Temperature, second week. - The outside temperature has less influence over the machine temperature after the first week, owing to the increasing amount of animal heat given off by the growing embryos. Machines using a hanging thermometer should be held at 103° F., while in those using contact thermometers, the heat should be increased to 103° F.
Temperature, third week. - Hold the temperature as near 103° as possible up to about the eighteenth day, when it may be allowed to run up to 104°.
The eggs. - The eggs should not be put in the machine until it has been run for several days properly regulated and all directions have been followed out in regard to setting up, paying special attention to the manufacturer's directions about ventilators, felts, trays, etc.
Incubate eggs of uniform size, shape, and color as far as possible, and eliminate those with very porous or otherwise defective shells.
Eggs from the heavy type of fowls usually take a few hours longer to hatch than Leghorn eggs; therefore it is not advisable to set the two kinds of eggs together in an incubator.