the levere f, till it comes into it’s present position: after which, their motions will be regularly continued. It is, then, evident, that the slide-valves are thus opened and shut, each during onequarterof a turn of the crank-shaftA B; and thus they remain stationary during another quarter, and that, in two positions of said shaft diametrically opposite to each other. And thus have we a simple mean, adaptable to every engine, of giving it much of the advantage of the hand-geering system, while preservingallthat of the slide-valve principle. And, were it desired to lengthen theinterregnumof the opening motion, it would be done by making the wheelc dsmaller, and the ratio ofntom(seefig. 6) larger in the same proportion.
I observe here, however, that care should be taken not to make the valve motionstoorapid, nor the intervals between them too long; for, I consider one of the best properties of this motion to be, that it actslike an excentric; that is, slowly at first, most rapidly afterwards, and finishes as slowly as it began; which is apreciousquality in all reciprocating machines.
Finally, I would remark, that the two lastroundsin the rack of the arcomight be rather larger than the intermediate ones, and turn, moreover, on pins, so as to suffer less friction when rolling on the conducting curvesqandt. There might also be a plate or cap rivetted or screwed over all the teeth, so as to strengthen each one, by the force of the whole, as is shewn infig. 1,Plate 29; from which, as before observed, this Mechanism is deduced.
The foregoing completes the Third Section of my work: and gives an article beyond the twenty, first intended:—which I thought important enough to claim this distinction. I now beg leave to add a remark or two on the text and plates of this, and the Second Part, by way of clearing up some obscurities, that might otherwise embarrass my readers.
And, first, infig. 1, ofPlate 21, the receiving vesselM, erroneouslyappearsto form part of the wheelD E; but is, in reality, placedbeforeit, as in all similar cases.—And, further, a small deviation of the circular lines, inPlate 22, has set the plate and it’s description, inpage 192,at variance; the difference between the lineso pandC qbeingnot“imperceptible,” as there stated. I wish, then, that the dotted radiusA o p, in the saidfig. 2, may be carried (or supposed) halfway betweenpandC. Finally, inpage 200, line 8, the 24th Plate is incorrectly called the 25th.
I shall conclude this Part, by an observation or two on the reception my System of Toothed Wheels, as described in this work, has met with—not intending to speak of the local difficulties I experienced at a former period. But,here, the interests of truth force me to break silence. The necessity I stood under of bringing out this work in Parts, has, at least, had one advantage: it has given me an opportunity of watching the workings of prejudice—not to say of envy,—and thus of neutralizing, in some degree, the effects of either: from which, however, I claim nothing but therightof makingmy labours the more extensively useful, by making them better known. I have, then, to say that, amonga fewother objections to the System,this errorhas come from so respectable a quarter, that it would be unjust to Science, and injurious to truth, to let it pass unrefuted. It has been said, that “my wheels are a Chinese Invention;” andthisproof has been adduced of it—namely, a sugar-mill, from China, having it’s cylindersfluted in a spiral direction. Now, the fact is, it would have been difficult to give a better proof that the wheels areNOTa “Chinese Invention;” for two inventions are then only alike when they produce the same effect, by similar means. But here the effects intended are totally different. A sugar-mill acts in or near the plane of the centres; and one of it’s cylinders is not intended to drive the other independently of pressure between them. This is so true, that the rollers of many sugar-mills are not fluted at all. Besides this, my wheels exert no pressure in that direction; and if they did, they would not be cog-wheels. In a word, their action isat right angles to the former, and has an object of quite a distinct nature. These, then, are by no means the same machine; and, therefore, mine is not a “Chinese Invention.”
Here, however, Ibegnot to be misunderstood! I should feel no regret at appearing on the mechanical stage, a few hundred years after so ancient and astonishing a nation as the Chinese! But, in this case, truth did not permit me to sanction, by my silence, this flagrant error.
Finally, an opinion exists,somewhere, that these wheelswillnever be generally used, from the difficulty of making them; and this opinion has been expressed, apparently, with no very amiable feeling. But, amiable or hateful, the opinion is highly erroneous! It is so far from fact, that, in a competent manufactory, they can be made more cheaply than others now are; andmanypersons are already calling for them from every quarter; nor is any thing wanted to insure their immediate prevalence but acommondegree of commercial energy.
