34 Introduction to the Study of Science 



a weather map ? (6) From what conditions can the velocity be roughly 

 inferred ? 



12. What is meant by "gradient"? 13. Describe the paths 

 followed by typical cyclones in the United States. 14. What is the 

 average velocity of cyclones? 15. Does any mass of air moving 

 spirally into a low commonly complete the circle? 16. What is the 

 average diameter of lows? 17. What is the general form of a low as 

 shown by the isobars? 18. Where, with reference to a low, is rain 

 most likely to occur? 19. What conditions as to clouds, rain, tem- 

 perature, and direction of wind indicate to an observer the approach 

 of a low ? 20. Describe the changes in direction of the wind when a 

 low passes to the north of an observer. To the south. 21. What are 

 the usual conditions of sky, wind, and temperature when a low is 

 receding ? 



22. What are the direction and character of the winds in a high? 

 In regions around a high? 23. With what pressure conditions do 

 cold waves occur? Blizzards and northers? 24. What are the typ- 

 ical paths of anticylones? 25. Anticyclones may be grouped into 

 what two types? 26. (a) Where do hurricanes originate? (6) What 

 are typical paths ? (c) In what season are they most likely to occur ? 



27. What are storms similar to hurricanes called in the Bay of 

 Bengal? In the China Sea? 28. What velocity may be reached 

 by winds in a hurricane? Over what area? 29. What rainfall per 

 hour would be considered very heavy? 30. Of what importance is 

 the prediction of hurricanes? 



VII. LOCAL STORMS 



There are two great types of local storms, the tornado and 

 the thunderstorm. The tornado belongs to the class of whirl- 

 winds which includes the simoom peculiar to the Sahara 

 desert, the waterspout, and the smaller whirlwinds formed 

 frequently in almost every part of the country. 



23. Tornadoes are of local origin and must not be confused 

 with cyclones, as they are often incorrectly called. The tornado 

 is comparatively small and operates within a limited range of 

 territory; but it is at the same time the most violent and 

 destructive of storms occurring on land or sea. The area of 

 the destructive sweep of tornadoes varies from twenty feet to 

 a thousand feet in diameter. They may travel anywhere from 



