108 FIRST YEAR COURSE IN GENERAL SCIENCE 



therefore highest pressure. Warm, saturated air is of the 

 least density and lowest pressure. 



115. Weather. The condition of the atmosphere as re- 

 gards temperature, humidity, and motion determines the 

 weather. " Cold, dry, and windy " may describe the weather 

 of one day. "Warm, moist, and still" would describe the 

 other extreme. (LABORATORY MANUAL, Exercise XII.) 



116. The Weather Bureau. The conditions of tem- 

 perature and wind are of such great importance to farming 

 and navigation that the United States government has es- 



FIG. 53. INSTRUMENTS USED BY THE UNITED STATES WEATHER 



BUREAU 



At the left are self-registering thermometers, which show the maximum 

 and minimum temperatures since they were last adjusted. Below is a 

 thermograph, which records, by a pen upon a slowly revolving paper cylinder, 

 the changes in temperature during 24 hours. 



In the center is an anemometer to measure the velocity of the \\liid. 

 The cups are exposed in an elevated place and their revolutions, as they 

 catch the wind, are recorded by a mechanism similar to that of a gas meter. 



At the right is a self-registering barometer, a barograph. 



Which one of these instruments would give practically the same record 

 in the house as out of doors? Why? 



tablished a Weather Bureau as a division of the Department 

 of Agriculture. A central office at Washington receives, 

 three times a day, reports of the weather from more than 

 a hundred stations scattered over the country. These 

 reports include the degree of cloudiness, direction and 



