OR, PLAIN TEACHING. 



163 



The section of a steam vessel, 

 488, shows the situation of the 

 engines, and their relation to the 

 paddle-wheels, a a is the frame- 

 work and heel of the ship ; B B, 

 the deck ; c c, the cylinders ; d d, 

 timbers of great strength, ex- 

 tending in a longitudinal direc- 

 tion, to support the weight of 

 the engines and boilers ; e e, the 

 shaft or axle, communicating with 



the paddle-wheels f f ; G G, the 

 cranks or bends, in the shaft, by 

 which the motions of the pistons 

 i I, are communicated, from the 

 force of steam in the cylinders 

 C C, to the paddle-wheels f f. 

 Tie other parts of the plan, 488, 

 consist of an iron framework 

 which gives firmness to the 

 vessel and the engine. 



A most imuortant improvement 



488. 



has been made by the introduction 

 of vibrating engines, in which the 

 cylinders swing to and fro upon a 

 pivot, instead of standing in a 

 fixed vertical position. This 

 prevents a great strain upon the 

 ship, and lessens the vibration of 

 her framework, because the engine 

 to some extent adapts itself to 

 the vessel. 



It will be seen that both in the 



locomotive and the marine engine, 

 motion is obtained by the action 

 of pistons upon cranks. In the 

 locomotive these cranks lie in the 

 axle, 1 2, in the marine engine, 

 488, they are situated in the shaft 

 G G. When we perform the 

 simple action of turning a grind- 

 stone, 4, we act upon a similar 



