No. C.
Upon so potent a help as these two last mentioned inventions, a water-work is, by many years' experience and labour, so advantageously by me contrived, that a child's force bringeth up, an hundred feet high, an incredible quantity of water, even two feet diameter. And I may boldly call it, the most stupendous work in the whole world: not only with little charge to drain all sorts of mines, and furnish cities with water, though never so high seated, as well to keep them sweet, running through several streets, and so performing the work of scavengers, as well as furnishing the inhabitants with sufficient water for their private occasions: but likewise supplying the rivers with sufficient to maintain and make navigable from town to town, and for the bettering of lands all the way it runs; with many more advantageous, and yet greater effects of profit, admiration, and consequence: so that deservedly I deem this invention to crown my labours, to reward my expenses, and make my thoughts acquiesce in way of further inventions. This making up the whole Century, and preventing any further trouble to the reader for the present, meaning to leave to posterity a book, wherein, under each of these heads, the means to put in execution and visible trial all and every of these inventions, with the shape and form of all things belonging to them, shall be printed by brass plates.—Besides many omitted, and some of three sorts willingly not set down, as not fit to be divulged, lest ill use may be made thereof, but to show that such things are also within my knowledge, I will here in myne owne cypher sett down one of each, not to be concealed when duty and affection obligeth me.
In bonum publicum, et ad majorem Dei gloriam.
NOTE.
The three last inventions may justly be considered as the most important of the whole "Century," and when united with the 68th article, they appear to suggest nearly all the data essential for the construction of a modern steam-engine. The noble author has furnished us with what he calls a "definition" of this engine; and although it is written in the same vague and empirical style, which characterises a large portion of his Inventions, it may yet be considered as affording additional proofs of the above important fact.
The Marquis's "definition" is exceedingly rare, as the only copy known to be extant is preserved in the British Museum.—It is printed on a single sheet without date, and appears to have been written for the purpose of procuring subscriptions in aid of a Water Company, then about to be established.
"A stupendous, or a water-commanding engine, boundless for height, or quantity, requiring no external, nor even additional help or force to be set, or continued in motion, but what intrinsically is afforded from its own operation, nor yet the twentieth part thereof. And the engine consisteth of the following particulars:—
'A perfect counterpoise, for what quantity soever of water.
'A perfect countervail, for what height soever it is to be brought unto.
'A primum mobile, commanding both height and quantity, regulator-wise.
'A vicegerent or countervail, supplying the place, and performing the full force of man, wind, beast, or mill.
'A helm or stern, with bit and reins, wherewith any child may guide, order, and control the whole operation.
'A particular magazine for water, according to the intended quantity, or height of water.
'An aqueduct, capable of any intended quantity or height of water.
'A place for the original fountain or river to run into, and naturally of its own accord incorporate itself with the rising water, and at the very bottom of the aqueduct, though never so big or high.
'By divine providence, and heavenly inspiration, this is my stupendous water-commanding engine, boundless for height and quantity.
'Whosoever is master of weight, is master of force; whosoever is master of water, is master of both: and consequently to him all forcible actions and atchievements are easie.'"
It may now be adviseable to trace the history of the steam-engine through some of its earlier modifications; and we shall find that, although the present form of this stupendous machine almost deserves the title of an invention, yet that many steps have been taken, and much labour and much ingenuity expended, before it was brought to that point from which the more modern improvements may be said to have begun. And whilst we admire the genius of those who have perfected the application of a mighty power, let us not refuse the tribute of praise to those, who first pointed out that such a power existed.
The first apparatus of this description, of which any authentic account has been preserved, was suggested by Hero of Alexandria, and consisted of a vessel F in which steam was generated by the application of external heat. The ball G was supplied with the elastic vapour thus procured, by means of the bent pipe E B, a steam tight joint being provided for that purpose. Two tubes bent to a right angle at A and D, are the only parts open to the air, and as the steam rushes out from very minute apertures, a rotatory motion is produced. An account of this apparatus is preserved in Hero's Spiritalia, published by the Jesuits in 1693; and a copy of this highly curious work, with a Latin translation prefixed, is now in the Library of the London Institution.
