294 AN EGG FARM. 



providing that the tension of the moisture in the two atmospheres 

 remains the same, and that the rate of movement of the air surround- 

 ing the eggs exercises a more powerful influence on evaporation than 

 the usual variations of humidity. In the construction of our hatching 

 chamber, therefore, there are four features of vital importance to be 

 considered, viz., a non-conducting wall that will protect the eggs 

 from outward changes of temperature ; a provision for maintaining 

 the atmospheric air within the chamber in a pure state; the mainte- 

 nance cf as great a tension of aqueous vapor in the inner as in the 

 outer atmosphere for their respective temperatures, and the control 

 of the movement of the air around the eggs. 



" In natural incubation the purity of the air surrounding the eggs is 

 maintained by exchanges with the outer atmosphere through the 

 wall or septum that intervenes. This wall is composed of down and 

 feathers, which allow of a spontaneous diffusion of gases or vapors 

 through them, while they are sufficiently dense to hold any current 

 in check by frictional resistance. It is therefore obvious that the nat- 

 ural provision for maintaining the purity of the air around the eggs 

 also provides, through the same medium, for the retention of warmth, 

 for an equilibrium between the relative humidity of the two atmos- 

 pheres, and for the control of the movement of the inner air. And as 

 it is the nature of the fabric of which the wall is constructed that con- 

 trols the physical forces of incubation, that is, the storage of warmth, 

 and the purity, humidity and movement of the air surrounding the 

 eggs, it is evident that we have not appreciated, or even understood, 

 its function." 



VENTILATION. 



This subject is, as we have said, intimately connected 

 with the supply of moisture. Indeed the three factors, 

 heat, moisture and pure air, are all closely related and 

 act and react on each other, rendering perfect artificial 

 incubation much more difficult than it would otherwise 

 be ; for in ventilating we may remove too much damp- 

 ness as well as heat, and in warming newly introduced 

 air we change its capacity for moisture, and make it 

 "drink like a fish." To hatch eggs in a good incubator 

 is rather easy, though demanding some ability ; to 

 hatch them well so that they will be real good ones is 

 moderately difficult, and to rear them in good shape, 

 artificially, is decidedly difficult. 



Nobody ever succeeded in hatching eggs the shells of 

 which had been made air-tight by a coat of varnish, or 

 eggs placed in a hermetically sealed chamber, showing 



