This author employed a circular oven of earthen-ware as a model of his great plan, heated by a cylinder of boiling water passing through its centre and resting on a fire-place below. This model, which proved sufficient for practice, is 28 inches high, by 24 in diameter ; and an inch thick in the sides. The top is arched ; and some inches below the commencement of the arch are four holes opposite to each other, two inches in diameter, for ventilators ; because in all these experiments ventilation must be strictly attended to; as also other four near the bottom, of one inch in diame ter, two of which penetrate the sides of the oven horizon tally, and two obliquely. All have cork stoppers. There is a door half way up the side of the oven, six or seven inches square, which may be opened to admit the hand for internal operations, with a hole and a cork stopper of an inch diameter in the middle. This oven, which, it will be observed, is of a cylindrical form, is closely luted to an earthen-ware table, two feet and a half square, and two inches thick, with a hole in the centre for receiving the column or cylinder of hot water. Below the table, and be tween its feet, there is a small stove, also of earthen ware, about ten inches deep and seven diameter, which, be sides a door on hinges like that of a common stove, six inches by five, has other two openings. One of these is in the centre of the top, three inches in diameter, to admit the base of the metal cylinder for water ; the other is in that side opposite the door, nearly three inches in diameter, and three inches lower than the former. Its use is to carry off the smoke from a grate of live coal whereon this stove is to be placed. But one of the most essential parts, the one in deed where the chief merit of the contrivance lies, consists in the means of heating the oven by a hollow tin cylinder, three inches in diameter, let down into the hole at the top of the arch above, and resting on the stove below, which is situated on the grate. By the boiling of water contained in it, the requisite heat is obtained ; and its degree is re gulated by the ventilators. The cylinder must be closely luted to all the three apertures through which it passes, that is, the top and bottom of the oven, and the top of the stove ; but it is necessary that about two inches should in tervene between the top of the stove and the table or bot tom of the oven. A moveable lid of block tin, with a hole of an inch diameter in the centre, covers the top of the cy linder, which projects a little above the oven. In practice, it is found more convenient to increase the cylinder to the diameter of four inches, and som. enlargement of the stove is also :iL,vantageous. The eggs may be deposited on cards or small shelves, three or four inches broad, ranged around the interior, and separated by intervals of three or four inches high, so as to contain above 300.
Should the reader understand the preceding description, he will easily comprehend the mode of enlargement of all the parts, when real service and operations on an extensive scale are required. A circular brick building, arched above, seven feet eight inches high to the spring of the arch within, seven feet of internal diameter, and eight inches thick in the wall, is to be erected. Ventilators, as before, are in the sides; and the door is four feet high, glazed in the upper part. Ten successive tiers of shelves, a foot broad, project from the whole internal circumference, leav ing an interval of seven inches between them ; and as 44 or 45 eggs occupy a foot square, these shelves will contain 8000. The cylinder of water must be a foot in diameter,
projecting above the building, and entering a stove below, over a furnace which is now to be sunk in the ground. It is necessary to keep a thermometer constantly immersed in it ; and a hygrometer is also required to ascertain the humidity of the interior of the edifice, which is to be lined all over with lambskins, and covered externally by woollen stuffs. Moveable skylights in the roof admit fresh air into the building. The advantage of using hot water is, the equal and uniform diffusion of temperature throughout the oven, which, at the edges of the shelves, should be 106°, and will be indicated by the thermometers deposited there.
After selecting the eggs, they are to be laid on a thin bed of very dry rubbed straw, and turned three or four times daily. The ventilators are to be opened twice a-day. On the sixth day it will be seen on inspection what eggs should be removed as unproductive, and this examination ought to be repeated on the fifteenth. Towards the nineteenth day it is proper to stretch mattings over the edges of the shelves, to guard the young brood, which will appear on the twentieth or twenty-first, from falling over. The period of exclusion is sometimes accelerated or retarded; the ope rator should continue removing the shells, and aiding the weaker chickens to free themselves; but the remaining eggs are to be withdrawn as unproductive only on the twen ty-third day.
With regard to the actual practice which the inventor of these methods followed, it appears that in two experiments on fifty eggs each, when the model was used, the first had but indifferent success, from the heat having been kept too low : but, in the second, chickens were obtained from the whole impregnated eggs, except three or four. Eight broods were attempted in the large oven, each quantity of eggs consisting at a medium of from 2000 to 3000, and the experiments were made at different seasons. At an average the product did not exceed one in six, while, in trying na tural incubation at the same time, about two-thirds of the eggs were hatched. The dryness of the internal air proved injurious, and chickens of larger size were procured, by obtaining an artificial humidity from the evaporation of wa ter in vessels.
It is generally understood, that chickens hatched in this way are not equal in strength and size to those procured by the regular process of nature ; many are maimed, and it is said that monstrosities are frequent.
When the young brood has escaped, the heat of the oven may be reduced to 95° or 90°, and they may be fed, though they can subsist a day or two without meat. They may then be consigned in great numbers to the care of capons, trained on purpdse. But as capons are very rare in this country, and as on the continent it was found more conve nient to prosecute the process without the intervention of other animals, artificial mothers have been contrived. These are of different kinds, but one of the best is a low cage, of two or more stages, stuffed within, and lined with feathers: or there is another equally useful, consist ing merely of two opposite shelves, near the ground, stuck over with feathers below, under which the animals may creep at pleasure. See Reaumur Art de faire eclore et d'Elever en toute raison des Oiseaux Domestiques ; and Ornithotrofihic ?rtcielle on art de faire eclore et d'Elever la Volaille liar le moyen d'un chaleur Rrtcielle. (c)