A modification of Hero's apparatus is represented beneath: It was constructed by Mr. Styles for the use of the Editor in his public lectures. The circular tube a is in this case supported by the upright pillar c d; and the flame of alcohol in the trough b, by generating high pressure steam, which rushes from the apertures e, produces a rotatory motion.
Brancas's revolving apparatus, as will be seen by reference to the diagram in the preceding page, was still more simple than that contrived by Hero. A copper vessel filled with water, (in the original figure made in the form of an ornamental head,) was furnished with a pipe c, through which the steam was propelled, and striking against the vanes of the float wheel d, readily gave motion to a pestle and mortar, which was employed in the alchemist's laboratory.
The only work in which a description of this engine has been preserved, was published in 1629; it is exceedingly rare, and the above diagram is engraved from a copy in the possession of Major Colby.
A slight examination of the principle upon which this simple apparatus is constructed, will shew that no very considerable force could have been obtained; as the steam passing through the atmosphere in its passage to the wheel, must, to a certain extent at least, be converted into water.
After the publication of the work by Brancas, more than thirty years elapsed ere the publication of the Marquis's "Century" recalled the attention of the scientific world to this important subject; and this invention, which he states as having been completely carried into effect, was evidently very different from that of his predecessors.
It is said that the Marquis, while confined in the Tower of London, was preparing some food in his apartment, and the cover of the vessel, having been closely fitted, was, by the expansion of the steam, suddenly forced off and driven up the chimney. This circumstance attracting his attention, led him to a train of thought, which terminated in the completion of his "water-commanding engine."[9] Of the Marquis's invention no record has been preserved beyond the articles to which we have already alluded in the present work: and in the absence of other data, the Editor readily introduces Professor Millington's design for an engine on similar principles; and which, with a few alterations, might be made available for the purposes recommended by our author.
In this diagram, q represents a strong and close vessel or boiler to contain water, set in brick work like a common copper, with a fire-place r underneath it, having a chimney s. The boiler thus constructed, is intended to afford the means of producing steam: and if we conceive two casks or strong hollow vessels of any form to be placed under the surface of the water, near the boiler, as at t and v, and that each of these vessels has a valve opening into it in its lower part as u u, and two pipes w w, proceeding from the upper part of the vessels to the top of the steam boiler q, while two other pipes x x proceed from the lower parts of these vessels into a cistern y, forty feet above the level of the water; an apparatus thus constructed will nearly form the water-commanding engine, for if the vessels t and v are both filled with water by the valves u u, and the cock z be opened after the steam has accumulated in the boiler, the elastic fluid thus generated will instantly rush down into the vessel t, and when the surface of the water is heated expel the whole of its contents up the pipe a x, into the cistern y, where it will be retained by a valve opening upwards in any part of that pipe, as at a. This done, the cock z must be shut, and after permitting the steam to accumulate for a short time, that at b must be opened, and the steam will rush into the vessel v and perform a similar office, c being the valve to prevent the return of the water. When the steam is shut off from the vessel t, the elastic fluid which had previously been introduced to expel the water, will be condensed by the cold media round it, and thus a vacuum will be produced in the vessel t, consequently a part of the water in which it is immersed will rush into it by the valve u, and occupy the whole internal cavity, thus putting it in a state of preparation for a second opening of the cock z, by which its contents will be again discharged into the cistern y, and so of the two vessels alternately; for while v is emptying, t will be filling, and vice versâ, which agrees with the Marquis's account when he says, "that the man is but to turn two cocks, that one vessel of water being consumed, another begins to force," &c.
The above suggestion for an engine capable of raising water may be still further improved by adding a suction pipe to the valves u u, and the pressure of the atmosphere will increase the working power of the engine more than thirty feet: and should a less height be required, the forcing pipe may be shortened in a proportionate degree: indeed this fact was attended to by the next person who claims the honour of having invented the steam-engine, to which it may now be adviseable to direct the reader's attention.
