CHAPTER XI. LOCOMOTIVE ENGINES ON TURNPIKE ROADS.

Railways and Turnpike Roads compared. — Mr. Gurney's inventions. — His Locomotive Steam Engine. — Its performances. — Prejudices and errors. — Committee of the House of Commons. — Convenience and safety of Steam Carriages. — Hancock's Steam Carriage. — Mr. N. Ogle. — Trevithick's invention. — Proceedings against Steam Carriages. — Turnpike Bills. — Steam Carriage between Gloucester and Cheltenham. — Its discontinuance. — Report of the Committee of the Commons. — Present State and Prospects of Steam Carriages.

(104.) We have hitherto confined our observations to steam-power as a means of transport applied on railways, but modern speculation has not stopped here. Several attempts have been made, and some of them attended with considerable success, to work steam-carriages on turnpike roads. The practicability of this project has been hitherto generally considered to be very questionable; but if we carry back our view to the various epochs in the history of the invention of the steam engine, we shall find the same doubt, and the same difficulty, started at almost every important step in its progress. In comparing the effect of a turnpike road with that of a railway, there are two circumstances which obviously give facility and advantage to the railway. One is, that the obstructions to the rolling motion of the wheels, produced by the inequalities of the surface, are very considerably less on a railway than on a road; less in the proportion of at least 1 to 20. This proportion, however, must depend much on the nature of the road with which the railway is compared. It is obvious that a well-constructed road will offer less resistance than one ill constructed; and it is ascertained that the resistance of a Macadamised road is considerably more than that of a road well paved with stones: the decision of this question, therefore, must involve the consideration of another, viz. whether roads may not be constructed by pavement or otherwise, smoother and better adapted to carriages moved in the manner of steam-carriages than the roads now used for horse-power?

But besides the greater smoothness of railroads compared with turnpike roads, they have another advantage, which we suspect to have been considerably exaggerated by those who have opposed the project for steam-carriages on turnpike roads. One of the laws of adhesion, long since developed by experiment, and known to scientific men, is, that it is greater between the surfaces of bodies of the same nature than between those of a different nature. Thus between two metals of the same kind it is greater than between two metals of different kinds. Between two metals of any kind it is greater than between metal and stone, or between metal and wood. Hence, the wheels of steam-carriages running on a railroad have a greater adhesion with the road, and therefore offer a greater resistance to slip round without the advance of the carriage, than wheels would offer on a turnpike road; for on a railroad the iron tire of the wheel rests in contact with the iron rail, while on a common road the iron tire rests in contact with the surface of stone, or whatever material the road may be composed of. Besides this, the dust and loose matter which necessarily collect on a common road, when pressed between the wheels and the solid base of the road act somewhat in the manner of rollers, and give the wheels a greater facility to slip than if the road were swept clean, and the wheels rested in immediate contact with its hard surface. The truth of this observation is illustrated on the railroads themselves, where the adhesion is found to be diminished whenever the rails are covered with any extraneous matter, such as dust or moist clay. Although the adhesion of the wheels of a carriage with a common road, however, be less than those of the wheels of a steam-carriage with a railroad, yet still the actual adhesion on turnpike roads is greater in amount than has been generally supposed, and is quite sufficient to propel carriages dragging after them loads of large amount.

The relative facility with which carriages are propelled on railroads and turnpike roads equally affects any moving power, whether that of horses or steam engines; and whether loads be propelled by the one power or the other, the railroad, as compared with the turnpike road, will always possess the same proportionate advantage; and a given amount of power, whether of the one kind or the other, will always perform a quantity of work less in the same proportion on a turnpike road than on a railroad. But, on the other hand, the expense of original construction, and of maintaining the repairs of a railroad, is to be placed against the certain facility which it offers to draught.

In the attempts which have been made to adapt locomotive engines to turnpike roads, the projectors have aimed at the accomplishment of two objects: first, the construction of lighter and smaller engines; and, secondly, increased power. These ends, it is plain, can only be attained, with our present knowledge, by the production of steam of very high temperature and pressure, so that the smallest volume of steam shall produce the greatest possible mechanical effect. The methods of propelling the carriage have been in general similar to that used in the railroad engines, viz. either by cranks placed on the axles, the wheels being fixed upon the same axles, or by connecting the piston-rods with the spokes of the wheels, as in the engine represented in fig. 55. In some carriages, the boiler and moving power, and the body of the carriage which bears the passengers, are placed on the same wheels. In others, the engine is placed on a separate carriage, and draws after it the carriage which transports the passengers, as is always the case on railways.

The chief difference between the steam engines used on railways, and those adapted to propel carriages on turnpike roads, is in the structure of the boiler. In the latter it is essential that, while the power remains undiminished, the boiler should be lighter and smaller. The accomplishment of this has been attempted by various contrivances for so distributing the water, as to expose a considerable quantity of surface in contact with it to the action of the fire; spreading it in thin layers on flat plates; inserting it between plates of iron placed at a small distance asunder, the fire being admitted between the intermediate plates; dividing it into small tubes, round which the fire has play; introducing it between the surfaces of cylinders placed one within another, the fire being admitted between the alternate cylinders,—have all been resorted to by different projectors.