PART FOURTH.A NEW CENTURY OFInventions.
A NEW CENTURY OF
Inventions.
One of the most prominent subjects of this essay, if not the most important, is the System of Toothed Wheels, with which the second and third Parts were introduced, and which still claims a share of my readers’ attention. As hinted a few pages backward, it seems not enough for me to exhibit and describe the System, but I must defend it against repeated objections, on pain of seeing it’s utility delayed, and the public deprived of it’s real and solid advantages. I amfarfrom wishing to impeach themotivesof those who still nourish or express dissent, when they deign to bring reasons for so doing; but the mere opinion—“it won’t do”—expressed by a man of reputation, may impede, for a time, the progress of an useful discovery, and thus produce a public evil. This, then, is a result I am anxious to avert; as the present Systemhasmany points of excellence, against which no insuperable objectioncanbe brought. Had I not declined, already, to name either the friends or enemies of the System, I might here appeal to persons who highly approve of it; and, indeed, who use it daily with manifest advantage. But, I forbear. If, by means of the Engines already given, andthatI am going to offer, it is proved, that the difficulty of making these wheels istrifling, comparedwith their utility, one important point will be gained: I shall not hear it repeated, “that the System cannot succeed,because of the difficulties of it’s execution.”
Cutting engine
The present Cutting Engine is shewn infigs. 1,2, 3, ofPlate 32. It’s immediate use is to form the teeth ofwooden models, for casting. These are previouslybuiltas usual, andlaggedwithbay-wood, of sufficient thickness to furnish the teeth, and leave a small thickness ofthatwood behind or under them.—A B, infig. 2, represents a wheel of this kind, ready for cutting;—mounted correctly on the centre pinC D, which latter is so formed as to befixablein any position on the table or benchE F. Under the wheelA B, there is a kind ofindexa b, put upon the said centre pinC D, which, by means of the clamp and screwb c d, can be occasionally connected with the wheelA Bso as to turn it, when it is itself turned by the means hereafter to be mentioned. To proceed with the description:Gis a slide, moving horizontally on the benchE F, as seen atf efig. 3; this slide being the basis of the headstockG H, which contains theperpendicularslideH I, itself the support of the cutter-frameK L, so constructed as to turn on it’s bolt aboveI, and take any proper position over the edge of the wheel or modelA B. This slide, then, with it’s appurtenancesH I K L, moves along the benchE F, as seen infig. 3atf e: and what gives it this motion, is, the screwg, furnished, purposely, with a left-handed thread, working in thehalf-nutcontained in the small frameh, which contains also a jointedcap, that can be lifted off in an instant, and the screw set at liberty. Moreover, the second use of this screwg, is tobethus disengaged from it’s nut, and lifted up to abouti, where it serves to push back the slideGtowards the wheel, without that loss of time it would occasion if pushed back by the working of the screw. The lettersM N, shew another important part of the Machine, applying to the cutting-process. It is an inclined plane, sloped to the same degree as the bottom of the teeth of the wheel. (See the linea k.) This inclined plane, then, is fastened, in any proper place, on the benchE F, by the wedgeN,justlike the puppet of a common turning lathe; and it passes through an opening in the slideG I, or rather suffers this to passover it, as better seen atM,fig. 3. Furthermore, the slideI(fig. 2), after gliding down this inclined planeM G, will have to be raised between each cutting: and that is the office of the workman’s hand acting on the leverO P, through the iron frameQ M, which is shewn atfig. 3, in another direction; and marked with the lettersQ l m. In fine, the slideGcarries on each side of the Machine a pulling barn, connected with the said slide, and with a smaller sliding pieceo, the use of which is to hold a pin (seen in the figure, but leaving no room for a letter of indication), whichturnsthe wheelA B, by the platep, as the slideGrecedes, and the cutter-systemI K Ldescends on the inclined plane before-mentioned. Having thus adverted to all the important parts of the Machine, we turn tofig. 1, for the purpose of shewingwhatthe plate (whose edge is seen ato p) means; and the effect it is intended to produce.