The engine suggested by Savery for the purpose of raising water, consisted of a boiler a furnished with a safety valve v. The steam-vessel r was connected with the well H, by a suction pipe n; and when water was to be raised the vessel r was filled with steam, which rushing in, soon expelled the air: when that was completely effected, the communication with the boiler was closed, and the steam condensed, which diminishing its bulk, formed a vacuous space within the vessel; the pressure of atmosphere then operating upon the surface of the water in the well, drove it up the pipe. In this form of the apparatus, the inventor was seldom able to raise water more than thirty feet: and when a greater altitude was required, it was effected by the impellent force of high pressure steam. This was accomplished by the ascending pipe k, which was sometimes carried sixty feet higher than the steam-vessel s; and a reference to the great expansive force of steam will show that this operation must be attended with considerable danger. After condensing the steam and filling the vessel r with water, a new supply of steam was then introduced, which pressing on the surface of the water, drove it up the pipe k; and it will be evident that the pressure on the internal surface of the boiler must be proportioned to the height of the column of water thus raised by the steam.
The principal objection to this form of the engine arises from the great consumption of fuel, a considerable portion of the caloric employed in the generation of the steam being absorbed in heating the new surface of cold water last raised from the well; and where great heights are required, there appears no mode of completely obviating this objection. Should it, however, be required merely to raise water about thirty feet, there are few contrivances more economical or better adapted for general use.
While speaking of Savery's apparatus it may be adviseable to notice the very ingenious adaptation of the same principle to the construction of a gas engine, by Mr. Brown. In the latter case a vacuum is formed by the introduction of an inflamed jet of carburetted hydrogen gas, which consumes the oxygen, and rarefies the nitrogen, by the increase of temperature which ensues. The vacuum thus produced is much more perfect than would at first view have been supposed, from the nature of the process resorted to by the patentee; but the economy of employing carburetted hydrogen gas as a substitute for condensible vapour is still somewhat problematic.[10]
To more fully understand the nature of Mr. Brown's engine, it may be better to revert to a diagram, which will sufficiently explain its general principles.
In the above view, the cylinders c and d, are the vessels in which a vacuum is alternately effected; g i g and h j h are two pipes, leading into the lower cylinders x x, shewn in the next page, from which the water rises along those pipes to fill the vacuum cylinders alternately. The water thus supplied is discharged through the pipes B into the tank or trough z, where it falls upon the overshot water-wheel, and, by the rotatory motion thus produced, gives power to such machinery as may be connected to it. The water runs from the wheel along a case surrounding the lower half, into a reservoir v, from which the lower cylinders x x, are alternately supplied.
The gas is supplied to the cylinders by the pipes k k k, which must be, of course, attached to a gasometer, or some other reservoir of gas. The gas also passes along the small pipe l l (which communicates also with the gasometer), and being lighted at both ends of that pipe, is kept constantly burning in order to ignite the gas within the cylinders.
The gas being admitted along the pipe k, the flame from the pipe l is now freely communicated to the gas in the cylinder, through the orifice, by the opening of the sliding valve s, which is raised by the arm r, lifted by the rod o by means of the beam.
The water in the reservoir v passing down one of the pipes w, into one of the lower cylinders x, causes the float y in that cylinder to rise, and, pushing up the rod o, raises the end b of the beam, which, of course, draws up with it the cap f, and forces down the cap e of the other cylinder c.
The alternate action of each cylinder is produced by chains and rods, attached to a glass or iron vessel p, more than half filled with mercury, and turning upon a pivot; each end receives its movements of elevation and depression from the rise and fall of the projecting arms q, by the action of the beam above; the mercury within flowing to the lower end, giving an impetus, and thus regulating the supply of gas to the cylinders, and the movement of the slide in the trough v. By this action the water from the reservoir flows down the pipe w, into the vessel x, and produces the elevation of the float y and the rod n, and raises the cap e by the ascent of the beam at a.
The motion thus produced in one part of the machinery, operates upon the corresponding parts on the other side, and hence a corresponding motion is obtained: the slider in the trough v, moved by the action of the mercurial tube p, being removed from its position, allows the water to fall into the other pipe w; and, as it ascends, suffers the float y to descend, and rising into the main cylinder, then lifts again the beam at b, and its connexions, and forces down the cap e on the top of the other cylinder.