(105.) First and most prominent in the history of the application of steam to the propelling of carriages on turnpike roads, stands the name of Mr. Goldsworthy Gurney, a medical gentleman and scientific chemist, of Cornwall. In 1822, Mr. Gurney succeeded Dr. Thompson as lecturer on chemistry at the Surrey Institution; and, in consequence of the results of some experiments on heat, his attention was directed to the project of working steam carriages on common roads; and since 1825 he has devoted his exertions in perfecting a steam engine capable of attaining the end he had in view. Numerous other projectors, as might have been expected, have followed in his wake. Whether they, or any of them, by better fortune, greater public support, or more powerful genius, may outstrip him in the career on which he has ventured, it would not, perhaps, at present, be easy to predict. But whatever be the event, to Mr. Gurney is due, and will be paid, the honour of first proving the practicability of the project; and in the history of the adaptation of the locomotive engine to common roads, his name will stand before all others in point of time, and the success of his attempts will be recorded as the origin and cause of the success of others in the same race.

The incredulity, opposition, and even ridicule, with which the project of Mr. Gurney was met, are very remarkable. His views were from the first opposed by engineers, without one exception. The contracted habit of mind, sometimes produced by an education chiefly, if not exclusively, directed to a merely practical object, subsequently confirmed by exclusively practical pursuits, may, perhaps, in some degree, account for this. But, I confess, it has not been without surprise that I have observed, during the last ten years, the utter incredulity which has prevailed among men of general science on this subject,—an incredulity which the most unequivocal practical proof has scarcely yet dispelled. "Among scientific men," says Mr. Gurney, "my opinion had not a single supporter, with the exception of the late Dr. Wollaston."

The mistake which so long prevailed in the application of locomotives on railroads, and which, as we have shown, materially retarded the progress of that invention, was shared by Mr. Gurney. Without reducing the question to the test of experiment, he took for granted, in his first attempts, that the adhesion of the wheels with the road was too slight to propel the carriage. He was assured, he says, by eminent engineers, that this was a point settled by actual experiment. It is strange, however, that a person of his quickness and sagacity did not inquire after the particulars of these "actual experiments." So, however, it was; and, taking for granted the inability of the wheels to propel, he wasted much labour and skill in the contrivance of levers and propellers, which acted on the ground in a manner somewhat resembling the feet of horses, to drive the carriage forward. After various fruitless attempts of this kind, the experience acquired in the trials to which they gave rise at last forced the truth upon his notice, and he found that the adhesion of the wheels was not only sufficient to propel the carriage heavily laden on level roads, but was capable of causing it to ascend all the hills which occur on ordinary turnpike roads. In this manner it ascended all the hills between London and Barnet, London and Stanmore, Stanmore Hill, Brockley Hill, and mounted Old Highgate Hill, the last at one point rising one foot in nine.

It would be foreign to my present object to detail minutely all the steps by which Mr. Gurney gradually improved his contrivance. This, like other inventions, has advanced by a series of partial failures; but it has at length attained that state, in which, by practice alone, on a more extensive scale, a further degree of perfection can be obtained.

(106.) The boiler of this engine is so constructed that there is no part of it, not even excepting the grate-bars, in which metal exposed to the action of the fire is out of contact with water. If it be considered how rapidly the action of an intense furnace destroys metal when water is not present to prevent the heat from accumulating, the advantage of this circumstance will be appreciated. I have seen the bars of a new grate, never before used, melted in a single trip between Liverpool and Manchester; and the inventor of another form of locomotive engine has admitted to me that his grate-bars, though of a considerable thickness, would not last more than a week. In the boiler of Mr. Gurney, the grate-bars themselves are tubes filled with water, and form, in fact, a part of the boiler itself. This boiler consists of three strong metal cylinders placed in a horizontal position one above the other. A section, made by a perpendicular or vertical plane, is represented in fig. 62. The ends of the three cylinders, just mentioned, are represented at D, H, and I. In the side of the lowest cylinder D are inserted a row of tubes, a ground plan of which is represented in fig. 63. These tubes, proceeding from the side of the lowest cylinder D, are inclined slightly upwards, for a reason which I shall presently explain. From the nature of the section, only one of these tubes is visible in fig. 62. at C. The other extremities of these tubes at A are connected with the same number of upright tubes, one of which is expressed at E. The upper extremities G of these upright tubes are connected with another set of tubes K, equal in number, proceeding from G, inclining slightly upwards, and terminating in the second cylinder H.

Fig. 62.

Fig. 63.

An end view of the boiler is exhibited in fig. 64., where the three cylinders are expressed by the same letters. Between the cylinders D and H there are two tubes of communication B, and two similar tubes between the cylinders H and I. From the nature of the section these appear only as a single tube in fig. 62. From the top of the cylinder I proceeds a tube N, by which steam is conducted to the engine.

Fig. 64.

