This contrivance does not differ in principle from the common winch, or from the key which winds a clock. The motion of the piston-rod backwards and forwards turns such a winch. At each termination of the stroke, the piston, from the peculiar position of the crank, loses all power over it. To remedy this, two cylinders and pistons are generally used, which act upon two cranks placed on the axle at right angles to each other; so that at the moment when one of the pistons is at the extremity of its stroke, and loses its power upon one crank, the other piston is at the middle of its stroke, and in full operation on the other crank. By these means an unintermitting force is kept in action.
So far as relates to the capability or power of the steam-engine, no difficulty attends its application to inland navigation. Either low pressure or high pressure engines may be applied to this purpose. Lightness and space are of some importance, but not so indispensable as to exclude low-pressure engines from the barges on canals or rivers, if they were preferable upon other accounts. There are, however, obstacles of a nature independent of the qualities of the steamengine, which seem to preclude the use of steam as a moving power upon canals, except in very rare instances. The agitation of the water produced by any impelling power which acts in the manner of paddlewheels or oars, as at present constructed, is found to be very destructive to the banks. Attempts have been made to remove this inconvenience by placing a paddle-wheel in the centre of the stern, acting as much as possible in the middle of the canal; and various contrivances have been suggested for feathering the paddles, so as to cause a diminished agitation in the water. None of these contrivances have, how-
