of the present day, and he will then understand what steam vehicles are now, and what they ought to be. A good carriage is, it must be recollected, the result of the combined skill and successive improvements of many ingenious competitors and admirable artists, not a machine that can be knocked together by any engineer who wishes to make an engine; and it includes a series of nicely-calculated and minutely-adjusted proportions which it requires a lifetime of study thoroughly to understand. What an exquisite structure is a modern carriage!-how simple in appearance, how beautiful in its form, proportions and position, yet how complex and intricate in its formation! What a combination are its wheels, tires and axles, its pole, its perch, and its springs, body, box, cushions, steps, braces, belts, lamps, blinds, and bags, each individually a chef-d'œuvre of art; yet every one of these refinements, necessary to expeditious travelling by horses, is thrown aside by the builders of steam-carriages, and they have at once reverted to a structure little better than the coal carts and brewers' waggons of the last century. Logs of wood have they for perches-hundred weights of metal for axletrees-springs have they, but they spring not, and braces, but they do not bend. Before inventors can expect to meet with any measure of success, they must reason thus:-We are not carriage inventors, nor improvers in the art of coach-building. One of the best Londonmade carriages is nearly perfect. Let us adopt it with all its improvements, and, if we can succeed in anything, it will be in propelling such a vehicle.-In no respect, therefore, but in the power of its boiler, is Mr. Stephenson's engine worthy of imitation in such as are intended for the common road.

Next to the engines of the Liverpool Railway, those of Mr. Goldsworthy Gurney, designed for common roads, have most strongly excited public attention, and held forth the greatest promise of ultimate success. We shall extract some account of that gentleman's engine from his friend Professor Lardner's "Lectures on the Steam-Engine," of which the author has just published a fourth edition, with an addition of two chapters of most disproportioned bulk, for the purpose of including an account of locomotion by steam. If this treatise had been revised and amplified in regard to more essential points, we think it might have been more useful to the public, as well as more creditable to the author; especially as the work of Mr. Gordon,* professedly devoted to that branch of the subject, might by some have been supposed to have rendered Dr. Lardner's additions on that score

* An Historical and Practical Treatise upon Elemental Locomotion, by means of Steam-Carriages on the Common Roads. By A. Gordon: London, 1832

uncalled for. Still, however, we have no objection to see the subject re-discussed, provided it is for the purpose of correcting errors, or opening extensive or useful views; as the passages we shall extract appear to exhibit Dr. Lardner's own opinions, they will enable our readers to form their own estimate of their value.

"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 chymist, of Cornwall. In 1822 Mr. Gurney succeeded Dr. Thomson as Lecturer on Chymistry 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 unremittingly devoted his exertions and expended his property 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 and advantage 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."-p. 216.

On this little matter of fame and honour we must be permitted to express our dissent from the opinion of the learned Professor of Natural Philosophy. Mr. Gurney may probably have to boast of having spent more of his own money and that of other persons in the furtherance of his views than any of his rivals, and of having produced greater excitement by the puffs of the metropolitan press, and his exhibitions to city crowds, than any other projector. But not to him, certainly, is due the honour of having been the first to prove the practicability of locomotion by steam on the common roads; that, indisputably, belongs to Mr. Trevithick, his predecessor. As to the matter of advantage, that, we fear, wants proof as much at this moment as at any prior date. Perhaps Mr. Gurney may yet be able to claim this only merit that now remains to be acquired :-nous verrons.

"The mistake which so long prevailed in the application of locomotives on rail-roads, and which as we have shown, materially retarded the progress of the invention, was shared by Mr. Gurney. 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."-p. 217.

In following the Professor's description of Mr. Gurney's engine, it may be well to keep in mind the five canons of criticism which we have laid down.

:

"The boiler of Mr. Gurney differs in the most striking manner from all other forms of boilers hitherto invented 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; the grate-bars themselves are tubes filled with water, and form, in fact, a part of the boiler itself. His boiler consists of three strong metal cylinders placed in a horizontal position one above the other. Proceeding from the side of the lowest cylinder, a row of tubes incline slightly upwards; the other extremities of these tubes are connected with the same number of upright tubes, and the upper extremities of these upright tubes are connected with another set of tubes equal in number, inclining slightly upwards, and terminating in the second cylinder. It will be perceived, therefore, that the space containing the fire is enclosed on every side by a grating of tubes, and that if water be supplied to the upper cylinder it will descend through the tubes into the under cylinder, and from it to the grating of the furnace and the other water-pipes that surround the fire. 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, of which it consists. The radiant heat of the fire acts upon the tubes forming the roof of the furnace, on the tubes at the back of it, and partially on the horizontal cylinders and the tubes by which they communicate. As the water in the lower tubes is heated, it becomes specifically lighter than water of a less temperature, and consequently acquires a tendency to ascend. It passes, therefore, rapidly into the higher part of the tubes. Meanwhile the colder portions descend, and the inclined positions of the tubes 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, and steam is rapidly generated."-p. 219.

