Incubator
2 of the 7 encyclopedias on this shelf carry an entry for Incubator. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a box-like contrivance or oven for the hatching of eggs by artificial heat. The incubator is by no means a modern idea. Over two thousand years ago the Egyptians were familiar with the method of hatching chickens in ovens, heated with straw. Artificial hatching machines are also credited to the Chinese. Incubators came into general use only within the past twenty years. American incubators are now shipped abroad to various European countries and to Australia. Artificial incubation is very simple, yet requires constant care. It is only necessary to keep the eggs in a warm place and to turn them daily. The most successful machines are constructed in such a way that heat is supplied from above rather than from below. They are furnished with a self-acting contrivance devised to keep the air of the chamber at a temperature of about 102 deg. the first half of the hatch and 103 deg. the second half. It is also important that the egg chamber be well ventilated. In imitation of the sitting hen that turns her eggs in the nest each day, the eggs may be turned by hand, or they may be placed in a double tray having a bottom and a top alike. To turn the eggs it is only necessary, therefore, to put on the top, whip the tray over, and remove the half which is now the top. While the proverbial impossibility of counting chickens before they are hatched applies to those in the incubator as well as to those under a hen, a successful poultry raiser expects to hatch at least nine chickens out of every dozen eggs. It is more difficult to take care of the little chicks after they are hatched than it is to bring them forth from the shell. One chicken raiser of Pembroke, New York , employs incubators to do the work of 1,000 hens in which 15,000 eggs are cared for. Heat is furnished by steam and hot water. A thermostat maintains a uniform temperature. See Chickens Rock hewn temple of Badami. Rock hewn temple, Ellora. East Indian temples
Collier's New Encyclopedia (1921)
a piece of apparatus in which a constant, predetermined temperature may be maintained. Its principal scientific use is for the growth of bacterial culture. It is frequently a double box of copper or other metal insulated with miner wool or felt. The space between the walls is usually filled with water, making it in effect a water bath. The source of heat is generally a Bunsen burner, although in some cases electric coils have been used. An adjustable thermostat which operates on the gas flow, is used to control the temperature. The temperature desired, and the type of work for which the apparatus is to be used, largely determine the design, but it is usual to provide a heavily insulated glass door, in order that the condition of the contents may be observed from time to time. See INCUBATION.