farther than what arises from slow combustion, and the use of Welsh coal, and both of these points may be attained in any boiler. This, we think, will appear clear enough by a reference to the representation of a Cornish boiler given in figs. 123, 124, and 125. This boiler produces no smoke, but there is no peculiarity of structure to bring about such a result, and the whole efficacy arises from a slow combustion and peculiar coal-advantages which are not exclusively Cornish. The diameter of this boiler is 6 feet 6 inches; length 33 feet 6 inches. Length of furnace 6 feet; breadth of furnace 3 feet 10 inches. A tube of about 19 inches in diameter, filled with water, runs through the main flue, which flue is a continuation of the furnace.

Figs. 126. and 127. represent a small tubular boiler constructed by Messrs. Horton and Son for a coasting steamer called the Zephyr. This boiler has been found to perform well, and is, in every respect, satisfactory. The tubes are of iron, 3 inches in diameter, and 6 feet long. Length of furnace 6 feet, number of tubes 168. 2 engines. Consumption of coal per hour, about 6 cwt. The pressure of steam is about 5 lbs. on the square inch. Figs. 128, 129, and 130. represent another boiler, by Messrs. Miller, Ravenhill, and Co., of the tubular kind. It is identical in all its main features with the boilers of the Tagus already described, and the same remarks apply to it. It has been found expedient to introduce a jet of steam into the chimney of this vessel to quicken the draught. The tubes are of brass, 3 inches in diameter, and the tube plates are of iron. A galvanic action between the brass and the iron has been found to arise in some boilers, which shows itself, not at the ends of the tubes, but at the ends of the athwartship stays which bind the sides of the boiler together; and the iron plate around these stays very soon acquires the appearance of having been scooped out by a knife; but in other boilers no action of this kind has been found to take place, and it has been doubted whether a leakage caused by the inadequate fastening of the stays has not had something to do with its production; nevertheless, in several cases of brass tubed boilers which have come underour observation, the action has been very remarkable in the situation we nave mentioned. The evil would probably be obviated by the application of a washer of zinc. The experience which has been obtained with tubular boilers since the first publication of the present work, certainly shows that brass tubes are on the whole the most eligible. Iron tubes are speedily eaten into holes by corrosion, and it is remarkable that the corrosion chiefly takes place upon the under side. Brass tubes, on the contrary, are found to

Scale three tenths inch=1 foot.

BOILER OF H. M. STEAMER INFERNAL, BY MESSRS, MILLER, RAVENHILL, AND CO.

Back View one-half in Section,

last many years. It appears to be the best plan to refrain from attempts at scaling brass tubes, but they may be withdrawn once a year, cleaned and re-inserted.

Figs. 131, 132, and 133. represent the boilers of the steam vessel Ocean. The tubes of these boilers are of iron 3 inches in diameter and 9 feet long; furnaces 7 feet long and 2' 1" wide. There are three boilers in all: the centre one with three furnaces, and the two wing ones with two furnaces each. Total breadth of boilers 19 feet; total length 14 feet; total number of tubes 378; two engines-diameter of cylinder 56 inches; length of stroke 5 feet; pressure of steam about 4 lbs; consumption of coal about 18 cwt. per hour. In ordinary coasting vessels we do not approve of the plan of firing from each end, as the length in the vessel occupied by an additional firing space is a manifest waste of room; and there will be no difficulty in short voyages, about maintaining the trim of the ship on account of the stowage of so evanescent a cargo as coal in the wake of the furnaces. The object should, we conceive, be to obtain the requisite number of furnaces in the breadth of the ship, and then to add a sufficient number of tubes above the furnaces to extract the heat given out in them. In cases where this cannot be altogether, and yet can be nearly done it is a less evil, we conceive, to put a few furnaces in a second tier into the midship boiler, rather than change the whole plan of the boiler by firing from both ends. In most cases we believe it will be possible to get sufficient room for the furnaces in the breadth of the ship if the engines be wrought expansively; and this may be done, without affecting the power, either by applying high pressure steam to the existing size of cylinders, or by introducing larger cylinders, and retaining the steam at a moderate pressure—that is, under 10 lbs. The latter plan in the case of new vessels is, in our judgment, greatly the preferable one; and we should recommend all new steam vessels to be made with the cylinders very large, while the boilers remain of the same dimensions as at present, except in the case of vessels impelled by the screw, where the engines may be worked at a very high speed - an increase in the speed being equivalent to an enlargement of the cylinder. A great force is thus available for the propulsion of the vessel when necessary, whether from adverse circumstances of wind and water, or otherwise, merely by diminishing the degree of expansion; while, in fair winds and smooth water, it becomes necessary to work with a very high measure of expansion to keep the engines supplied

pany. These boilers are well worthy of the attention of the engineer, as they have approved themselves more economical than any of the other boilers employed in those vessels, at the same time that there is an abundance of steam, and the speed of the vessel is well maintained. The following are some of the more important particulars:- There are four boilers, with three furnaces in each, making 12 furnaces in all. Length of each boiler, 13' 6"; breadth, 9' 10"; height, 14' 11". There is a fore and aft passage between the boilers, 2 feet wide, and an athwart passage 18 inches wide. Length of furnace, 7' 4"; breadth of furnace, 31 inches; diameter of chimney, 67 inches; height of flues, 5 feet.