When the vacuum is produced in the cylinders, the air must be admitted to allow the water to be discharged, and the caps to be raised: this is effected by a sliding valve in the air-pipe m m, acted upon by chains t t, attached to the floats in the reservoir, and as motion is given to them, the valve is made to fly backwards and forwards, so as to allow the free admission of atmospheric air.
Chains u u, with suspended weights, open the cocks in the pipe k k, and produce the alternate flow of the gas, and regulate and modify its supply. In the pipes g i g, and h j h, are clacks to prevent the return of the water, when the air is admitted into the cylinders.
A piston may be worked as is above described, with the machinery attached; but it may also be worked in a distinct vessel so as to communicate with several cylinders, and, consequently, several pistons may work at the same time, the air and vacuum valves being opened and closed by similar means to those adapted to work the induction and eduction valves of steam-engines.
The atmospheric engine comes next in order, and its claim to practical utility is of a very early date.
The cylinder b, is in this engine placed over a boiler n, and if we suppose the piston p made to fit air-tight, it will be evident, that it must be driven up by the action of the steam beneath, should a sufficient supply of heat be applied; when this is effected, the condensible vapour may be reduced to its original bulk, by the introduction of water from the cistern i. In the working engine however, the ascent of the piston is effected by the action of the lever e g, acting on the fulcrum f. To the end g of this lever or working beam is attached the pump-rod h, and it will be evident that whenever that preponderates over the piston p, that the latter must be drawn up. On the readmission of the steam, a new supply of condensing water is introduced by turning the cock l, and the pressure of the atmosphere above the piston being unbalanced by any resistance beneath, the end e is again depressed, and the pump-rod again elevated. The pipe g is employed to carry off the condensing water, which would otherwise accumulate within the cylinder; and the small forcing pump, with its rod v s, supplies the condensing cistern i, by the pipe t.
At the beginning of the last century, the atmospheric engine had made considerable progress in the mining districts, and in 1718, the patentees agreed to erect an engine for the owners of a colliery, in the county of Durham, where several hundred horses had previously been employed. Mr. Henry Beighton, who was engaged as an agent in this concern, materially improved the engine by making it self-acting, and divesting it of nearly all the complicated machinery, which had been previously employed for that purpose.
A very simple and at the same time ingenious mode of illustrating the operations of an atmospheric steam-engine will be found in the annexed apparatus, suggested by Professor Brande, and employed in his lectures at the London Institution.
The glass tube and bulb b is shewn with its piston a, the rod being hollow and closed by a screw c. If steam be generated by the spirit lamp d, the air will speedily be expelled, and after this is effected, the screw c may be closed, and a working stroke produced by artificial condensation.
We come now to a new and distinct era in the history of this important invention, and in noticing the labours of Mr. Watt, we may almost speak of his engine as the gigantic offspring of a hand giving birth to an automaton, no less powerful than that of the fabled enchanters of the olden time.
Mr. Watt's first great improvement in the engine of Newcomen may be best understood by reference to the annexed diagram, in which a represents the cylinder, and b its plug or piston made to fit air-tight. The pipe d is furnished with a stop-cock, by means of which the elastic vapour is occasionally admitted.—A similar pipe, furnished with a stop-cock at f, passes from the other side of the cylinder, and enters the vessel g; e being the reservoir to contain water.
If we now suppose the piston at the bottom of the cylinder, and steam admitted by the pipe d, its expansive force will elevate the piston, and when the air is expelled, the whole internal cavity of the tube will be filled with condensible vapour. On closing the steam-cock, and opening that connected with the vessel g, a portion of the vapour will immediately expand itself, and coming in contact with the cold sides of the vessel, a portion of its heat must be absorbed by the water at e. A new portion of steam then descends, and is also condensed, and indeed the same process continues till the whole of the steam is drawn from the tube. A vacuum being thus formed, the pressure of the atmosphere will preponderate, and the piston rod be depressed to the bottom of the tube. On closing the stop-cock f, a new supply of steam may be admitted by the other pipe, and after raising the piston, the process of condensation may be readily repeated.
The advantages that arise from this mode of forming a vacuum are very considerable, not the least important of which, is a saving of nearly half the fuel.