It will be perceived that the space F is enclosed on every side by a grating of tubes, which have free communication with the cylinders D and H, which cylinders have also a free communication with each other by the tubes B. It follows, therefore, that if water be supplied to the cylinder I, it will descend through the tubes, and first filling the cylinder D and the tubes C, will gradually rise in the tubes B and E, will next fill the tubes K and the cylinder H. The grating of water pipes C E K forms the furnace, the pipes C being the fire-bars, and the pipes E and K being the back and roof of the stove. The fire-door, for the supply of fuel, appears at M, fig. 64. The flue issuing between the tubes F is conducted over the tubes K, and the flame and hot air are carried off through a chimney. That portion of the heat of the burning fuel, which in other furnaces destroys the bars of the grate, is here expended in heating the water contained in the tubes C. The radiant heat of the fire acts upon the tubes K, forming the roof of the furnace, on the tube E at the back of it, and partially on the cylinders D and H, and the tubes B. The draft of hot air and flame passing into the flue at A, acts upon the posterior surfaces of the tubes E, and the upper sides of the tubes K, and finally passes into the chimney.

As the water in the tubes C E K is heated, it becomes specifically lighter than water of a less temperature, and consequently acquires a tendency to ascend. It passes, therefore, rapidly into H. Meanwhile the colder portions descend, and the inclined positions of the tubes C and K give play to this tendency of the heated water, so that a prodigiously rapid circulation is produced, when the fire begins to act upon the tubes. When the water acquires such a temperature that steam is rapidly produced, steam bubbles are constantly formed in the tubes surrounding the fire; and if these remained stationary in the tubes, the action of the fire would not only decompose the steam, but render the tubes red hot, the water not passing through them to carry off the heat. But the inclined position of the tubes, already noticed, effectually prevents this injurious consequence. A steam bubble which is formed either in the tubes C or K, having a tendency to ascend proportional to its lightness as compared with water, necessarily rushes upwards; if in C towards A, and if in K towards H. But this motion of the steam is also aided by the rapid circulation of the water which is continually maintained in the tubes, as already explained, otherwise it might be possible, notwithstanding the levity of steam compared with water, that a bubble might remain in a narrow tube without rising. I notice this more particularly, because the burning of the tubes is a defect which has been erroneously, in my opinion, attributed to this boiler. To bring the matter to the test of experiment, I have connected two cylinders, such as D and H, by a system of glass tubes, such as represented at C E K. The rapid and constant circulation of the water was then made evident: bubbles of steam were formed in the tubes, it is true; but they passed with great rapidity into the upper cylinder, and rose to the surface, so that the glass tubes never acquired a higher temperature than that of the water which passed through them.

This I conceive to be the chief excellence of Mr. Gurney's boiler. It is impossible that any part of the metal of which it is formed can receive a greater temperature than that of the water which it contains; and that temperature, as is obvious, can be regulated with the most perfect certainty and precision. I have seen the tubes of this boiler, while exposed to the action of the furnace, after that action has continued for a long period of time, and I have never observed the soot which covers them to redden, as it would do if the tube attained a certain temperature.

Every part of the boiler being cylindrical, it has the form which, mechanically considered, is most favourable to strength, and which, within given dimensions, contains the greatest quantity of water. It is also free from the defects arising from unequal expansion, which are found to be most injurious in tubular boilers. The tubes C and K can freely expand in the direction of their length, without being loosened at their joints, and without straining any part of the apparatus; the tubes E, being short, are subject to a very slight degree of expansion; and it is obvious that the long tubes, with which they are connected, will yield to this without suffering a strain, and without causing any part of the apparatus to be loosened.

When water is converted into steam, any foreign matter which may be combined with it is disengaged, and is deposited on the bottom of the vessel in which the water is evaporated. All boilers, therefore, require occasional cleansing, to prevent the crust thus formed from accumulating; and this operation, for obvious reasons, is attended with peculiar difficulty in tubular boilers. In the case before us, the crust of deposited matter would gather and thicken in the tubes C and K, and if not removed, would at length choke them. But besides this, it would be attended with a still worse effect; for, being a bad conductor, it would intercept the heat in its transit from the fire to the water and would cause the metal of the tube to become unduly heated. Mr. Gurney of course foresaw this inconvenience, and contrived an ingenious chemical method of removing it by occasionally injecting through the tubes such an acid as would combine with the deposite, and carry it away. This method was perfectly effectual; and although its practical application was found to be attended with difficulty in the hands of common workmen, Mr. Gurney was persuaded to adhere to it by the late Dr. Wollaston, until experience proved the impossibility of getting it effectually performed, under the circumstances in which boilers are commonly used. Mr. Gurney then adopted the more simple, but not less effectual, method of removing the deposite by mechanical means. Opposite the mouths of the tubes, and on the other side of the cylinders D and H, are placed a number of holes, which, when the boiler is in use, are stopped by pieces of metal screwed into them. When the tubes require to be cleaned these stoppers are removed, and an iron scraper is introduced through the holes into the tubes, which being passed backwards and forwards, removes the deposite. The boiler may be thus cleaned by a common labourer in half a day, at an expense of about 1s. 6d.

