no OUR PHYSICAL WORLD 



experiments as a foundation for the comprehension of the science 

 that is involved. Sooner or later he is bound to know why the 

 balloon rises. The little child may be satisfied temporarily by 

 some analogy to experiments with which he is more or less famil- 

 iar. Thus you may tell him that just as a cork rises and floats 

 on the surface of the water so the balloon tends to rise to the 

 upper levels of the air. He may have had the actual sensation 

 of being lifted off his feet when in swimming, and if he has learned 



FIG. 46. A dirigible balloon, the "Shenandoah," over New York Harbor 



to float his experiences may lead him to some appreciation of 

 the way in which a balloon rises, but in time he will persist in 

 knowing more in detail the forces that are operative. 



In order to understand why the balloon goes up, the child 

 must have, as a rule, a number of new experiences that will 

 clarify and render exact his hazy conceptions. The balloon 

 rises because of the pressure of the air, and the child is neither 

 familiar with gases nor with the law of pressure. When informed 

 that the air is a gas he gains little notion of the characteristics of 



