The Weather 19 



24. (a) About how deep is the atmosphere? (6) What pressure does 

 it exert per square inch? 25. By what means can the pressure of 

 the air be determined? 26. How do changes in air pressure make 

 changes in the height of the mercury column? 



27. Describe the process of making a simple barometer. 28. Show 

 how important small differences in barometric readings are. 29. How 

 may altitude be determined approximately by means of the barom- 

 eter? 30. Why is mercury more convenient than water for making 

 a barometer? 31. In what position is each of the valves of a lift 

 pump when the plunger goes up ? When it goes down ? 32. Explain 

 why the suction pump does not lift water from the well. 33. (a) In 

 what units is pressure of the air ordinarily expressed? (6) What 

 units are often used in the laboratory for the same purpose? 

 34. (a) Describe the construction and operation of an aneroid barom- 

 eter. (6) What advantages does it possess? 35. What is (a) a 

 thermograph? (6) A barograph? (c) A baro thermograph ? 



V. WINDS 



14. Direction of winds. Locate on the weather map for 

 December 26, page 6, the places showing the greatest differ- 

 ences in pressure. Estimate the approximate distance between 

 a high and a low area, such as those over the Atlantic coast 

 states. Consider the direction of the wind, as indicated by 

 arrows, between the two centers. Do the winds move directly 

 away or outward from the high? Do they move at right 

 angles to the isobars, this being the shortest path between the 

 two areas? About halfway toward the low, do the arrows 

 indicate the wind to be going directly toward the low? Com- 

 pare the diagrammatic map (Fig. 8), in which these points 

 are emphasized more sharply. Is the direction of the winds 

 between the two eastern high and low centers eastward? 

 Follow the course of a wind toward the center of a low and 

 describe its general direction. As a matter of fact, winds 

 about high and low centers do not always complete a circular 

 course, but they do have a general direction which may be 

 described as circular or spiral. 



With this understanding of the general circular or spiral 