In the old engine, the condensing water must reduce the temperature of the internal surface of the cylinder to that of the atmosphere, before a vacuum could be produced, and when the condensing water was applied more sparingly, the elastic vapour remaining in the cylinder was found to materially reduce the pressure of the air operating above. From this it will be seen that the great advantage of Mr. Watt's apparatus consists in performing the condensation in a separate vessel, so that the cylinder is always preserved at the temperature of boiling water.
Having thus produced a vacuum without the intervention of condensing water beneath the piston, Mr. Watt's next improvement consisted in closing the top of the cylinder, so that the piston-rod worked through an air-tight hole in the centre of the cap; and to ensure the necessary pressure within the cylinder, steam with an elastic force greater than that of the atmosphere was admitted above the piston. The atmospheric engine of Newcomen was thus converted into a steam-engine, and its power was easily regulated.
A cylinder and piston constructed on the most improved principles may now be examined.
In the annexed diagram, the cylinder A is furnished with a steam-tight piston, the rod of which is supposed to be connected with the working beam. B represents the pipe which admits the steam from the boiler, the quantity being regulated by the throttle valve c, and the elastic vapour is now passing through the box d d, so that it enters beneath the piston. At the same instant of time, a communication is formed through the aperture m n to the pipe p, which leads to the condenser. When the piston reaches the top of the cylinder, the sliding bridge or valve has its direction changed, so that the pipe r, and consequently the bottom of the cylinder, is connected with the condenser, while a passage is opened from the pipe m n to the steam box. Thus a communication is alternately made between the top and bottom of the piston.
The slide-valve represented above is not invariably employed in the double-acting engines, and we frequently find the annexed contrivance resorted to, in some of the best engines.
The pipe 14 represents the passage to the cylinder, and a communication is now opened with the steam chamber g. The raised valve is perforated and a similar valve beneath closed by the rod which passes through it. On closing the valve g, the lower valve h is opened, and a free passage between the condensing pipe beneath and the upper part of the cylinder is the result. If we now suppose a similar double valve placed at the bottom of the cylinder, it will easily be seen that an effect similar to that described in the sliding valve will be produced.
The speed of the engine is regulated by a very ingenious contrivance introduced by Mr. Watt, called the governor, and represented beneath.
The balls i i are supported by the bent levers h f, and as they are made to revolve with the fly wheel axis, by means of a band passing round the pulley c, any increase in the speed of the engine will cause the balls to diverge. The moment this takes place, the shorter arm of the lever n is depressed, and as the extremity l is connected with the steam-pipe by the throttle valve, the supply of steam must of necessity be diminished, and the speed of the engine reduced.
As the working power of the engine depends very materially on the accurate fitting of the piston, it may be adviseable to examine some of the modes of effecting this important object.
Mr. Smeaton, who greatly improved the atmospheric engine, coated the under side of the piston with elm or beech planks about two inches thick; the wooden bottom being screwed to the iron with a double thickness of flannel and tar, to exclude the air between the iron and the wood. By the adoption of this improvement, its property of conducting heat was reduced, and the wood having been previously jointed, with the grain radiating in all directions from the centre, was not liable to expand by the heated steam. This piston was kept air-tight by a small stream of water continually falling on its upper surface; but in Mr. Watt's engine he was compelled to make the piston fit tight without any other media than the oil that was employed to lubricate it.
The piston is now cast with a projecting rim at bottom, which is fitted as accurately as possible; the part above the rim being about four inches less than the cylinder, thus leaving a circular groove for the hemp which forms the packing. To keep this in its place, a lid or cover is put over the top of the piston, with a projection which enters into the circular groove for the packing, and pressing upon it, the plate is forced down by screws, which work into the body of the piston. By this means the packing is made to fill the internal part of the cylinder with tolerable accuracy, and thus prevents for a time any steam passing between the piston and the cylinder. When, however, by continued working, the packing ceases to fit, it occasions a waste of steam, to remedy which, the cylinder cap must be removed, and as this is attended with a considerable degree of trouble to the engine-man, it is seldom attended to till a considerable loss of power has arisen. There are two improvements on the piston, by which this inconvenience is to a certain extent obviated.
