34 



WEATHER AND CLIMATE 



Experiment 23. How are fogs and clouds produced? 



Thoroughly clean and dry a large flask or quart milk 

 bottle. Insert a glass tube about four inches long into a 



one-hole stopper which fits the 

 flask and connect the glass tube 



with an ordinary automobile or 



LJ\\ TI? bicycle pump by means of a 

 if \\ rubber tube. Place a small 



quantity of water in the bottom 

 of the flask and shake in a lit- 

 tle chalk dust. Insert the stop- 

 per. While holding the stopper 

 tightly in the flask, pump in as 

 much air as you can and then 

 allow the air inside to expand 

 very rapidly by blowing the 

 stopper out. 



FIG. 56. PRODUCING FOG I n y ur notebook 1 record the 



notes of this experiment and 

 complete the statement given below. 



The expansion of the air it below its point 



temperature and some of the formed in the flask as a 



READINGS WHICH WILL HELP ANSWER THE 

 PROBLEM QUESTIONS 



What causes moisture to come out of the air? 



Everyone has experienced those sultry days in sum- 

 mer when water pipes and iced-water pitchers sweat, 



1 See workbook, p. 14. 



and when the atmosphere is oppressive and we are 

 very warm and uncomfortable. On such days the air 

 is holding nearly all the moisture possible at the time, 



and the relative humid- 

 ity is nearly one hun- 

 dred per cent. Because 

 moisture from the body 

 cannot evaporate to 

 cool us, we feel hot. 



In the first topic of 

 this unit you learned 

 that at high tempera- 

 tures the air can hold 

 more water vapor than 

 it can when it is cooler. 

 Experiment 23 in this 

 topic has taught you 

 that some of the water 

 vapor in the air, at any 

 given time, can be made 

 to condense into a li- 

 FIC 57 quid if the air is cooled 



below dew point tem- 

 perature. This is the temperature where the amount 

 of water present at any time is sufficient to saturate 

 the air or make the relative humidity one hundred per 

 cent. When air is cooled below its dew point, it cannot 



Saturated air 

 forms clouds 



Cold dry air 

 falls towards 



.\ 



1 1 1 ' 'Water condenses ' ' * 



x \ 



Air rises \ 



, and expands 



v \\\ \ holding capacity 



FIG. 



RAIN CYCLE 



