510 SCIENCE OF HOME AND COMMUNITY 



is used to determine elevation; as shown in figure 203, this 

 looks something like a clock. The back is covered with a 

 very thin diaphragm which is pressed down by the weight 

 of the air. This is connected with a hand on the front which 

 records the pressure. 



DEMONSTRATION 35 



Purpose. To find the height of a hill by means of a barometer. 



Directions. Take the reading of the barometer at the top of 

 the hill. Take it again at the bottom. Subtract these readings. 

 The approximate height may be found by multiplying by ninety 

 this difference expressed in tenths of an inch. 



Barometer and weather predictions. The barometer is a 

 very important instrument in making weather observa- 

 tions, because the air pressure is the most important factor 

 in foretelling weather changes. In general a rising barom- 

 eter indicates fair weather, while a falling barometer indi- 

 cates stormy weather. 



Thermometers. For measuring the prevailing tempera- 

 ture, the thermometer is used, as explained in Chapter I. 



FIG. 204. Minimum and maximum thermometers. 



besides this, maximum and minimum thermometers are 

 used to record the highest and the lowest temperatures. 

 These thermometers will register the highest and the lowest 

 temperatures for the time they are left. They are usually 

 set every day. The maximum thermometer is constructed 

 .so that some of the mercury remains at the highest point 

 to which it is forced. The minimum thermometer is so 

 constructed that a small index moves with the liquid and 



