22 Introduction to the Study of Science 



earth. Where, relative to the target aimed at, will the bullet 

 be when it reaches the 45th parallel ? Will it be to the east or 

 west of the target? Apply this to the change in the direction 

 of the winds when moving from a high-pressure area in the 

 south to a low-pressure area due north. Will a moving mass 

 of air hit the center of the low or pass to the east of it ? 



Exercise. Suppose that a mass of air, a wind, starts from a high- 

 pressure area in the north towards a low-pressure area due south. In 

 what direction will it be deflected by the rotation of the earth? Ex- 

 plain and illustrate. 



Every weather map shows that the general direction of the 

 wind may be modified locally by the character and temperature of 

 the land surface. Mountains and valleys, proximity to the 

 ocean or other large body of water, and the temperature dif- 

 ferences peculiar to each, may be taken as the chief causes of 

 such change in the wind's direction. Land surface with its 

 marked inequalities offers greater resistance to winds than does 

 the ocean. Consequently, on the ocean the wind tends to 

 circulate completely about the center of a low-pressure area, 

 while on land the circulation is more or less interrupted. Strong 

 winds are more noticeably interrupted by land surface con- 

 ditions than are gentle winds and breezes. If winds of your 

 locality diverge from the general wind system to which they 

 belong, find causes and explain. 



15. Velocity of wind. Common experience has hit upon 

 certain signs as indicative of the strength or velocity of wind. 

 When the leaves of trees and bushes are lazily swinging to and 

 fro, the wind is described as a light breeze, and as a fresh breeze 

 when twigs and branches are swinging gently. When branches 

 and tops of trees are vigorously swayed to and fro, and fallen 

 twigs and smaller branches are moved over the ground, the 

 wind is said to be strong to high; and if branches or tops are 

 broken and bushes bend close to the ground, it is called a gale. 

 A hurricane with a varying velocity of eighty to one hundred 



