rilE INCUBATION OF HENS' EGGS 205 



is likely to be a difference in temperature of several degrees 

 between opposite corners, and the trays are heavy and 

 awkward For the ordinary person to handle, when they 

 are full of eggs. 



The so-called mammoth incubators, with egg capacities 

 running into tlie thousands, are made >ip of a larger or smaller 

 number of ordinary sized incubator units built together. 

 Aside from the fact that there is a central heating system, 

 each unit is independent of every other unit, having its own 

 regulator, nursery, and trays. It is entirely possil)le to be 

 bringing off a hatch in one compartment and just starting 

 another one in the next one. 



Principles of Operation. — So far as present knowledge 

 indicates, successful incubation depends primarily upon four 

 conditions. These are (1) temperature, (2) moisture, (3) 

 ventilation, and (4) position. The principles involved in 

 the operation of incubators have to do with making these 

 conditions favorable. 



Place of Operation. — The place of operation has much to 

 do with furnishing proper incubating conditions. It is 

 highly desirable (1) that it shall not be subject to frecjuent 

 or sudden changes in temperature; (2) that an abundance 

 of fresh air may be admitted, while the heavy gases near 

 the floor and the light gases near the ceiling have means of 

 escape; {'■]) that the relative humidity be rather high; (4) 

 that it be impossible for the sunlight to strike the incubator 

 at any time of day. 



A cellar, and particularly a cave cellar, having a grade 

 entrance and a top ventilator, will come about as near meeting 

 these conditions as any room found on the farm. Outside 

 changes do not cpiickly affect it, it is likely to be reasonably 

 damp, does not admit the sunlight, allows the light gases 

 to escape above and tlie heavy ones that have settled to the 

 floor to flush out every time the door is opened. 



Temperature. — The temperature at which eggs are incu- 

 bated naturally depends ])rimarily upon the temperature 

 of the setting hen. As will be seen in Table XXVIII, this 

 temperature is quite variable between different hens on the 

 same day and for the same hen on different days. This 



