38 



WEATHER AND CLIMATE 



anticyclone a large mass of slowly whirling cool air 

 which is descending ; a high-pressure area. 



clockwise turning in the same direction as the hands 

 of a clock. 



counter-clockwise or anti-clockwise turning in the di- 

 rection opposite to that of the hands of a clock. 



convection currents currents set up in gases or liquids 

 due to a difference in temperature and therefore in 

 the weight of equal volumes of different parts of the 

 gas or liquid. 



cyclone a mass of slowly whirling warm air which is 

 rising; a low-pressure area. 



doldrums large masses of heated ascending air near 

 the equator. These are sometimes called the equatorial 

 calms. 



high a large mass of descending air in a region of high 

 barometric pressure or an anticyclone. 



low a large mass of ascending warm air in a region of 

 low barometric pressure or cyclone. 



EXPERIMENTS OR DEMONSTRATIONS WHICH WILL 

 HELP ANSWER THE PROBLEM QUESTIONS 



Experiment 24. What happens to air when it is heated? 



Grease a solid rubber stopper and place it in the mouth 



of a flask. Heat the flask 

 gently over a very low bun- 

 sen flame. Explain the re- 

 sult. Through a one-hole 

 stopper placed in a small 

 flask, insert a one-foot 

 length of glass tubing. 

 Place the end of the tube 

 under the surface of some 

 water in a beaker. Gently 

 heat the flask and observe 

 what happens. Allow the 

 flask to cool with the tube 

 still under water. 



In your notebook 1 re- 

 cord the notes of this ex- 

 periment and complete the 

 following statements. 



When the flask was heated the stopper When the 



second flask was heated through the water. When 



it was allowed to cool entered the tube. This shows 



that . caused the air to and drove as much of it 



from the flask as there was water which when the 



flask was allowed to cool. 



Experiment 25. Which is heavier, warm air or cold 

 air? 



Suspend two flasks of 400 or 500 cubic centimeter ca- 

 pacity from the arms of a balance or from the ends of a 

 yard stick pivoted in the center. If they do not quite bal- 

 ance, place sand in the lighter one until it weighs the same 

 as the other. Gently heat one of the flasks and carefully 

 observe what happens. Allow to cool and heat the other 

 flask. 



1 See workbook, p. 15. 



FIG. 63 



FIG. 64 



In your notebook 2 record the notes of this experiment, 

 complete the following state- 

 ments, and make the re- 

 quired drawing. 



The air in the flask that 

 was heated became (heav- 

 ier, lighter) The air 



in the flask that was cool 

 seemed to be (A dia- 

 gram should be drawn to 

 show their position.) When 

 the other flask was heated 



it and the cool one 



This experiment 



would seem to indicate that 



air is lighter than . 



air. 



Experiment 26. What 

 causes winds to blow? 



From a tight box about one foot long, seven inches 

 high, and five inches wide, make a wind box similar to the 

 one shown in Figure 65. Groove the front edge so that 



a glass may be placed in it. 

 Cut two holes in the top and 

 insert lamp chimneys or mail- 

 ing tubes. Place a short candle 

 under one of the chimneys 

 and hold a smoking paper 

 over it. Now hold the smok- 

 ing paper over the other 

 chimney. Trace the air cur- 

 rent in each chimney by the 

 smoke. Trace the air current 

 direction inside the box by 

 observing the smoke. A good 

 smoke paper can be made by 

 soaking strips of blotting 

 paper in potassium nitrate 

 and allowing them to dry. 



In your notebook 3 record the notes of this experiment 

 and complete the following statements. 



The air current rose in the (cool, warm) chim- 

 ney and fell in the (cool, warm) chimney. Inside 



the box the air moved toward the (warm, cool) 



chimney. Using the data from the two previous experi- 

 ments I should explain this experiment in the following 



way. When air is heated it and grows (heavier, lighter) 



. The heated air in the chimney over the candle (ex- 

 panded, contracted) , became (heavier, lighter) , 



and was pushed up by the (warm, cool) air in the 



other chimney which was (rising, falling) because 



of its weight. 



If on a certain day it was cloudy and cool over the Rocky 

 Mountain states while it was sunny and warm over the 

 states of the Mississippi valley, predict what would prob- 

 ably result on the basis of your experiment. Record in 

 your notebook. 



Experiment 27. How do the winds blow about a low 

 and high pressure area? 



Carefully study the weather maps (Fig. 66) and find 

 areas marked "Low" on them. Find others marked "High." 



2 See workbook, p. 15. 

 "See workbook, p. 16. 



FIG. 65 



