276 NATURE-STUDY REVIEW [12:6-Sept., 1916 



time. When our collars feel tight in summer it is because our 

 throats are actually expanding. The wagon maker knows of this 

 principle for he heats the iron tires for his wagon wheels and then 

 when he has placed them on the rim of the wheels he tightens them 

 by plunging the whole wheel in cold water. 



EXPERIMENT SIX 



To prove that heat will expand a gas, we used an empty Flor- 

 ence flask, corked with a single holed rubber stopper, through 

 which a glass tube had been thrust. The end of the glass tube 

 was then placed in a tumbler of water and the Florence flask (in- 

 verted) was heated by the Bunsen flame. As the air inside ex- 

 panded it came out of the flask and bubbled up through the water. 

 We then allowed the flask to cool; and many of the class were 

 surprised to see that the water began to ascend the glass tube and 

 fill up the neck of the Florence flask. Of course, it was the air 

 pressure trying to fill up the partial vacuum which caused this phe- 

 nomenon. I departed from this experiment to show that the move- 

 ments of the air or winds were caused by unequal heating of the 

 earth's surface. We then developed the thought of high and low 

 pressure areas and explained that clouds were only masses of vapor. 

 The explanation of rain, snow and hailstones can be very well 

 given after this experiment is worked. 



EXPERIMENT SEVEN 



The apparatus in this experiment consisted of a Florence flask 

 partly filled with water, a Bunsen burner, and some crystals of 

 potassium permanganate. By means of these we endeavored to 

 show the movement of heated water. When the water had been 

 heated to a boiling point a few of the permanganate crystals were 

 dropped in the water. The Bunsen flame had been placed just 

 under the center of the bottom of the flask. We noted that the 

 crystals went down the sides of the flask and ascended in the cen- 

 ter. They traveled in circles. If their movement is shown dia- 

 grammatically on a blackboard it can readily be seen that the 

 whirling crystals illustrate the movements of the land and sea 

 breeze and of ocean currents. 