The frequency of the periods at which a boiler of this kind requires cleaning must depend, in a great degree, on the nature of the water which is used; one in daily use with the water of the river Thames would not require cleaning more than once in a month. Mr. Gurney states that with water of the most unfavourable description, once a fortnight would be sufficient.

(107.) In the more recent boilers constructed by Mr. Gurney, he has maintained the draught through the furnace, by the method of projecting the waste steam into the chimneys; a method so perfectly effectual, that it is unlikely to be superseded by any other. The objection which has been urged against it in locomotive engines, working on turnpike roads, is, that the noise which it produces has a tendency to frighten horses.

In the engines on the Liverpool road, the steam is allowed to pass directly from the eduction pipe of the cylinder to the chimney, and it there escapes in puffs corresponding with the alternate motion of the pistons, and produces a noise, which, although attended with no inconvenience on the railroad, would certainly be objectionable on turnpike roads. In the engine used in Mr. Gurney's steam-carriage, the steam which passes from the cylinders is conducted to a receptacle, which he calls a blowing box. This box serves the same purpose as the upper chamber of a smith's bellows. It receives the steam from the cylinders in alternate puffs, but lets it escape into the chimney in a continued stream by a number of small jets. Regular draught is by this means produced, and no noise is perceived. Another exit for the steam is also provided, by which the conductor is enabled to increase or diminish, or to suspend altogether, the draught in the chimney, so as to adapt the intensity of the fire to the exigencies of the road. This is a great convenience in practice; because, on some roads, a draught is scarcely required, while on others a powerful blast is indispensable.

Connected with this blowing box, is another ingenious apparatus of considerable practical importance. The pipe through which the water which feeds the boiler is conducted to it from the tank is carried through this blowing box, within which it is coiled in a spiral form, so that an extensive thread of the feeding water is exposed to the heat of the waste steam which has escaped from the cylinders, and which is enclosed in this blowing box. In passing through this pipe the feeding water is raised from the ordinary temperature of about 60° to the temperature of 212°. The fuel necessary to accomplish this is, therefore, saved, and the amount of this is calculated at 1/6th of all that is necessary to evaporate the water. Thus, 1/6th of the expense of fuel is saved. But, what is much more important in a locomotive engine, a portion of the weight of the engine is saved without any sacrifice of its power. There is still another great advantage attending this process. The feeding water in the worm just mentioned, while it takes up the heat from the surrounding steam in the blowing box, condenses 1/6th of the waste steam, which is thence conducted to the tank, from which the feeding water is pumped, saving in this manner 1/6th in weight and room of the water necessary to be carried in the carriage for feeding the boiler.[33]

So far as the removal of all inconvenience arising from noise, this contrivance has been proved by experience to be perfectly effectual.[34]

In all boilers, the process of violent ebullition causes a state of agitation in the water, and a number of counter currents, by which, as the steam is disengaged from the surface of the water, it takes with it a considerable quantity of water in mechanical mixture. If this be carried through the cylinders, since it possesses none of the qualities of steam, and adds nothing to the power of the vapour with which it is combined, it causes an extensive waste of heat and water, and produces other injurious effects. In every boiler therefore, some means should be provided for the separation of the water thus suspended in the steam, before the steam is conducted to the cylinder. In ordinary plate boilers, the large space which remains above the surface of the water serves this purpose. The steam being there subject to no agitation or disturbance, the water mechanically suspended in it descends by its own gravity, and leaves pure steam in the upper part. In the small tubular boilers, this has been a matter, however, of greater difficulty. The contracted spaces in which the ebullition takes place, causes the water to be mixed with the steam in a greater quantity than could happen in common plate boilers: and the want of the same steam-room renders the separation of the water from the steam a matter of some difficulty. These inconveniences have been overcome by a succession of contrivances of great ingenuity. I have already described the rapid and regular circulation effected by the arrangement of the tubes. By this a regularity in the currents is established, which alone has a tendency to diminish the mixture of water with the steam. But in addition to this, a most effectual method of separation is provided in the vessel I, which is a strong iron cylinder of some magnitude, placed out of the immediate influence of the fire. A partial separation of the steam from the water takes place in the cylinder H; and the steam with the water mechanically suspended in it, technically called moist steam, rises into the separator I. Here, being free from all agitation and currents, and being, in fact, quiescent, the particles of water fall to the bottom, while the pure steam remains at the top. This separator, therefore, serves all the purposes of the steam-room above the surface of the water in the large plate boilers. The dry steam is thus collected and ready for the supply of the engine through the tube N, while the water, which is disengaged from it, is collected at the bottom of the separator, and is conducted through the tube T to the lowest vessel D, to be again circulated through the boiler.

