SELF-FEATHERING PADDLE-WHEEL 17 



only was a considerable weight of water raised by each blade 

 after it passed the middle of its stroke, but the steam power 

 was given nearly as much to lifting and shaking the vessel as 

 to propulsion. 



A new kind oi ; paddle-wheel was then invented, in which 

 the blades were ingeniously jointed to the wheel, so that they 

 presented their flat surfaces to the water while propelling, and 

 their edges when the stroke was over. This, which is known by 

 the name of the "Self-feathering Paddle-wheel," was thought 

 to be a very clever invention, and so it was ; but not even the 

 inverters were likely to have known that if they had only 

 looked into the book of Nature, they might have found plenty 

 of self -feathering paddle-wheels, beside the few which my 

 limited space enables me to give. 



If the reader will look at the illustration, he will see that on 

 one side is represented the self-feathering paddle-wheel of Art, 

 with its ingenious arrangement of rods and hinges. On the 

 other side there comes, first, the common Prawn, shown with its 

 tail expanded in the middle of its stroke. 



Just below it is a Cydippe of its ordinary size, showing the 

 paddle-bands, one of which is drawn at the side much mag- 

 nified, so as to show the arrangement of the little paddles. 

 As to the tentacles which trail from the body, we shall treat of 

 them when we come to our next division of the subject of the 

 work. 



Lastly, there is a representation of the self- feathering feet 

 of the Duck, the left foot expanded in striking the water, and 

 the right closed so as to offer no resistance when drawn forward 

 for another stroke. The swan's foot shows this action even 

 more beautifully than does that of the duck. 



WE now come to another mode of propulsion, namely, that 

 which is not due to direct pressure of a more or less flat body 

 against the water, but to the indirect principle of the screw, 

 wedge, or inclined plane. 



Space being valuable, I will only take two instances, namely, 

 the well-known mode of propelling a boat by a single oar 

 working in a groove or rowlock in the middle of the stern, and 

 the ordinary screw of modern steamers. 



Most of my readers must have seen a sailor in the act of 



c 



