INCUBATION, TUE PERIOD OF, or the duration of the time in which birds sit on their eggs before the young are hatched, varies in different species, but is nearly constant in each. In the humming-birds, the smallest animals of this class, it is only 12 days; in canaries, it is from 15 to 18 days; in the common fowl, it is 21 days; in the duck, it is from 28 to 30 days; in the guinea-fowl, it is 28 or 29 days; in the turkey, 30 days; and in the swan, from 40 to 45 days. A certain degree of heat (about 104°) is necessary for the development of the young bird; that of the sun is sufficient, during the day, to hatch the eggs of some birds (for example, the ostrich) inhabiting tropical countries, but in general the mother keeps up a suitable temperature by placing the eggs in a warm and carefully constructed nest (q.v.), and by covering them with her own body. In some eases, the male bird takes part in this duty; usually, however, his services are restricted to provid ing his mate with food.
Eggs may, however, be hatched without the aid of the parent bird. From time immemorial, the Egyptians have hatched eggs by artificial warmth in peculiar stoves called mammals. In 1777 Mr, Bonnemain devised an apparatus by which, for several years before the French revolution, he supplied the Parisian markets with excellent poul try, at a period of the year when the farmers had ceased to supply it. A description of
this apparatus is given in tire's Dictionary of Arts, etc., 7th ed. 1875, vol. ii.
The process of artificial incubation was publicly exhibited some years ago in London, by means of the eccaleobion machine (derived from ekkaleo, I call forth, and Lion, life),which was invented by Mr. Bucknell, and is described in his Treatese on Artificial Incubation. This machine possessed a perfect! control over temperature from 300' Fahrenheit to that of cold water for any length of time, and " by means of this absolute and complete com mand over the temperature, the impregnated egg of any bird, not stale, placed within its influence at the proper degree of warmth, is, at the expiration of its natural time, elicited into life, without the possibility of failure." That chickens were hatched in large lum bers by this machine is undoubted, but for some reason—probably from the process not proving sufficiently economical for commercial purposes—the eccalcobion has not been lately heard of. In 1825 M. D'Arce obtained chickens and pigeons at Vichy by artificial incubation effected by the thermal waters there.