In the first, by Mr. Woolfs, each of the screws is furnished with a wheel or nut, and these are all connected together by means of a central wheel, working loose upon the piston-rod in such a manner, that if any one of the screws be turned, a similar motion is given to the remainder.
In a piston thus constructed, there is little difficulty in drawing down the packing, by applying a key to the square head of the projecting screw, employed to communicate with the rest: the key-hole being afterwards closed by a cap.
The second contrivance is by Mr. Barton, a diagram of which, accompanied by a piston as it is usually constructed, is shewn beneath.
In the first piston, the screws i i are made to compress the packing h h, by acting upon the plate n n, the piston-rod r being firmly attached by the nut c.
In one of the modifications of Barton's piston, on the contrary, the packing is dispensed with, as the flexible springs t t t press upon the wedges c c c, and expand the intermediate plates. A break-joint is readily formed, by making the series of plates double; the second set of plates falling upon the spaces which occur between the first row.
The action of the high pressure engine depends upon the great elastic force acquired by steam, when exposed to the action of heat at very high temperatures.—It may indeed be considered as a return to the principle of Brancas and the Marquis of Worcester, as in this engine no condensing water is necessary; and it acts merely by the elastic or repellant force of steam. In the high pressure engine, the condenser is taken away; and the steam, instead of being converted into water by artificial cold in a close vessel, is allowed to escape into the atmosphere from one side of the piston, while it is acting forcibly on the other.
The advantages of the high pressure engine over that used with a condenser, are cheapness in construction, and a saving of the whole expense attendant on procuring a sufficient supply of condensing water, which in some cases is an object of considerable importance.
In the annexed section, the piston B passes through an air-tight stuffing box, and the steam is entering beneath it, by the four-way cock E. If we now suppose the piston at the top of the cylinder, a new arrangement of the communicating pipe takes place, as the steam which was beneath escapes, while a fresh supply enters above. The four-way cock may be best explained by a section in the opposite direction. Two pipes are seen at the lower extremity of the cock, which communicate with the upper and under sides of the piston. The aperture D opens to the air, while the pipe C serves for the admission of steam from the boiler.
We have now to notice the double cylinder engine constructed by Woolfs, which will be found, by reference to the diagram in the preceding page, to consist of a high pressure cylinder, connected with a condensing apparatus.
A and B represent the two cylinders, in the larger of which the steam is allowed to expand itself, after passing from the high pressure cylinder B. The steam, which in the first instance is of considerable elasticity, is admitted to the cylinder B, by the tube and valve E, and entering the cylinder above its piston, impels it to the bottom. When this is effected, a communication is opened between the upper part of the cylinder B, and the under side of the cylinder A. The communication between the cylinder B and the steam-pipe E, is now reversed, and the steam is made to press on the under side of the piston B, a communication being at the same time formed between the upper part of the cylinder A, and the pipe leading to the condenser which is seen beneath. So that if we suppose the two pistons connected by means of their rods with one end of an ordinary working beam, the upward and downward strokes of each will be performed at the same time. We have hitherto considered the steam as passing direct from the boiler to the cylinder B; this, however, is in reality effected by a more circuitous route, as it is in the first instance admitted to the steam-case of the larger cylinder by the pipe C, and passing round a similar case, encircling the cylinder B, it is then made to enter at E. The pipe at D is merely intended to form a communication for carrying back to the boiler any water that may be produced by condensation in the steam-case, before the engine arrives at a proper temperature for working.
Having thus briefly examined the nature of Mr. Woolf's engine, it may now be advisable to revert to the boiler, by which he proposes to generate steam of sufficient elasticity for the use of the small cylinder, which requires elastic vapour of great expansive force. The boiler, represented by the diagram beneath, consists of a series of tubes, of cast-iron, connected by screw-bolts with the under side of a larger vessel A A, communicating with the engine. The upper boiler is furnished with four, and in some cases, with five apertures; the first of which is intended for the admission of water, to supply the waste which continually arises from evaporation. The safety valves, man-hole, and water-pipe are also shewn.
The mode of setting this boiler is also of considerable importance, as it is advisable to give a long and waving course to the chimney.
A A still represents the principal boiler, while the figures 1, 2, 3, &c. indicate the passage of the flame and heated air; a section of the chimney being shewn at O.
