438 SUPPLEMENT. 



on which (here are no teeth are cut down so, as to be 

 even with the bottoms of the teeth where they stand. 



The teeth of these four wheels take alternately into 

 the teeth of four racks, which hang by two chains over 

 the pullies Q and L ; and to the lower ends of these 

 racks there are four iron rods fixed, which go down into 

 the four forcing pumps, S, R, M and N. And, as the 

 wheels turn, the racks and pump-rods are alternately 

 moved up and down. 



Thus, suppose the wheel G has pulled down the rack 

 /, and drawn up the rack K by the chain : as the 

 last tooth of G just leaves the uppermost tooth of /, 

 the first tooth of H is ready to take into the lowermost 

 tooth of the rack K, and pull it down as far as the teeth 

 go ; and then the rack / is pulled upward through the 

 whole space of its teeth, and the wheel G is ready to 

 take hold of it, and pull it down again, and so draw up 



the other. In the same manner, the wheels E and F 



work the racks O and P. 



These four wheels are fixed on the axle of the great 

 wheel in such a manner, with respect to the positions of 

 their teeth, that, whilst they continue turning round, 

 there is never one instant of time in which one or other 

 of the pump-rods is not going down, and forcing the 

 water. So that, in this engine, there is no occasion for 

 haying a general air-vessel to all the pumps, to procure 

 a constant stream of water flowing from the upper end 

 of the main pipe. 



There is an engine of this sort, described in Ramelli's 

 work, but I can truly say, that I never saw it till some 

 time after I had made this model. 



The said model is not above twice as big as the 

 figure of it, here described. I turn it by a winch fixed 

 on the gudgeon of the axle behind the water wheel ; 

 ind, when it was newly made, and the pistons and 

 valves in good order, I put tin pipes 15 feet high upon 