Design of wheel
In that figure, letB A cbe the section of any wheel it is desired to cut on this principle. The width of the face of such wheel is shewn by the linea b; anda cis called theprojectionof that face, on the base of the cone of which the wheelA Bis a portion; it’s summit being atC. The linee d, shewsoneof the spiral teeth with which the wheel is to be furnished; and I make it by this uniform process: The pitch of the wheel, whatever it be, is set off frometof: and that pitch is divided intoeightparts, (shewn here asfouron account of their smallness) while the width of the facef d, is divided intonineparts, shewn here (for the same reason) byfour and a halfdivisions. This latter division is more numerous than the former, that the principle may be a littleoverdone; or that the teeth may overlap each other by1⁄9of the pitch: To which purpose, beginning the spiral linee date, I move in the second circular line frometo the second radial lineC i, and drawthat diagonalwhich forms the first part of the curved linee d. From this second point, I go to the third circular line, taking also the third radial line, and drawing the diagonal. This I do until arrived at the fifth circular line, when I find myself likewise at the fifth radial lineC d f. These four spaces thus gone over, represent the eight parts into which this part of the facea bwould have beendivided, had the figure been larger: and thereremains a small division neard, equal to one half the others, through which the curvee dis prolonged by a similar process; and this latter portion is what the successive teethoverlapeach other, as before stated.
Now, it will be seen below, that the needfulcircularmotion is given to this wheel, by a movement that takes place in a direction parallel to the basea c Bof thisfigure. The curvee d, must, therefore, be transferred from the surface of the cone, to this basea c B. To do this, I place a point of the compasses atA, and trace, with the openingsA a,A c, &c., the sixquadrantsincluded in the spacea c g h, which are now the projections, on the base, of the circular linesa b f don the surface of the said cone. Here, a slight difficulty should be obviated: strictly speaking, thisprojectionwould be horizontal, and, of course, invisible in this position of the wheel. But I have supposed the figurea c g h, turned ninety degrees downward, round the horizontal linea B, so as to make one representation suffice; and also to shew the connection of the linesa b g h, with thosef d a b. The curvek l, is thus acopyof thate d, onlyshortenedin the proportion ofa btoa c—that is, of the side of the conea C, to the half-basea A.
To secure, then, the coincidence of the pitch, as set off on the circumferencesa fanda g, we must divide a similar portion of both into an equal number of parts,e f; and treatthem, on the linesa c g h, as we did on thosea b d f; by which means we shall get the curvek l,the projection of thate d. And this curvek l, must be made part of aplatek l m n(about1⁄10of an inch in thickness), the use of which is as follows:
This Platek l m n, is no other than that markedo pinfig. 2; and it is there fixed to the indexa b, directed to the central pinC D, as it is infig. 1to the centreA—insomuch, that thepinshewn infig. 2nearo, acting on theslopingcurvek l, will turn that index (and with it the wheel) by the very motion which draws back the slideG(fig. 2), and lets down the slideIon it’s inclined planeG M.
We may remark, lastly, that as the present Machine is adapted tolargemodels, it is not, now, provided with a dividing-plate, although the means of so doing are self-evident. On the contrary, the division dots are seen on the edge of the wheelA B, as is likewise one dot, nearb, on the clampb c, from which a given distance is set off to each of the dots on the wheel, so as to give the pitch required. By these means, then, the wheel is divided and cut, ingood, if not in exquisite divisions; and all the teeth take their shape from the Plateo p(ork l m noffig. 1), and are thus good, in that respect also.
