MECHANICAL PARADOXES. 



In reality, however, the sails and wind 

 are not free from friction. Still less are the 

 ship and the water. Much force is required 

 to overcome this friction, and to lift aside the 

 water in the formation of waves. The result 

 is that the sails do not move quite freely side- 

 ways ; the wind does not go straight on, but 

 is to some extent deflected along the face of 

 the sails ; and the actual speed of the ship 

 does not correspond to the proportions of the 

 diagram. Nevertheless, there is a kind of 

 sailing frame so contrived that nearly all the 

 most serious friction that between ship and 

 water is got rid of, while the wave-making 

 power is abolished altogether. 



This is the so-called ice-boat, which is 

 used for sporting purposes on the great lakes 

 of the United States and Canada (see Plate II.), 

 when their surface is frozen over in severe 

 winters. These ice-boats consist of a frame 

 mounted on runners resembling large skates, 

 which slide upon the ice, and furnished with 

 a mast which supports a sail to obtain driving 

 power from the wind, much as an ordinary 

 boat does. 



Now the friction between the smooth 

 runners and the hard smooth ice is almost 

 nil. The power lost in lifting water aside and 

 making waves is in this case actually nil. 

 And so the ice-boat approaches the conditions 

 of the third diagram sufficiently to be really 



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