Mr. Francis Humphery obtained a patent in 1835 for an arrangement in which not merely the side beams, but likewise the piston-rod was dispensed with: the power of the engine being transmitted direct from the piston to the crank by the connecting rod. To this novel form of engine he gave the distinguishing name of the Trunk Engine: it is remarkable alike for originality, simplicity, and ingenuity. The annexed cut (p. 694) represents a vertical section of the engine, a is the cylinder; b the piston; c the connecting rod, the upper end of which is connected to the crank d, and the lower end passes through an aperture in the piston, and carries a pin, c, the ends of which work in bearings attached to the under side of the piston; f is a bonnet enclosing the bearings and end of the connecting rod. The connecting rod works within a case or trough, g, which is bolted at bottom to the top of the piston, and which slides in a stuffing-box, k, on the cylinder cover. The sides of the trough are straight, and parallel to each other; and the ends are semicircular; the width is just sufficient to receive the connecting rod without rubbing, and the distance between the semicircular ends is such as to allow the vibration of the connecting rod during the revolution of the crank. k is the slide valve, and m m the columns supporting the entablature n, which carries the plummer blocks, in which the shaft revolves; p bonnet, covering the manhole in the cylinder bottom.
A pair of engines of this description, 90 horse-power, were constructed by Messrs. J. & E. Hall, for a packet named the Dartford,