OBSERVING THE WEATHER 177 



their journeys to measure the temperatures experienced in 

 different lands. The beginnings of weather science ap- 

 peared about 150 years ago, and much of our present exact 

 knowledge has been gained in the last hundred years. 



205. Weather Caused Primarily by the Sun. All weather 

 is made up chiefly of some combination of the temperature, 

 moisture, and movements of the air. The moisture is carried 

 by the winds; the winds are indirectly caused by temperature 

 conditions; and the temperature conditions are controlled 

 principally by the reception of heat from the sun and the 

 loss of heat by radiation into space. The heat received from 

 the sun (and lost to space) is the great primary cause of all 

 weather. How the sun's heat produces wind and cloud and 

 storm and cold as well as the bright and sunny day is an 

 interesting story. To study weather best, we begin by 

 observing the weather about us. 



I. OBSERVING THE WEATHER 



206. Observing Weather Without Instruments. Can you 



describe yesterday's weather in your locality? Do so. Was 

 the day clear or cloudy? Was it warm or cold for the season? 

 What was the direction of the wind? Was it strong or 

 light? What changes in direction occurred during the 

 day? Can you tell anything about the clouds and in what 

 direction they were moving? If there was rain or snow 

 during what hours did it fall? Was the fall heavy or light? 

 Describe today's weather fully, giving all changes that have 

 occurred since morning. 



207. Recording Weather. Several features of the weather 

 are best measured and recorded by instruments made es- 

 pecially for that purpose. The thermometer, the barometer, 

 and the raingauge are needed in class work and will be studied 

 later. But an interesting and useful record of many weather 

 conditions may be made without any instruments. Such 

 records are kept at weather stations all over the world in 

 addition to the records made by weather instruments. 



12 



