vessels of this size perfectly manageable. Mr. Buchanan, however, recommends the use of a vessel, whose dimensions shall not exceed seventy feet in keel, and ninety tons burden, as the most eligible size for a luggage and passage boat.

It has been stated, and we think with some degree of reason, that the security and comfort of passengers by steam-boats would be best consulted by the employment of a subsidiary vessel of sufficient burden to convey the engine and heavy luggage. By the adoption of this plan, the danger to the passengers from the bursting of the boiler, or other apparatus, would be entirely prevented, and the high-pressure engine generally employed. It would also remedy the loss and inconvenience attendant on the continual shaking of the vessel, which, if large and lightly constructed, will be shaken asunder by the engine in a very short period. And last, though certainly not the least among the advantages likely to accrue from the adoption of this plan, it would materially diminish the disagreeable effect arising from the heat of the furnace and noise of the engine.

To remedy the inconvenience that has sometimes been experienced from the difference in the draught of vessels by which the paddle-wheels are at one time sunk beneath the centre of their axis, while at another time they scarcely touch the water, a mode of adjusting their relative height has been introduced. An apparatus calculated to effect this very desirable object, without retarding

the motion of the vessel, was lately presented to the Society of Arts, by Mr. Dickson, who received the silver medal for the above communication.

Mr. D. states, that the great utility of this improvement consists in its application to sailing vessels: for instance, suppose a steam vessel to be going direct against the wind by means of the whole power of her steam engine, and that the wind should change and become favourable, the propellers may, by these means, be immediately raised out of the water, and the vessel allowed to have the whole effect of the sails, thereby saving the expense of fuel. All steam vessels now in use, experience so great an impediment from the propellers being always in the water, as to render sails of no benefit. Another advantage will be derived when there is only a gentle breeze in the vessel's favour, as the propellers can be set to work, which will take hold of the water at pleasure, and thereby unite the power of the steam to that of the wind, which will secure the passage in the given time, at much less expense, as the engine will only consume fuel in proportion to the labour it has to perform. A farther advantage will be found when the vessel has only a side wind; for, by the use of this contrivance, one of the propelling wheels can be worked with its full power in the water, and the other entirely lifted out, if necessary.

For the purpose of accurately trimming the ves

sel, Mr. Dodd recommends the use of a tank or cistern, placed beneath the projecting deck on each side the vessel, the water ballast for which may be raised by the working of the engine. This, on being discharged by means of a plug, would give a preponderance to the opposite side of the vessel, and as it would be placed at the end of a lever, the fulcrum of which is the keel, a small quantity of water would have considerable effect. A contrivance nearly similar to this, has been adopted for a considerable period of time on board one of the Gravesend steam vessels. It consists in the use of a small carriage made to contain an iron cable, which is occasionally employed to moor the vessel, and its weight is such that the vessel may readily be trimmed by moving it from side to side.

Mr. Maudslay has lately constructed a large engine for a steam-boat invented by Mr. Brunel, which has two cylinders acting alternately upon different cranks, formed upon the same axis at right angles to each other, so that the motion is continued without the action of a fly-wheel. In this engine, one boiler is placed between the two cylinders, and one air-pump and condenser exhaust them both; so that by these means an engine of considerable power is contained in the smallest possible space.

Some idea of the prevalence of steam navigation in the more northern parts of our island, may be formed from the following estimate of the number

The greatest number of boats now in use either on the Thames or Clyde navigation, are fitted up for the conveyance of passengers. They have two cabins, one before the engine, which is smaller, and at a reduced price, while the second, or large cabin, is usually fitted up in the most elegant manner. In some cases the cabins enjoy the additional advantage of being heated by steam, while others are heated by means of a pump, which forces a current of air over the chimney into the cabin. The engine-room is seldom more than twenty feet in length, and little more than half as many in width; this being sufficiently large for an engine of twenty horses' power, with all requisite apparatus, two boilers, and abundant stowage for coals. By an ingenious contrivance, the chimney, which is of considerable height, is made to lower nearly level with the deck. The joint that covers the flue during this process, acting upon the same principle as the sliding shells of a lobster's back, which completely prevents the escape of smoke.

From a series of accurate experiments and calculations lately made, it appears, that the expense attendant on the navigation of a small vessel is much larger in proportion, than where an engine of greater power is employed; and, consequently, we find that steam-boats of great burden are now constructed. In America, more particularly, these boats usually run from three to four hundred tons burden, the great width of their rivers rendering

vessels of this size perfectly manageable. Mr. Buchanan, however, recommends the use of a vessel, whose dimensions shall not exceed seventy feet in keel, and ninety tons burden, as the most eligible size for a luggage and passage boat.

It has been stated, and we think with some degree of reason, that the security and comfort of passengers by steam-boats would be best consulted by the employment of a subsidiary vessel of sufficient burden to convey the engine and heavy luggage. By the adoption of this plan, the danger to the passengers from the bursting of the boiler, or other apparatus, would be entirely prevented, and the high-pressure engine generally employed. It would also remedy the loss and inconvenience attendant on the continual shaking of the vessel, which, if large and lightly constructed, will be shaken asunder by the engine in a very short period. And last, though certainly not the least among the advantages likely to accrue from the adoption of this plan, it would materially diminish the disagreeable effect arising from the heat of the furnace and noise of the engine.

To remedy the inconvenience that has sometimes been experienced from the difference in the draught of vessels by which the paddle-wheels are at one time sunk beneath the centre of their axis, while at another time they scarcely touch the water, a mode of adjusting their relative height has been introduced. An apparatus calculated to effect this very desirable object, without retarding