68 



THE PRACTICAL POULTRY KEEPER. 



will alter that curve with any change of temperature. The 

 latter kinds of thermostat are independent of barometrical 

 pressure, whereas all depending upon expansion of vapour 

 are affected by it, and need watching on that account. 

 In spite of this, on the whole some variety of capsule is 

 found the most generally satisfactory form of regulator, and 

 is most used. 



Fig. 19. The " Protester " in section. 



In " atmospheric " machines there is no water-tank, but 

 heated air passes direct into the egg chamber. There may 

 be said to be two sub-types of this class, and we will take as 

 our illustration one from the simplest of these, in which 

 more or less of the products of combustion from the lamp 

 are admitted, as well as pure heated air. The example is 

 Messrs. Roberts and Co.'s "Forester" machine, Fig. 18, 

 giving the general arrangements clearly, while Fig. 1 9 is a 

 section. Here cc is the hatching chamber, closed by a pane 



