HATCHING, is the maturation of, or communicating life to, fecundated eggs, either by the incubation and warmth of the parent bird, or by artificial heat.
The art of hatching chickens by means of ovens, has been long practised in Egypt, where it is confined to the knowledge of the inhabitants of a single village and its vicinity. This method being easily understood, we shall only observe, that each brood is supposed to consist of 30,000 chickens; the number of ovens amounts to 386, which are in constant employ for six months; and, as the eggs are completely hatched in three weeks, or about the same period as a hen continues to sit upon a brood, it has been calculated that the ovens of Egypt every year communicate life to at least 92,640,000 chickens!
A very ingenious, and useful method of hatching eggs, we conceive, is that invented by the celebrated naturalist Reaumur, who reduced this art to fixed principles. The degree of heat necessary for the purpose, is nearly the same as that marked 36° on his own thermometer, which is equal to about 96° of Fahrenheit, as well as to the heat both of the skin of the hen and all other fowl.
M. Reaumur employed stoves of any shape, which were heated by means of a baker's oven; or in a room warmed by an oven underneath: the eggs were here deposited, and occasionally shifted in a similar manner as the parent birds move them; in order that each egg might equally participate in the irregularities of the stove. The only important object is, to ascertain the precise degree of heat: with this design, he melted and poured into a phial two parts of butter and one of tallow. When the heat was of a proper temperature, the liquid grease resembled a thick syrup; if it was too great, the mixture flowed like oil, on holding the phial sideward; but, when the heat was too low, it remained fixed in a lump. Thus, by placing the phial into the stove, the proper degree of heat may be easily regulated. He also invented a kind of hollow covers, or low boxes, without bottoms, and lined with fur, which he called artificial parents. These not only shelter the chickens, when hatched, but also afford them a genial warmth, so that they fly under the boxes as readily as they resort to the protection of the wings of the hen. In a few days, they may be turned out into the open air, and committed to the care of capons, or even cocks, which may be taught to perform the maternal office, and watch them with as much solicitude as is evinced by hens.