The pistons of the engine work on the axles of the hind wheels of the carriage which bears the engine, by cranks, as in the locomotives on the Manchester railway, so that the axle is kept in a constant state of rotation while the engine is at work. The wheels placed on this axle are not permanently fixed or keyed upon it, as in the Manchester locomotives; but they are capable of turning upon it in the same manner as ordinary carriage wheels. Immediately within these wheels there are fixed upon the axles two projecting spokes or levers, which revolve with the axle, and which take the position of two opposite spokes of the wheel. These may be occasionally attached to the wheel or detached from it; so that they are capable of compelling the wheels to turn with the axle, or leaving the axle free to turn independent of the wheel, or the wheel independent of the axle, at the pleasure of the conductor. It is by these levers that the engine is made to propel either or both of the wheels. If both pairs of spokes are thrown into connexion with the wheels, the crank shaft or axle will cause both wheels to turn with it, and in that case the operation of the carriage is precisely the same as those of the locomotives already described upon the Liverpool and Manchester line; but this is rarely found to be necessary, since the adhesion of one wheel with the road is generally sufficient to propel the carriage, and consequently only one pair of these fixed levers are generally used, and the carriage propelled by only one of the two hind wheels. The fore wheels of the carriage turn upon a pivot similar to those of a four-wheeled coach. The position of these wheels is changed at pleasure by a simple pinion and circular rack, which is moved by the conductor, and in this manner the carriage is guided with precision and facility.

The force of traction necessary to propel a carriage upon common roads must vary with the variable quality of the road, and consequently the propelling power, or the pressure upon the pistons of the engine, must be susceptible of a corresponding variation; but a still greater variation becomes necessary from the undulations and hills which are upon all ordinary roads. This necessary change in the intensity of the impelling power is obtained by restraining the steam in the boiler by the throttle valve, as already described in the locomotive engines on the railroad. This principle, however, is carried much further in the present case. The steam in the boiler may be at a pressure of from 100 to 200 lbs. on the square inch; while the steam on the working piston may not exceed 30 or 40 lbs. on the inch. Thus an immense increase of power is always at the command of the conductor; so that when a hill is encountered, or a rough piece of road, he is enabled to lay on power sufficient to meet the exigency of the occasion.

The two difficulties which have been always apprehended in the practical working of steam carriages upon common roads are, first, the command of sufficient power for hills and rough pieces of road; and, secondly, the apprehended insufficiency of the adhesion of the wheels with the road to propel the carriage. The former of these difficulties has been met by allowing steam of a very great pressure to be constantly maintained in the boiler with perfect safety. As to the second, all experiments tend to show that there is no ground for the supposition that the adhesion of the wheels is in any case insufficient for the purposes of propulsion. Mr. Gurney states, that he has succeeded in driving carriages thus propelled up considerable hills on the turnpike roads about London. He made a journey to Barnet with only one wheel attached to the axle, which was found sufficient to propel the carriage up all the hills upon that road. The same carriage, with only one propelling wheel, also went to Bath, and surmounted all the hills between Cranford Bridge and Bath, going and returning.

A double stroke of the piston produces one revolution of the propelling wheels, and causes the carriage to move through a space equal to the circumference of those wheels. It will therefore be obvious, that the greater the diameter of the wheels, the better adapted the carriage is for speed; and, on the other hand, wheels of smaller diameter are better adapted for power. In fact, the propelling power of an engine on the wheels will be in the inverse proportion to their diameter. In carriages designed to carry great weights at a moderate speed, smaller wheels will be used; while in those intended for the transport of passengers at considerable velocities, wheels of at least 5 feet in diameter are most advantageous.

Among the numerous popular prejudices to which this new invention has given rise, one of the most mischievous in its effects, and most glaring in its falsehood, is the notion that carriages thus propelled are more injurious to roads than carriages drawn by horses. This error has been most clearly and successfully exposed in the evidence taken before the committee of the House of Commons upon steam carriages. It is there fully demonstrated, not only that carriages thus propelled did not wear a turnpike road more rapidly than those drawn by horses, but that, on the other hand, the wear by the feet of horses is far more rapid and destructive than any which could be produced by the wheels of carriages. Steam carriages admit of having the tires of the wheels broad, so as to act upon the road more in the manner of rollers, and thereby to give consistency and firmness to the material of which the road is composed. The driving wheels, being fully proved not to slip upon the road, do not produce any effects more injurious than the ordinary rolling wheels; consequently the wear occasioned by a steam carriage upon a road is not more than that produced by a carriage drawn by horses of an equivalent weight and the same or equal tires; but the wear produced by the pounding and digging of horses' feet in draught is many times greater than that produced by the wear of any carriage. Those who still have doubts upon this subject, if there be any such persons, will be fully satisfied by referring to the evidence which accompanies the report of the committee of the House of Commons, printed in October, 1831. In that report they will not only find demonstrative evidence that the introduction of steam carriages will materially contribute to the saving in the wear of turnpike roads, but also that the practicability of working such carriages with a great saving to the public—with great increase of speed and other conveniences to the traveller—is fully established.

The weight of machinery necessary for steam carriages is sometimes urged as an objection to their practical utility. Mr. Gurney states, that, by successive improvements in the details of the machinery, the weight of his carriages, without losing any of the propelling power, may be reduced to 35 cwt., exclusive of the load and fuel and water: but thinks that it is possible to reduce the weight still further.