To recapitulate the steps of this process—The workman stands behind the Machine, nearE; and, working the screw with his right hand, draws back the slideG, (thepowerthenturning the cutterrvery swiftly) by which means, the slideIglides down the inclined planeM, and the cutter, impinging on the sloping face of the wheel, cuts it to the depthr a; the shape of the tooth (by the turning of the wheel) being the spiral forme doffig. 1. It may be added, that the lifting leverOpermits this descent of the barQ M, because it is suffered to fall lower thannowrepresented. Thus, when the slideGis arrived nearh, the tooth is finished; and the cutter leaves the wheel ata: after which, the cutter-frame and slideI K Lare raised by means of the leverO—the screwgtaken out of it’ssteps, and the slideGpushed back by it, until the vertical slideIrests again on the inclined planeM, as it at first did. Nothing, now, remains to prepare for cutting a new tooth, but to change the division-dot, by the application of the gauge or compasses, frombto the next point on the wheel; to do which, of course, the clampb cmust be loosened and refastened by the thumb-screwd. I would just notice the4th figure—to say, it is a sketch of one quarter of a bevil wheel; intended merely to shew the form and position of these teeth, and the general appearance of the System.
Quarter wheel
Finally, my readers will please to advert to what has been already said on theformsof these teeth, and their uses: and recollect especially what was observed on the epicycloid, as applied to them. It will easily be perceived, that toputthat form on one of these teeth would be an almost hopeless attempt!—and, happily, it is not necessary. We can,however, by using the cutterrwith various slopes, and going several times through eachspace, cutfacetson the teeth, quite near enough to the theoretical form to make them workwelltogether; and, as before observed, nothing is wanting to make the teethperfect, but to run them together with the wheels placed in due position.
To form a true estimate of the value of any new machine, it is necessary to examine the nature and operation of those that have been used before for similar purposes. And this is the more needful here, because the presentDash-wheelis essentially good, both in it’s properties and effects. The only room left for improvement, seemed to respect thequantityof work done by it: and this is, the chief point of comparison we shall establish in what follows:—
Traditional dash wheel
Thethird figure, inPlate 33, is a sketch of the common Wash or Dash-wheel. The pieces of calico (or other goods) are put into it through the round holes, dotted in the figure; and, by the revolution of the wheel from right to left, are carried up fromatob, or nearly so; from whence they drop by their weight toaboutthe pointc, where they meet the angle formed by the circumference of the wheel and one of the four arms or partitions, by which it is divided. If the wheel go too fast, the line of falling becomes more like the curveb d, and the goods strike the circumference too high, and in an oblique direction;—whence the blow is reduced, and the washing becomes imperfect. If, on the other hand, the wheel movetoo slowly, the piecesslidedown the ascending partition (a) before it comes to the vertex, and thus only fall from the axis to the lowest point of the wheel;—whence, also, an inefficient stroke. Thus, do these wheels require a moderate velocity: and they are reckoned to do their work best when making from 22 to 24 turns, and giving, of course, four times that number of strokes per minute.
The produce of these wheels is thus circumscribed by anaturalcause that cannot be altered—namely, by the law of falling bodies; and my Invention has in view toeludethe shackles which confine this process, and to produce a much greater effect in the same space,—the same time,—and with the same expence of workmanship.
Improved dash wheel
To this end (seefigs. 2 and 4, of the samePlate) I place two, four, or more boxesa,b,c,d, on as many wheelse f, toothed on my Patent principle; the latter, in the present case, being about two feet in diameter, and the boxes, in length, three quarters of that diameter: and ofanyconvenientwidth, according to the size of the pieces. The wheelse fare mounted on the strong shaftsC D, which run, below, in the wheelE; and by which, also, they are turned round the common centre, by means of the vertical wheelF. Further, in the centre, and between the wheelse f, I place the bevil wheeli, of half the diameter, in which the main shaft runs loosely, and which is itself fixed to the upper frame work, so as not to turn at all. The threePatentteeth ate i fshew that these wheels are to geer into each other on that principle: and it is likewise seen that this whole mechanism is included in a set of rails, of an octagonal form, for the purpose of preserving the men from danger, while in the act of charging and discharging the boxes. And here it is worthy ofsomeremark, that this process must beeasier, and more quickly performed, with theseopenboxes, than through holes made in theverticalside of a Dash-wheel, on the usual principle.
To account, now, for the sloping position of the shaftsC D, and the consequent slope of the boxes, they are thus placed, in order that the goods may not drag too much on the bottoms of the boxes, when passing from one end of them to the other. Instead of this, they are, in fact,thrown, by the centrifugal force, from the inner angleh(fig. 2) to some pointkup that side of the box which is then outwards; where they strike, and thenfallinto the contiguous angle underk, to be again projected thence, after one revolution round the common centre; for, it should here be remembered, that, by the given proportion of the wheels, the circulating wheelse fturn on their own axes exactly one half round, for every whole revolution round the common centreA B.
