THE TEMPERATURE 337 
cool room of perhaps 45° or 50° to one with a temperature 
of 100° to 103°. Allow the eggs to warm up for a short time 
in the incubator room before placing them in the incubator. (2) 
It is a good plan to set the eggs on end, large end up, for six 
to twelve hours previous to putting them into the incubator. 
This allows the air cell to adjust itself, and the yolk to float 
in normal position. (3) When placed in the tray, the eggs should 
completely cover it, but not be piled one upon another. ‘The 
temperature varies approximately one degree for every inch of 
height, and it would be impossible to subject all the eggs to 
a uniform temperature. The process of turning, too, would be 
more laborious, with greater danger of cracking the eggs. (4) 
When it is desirable, for any reason, to keep a record of the 
ancestry of the progeny, pedigree egg trays must be used, except 
where a small number of eggs are so hatched; in such cases, it 
may be possible to put eggs from hens of different color in the 
sume compartment, although this practice is not always conducive 
to the best results in hatching. Pedigree egg trays are composed 
of small compartments in which eggs of different hens or different 
breeds may be incubated, the chicks when hatched being plainly 
marked for future identification. 
Source of Heat.—Keep up the degree of heat best suited to 
develop and hatch vigorous chicks; in natural incubation this heat 
is generated by the mother hen. To accomplish it artificially, oil, 
coal, gas, and electricity are commonly used. ‘The kind of fuel 
used is immaterial, so long as it is adapted to the machine used. 
The small or individual incubator is usually heated by oil. A very 
good method is to have the machine piped for illuminating gas, 
a round burner being used; this provides a uniform degree of heat 
with a minimum amount of labor. Electricity is sometimes used 
in the individual machine, but not commonly. Coal is used almost 
entirely in the mammoth machines. 
The temperature of eggs during incubation is approximately 103° 
F., or from two to three degrees lower than the body temperature 
of the hen. The temperature of eggs under hens has been found 
to vary from 101° to 104°, the average being approximately 1038”. 
There are two methods of testing the temperature of the incu- 
bator; one is by placing the bulb of the thermometer in contact 
with an egg, and the other is to take the temperature of the air 
above the eggs. The former permits-a possible error from the 
fact that the bulb of the thermometer may rest upon an infertile 
22 