A steam carriage constructed by Mr. Gurney, weighing 35 cwt., working for 8 hours, is found, according to his statement, to do the work of about 30 horses. He calculates that the weight of his propelling carriage, which would be capable of drawing 18 persons, would be equal to the weight of 4 horses; and the carriage in which these persons would be drawn would have the same weight as a common stage coach capable of carrying the same number of persons. Thus the weight of the whole—the propelling carriage and the carriage for passengers taken together—would be the same with the weight of a common stage coach, with 4 horses inclusive.

(108.) There are two methods of applying locomotives upon common roads to the transport of passengers or goods; the one is by causing the locomotive to carry, and the other to draw the load; and different projectors have adopted the one and the other method. Each is attended with its advantages and disadvantages. If the same carriage transport the engine and the load, the weight of the whole will be less in proportion to the load carried; also a greater pressure may be produced on the wheels by which the load is propelled. It is also thought that a greater facility in turning and guiding the vehicle, greater safety in descending the hills, and a saving in the original cost, will be obtained. On the other hand, when the passengers are placed in the same carriage with the engine, they are necessarily more exposed to the noise of the machinery and to the heat of the boiler and furnace. The danger of explosion is so slight, that, perhaps, it scarcely deserves to be mentioned; but still the apprehension of danger on the part of the passengers, even though groundless, should not be disregarded. This apprehension will be obviously removed or diminished by transferring the passengers into a carriage separate from the engine; but the greatest advantage of keeping the engine separate from the passengers is the facility which it affords of changing one engine for another in case of accident or derangement on the road, in the same manner as horses are changed at the different stages: or, if such an accident occur in a place where a new engine cannot be procured, the load of passengers may be carried forward by horses, until it is brought to some station where a locomotive may be obtained. There is also an advantage arising from the circumstance that when the engines are under repair, or in process of cleaning, the carriages for passengers are not necessarily idle. Thus the same number of carriages for passengers will not be required when the engine is used to draw as when it is used to carry.

In case of a very powerful engine being used to carry great loads, it would be quite impracticable to place the engine and loads on four wheels, the pressure being such as no turnpike road could bear. In this case it would be indispensably necessary to place a part of the load at least upon separate carriages to be drawn by the engine.

In the comparison of carriages propelled by steam with carriages drawn by horses, there is no respect in which the advantage of the former is so apparent as the safety afforded to the passenger. Steam power is under the most perfect control, and a carriage thus propelled is capable of being guided with the most admirable precision. It is also capable of being stopped almost suddenly, whatever be its speed; it is capable of being turned within a space considerably less than that which would be necessary for four-horse coaches. In turning sharp corners, there is no danger, with the most ordinary care on the part of the conductor. On the other hand, horse-power, as is well known, is under very imperfect control, especially when horses are used, adapted to that speed which at present is generally considered necessary for the purpose of travelling. "The danger of being run away with and overturned," says Mr. Farey, in his evidence before the House of Commons, "is greatly diminished in a steam coach. It is very difficult to control four such horses as can draw a heavy stage coach ten miles an hour, in case they are frightened or choose to run away; and, for such quick travelling, they must be kept in that state of courage that they are always inclined to run away, particularly down hill, and at sharp turns in the road. Steam power has very little corresponding danger, being perfectly controllable, and capable of having its power reversed to retard in going down hill. It must be carelessness that would occasion the overturning of a steam carriage. The chance of breaking down has been hitherto considerable, but it will not be more than in stage coaches when the work is truly proportioned and properly executed. The risk from explosion of the boiler is the only new cause of danger, and that I consider not equivalent to the danger from horses."

That the risk of accident from explosion is very slight indeed, if any such risk exists, may be proved from the fact that the boilers used on the Liverpool and Manchester railroad being much larger, and, in proportion, inferior in strength to those of Mr. Gurney, and other steam carriage projectors, have never yet been productive of any injurious consequences by explosion, although they have frequently burst. I have stood close to a locomotive on the railroad when the boiler burst. The effect was that the water passed through the tubes into the fire and extinguished it, but no other consequence ensued.

In fig. 65. is represented the appearance of a locomotive of Mr. Gurney's drawing after it a carriage for passengers.

Fig. 65.

