64 LABORATORY LESSONS IN GENERAL SCIENCE 



6. In what ways is the manner of life of a people affected 

 (a) by the excessive year-round heat of the torrid regions 

 of earth ; (b) by sudden and extreme weather changes ; (c) 

 by long-continued wet or dry periods? 



7. Of what value to people are weather forecasts that are 

 reasonably accurate? Upon what must such predictions 

 be based to have any especial worth? For about how long 

 in advance can reliable forecasts be made? 



8. How much is known of the causes of deficient rainfall 

 in any region some years, and of excess in other years? 

 What control over these conditions has man? Explain 

 what the mountain ranges of western United States have to 

 do with any semi-arid conditions to the eastward of them. 



FIG. 26. An irrigation reservoir. 