The steel-yard safety-valve which was employed in all the early engines is simple, and the nature of its construction may readily be understood. A represents a portion of the upper part of the boiler; B the safety-valve or plug made to fit air-tight on the valve-seat beneath; C the lever working on its axis at D, and furnished with a moveable weight E, adjusted to balance the pressure of steam within the boiler.
When steam of great elasticity is required, the weight is placed at the extremity of the lever, and as such, acts with greater force on the safety-valve, than when removed to a point nearer to the axis on which it revolves: so that should low pressure steam, or that which has a less expansive force, be required, it will only be necessary to remove it nearer towards the axis on which it turns.
The lever and balance-ball safety valve already described, appear but little calculated for those engines in which high pressure steam is employed, as the engine-man, in an over anxious zeal for the full performance of the machinery confided to his care, has been frequently known to increase the internal pressure of a large boiler many thousand pounds beyond the resistance to which it was originally proved. To prevent a recurrence of those accidents, which first drew the attention of the legislature to this important part of the engine, it appears advisable to inclose the safety-valve in an iron case, of which a section is annexed.
The valve B in this case rests upon a conical seat in the boiler A, and is furnished with a series of small moveable plates lettered c, which are employed to increase or diminish the entire weight of the safety-valve, the whole being covered by the box D; and as this is pierced with a number of small holes, the steam readily escapes when the expansive force exceeds the resistance offered by the loaded valve.
The patent revolving wheel invented by Mr. Masterman, appears to promise the best results of any rotatory engine yet invented, the friction being much less than in any other apparatus in which steam is employed as a prime mover. In this engine, Mr. Masterman proposes to employ water, or the fluid metal mercury as the immediate agent, which he effects by inclosing it in the tubular rim of a large wheel, furnished with valves opening in one direction. This wheel, as is shewn in the opposite diagram, is made to revolve on a hollow axis connected with the steam boiler. The arms or spokes which radiate from the axis are also hollow; and on the admission of steam from the boiler, it is conducted through the arm immediately opposite, and entering the rim of the wheel, comes in contact with, and presses against the column of water beneath and the closed valve above the arm. The water being previously heated to the boiling point, no condensation ensues, but the whole weight of water, which was previously balanced in two columns of equal height, is driven, by the pressure of the steam, to the side opposite to that at which the elastic vapour entered, and that side of the wheel will necessarily preponderate. If this process be repeated, the steam being allowed to blow through each radiating arm in succession, a continuous rotatory motion will be produced. Should it be advisable to employ steam of less elasticity, a condenser may be added, and that too without materially increasing the expense.
The application of steam-engines to the propelling of carriages on the public road, has hitherto been considered as a refinement in mechanics, rather to be wished for than a matter of reasonable expectation. The locomotive engine was first employed for this purpose by Messrs. Trevithick and Vivian, in 1802; and it found a ready introduction to the mining districts where rail-roads are general. In some cases, five, six, and even ten waggons laden with coal are dragged up an inclined plane by means of these vehicles; and of course impelled by a high pressure engine, from the utter impossibility of carrying condensing water in a moveable vehicle.
An engine of four horses' power, employed by Mr. Blenkinsop, impelled a carriage lightly loaded on a rail-road at the rate of ten miles an hour, and when connected with thirty coal waggons, each weighing more than three tons, its average rate was about one-third of that pace.
When the locomotive engine was first tried, it was found difficult to produce a sufficient degree of re-action between the wheels and the tract road; so that the wheels turned round without propelling the vehicle. This inconvenience was, however, obviated by Mr. Blenkinsop, who, when he adopted the locomotive engine, took up the common rails, on one side of the whole length of the road, and replaced them by a series of racks, or rails, furnished with large teeth. The impelling wheel of the engine was made to act in these teeth, so that it continued to work in a rack which insured a sufficient degree of re-action.
