128 OUR PHYSICAL WORLD 



a hole through the cork and then with a small tack fasten a flap 

 of leather so that it will cover the hole on the handle side, the 

 tack being placed at one side of the hole. The cork should be 

 free to slip up and down rather tightly in the tube when worked 

 by the lift handle. Put a cork in the lower end of the tube, 

 having first made a hole in it, and cover the hole with a leather 

 flap held by a tack, the flap being on the inner face of the cork. 

 Put this corked end of the tube in the water and work the plunger 

 back and forth. If properly constructed, the water rises in the 

 tube and is pumped out at the top. A tube made of rolled paper 

 may be set with glue in the mailing tube or bamboo, to serve as a 

 spout. 



To make a squirt gun fit a cork into one end of a good- 

 sized glass tube or length of bamboo, but before inserting it 

 file or cut a groove on one side. Make a plunger, as was done 

 for the pump, except that there will be no valve in this. Put 

 the head of the plunger into the free end of the tube or length of 

 bamboo, drive it down nearly to the cork, put the corked end 

 under water, draw the plunger back slowly, lift the corked end 

 above the water, and drive the plunger rapidly down. This 

 squirt gun illustrates the principle of the force pump. 



As the stream of water comes from the force pump of the 

 waterworks into the faucets in the house, or from the hose nozzle 

 connected to the fire engine, the stream is a steady stream and 

 not a succession of spurts. This change is brought about by the 

 addition of an air chamber, which has an inlet and an outlet. 

 The water coming in, in a succession of spurts, crowds up against 

 the cushion of elastic air, the pressure of which sends the water 

 out in a steady stream. Replace the cork in the squirt gun with 

 one having two holes, one for intake, one for outlet. Put short 

 lengths of glass tubing in each so that the ends are flush with the 

 small end of the cork. Attach a leather valve over the intake 

 tube so that it will let water in but not out. Attach a rubber 

 tube to the intake pipe and let its free end set in a glass of water. 

 Fit a cork with two holes intp a 4-ounce wide-mouthed bottle. 