(109.) One of the greatest difficulties which locomotives upon a turnpike road have to encounter is the ascent of very steep hills, for it is agreed upon all hands that hills of very moderate inclinations present no difficulty which may not be easily overcome, even in the present state of our knowledge. The fact of Mr. Gurney having propelled his carriage up Old Highgate Hill, when the apparatus was in a a much more imperfect state than that to which it has now attained, establishes the mere question of the possibility of overcoming the difficulty; but it remains still to be decided whether the inconvenience caused by providing means of meeting the exigency of very steep hills may not be greater than the advantage of being able to surmount them can compensate for: and Mr. Farey, whose authority upon subjects of this kind is entitled to the highest respect, thinks that it is upon the whole more advantageous to provide, at very steep hills, post horses to assist the steam carriage up them, than to incur the inconvenience of providing the necessary power and strength of machinery for occasions which at best but rarely occur. If the question merely referred to the command of motive power, it appears to me that Mr. Gurney's boiler would be amply sufficient to supply all that could be required for any hills which occur upon turnpike roads; but it is not to be forgotten, that not merely an ample supply of motive power, but also a strength and weight in the machinery proportionate to the power to be exerted, is indispensably necessary. The strength and weight necessary to ascend a very steep hill will be considerably greater than that which is necessary for a level road, or for hills of moderate inclinations; and it follows that if we ascend those steep hills by the unaided power of the locomotive, we must load the engine with all the weight of machinery requisite for such emergencies, such additional weight being altogether unnecessary, and therefore a serious impediment upon all other parts of the road, inasmuch as it must exclude an equivalent weight of goods or passengers, which might otherwise be transported, and thereby in fact diminish proportionally the efficiency of the machine. It is right, however, to observe, that this is a point upon which a difference of opinion is entertained by persons equally competent to form a judgment, and that some consider that it is practicable to construct an engine without inconvenient weight which will ascend all the hills which occur upon turnpike roads.

However this may be, the difficulty is one which the improved system of roads in England renders of a comparatively trifling nature. If horses were resorted to as the means of assistance up such hills as the engine would be incapable of surmounting, such aid would not be requisite more than twice or thrice upon the mail-coach road between London and Holyhead; and the same may be said of the roads connecting the greatest points of intercourse in the kingdom. Such hills as the ascent at Pentonville upon the New Road, the ascent in St. James's Street, the ascent from Waterloo Place to the County Fire Office, the ascent at Highgate Archway, present no difficulty whatever. It is only Old Highgate Hill, and hills of a similar kind, which would ever require a supply of horses in aid of the engine. I therefore incline to agree with Mr. Farey, that, at least for the present, it will be more expedient to construct carriages adapted to surmount moderate hills only, and to provide post horses in aid of the extreme emergencies to which I have just alluded.

(110.) In the boiler to be used in the steam carriage projected by Mr. Walter Hancock, the subdivision of the water is accomplished by dividing a case or box by a number of thin plates of metal like a galvanic battery, the water being allowed to flow between every alternate pair of plates, at E, fig. 66., and the intermediate spaces H forming the flue through which the flame and hot air are propelled.

Fig. 66.

In fact, a number of thin plates of water are exposed on both sides to the most intense action of flame and heated air; so that steam of a high-pressure is produced in great abundance and with considerable rapidity. The plates forming the boiler are bolted together by strong iron ties, extending across the boiler, at right angles to the plates, as represented in the figure. The distance between the plates is two inches.

There are ten flat chambers of this kind for water, and intermediately between them ten flues. Under the flues is the fire-place, or grate; containing six square feet of fuel in vivid combustion. The chambers are all filled to about two thirds of their depth with water, and the other third is left for steam. The water-chambers, throughout the whole series, communicate with each other both at top and bottom, and are held together by two large bolts. By releasing these bolts, at any time, the chambers fall asunder; and by screwing them up they may be all made tight again. The water is supplied to the boiler by a forcing-pump, and the steam issues from the centre of one of the flues at the top.

These boilers are constructed to bear a pressure of 400 or 500 lbs. on the square inch; but the average pressure of the steam on the safety valve is from 60 to 100. There are 100 square feet of surface in contact with the water exposed to the fire. The stages which such an engine performs are eight miles, at the end of which a fresh supply of fuel and water are taken in. It requires about two bushels of coke for each stage.

The steam carriage of Mr. Hancock differs from that of Mr. Gurney in this,—that in the former the passengers and engine are all placed on the same carriage. The boiler is placed behind the carriage; and there is an engine-house between the boiler and the passengers, who are placed on the fore part of the vehicle; so that all the machinery is behind them. The carriages are adapted to carry 14 passengers, and weigh, exclusive of their load, about 3-1/2 tons, the tires of the wheels being about 3-1/2 inches in breadth. Mr. Hancock states, that the construction of his boiler is of such a nature, that, even in the case of bursting, no danger is to be apprehended, nor any other inconvenience than the stoppage of the carriage. He states that, while travelling about 9 miles an hour, and working with a pressure of about 100 lbs. on the square inch, loaded with 13 passengers, the carriage was suddenly stopped. At first the cause of the accident was not apparent; but, on opening one of the cocks of the boiler, it was found that it contained neither steam nor water. Further examination proved that the boiler had burst. On unscrewing the bolts, it was found there were several large holes in the plates of the water-chamber, through which the water had flowed on the fire; but neither noise nor explosion, nor any dangerous consequences ensued.

