Fig. 14). The right hand boiler and fire place is shown open with the flame acting upon one of the tubes of its boiler, while the left hand boiler, re presented shut, is shown with a case g, as it appears when in use, In the open boiler the direction taken by the flame to the chimney pipe or flue s, is pointed out by arrows, The flue s is common to the two boilers. The ash pit is shown at d, and v is the bridge for directing the passage of the flame. The extremities of the chambers which receive the ends of all the bent tubes that form the boiler, are shown at c, c, the separators at a, a, with their safety valves b, b, and page cocks e, e, formerly described.
The engine has neither beam nor parallel motion. The cylinders h, k, are suspended like guns on trun nions at p, so that • they can vibrate up and down. The steam is brought from the separators by pipes in the direction w,w, which introduce the steam through the trunnions. The opening and shutting of the valves is effected by a series of levers g, r, which act like hand gear. The piston rod of each cylinder is attached to cranks m, n, rising from the main shaft o, which carries the paddles, and are placed at right angles to each other, that when the one is in the posi tion of producing a maximum force, the other is in the position of producing no effect at all. The main shaft o, the trunnions of the cylinders, and the work ing parts of the machinery, arc supported on a frame work marked i i i, u u u.
Mr. Gurney is said by Captain Ross to have suc ceeded in contriving a modification of the centrifugal blast, as a substitute for the chimney, by which a cur rent of air is diffused below the whole furnace over a large body and surface of fire, at a very low and con stant pressure, sufficient merely for the perfect igni tion of every part of the fuel. in this way the smoke is nearly consumed, the awkward funnel is rendered unnecessary, and the fuel is economised.
Mr. Gurney has added a small separate cylinder for working the supply pump, and also the blower. Tho price of a boat engine of It) horse power, with one cylinder, is X400, and .-Cioo for collateral expenses, such as paddles, wheels, shaft, fixing, &c. For higher or lower powers LSO must be added for every horse power. Captain Ross states, that, though Mr, Cur.
ney's engine has not made its way in this country, yet it has in France. 11e ascribes this to its never
having had a fair trial in England, in consequence of the inventor not having capital to bring it for ward against the opinion of those who have an interest in keeping up the low pressure engine, which is the most profitable to the manufacturer.
The following table has been given by Captain Ross, as calculated to show the crews which are proper for steam vessels employed in conveying goods and pas sengers, and which each should be obliged to have on board.
The average force of the steam is 9 inches of mer cury above the atmosphere, and the maximum force, 14 inches. The distance from New-York td Albany is nearly 160 miles, and the voyage is performed, at an average, in 12 hours. The boilers are placed be fore, and the machinery abaft the paddle wheels. The two engines consume two cords of wood in an hour and 25 cords of wood during the above voyage. A cord of wood weighs about 3826 lbs. and the ratio of coal to wood is about 22 to 26.6, so that the equiva lent quantity of coal per hour would be 161 cwt. nearly.
In our article SHIPBUILDING, p, 247, 249, the reader will find very copious tables of the dimensions of the earlier steam-boats.
One of the most important desiderata in the con struction of steam-vessels is the proper formation of the paddle wheels. Hitherto they have almost univer sally resembled common undershot wheels, in which the float boards are a continuation of the radii of the wheel, and though such wheels have theoretical dis advantages, yet their firmness and strength have given them a superiority over other contrivances, which, con. sisting of numerous parts and movable float-boards, are very liable to be broken.
There is, perhaps, no branch of the mechanical arts that has called forth so many inventions as the subject of paddle-wheels, and yet, so far as we know, no mo dification of them has appeared which is likely to su persede those of the common form.
One of the latest and most ingenious of these is the invention of Mr. John Oldham, engineer to the bank of Ireland, By a simple and elegant mechanism the float-boards revolve on axes, independent of the axis of the wheel, and each float-board revolves once, during every two revolutions of the wheel, and in an opposite direction.