THE INCUBATION OF THE EOG 



197 



expand and contract readily with rising and falling tempera- 

 tures. This kind of thermostat is most used because it is 

 the cheapest. When new and in perfect condition they are 

 fully as sensitive as the bimetallic type, but are likely to 

 lose their sensitiveness after a season's use or even before. 



Heating Systems. — ^There are three methods of heating 

 incubators in common use, with a fourth that has been 

 frequently attempted but which has not yet been put into 



Fig. 99 



l^xy^yry-yrxYin 



Showing combination of radiation and diffusion methods of heating with 

 hot air as the medium. A, inlet pipe from heater, which discharges air into 

 box or inclosure, P; B, metal radiators in top of egg chamber; C, insulating 

 material; D, nursery; E, eggs, place on tray; H, discharge outlet of the 

 ventilating current in bottom of incubator; K, one of four pipes to discharge 

 air from the above level of the eggs in the egg chamber to false bottom 

 underneath nursery; L, moisture pan; M, dead air-space insulation in bottom 

 of incubator. (Courtesy of Prairie State Incubator Company.) 



successful operation. These are (1) diffusion, (2) radiation, 

 (3) a combination of radiation and diffusion, and (4) contact. 



With the diffusion method, air is the medium of trans- 

 mission. It is heated and poured into the heating chamber 

 of the incubator, from whence it passes into the egg chamber 

 usually through a diaphragm of light cloth (see Fig. 92). 



Where the radiation method is employed the medium for 

 carrying the heat may be either air or water. If air is used 