This boiler has some obvious defects. It is evident that thin flat plates are the form which, mechanically considered, is least favourable to strength; nor does it appear that any material advantage is gained to compensate for this by the magnitude of the surface exposed to the action of the fire. It is a great defect that a part of the surface of each of the plates is exposed to the action of the fire while it is out of contact with the water; in fact, in the upper part of the spaces marked E, fig. 66., steam only is contained. It has been observed by engineers, and usually shown by experiment, that if steam be heated on the surface of water it will be decomposed, and its elasticity destroyed; this is not the only evil connected with the arrangement, for on this part of the metal, nevertheless, the fire acts,—with less intensity, it is true, than on that part which contains the water,—but still with sufficient intensity to destroy the metal. Mr. Hancock appears to have attempted to remedy this defect by occasionally inverting the position of the flat chambers, placing that which at one time was at the bottom at the top, and vice versâ. This may equalise the wear produced by the action of the fire upon the metal out of contact with water, but still the wear on the whole will not be less rapid. There appears to be no provision or space for separating the steam from the water with which it is charged; in fact, there are no means in this engine of discharging the function of Mr. Gurney's separator. This will be found to produce considerable waste and loss of power in practice.

The bars upon which the fire rests are of solid metal; and such is the intense heat to which they are subject, that, in an engine constantly at work, it is unlikely that they will last, without being renewed, more than about a week, if so much. The draft is maintained in this engine by means of a revolving fan worked by the engine. This, perhaps, is one of the greatest defects as compared with other locomotives. The quantity of power requisite to work this bellows, and of which the engine is robbed, is very great. This defect is so fatal, that I consider it is quite impossible that the ingenious inventor can persevere in the use of it. Mr. Hancock has abandoned the use of the cranks upon his working axle, and has substituted an endless chain and rag-wheels. This also appears to me defective, and a source by which considerable power is lost. On the other hand, however, the weakness of the axle which is always produced by cranks is avoided.

(111.) Mr. Nathaniel Ogle of Southampton obtained a patent for a locomotive carriage, and worked it for some time experimentally; but as his operations do not appear to have been continued, I suppose he was unsuccessful in fulfilling those conditions, without which the machine could not be worked with economy and profit. In his evidence before a committee of the House of Commons, he has thus described his contrivance:—

"The base of the boiler and the summit are composed of cross pieces, cylindrical within and square without; there are holes bored through these cross pieces, and inserted through the whole is an air tube. The inner hole of the lower surface, and the under hole of the upper surface, are rather larger than the other ones. Round the air tube is placed a small cylinder, the collar of which fits round the larger aperture on the inner surface of the lower frame, and the under surface of the upper frame-work. These are both drawn together by screws from the top; these cross pieces are united by connecting pieces, the whole strongly bolted together; so that we obtain, in one tenth of the space, and with one tenth of the weight, the same heating surface and power as is now obtained in other and low-pressure boilers, with incalculably greater safety. Our present experimental boiler contains 250 superficial feet of heating surface in the space of 3 feet 8 inches high, 3 feet long, and 2 feet 4 inches broad, and weighs about 8 cwt. We supply the two cylinders with steam, communicating by their pistons with a crank axle, to the ends of which either one or both wheels are affixed, as may be required. One wheel is found to be sufficient, except under very difficult circumstances, and when the elevation is about one foot in six, to impel the vehicle forward.

"The cylinders of which the boiler is composed are so small as to bear a greater pressure than could be produced by the quantity of fire beneath the boiler; and if any one of these cylinders should be injured by violence, or any other way, it would become merely a safety valve to the rest. We never, with the greatest pressure, burst, rent, or injured our boiler; and it has not once required cleaning, after having been in use twelve months."

(112.) Dr. Church of Birmingham has obtained a succession of patents for contrivances connected with a locomotive engine for stone roads; and a company, consisting of a considerable number of individuals, possessing sufficient capital, has been formed in Birmingham for carrying into effect his designs, and working carriages on his principle. The present boiler of Dr. Church is formed of copper. The water is contained between two sheets of copper, united together by copper nails, in a manner resembling the way in which the cloth forming the top of a mattress or cushion is united with the cloth which forms the bottom of it, except that the nails or pins, which bind the sheets of copper, are much closer together. The water, in fact, seems to be "quilted" or "padded," in between two sheets of thin copper. This double sheet of copper is formed into an oblong rectangular box, the interior of which is the fire-place and ash-pit, and over the end of which is the steam-chest. The great extent of surface exposed to the immediate action of the fire causes steam to be produced with great rapidity.

An obvious defect which such a boiler presents is the difficulty of removing from it any deposite or incrustation, which may collect between the sheets of copper so closely and intricately connected. Dr. Church proposes to effect this, when it is required, by the use of an acid, which will combine readily with the incrustation, and by which the boiler may therefore be washed. This method of cleansing boilers was recommended by Dr. Wollaston to Mr. Gurney, who informed me, however, that he found that it was not practicable in the way in which boilers must commonly be used.

I apprehend, also, that the spaces between the sheets of copper, in Dr. Church's boiler just described, will hardly permit the steam bubbles which will be formed to escape with sufficient facility into the steam-chest; and being retained in that part of the boiler which is exposed to the action of the fire, the metal will be liable to receive an undue temperature.

I have, however, seen this engine working, and its performance was very satisfactory.

(113.) Various other projects for steam carriages on common roads are in various degrees of advancement, among which may be mentioned those of Messrs. Maudslay and Field, Col. Macerone, and Mr. Russell of Edinburgh; but our limits compel us to omit any detailed account of them.