In this latter picture, too, wherein the tow-boat is seen steaming along, _A_ denotes, of course, the chimney “coming from the furnace,” while _B_ is the tow-boat and _CC_ are the two pieces of timber which are framed to support the machine. It will be noticed that inboard are three wheels marked respectively _Da_, _D_, and _Db_. These are on one axis and receive the ropes as shown. _Ha_ and _Hb_ are two wheels also on the same axis projecting beyond the stern, and the six fans or paddles are marked _I_, which move alternately in such a manner that when the wheels _Da_, _D_, and _Db_ move backwards or forwards they keep the fans or paddles in a direct motion. When these three wheels _Da_, _D_, and _Db_ move forward then the rope _Fb_ must move the wheel _Hb_ forward, and so cause the paddles to revolve in the same direction. So also the rope _Fa_ connects the wheel _Ha_ to _Da_, and when the latter and its two sister wheels revolve the wheel _Da_, then the wheel _Ha_ draws the rope _F_ and raises the weight _G_ (barely decipherable in the sketch to the left of _Da_), at the same time as the wheel _Hb_ brings the paddles forward. Furthermore, when the weight _G_ is raised while the wheels _Da_, _D_ and _Db_ are moving backwards, the rope _Fa_ gives way and the power of the weight _G_ brings the wheel _Ha_ forward and the paddles with it: so that the latter always keep going forward, notwithstanding that the three wheels _Da_, _D_, and _Db_ move backwards and forwards as the piston moves up and down in the cylinder. _LL_--scarcely recognisable owing to the reduction of the sketch--indicate the teeth for a catch to drop in from the axis, and are so contrived that they catch in an alternate manner to cause the paddles to move always forward, for the wheel _Ha_, by the power of the weight _G_, is performing its work while the other wheel _Hb_ goes back in order to fetch another stroke. Hulls explains that the weight _G_ must contain but half the weight of the pillar of air pressure on the piston, because the weight _G_ is raised at the same time as the wheel _Hb_ is doing its duty, so that in effect there are really two machines acting alternately by the weight of one pillar of air of such a diameter as is the diameter of the cylinder. Hulls expressed another crude idea for when the ship was navigating “up in-land Rivers” and the bottom could be reached. The paddles were then to be removed and “cranks placed at the hindmost Axis to strike a Shaft to the bottom of the River, which will drive the Vessel forward with greater Force.”