VARIOUS INCUBATOKS. 65 



generally used than any other ; and there is no question 

 that his incubator known as the " Champion," for which it 

 was designed, in the earlier years gave a very great stimulus 

 to artificial hatching by really automatic machines. It 

 depends for efficiency upon the fixed boiling point of a fluid. 

 Just as water boils at 212, so sulphuric ether boils and 

 expands into vapour at 94. Other liquids boil at higher 

 temperatures ; and as a mixture generally boils at a heat 

 intermediate between that of its two components, it is easy 

 to prepare a slightly modified ether which shall boil (at 

 ordinary barometrical pressures) at 98 or 99, the loivest 

 admissible incubator temperature. The capsule regulator 

 consists of a few drops of such volatile fluid enclosed between 

 two brass plates, soldered together all round their edges 

 into a close flattish capsule. Then, directly the heat of 98 

 is exceeded, at atmospheric pressure, the two plates "bulge" 

 under the ether vapour which is formed. The boiling tem- 

 perature is increased by pressure or weight upon the capsule ; 

 and hence we have a very powerful and easily adjustable 

 force, which acts upon the regulator. 



The machine for which this regulator was invented is 

 still a deserved favourite, and we will take it as a type of 

 its class, or of the " tank " machines. Its present form is 

 shown in Fig. 17. The tank A A is traversed by the flue LL, 

 which really returns again to the same side in which it 

 enters, but is shown carried out at w on the other side to 

 simplify the diagram. The heat enters from the flame x of 

 the lamp T from the bottom L of the chimney ; and the top 

 v of the chimney is covered by the valve, or damper, F, 

 When this rests close on v the heated air does not escape 

 there, but the whole has to traverse the entire flue L L to 

 the exit w. When the damper is raised, some of it escapes 

 and if much raised the whole heat escapes at F, none going 

 through the flue. This arrangement is worked by the 



y 



