THE THERMOMETER. 



liquid. The instrument is so adjusted that, when the drop of 

 liquid is at the middle oT the horizontal tube, the air in the bulbs 



Fig. 11. 



has the same pressure ; and having equal volumes, the quantities 

 at each side of the liquid are necessarily equal. If the bulbs be 

 affected by different temperatures, the liquid will be driven from 



Fig. 12. 



that side at which the temperature is greatest, and the extent of 

 its departure from the zero or middle is indicated by the scale. 



By these instruments changes of temperature, not exceeding 

 the 6000th part of a degree, are rendered sensible. 



160 