Schematic
To elucidate this still further, I have outlined, atAfig. 1, the central wheeli, offig. 2, together withoneof the excentric wheelsB, and the linesa b,a b, &c., representing the boxes,aresupposedto be wires with the ballsb b, &c. sliding on them, as is usual in some experiments on theWhirling Machine—(See “Ferguson’s Lectures,”) Of thesewires, I have given the true directions in 12 positions of the wheelB: the epicycloidb b b, &c., shewing the steps by which the ballbis broughttowardthe common centre, duringthree quartersof the revolution; and also the position of the wire on which it slides: where it is evident that the ballbhas a tendency to preserve it’s station, at thefirstend of the wire, until the latter takes the positionb b c, when it forms (or nearly) a tangent to the curve, and is, at the same time, at right angles to theradius of motion,A b d. From this moment, then, the ball is free to leave the centre, and to fly off in a tangent with the velocity with which the curve itself is generated at that point. We might, thus, during the rest of it’s flight, seek it somewhere in the lineb f g; but, as the wirecontinuesto change it’s position, andmustturn half round on it’s own axis, by the time it arrives atB b, or describes a quarter-circle on the common centre, it will again overtake the ball—and, giving it a curvilinear direction, will finally carry it to it’s other extremity, at or near the pointB—where it’s motion first began: and thus shall we give as many strokes to the ball, ashalf turnsto the wheelB; or, in other words, as manydashesto the cloth, as we give turns to the boxes, round the common centre.
By this process, then, substituted for that of the common Dash-wheel, we can increase almost indefinitely, the number ofpassages of the cloth from one end of the boxes to the other; and the force of thedashwill be as the squares of those numbers; since (asFergusonexpresses it) “a double centrifugal force balances a quadruple power of gravity.” If, then, with four boxes we turn this machine 60 times in a minute, we shall have 240 strokes in that time, instead of about 90 given by a common Dash-wheel; and this difference might be more than doubled, if so desired: for should, then, the stroke be found too severe, the boxes might be shortened, so as to lessen it’s violence, though preserving all it’s frequency.
There aretwoother objects that present enough analogy to thisWashingprocess, to be here mentioned. The first is the operation ofFulling, as applied to woollen cloths in general. That process, I fear, is not performed at present in the best manner possible; and I feel persuaded that the centrifugal motion might be applied to it with advantage—whether as to quantity of produce, or perfection of effect: and having thus said, I shall leave the idea to the riper judgment of my manufacturing readers.
The second object I shall just introduce is, that ofKneading Dough, for bread, by the same centrifugal agency. It is well known, that an ingeniousbaker, of Paris, invented, some time ago, a method ofkneading; which consists in letting the lump of dough fall successively from the four sides of a square box, revolving on a horizontal centre. As this idea seems to havesucceededperfectly, I offer the Centrifugal System, as tending to quicken, almost indefinitely, such a process; and I particularly recommend it to the attention of Government, and of alllargeestablishments as a mean of doing well and rapidly,by power, what is frequently done slowly and ineffectually, by the usual methods.Verbum sat.
Hydraulic table lamp
I call this an Hydraulic Lamp, to distinguish it from the Hydrostatic Lamps, commonly so named: and I think the distinction proper, because this Machine acts in a different manner. It’s principle will be seen in a moment, by turning to the5th figure, ofPlate 33. If, there, we pour oil (or any liquid) into the bent tubeA D GatA, the first effect will be to raise it toC, in the rising branchB C; and fromCit will trickle down the branchC D, leavingthe air, there, to occupy it’s own place. Continuing to pour, slowly, more oil intoAthe trickling oil inC Dwill ultimately fill the rising tubeE D, expelling the air before it; and, now, the weight to balance the column inA Bwill beboththe columnsB CandE D; whence, of course, that column will rise as far aboveCasCis aboveB; that is, half-way betweenCandA. Here,there would bea small deduction to be made, if the heightB Cwere considerable; but, as it is only supposed to be about a foot, the compression of the air inC D, &c., (being about1⁄3of a foot or1⁄90of an atmosphere) may be neglected. Continuing, then, to pour oil intoA, we shall again fill,notthe descending tubeE F, but the rising tubeF G; whose column will thus be to be added to thoseB CandE D; so that now the columnA Bwill rise toA, andthere abide, as long as the mouthGis kept full, or nearly so.
