Wind and Weather 



139 



It, E. Knott Apparatus Co. 



THE ANEROID BAROMETER 



It records the pressure of the at- 

 mosphere and predicts the weather. 



One indicates the air pressure, the other may be set at any reading. 

 The difference in the readings of the two pointers shows the 

 change in air pressure. Within the outer casing is a metal box 

 from which nearly all the air has been removed. The top of the 

 box is flexible, and is connected to 

 one of the pointers by means of 

 a series of levers and wheels. 

 When the atmospheric pressure in- 

 creases or decreases, the top curves 

 slightly inward or outward accord- 

 ingly. These movements affect the 

 system of levers and wheels and 

 cause the pointer on the face of the 

 dial to indicate the air pressure in 

 "inches and fractions thereof." 



The barograph is made on the 

 same principle as the aneroid ba- 

 rometer. It is a self-recording in- 

 strument, having mechanism so arranged as to indicate the record 

 of the air pressure on a chart attached to a cylinder which rotates 



by means of clock work. 



The anemometer is an in- 

 strument used to measure the 

 force of the wind. It consists 

 of four cups so arranged on 

 an axis that they revolve when 

 the wind strikes them. Revo- 

 lutions are recorded on a dial 

 so set up that five hundred 

 revolutions per hour indicate 

 one mile velocity of wind. 



Paths of Storms Across 

 the United States. In con- 

 sidering the storms of any 

 section, it should be borne in 

 mind that land heats in the 

 N fe M of?h R e wind. sun's rays more rapidly than 



