WINDS AND WEATHER 



185 



(remember mountain tops) and latitude increase, the 

 temperature, generally speaking, increases. So it does not 

 surprise us to learn (see Fig. 67) that the isotherms show 

 a general tendency to run parallel to the parallels (lines of 

 latitude). Nor need the bends (away from the parallels) 

 of the isotherms surprise us when we remember the local 

 effects that land and water and wind have on temperature. 

 As to altitude effects, these are not shown on the maps. 

 Allowances are made, when the 

 reports are computed, so that 

 the isobars and isotherms are 

 drawn on the maps as though 

 all the land were at sea-level. 

 This is because altitude is so 

 local a condition that to take 

 account of it on weather-maps 

 would only confuse a record 

 which is meant to be general. 

 Fig. 68 indicates the gen- 

 eral directions of the winds 



of earth. This diagram is not difficult to understand if 

 you keep in mind a picture of the rotating earth, and 

 try to realize the effects which this rotation is certain to 

 produce upon the atmospheric movements. At the equa- 

 tor the rotation movement is over a thousand miles an 

 hour; to north and south it gradually diminishes until 

 exactly at the poles it is zero. Now, of course, the atmos- 

 phere very nearly keeps up, in this rotating movement, 

 with the rest of earth. Otherwise we should constantly 

 have storms of enormous violence. As it is, even in hurri- 

 canes, the wind velocity rarely becomes greater than one 

 hundred miles per hour. However, the rotation does 



FIG. 68. Diagram showing the gen- 

 eral direction of the winds of the 

 earth. 



