The steam engine familiarly explained and illustrated; with an historical sketch of its invention and progressive improvement; its applications to navigation and railways; with plain maxims for railway speculators. By the Rev. Dionysius Lardner ... With additions and notes by James Renwick ...

;58 THE STEAM tNGI:t,
Fig. 67.
figure 67,'Iet o be the shaft on which the common paddle
viwheel revolves; the position of the paddle boards are represented at A, B, C, &c.; x, Y represents the water line, the
tcourse of the vessel being supposed to be from x to -; the
arrows represent the direction in which the paddle wheel revdIves. The wheel is immersed to the depth of the lowest
paddle-board, since a less degree of immersion would render
a portion of the surface of each paddle board mechanically
useless.'In the pos'ition A the whole force of the paddle
board is efficient for propelling the vessel; but, as the paddle enters the water -in the position H, its action upon the
water, not being horizontal,'is only partially effective for propulsion: a part of the force which drives the paddle is expended in depressing the water, and the remainder in driving it contrary to the course of the vessel, and, therefore, by
its reaction producing a certain propelling effect. The tendency, however, of the paddle entering the water at H, is to
form a hollow or trough, which the water, by its ordinary
property, has a continual tendency to fill up. After passing
the lowest point A, as the paddle approaches the position B,
where it emerges from the water, its action again becomes
oblique, a part only having a propelling effect, and the re