12 



A thermometer is attached to the barometer to indi- 



Fig. 2. 



Fig- 3 



25 



cate the temperature of the mercury in the cistern ; all 

 bodies expand by heat and contract with cold ; the ex- 

 pansion of mercury is easily tested by exposing a mer- 

 curial thermometer to the heat of a fire, or by placing 

 it in hot water : as the warmth increases, the mercury 

 will expand and ascend into the tube ; as it diminishes, 

 it will contract and fall towards the bulb : if the ther- 



