THERMOSTATIC INCUBATOR. 



81 



keepa the joint air-tight. When the air expands, the diaphragm 

 swells out and presses down the button at the end of the lever 

 shown, and so lifts the valve connected with the egg-drawer, 

 and. allows hot air to escape. On the other hand, if the 



Fig 19. Christy's Thermostatic Incubator. 



heat falls, the india-rubber bulges in, and the button rises and 

 drags down the valve, which is never quite closed, but always 

 allows a little air to escape. This regulator is liable to be 

 affected by a high barometer, which checks the expansion; 

 but with a sufficiently large tank it acts efficiently. 



