72 THE PRACTICAL POULTRY KEEPER. 



and studied, and carried out. If even a particular oil be 

 indicated, to use a commoner quality may quite possibly 

 bring about disaster. 



2. The machine should be in as quiet and undisturbed a 

 place as a sitting hen. Sudden noises or concussions are 

 known to cause deformities. As near as possible to a 

 regular temperature will also save much trouble. Cellars do 

 well, if neither very cold nor hot ; and in the large hatching 

 concerns of America, it is found worth while to arrange the 

 incubator-rooms half-way under ground. The machine 

 must not be in a draught, or eggs will be chilled when 

 airing, unless a piece of coarse sacking or other porous 

 material be laid over them while being aired. 



3. The temperature should be regulated and steady for 

 a day before any eggs are attempted. The first trial should 

 be made with cheap, but fresh and strong eggs. Loss may 

 be thus saved. After all we cannot quite imitate Nature, 

 and any weakness in the eggs is found out. 



4. It is of very great importance to possess as a standard 

 one really good " clinical " thermometer, such as doctors 

 use, with which any new thermometers can be compared. 

 The one by which the machine is run should be just at the 

 top of the eggs in the drawer, on a fertile egg. It seems too 

 often supposed that the machine once regulated needs no 

 further attention. This is not so. In most machines the 

 bottom of the egg is much cooler than the top, and the 

 centre a sort of mean between the two. Hence the ther- 

 mometer should read higher in cold weather m the proportion 

 generally of about i degree to 10 degrees of outside tem- 

 perature, though incubators differ in this respect.* Hence 

 the regulator frequently needs a little adjustment accordingly, 

 and it must be found by experience how much movement of 



* The principle of the regulator shown in Fig. 20 seems likely to meet 

 this condition automatically to a large extent. 