The above is the principle of the Lamp announced in the title; whose effect depends, then, on the number ofbendsmade in the tubeA D G, which number (whatever be theform) it would be well to make rather greater than smaller, as the heightB C, &c., might be so much the less, compared with the whole height of the columnA B; by which means, also, a smaller difference in the level of the columnbelow, wouldreturnthe oil necessary for the consumption of the wickabove.
Better form of lamp
I have given this idea what I think a better form infig. 6. Instead of the bent tubeA G, offig. 5,thisform supposes a series ofair-tight cups, embracing each other; one half of them with their mouths openingupwards, and the other half withtheirsopeningdownwards. They are shewn, by a section only, in thisfig. 6; wherea b c,c b a, present the under cups, forming one piece with the outer surface of the bottom vesseld a c,c a e: and, while speaking of this part of the Machine, I would just indicate it’s coverd e f gput on like the lid of a snuff-box, and carrying a case or tubef g, the use of which will be mentioned in a moment. To proceed, then, the upper vessel is shewn by the edges of it’s cups seen immediately over thefigures1 2 3, 4 5 6, placed between thelettersa b c, &c.—These inverted cups make alsoone bodywith the moveable cover shewn betweendande, and to which is soldered the tubeh i—which, sliding in the casef g, keeps this invertedvessel steady. Where note: that there is aninnertube soldered into the tubeh i, through which alone the oil rises, and which can hardly be made too small, since it has only to supply the consumption of a lamp—namely, a few ounces of oil in a whole evening. We may, finally, take notice of the weight placedunderf g, upon the said inverted vessel, and which helps to counterpoise the oil in the rising tubeh i; which tube, as before observed, may be as many timeshigherthan the distancea dore a, as there are rising columns between the cupsa b cand those 1 2 3, &c.
I am not wholly prepared to say what portion of the oil it might be best to re-elevate by the pressure of the aforesaid weightf g; but, if it were a considerable part of that contained in the central compartmentc c,thatcolumn would be shortened in proportion; and the reservoir atiwould, doubtless, feel the want of it to preserve it’s level. I think, therefore, it might be well to use, below, acupor two more than sufficient, so as to raise the main column higher than actually wanted; and to coerce this rising tendency, by a small stop-cock in the rising branch, to begentlyopened at the will of the person using the lamp. I cannot say I have exhausted this subject; either in these respects, or as to it’s technical capabilities. But I have fullytriedthis method of raising oil above it’s level; and used, for some time, a lamp made on this principle, and which is still in my possession: and, at some future time, I intend to bring forward an Hydraulic Machine, founded on the same principles.
It is not supposed that this Essay can lead, immediately, to any result of magnitude; but it is thought to be a subject capable of further extension, and thus, finally, of future usefulness. Were this process only sufficient to supply a single house with water, at a small expence, the labour bestowed on it would not be altogether in vain.
By General Roy’s experiments, cast iron (and steel) expanded by 180° of heat (or, by passing from the freezing to the boiling point ofFahrenheit) 0.013 of an inch per foot.
Constuction with expanding tubes
Supposing, then (Plate 34,fig. 1), the tubesA B Cto be 20 feet long, their whole expansion will be 0.26 hundredths of an inch. But, as the tubes are placed in the figure, thehalftubesA D B Dact together on the sphereD, and, both together, drive it in the directionE D,morethan as the above expansion, in the proportion of the lineE Dto thatA D. Taking, then, one half only of the above expansion = 0.13 hundredths of an inch,thatmust be augmented in the ratio of the sine of 60 degrees to radius, or in that ofA DtoE D. I, therefore, multiply this decimal 0.13 by the fraction1000⁄866, whichgives 1300 to be divided by 866, or very nearly 0.15 for the expansion, in the directionE D, occasioned by the two half barsA D B D: and the same is true at the other anglesFandG.
