394 



OUTDOOR RECREATION 



When sailing into the wind, observe that only a part of the wind force presses on the 

 sail and that only a part of the wind pressure on the sail produces a forward push 

 on the boat. 



higher in the air. A much more efficient kind is the box 

 kite, with its double surface. This, as we can readily see, 

 was the forerunner of the glider, which in turn preceded 

 the airplane of the present day. Sailboats also make 



use of the force of the wind 

 against the sails. An interest- 

 ing project would be to work 

 out the reason why it is pos- 

 sible to make a boat sail 

 against the wind. 



The simple microscope. 

 If you hold a double convex 

 lens over a small object such 

 as an insect or a bug, the 

 object appears larger than it 

 really is. The reading glass 

 is a simple microscope consist- 

 ing of a convex lens. We can 

 even make one ourselves by 

 A simple microscope. blowing a small bulb at the 



\SmoJl insect 



