THERMO-REGULATORS 



cup to receive the lower end of a rigid rod, through 

 which the movements of the walls of the capsule are 

 transmitted to the gas valve fixed outside the incubator. 



The gas valve or governor is shown in figure 1 16. A 

 is the inlet for gas, C the outlet to burner heating the 

 water jacket, B D a lever pivoted to standards at G, 

 and acted upon by the capsule, through the rigid rod 

 which enters the socket below the screw P. 



The construction of the valve is such that, when- 

 ever the short arm of the lever B D presses on the disc 

 below the end B, the main supply of gas is entirely cut 

 off. At such times, however, a very small portion of 

 gas passes from A to C, through an aperture inside the 

 valve, the size of which aperture can be adjusted by 



FIG. 116. Capsule thermo-regulator. 



the screw needle S, hence the gas flame below the incu- 

 bator is never extinguished. 



The expansion of the metal walls of the capsule, 

 which takes place upon the boiling of its contents, pro- 

 vides the motive force, transmitted through the rigid 

 rod to raise the long arm of the lever B D, and as this 

 expansion only takes place at a predetermined temper- 

 ature, the lever will only be acted upon when the criti- 

 cal temperature is reached, no sensible effect being pro- 

 duced at even i C. below that at which the capsule is 

 destined to act. 



W is a weight sliding on the lever rod D ; by increas- 

 ing the distance between the weight and the fulcrum 