Again, to find the expansion (andcontraction) of the barsa b c, we must compute their length as compared with the half tubes above-mentioned; and that length is to 10 feet (the half tubeA DorB D) as 866 is to 1000 = 11.54 nearly: the expansion of which is thus found:—if 10 feet expand 0.13, what will 11.54?—Answer, 0.15. Now, as the machine acts by theheatingof the pipesA B Csimultaneously with thecoolingof the barsa b c, we must add the former expansion to thiscontraction, which gives us 0.30, orthree tenthsof an inch for this combined effect at the three angles of the Machine. And,supposing, now, any pair of bars to act directly against each other, as atH I K; and that, further, the bars be stretched until the angle with the horizon be only 2 degrees, then the vertical motion atIwill be to the horizontal (arising from the expansion aforesaid) as 1000 to 35, the sine of 2; that will be, in round numbers, 28 times as great, or 28times three tenths of an inch= 8.4 inches, which is thestrokeof this Machine in these dimensions.
In this calculation, I have not forgotten that the vertical and horizontal motions arenearer alike, when the bars are not drawn so tight atK H; that is, when the jointIis lowered.But it is equally true that, when the jointIrises still more, the difference between these motions isstill greater; so that, as a medium effect, I think we may reckon on aneight-inch strokein the present case.
The question now recurs, of whatstrengthare these strokes? Are they sufficiently powerful to produce a useful effect with soshorta motion? This I cannot say from experience; but, from the known strength of iron and steel, their power, in these dimensions, must bevery great. A few more observations may occur in the course of the enlarged description we shall give of the Machine itself.
A B Care three pipes of cast iron, well turned at the end, and having conical points of iron, well steeled, let into them, so as to have no tendency tobend.a b care three steel bars, placed in troughs, so as to be heated or cooled by water poured into the latter. Or, these troughsmaybe exchanged for tubes, to admit heated or cooled air, according to the means used to cause these mutations. In a word, although I have represented these bars as contained in troughs, I intend to finish my description, on the supposition that they aretubes, because I intend to suppose the Machine worked byairinstead of water.
Fire place
To proceed: atdis an openingunderthe tubeB, into which air enters, andCis an openingonthe top of the tube which emits the same air, the three pipes being made to communicateby means of a short junction-pipe at each of the anglesDandG. Here, then, the fire-placef g,fig. 2, must be noticed: the use of which is both to heat and cool the Machine; and the following are the means:—This little instrument contains fire in it’s middle compartment, and that fire drawsairinto the partf, and drives it out of the partg. It alsoturnson a centre-pin, seen in thefigure. This chaffing-dish, then, is placed ati d, and there serves a double purpose. When it’s pipegconveys heated air into the pipesB A C(andoutatC), it heats those pipes and expands them; but, at the same time, the pipefof this instrument draws cold air through the three tubesa b c, in which are the steel bars that require to becontracted: both which operations conduce alike to the above-described effect. By these means, the weightwis raised, and (for example) water sucked into the pumpX. But, turning the fire-place half round, we reverse this effect. Thehotair is now drawn, out of the pipesA B C, andcoldair drawn through them, by which they arecooled; while the hot air, from the fire, is thrown through the pipeginto the tubesa b c, and passing through the chimneysk l, there heat the bars and expand them,—both which operations concur inletting downthe weightE, and thus, in forcing the water of the pump to whatever destination was previously assigned it.
Many people, in these parts, have seen a certain machine, said to have been invented by an inmate of that laudable institution the Liverpool Asylum for Blind People; for the purpose of making laces, covering whips, &c. I hope the similarity of name will not induce any reader to suppose that I have had that machine in view, and am endeavouring to cast it into the shade, or purposely to supersede it. If any person should thus think, I have asafereply at hand. My own invention (somewhat less perfect than it now is) was made, many years ago, on purpose to servean Asylum for the Blind in Paris!—a reflection with which I shall, at once, close this, perhaps, unnecessary apology.