1736,

12 STEAM NAVIGATION.

Many writers have fallen into error in ascribing to Hulls the dis-covery of the crank applied to a steam engine, so as to obtain rotarymotion therefrom."This would have been in his time an importantdiscovery, and there can be little doubt that the steam engine wouldthen have been applied not only to propel boats, but to various otheruseful purposes.

In deseribing his mode of obtaining rotary motion by ratchetwheels, a weight, and ropes, Hulls states that he uses two axes, onebehind the other, each of which is essential to the object; and he thenadds, that when his“ tow-boat is to be used in shallow rivers, theMachine works by two cranks fixed to the hindermost axis, to whichcranks are fixed two shafts(or poles) of proper length to reach thebottom of the river, and which move alternately forward from themotion of the wheels by which the vessel is carried on;” so thatthe cranks, as described by Hulls, receive rotary motion from theaxis on which they are placed, and do not, as has been erroneouslystated, impart that motion to it.”

A prize being offered by the Academy of Sciences for the bestessay on the manner of impelling vessels without wind, it was ob-tained by Daniel Bernouilli, who proposed inclined planes movedcircularly like the sails of a wind mill:“ two apparatus of this natureshould be placed at each side of the Vessel, and two more behind;one of which, such as should be placed at the side of the Vessel, maybe formed as follows, of a size proper for a ship of 100 guns.

«The apparatus consists of three parts—the implement for acting onthe water, the frame which sustains it in its place at the side of theVessel, and the machinery for putting it in motion."The instrumentfor acting on the water consists of an arbor fourteen feet long andtwo inches in diameter, of iron; this carries eight wheels for actingon the water, to each of which it is perpendicular, and forms an axis

messen h*

* Hulls’ Specification is printed in the Repertory of Arts, vol.. xl. third Series, p.247, and in many other scientific works.