This gentleman, we are informed, began his experiments in the year 1824, with an engine of his own invention, and of a very singular construction ; but which he imagined was peculiarly suitable for locomotive purposes. The engine had neither cylinder nor piston, but consisted of two flexible bags, made of his brother's patent artcial leather, composed of caoutchouc, combined with several layers of linen. Communications, by means of a four-way cock, admitted the steam alternately into these bags, which being attached to a suitable frame with a slide motion, the alternate filling and exhausting took place, and the recipro cation produced by their expansion and contraction was communicated to a crank, which converted it into circular motion. The caoutchouc was found to answer for a short time, but the heat soon rendered the bags permeable, and ef course the engine useless. Having satisfied his mind that caoutchouc could not be efficaciously employed in this way, he resorted to cylinders of the ordinary metallic kind, and in a short time had completed a model therewith of a steam carriage. which was tried on the public road. The indications of success which this model gave, decidedly convinced him of the feasibility of the project of steam propulsion on the common road, and that the principal thing required, was a compact, light, and powerful boiler, which be next set about to con trive.
The difficulties which had been rienced by various individuals in the construction of tubular boilers, led Mr. Hancock to consider of some arrangement by which the water, ex- to the action of the fire, might re leas divided, and yet extended over a large surface ; and the plan now occurred to him, which he has since successfully followed in the several steam-carriages he has built, and has applied to other purposes. In the annexed figure is represented an elevation of the first modification of this boiler, with a part of the casing removed to show the interior structure. At B is the fire-place ; D the hole ; E E are a series of fiat parallel chambers to hold the water, made of the toughest •heet-iron, and placed side by side, at a sufficient distance apart for the flames and heated air to between them, as shown at 1. Each of these fiat vessels ex tends across the furnace chamber, so as to fill its whole area in a vertical plane ; and they are all connected at the bottom, for keeping the water in each at a uniform level; and at the top of each of the chambers there is a steam-pipe that leads into another larger steam-pipe, common to them all, and by which the engines are supplied. To keep the individual water chambers E E at uniform distances apart, and confer, at the same time, adequate strenfth to them, a series of vertical bars or fillets are fixed between each pair. Therefore, instead of the flames ascending between each pair of plates in one unbroken sheet, it is subdivided, and made to pass through a number of rectangular channels, representing in their outline so many square tubes. This combination of water chambers and alternate flues, is bound together by a system of very massive bolts externally, proved to be capable of sustaining a vastly greater pressure than the boiler is ever subjected to ; and it is unquestionably a great merit in this boiler, that the thinness of metal, and consequent weakness of the individual water chambers, constitutes each, in effect, a safety valve. A better arrangement than this for absorbing the
heat of the furnace, and, consequently, for the rapid production of steam, seems scarcely to have been requisite ; but the active mind of the inventor, ever bent upon improvement, soon found means to increase its efficiency, and reduce its weight; which are, of course, objects of the utmost importance in steam loco motion.
The increased efficiency was obtained by " embossing" the plates; by punching or pressing them between dies, so as to cause a series of hemispherical bosses, of nearly the shape and sire of watch-glasses, to be projected all over their external surfaces ; so that when the chambers are brought together, the tops of these come into contact, and thus a series of spaces are formed between them, as shown at hhh in the cut on the following page ; r e being the water chambers, the projections on which are eufficiently obvious; the surface of metal covered with water is thus greatly extended, and the ascending current of heated matters is made to impinge against their projections, which are not placed in vertical lines upwards, but zig-zag, as shown in the following cut, which represents a side view of a portion of one of the chambers. The vertical bars, described in the first modification, are therefore here entirely got rid of, and their entire weight; and, at the same time, a much more powerful boiler obtained; and one that it is scarcely possible to exceed in compactness, which is a property of considerable importance in locomotion : and in the facility of repair, which it admits o4 it excels all others ; there being nothing more to do than to unscrew the great in ternal bolts, take out the faulty chamber, and replace it by a new one, reconnect ing the steam and water pipes, and screwing up the great bolts again. It is a remarkable circumstance, that Dr. Lardner condemns this boiler of Mr. Han cock's on the very grounds that we think its merit consists ; which we shall here briefly state, in order that his opinion may have its due weight with our readers. In his Treatise on the Steam Engine, the Doctor observes, with respect to this invention, that "thin plates are the form which, mechanically considered, are unfavourable to strength." The inferences to be drawn from this remark are, that the plates have no support at their sides, and that Mr. Hancock was so weak minded as to depend for strength in a high-pressure boiler upon thin plate-iron ; both of which inferences are obviously absurd and untrue. (Were we disposed to be hypercritical, we should say that the learned Doctor's position is, in every view, untenable—for we conceive that thin sheet-iron is, "mechani cally considered," stronger than thick sheet-iron, having acquired by the rolling lnille more tenacity and ductility.) The advantages of the thin metal above thick in Mr. Hancock's boiler, are evidently these ; that every one of the com partments between the supports is not only in effect a perfect safety-valve, as before observed, but a much more rapid conductor of the heat to the water, than if it were formed of thick metal.