From the great weight of an ordinary locomotive engine as well as the construction of its impelling wheel, it must be evident that the employment of this species of prime mover on the public roads would be in the highest degree destructive; and as such that its use will for some years to come be partially confined to the mining districts, in which the greatest facilities are offered for its general adoption. Indeed, we find in one neighbourhood alone, and within a space of less than thirty square miles, more than twenty miles of road admirably adapted for this species of conveyance; and it is a well known fact, that there are many situations in which iron rail-roads might be advantageously employed, in which it would be quite impossible to open a navigable canal. In illustration of the above fact, it may be proper to state, that a company, with a large capital, is now forming for the express purpose of facilitating the conveyance of goods by locomotive engines.
The mode of applying the steam-engine to the purposes of navigation is equally simple with its employment in our manufactures.
It is generally supposed that the steam-boat is of very recent invention; on the contrary, however, the possibility of employing steam as a prime mover in the propelling of vessels was suggested as far back as the reign of Charles I.
In one of the old tracts preserved in the library of the London Institution there is a very curious representation of a steam-boat, constructed by an engineer of the name of Hulls. And this individual, now so little known, was undoubtedly the first who applied a steam-engine to the purpose of navigation.
To impel a vessel by this means, two paddle wheels, like those used in an under-shot water-wheel, are connected by means of a long axis and crank, with the working beam of the steam-engine; and if this motion is not found sufficiently rapid, a wheel and pinion are added, which, although it decreases the effective power of the engine, yet increases the velocity of the paddle wheels.
To illustrate the great advantages possessed by the steam-engine, even in its rudest state, over every other species of prime mover yet enumerated, it may now be advisable to examine its effective force when employed in the working of pumps. It has been found that one hundred weight of coals burned in an engine on the old construction, would raise at least twenty thousand cubic feet of water twenty-four feet high; an engine with a twenty-four inch cylinder doing the work of seventy four horses. An engine on Capt. Savery's plan, constructed by Mr. Keir, has been found to raise nearly three millions of pounds of water, and Mr. Watt's engine, upwards of thirty millions of pounds the same height.
To the mining interests this valuable present of science to the arts has been peculiarly acceptable; as a large portion of our now most productive mineral districts must long ere this have been abandoned, had not the steam-engine been employed as an active auxiliary in those stupendous works. In the draining of fens and marsh lands, this machine is in the highest degree valuable; and in England, particularly, it might be rendered still more generally useful. In practice it has been ascertained that an engine of six-horse power will drain more than eight thousand acres, raising the water six feet in height; whilst the cost of an engine for this species of work, including the pumps, will not exceed seven hundred pounds. This is more than ten windmills could perform, at an annual expenditure of several hundred pounds; while, in the former case, the outgoings will not exceed one hundred and fifty pounds per annum. To the mariner also, the steam-engine offers advantages of a no less important and novel nature than those which have already been described. By its use he is enabled to traverse the waters both against wind and tide, with nearly as much certainty, and, as the machinery is now constructed, with much less danger, than by the most eligible road conveyance. It too frequently, however, happens that the faults of any new invention are unjustly magnified, while its real advantages are seldom duly appreciated; and this axiom has been fully verified, in the clamour so unjustly raised against the application of the steam-engine to nautical purposes. Accidents are now, however, but of rare occurrence; and it is more than probable, that the great improvements which have been made in the boiler and safety-valve will effectually secure these parts of the engine from a recurrence of such tremendous explosions as characterised the first introduction of steam navigation. And, lastly, the political economist must hail with the most heartfelt gratification, the introduction of so able and efficient a substitute for animal labour as the steam-engine. For it has been calculated that there are at least ten thousand of these machines at the present time at work in Great Britain, performing a labour more than equal to that of two hundred thousand horses, which, if fed in the ordinary way, would require above one million acres of land for subsistence; and this is capable of supplying the necessaries of life to more than fifteen hundred thousand human beings.[11]
An ingenious foreigner, who lately visited England, has published an estimate of the mechanical force set in action by the steam-engines of this country.
He supposes that the great pyramid of Egypt required for its erection the labour of more than 10,000 men for 20 years:—but if it were required again to raise the stones from the quarries, and place them at their present height, the action of the steam-engines of England, which are managed at most by 36,000 men, would be sufficient to produce the same effect in 18 hours.
THE END.
LONDON:
PRINTED BY C. ROWORTH, BELL YARD,
TEMPLE BAR.