The Professor then proceeds to favour us with an account of some experiments undertaken by himself, with the view of demonstrating that the effect of the circulation accomplished in Mr. Gurney's boiler is so admirable, as constantly to keep the temperature of the metal of which it consists, at as low a point as that of the water which it contains! This is indeed a most important discovery! and lest we should in any way misrepresent the doctor's opinion, we give it in his own words :

"This I conceive to be the cardinal 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 contiuued 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."-p. 224.

Such is Dr. Lardner's idea of the perfection of these boilers! He states, that it is impossible that any part of the metal between the water and the fire, can become hotter than the water within the boiler. Surely the doctor must either have ill-expressed his meaning, or we have misunderstood him. Does he mean to assert, in contradiction to all the established laws of the propagation of heat through solid bodies, that the outside of a metallic plate when exposed to the action of flame, at an inconceivably higher temperature than that of boiling water, will not become hotter than water whose ebullition is in the act of commencing? Surely the doctor will allow, that water, when boiling in a common kettle, circulates more freely than in the tubes of Mr. Gurney's boiler; and will he really assert that the bottom of the kettle and the water it contains are of the same temperature? Judging from the ordinary laws of nature, our statement would be exactly the reverse; that the metal between the water and the fire which heats it, must always be at a higher temperature than the water, and a lower temperature than the fire. It is in fact the metal that heats the water, while the fire only communicates to the metal such a temperature as will sustain it at a medium between the water and the fire; and the more rapidly the steam is generated, that is, the greater the excess of the heat of the metal of the boiler above that of the water which rests upon it, the more efficient will the boiler become. The circulation alluded to is necessarily slower in Mr. Gurney's boiler than in any other yet constructed, so that what Dr. Lardner regards as its cardinal excellence, is, in reality, its radical defect; and his wonderful discovery in the propagation of caloric, at variance with all the observed phenomena and established laws of that fluid. What may have been the motives that induced the doctor to give so decided a preference to Mr. Gurney's boiler above all others, it is not our business to inquire, but it is certainly rather amusing to find the reasons adduced for this preference elsewhere employed for the purpose of depreciating another engine. In speaking of the Liverpool engines, a few pages before, Dr. Lardner had observed, (p. 170), that " Air being a bad conductor of heat, it is necessary that the air in the flues should be exposed to as great an extent of surface, in contact with the water as possible." And again, that "the shape of a tube, geometrically considered, is most unfavourable for the exposure of a fluid contained in it to its surface." So much for the Liverpool engines. Now, observe

how admirably these reasons are converted, by a slightly varied mode of expression, into high panegyric upon Mr. Gurney's engine. In addition to the " cardinal excellence" above quoted, it is said, that "every part of this boiler, being cylindrical (or tubular) it has the form which, mechanically considered, is most favourable to strength, and which, within given dimensions, contains the greatest quantity of water;" that is, it contains the greatest quantity of useless water, and exposes the least possible, useful, or heating surface!

The fact is, that Mr. Gurney's boiler is by no means well adapted to carriages. In the first place, it is well known that from the inclined position of the tubes, the steam, when once generated, cannot escape from them without partially emptying the water they contain; then the flame is not in contact with the metal sufficiently long to give out its heat, but merely strikes en passant upon the sides of the tubes, and between each pair of adjacent tubes there is a space, through which the flame passes without producing any good effect; while there should have been a double row of tubes above the spaces of the others to receive this heat. Again, the fire is not wholly surrounded by water; on two sides it is exposed and the heat wasted: the steam, also, is not used as it comes most elastic from the contact of heated metal, but is collected in a cooler vessel, removed from the fire, and called a separator. From all these defects in the nature of the boiler, it follows that it is by no means well suited for steamcarriages; and, indeed, in all the examples we have seen of Mr. Gurney's engines, there has been a deficiency in the supply of steam, so that the rate of motion was limited to a very low point; and where obstacles occurred, they were only conquered by allowing the carriage to stand still till the accumulation of steam should give an increase of power. But the defects of Mr. Gurney's boiler would not be sufficient to condemn the whole of his engine, provided there existed judicious arrangements in other elements of his machine. According to the institutes of criticism we have here established, the next subject of inquiry is the passage of the steam into the cylinders, and its operation when there. We have shown that the strength of a current of steam, as it passes from the boiler into the working part of the engine, depends mainly upon the directness and shortness of the pipe by which it is conducted. As the force of a current of wind is broken by the turns of narrow streets and lanes in a city, so is the power of a current of steam reduced by the cooling and resistance it encounters in a sinuous and contracted passage. Now in Mr. Gurney's engine the boiler is situated at the back of the carriage, and the cylinders work in the under part below the body.