Page:The New International Encyclopædia 1st ed. v. 10.djvu/591

* INCUBATOR. 517 INCUNABULA. evenly balanced. There are liundreds of different makes of incubators on the market, many of them verj' efficient when properly liandled. An average liatcli of over 80 per cent, of fertile eggs is secured by experienced poultrj'men, but experi- ence, skill, and careful attention to details are essential to such success. The essentials of a good incubator are an egg- ehamber uniformly heated, preferably from above ; a, self-regulating source of heat, controlled b_v a ihernio-regul.ator, the actuating arm of v.hich is situated in the egg-chamber, and which is sensitive to 1°, or preferably V2°> above or below the desired temperature; and provisions for the ventilation of the egg-chamber, and for I'.iaintaining the proper degree of humidity there- in. In addition to these, saj's Watson, "a con- VI n lent appliance for turning the eggs, positive in action, should accompany each incubator. This may be an extra tray that is to be plaeed bottom side up over the Ira.v of eggs and held firmly in tlii-i position while both trays are turned, thus completely transferring the eggs from one tray to another without jar. The dill'erent machines have very different appliances for accomplishing this result." The object sought in artificial in- cubation is to imitate as closely as possible the conditions of heat, air, moisture, etc., which ob- tain in natural incubation under the hen. The temperature is carefully maintained at about 100° F. or only a few degrees above by placing the incubator in a basement, cellar, or other room where the temperature is stable, and by using a sensitive thermo-regulator to control the heat applied; the moisture of the air in the egg- chamber is carefully controlled, so that evapora- tion from the eggs proceeds as luider normal conditions; and a sufficient amount of fresh air is supplied to the chamber to carry off the harm- ful gases which may accumulate and kill the in- cubating chick. The frequent turning of the eggs during the earlier stages of incubation is believed to have an analogy in the practice of the hen. However, it is not considered advisable to disturb the eggs after the eighteenth day. or to open the incubator thereafter until the hatch is complete, and the chicks dry. As the success of incubation depends so largely upon maintaining the proper moisture conditions in the air of the egg-cham- ber, some reliable ineans of controlling these conditions is essential. It has been proposed to v.se the normal loss of weight of eggs during incu- bation under brooding hens as a guide for this purpose. The West Virginia Agricultural Ex- periment Station foimd that the eggs which hatched under hens lost on an average 16. .5 per cent, of their weight in nineteen days. The in- fertile eggs and those which did not hatch lost from 1 to 2 per cent. less. The normal loss of weight of 100 eggs under natural incubation was fcund to be about 10 ounces in 6 days, 20 ounces in 12 days, and 31 ounces in 18 days. By weighing the eggs in the tray at the beginning of incubation, and at intervals during the process, the progress of evaporation (loss of weight) may be determined, and the ventilation and himiidity so controlled ii-s to make the loss of weight conform to the normal figures. Except in very dry climates there is said to be more danger of over-saturation than under-saturation of the air. A hiimidity of 45 [ler C(>nt. saturation is considered safe, as a rule. If artificial incubation is practiced, some pro- vision must be made fur the care of the chicks when they leave the incubator. Variously arti- ficially heated devices known as brooders are used for this purpose. These may be very simple and cheap, or elaborate and expensive. Almost all manufacturers of incubators also make brood- ers, and there is consequently a great variety of forms to choose from. The requisites of a good brooder are that it should be: (1) Warm (90°- 100° during the first week, with gradually lower- ing temi^erature thereafter), and economical of heat, which is preferably applied mainly from the sides or above; (2) clean, dry. and well-venti- lated; (3) simple in construction, and so ar- ranged that the chicks may be seen. The brooder should be so constructed that the chicks may go out for exercise, and return at will. BiBLiOGB.Puy. The literature of the subject is voluminous. All up-to-date treatises on poul- try-raising explain the processes of artificial incubation, and describe methods and appliances. Among the books which may be consulted are: Watson, Farm Poult ri/ (t^ew York, 1901) ; Beale, Profitable Poultry Keeping (New York. 1895); Stoddard, The Sew Egg Farm (New York, 1900) ; Cyphers, Incubation and Its Natural Laus< (Bos- ton, 1894) : Incubators and Chicken-Raising Ap- pliances (London. 1899); Fiske, Poultry Appli- ances and Ilandicraft (New York, 1902). See Fowl. INCUBUS (Lat, nightmare). (1) A sprite or demon, thought to have been the cause of nightmare. In the iliddle Ages it was very commonly believed that the incubus had carnal knowledge of women while asleep, and that from this connection deformed children sprang. The succuba. was the corresponding female sprite, supposed to consort with sleeping men. (2) Metaphorically, a burden upon mind or spirit. (3) A genus of parasitic hymenopters of the family P>raconid;e. INCUMBRANCE (OF. encomhrance, from encombrer, to incumber, from en, in -j- combrer, to cumber, from combre. obstruction, from Lat. cumulus, heap). A generic term including every kind of charge or burden upon land; every right to or interest in land which may he held by a third person in diminution of its value, but not preventing the passing of the fee from a grantor to a grantee. The most frequent examples are afforded by judgments, leases, mechanics' liens, mortgages, easements, and similar burdens. A covenant against incumbrances is one of the usual "covenants for title' contained in a convey- ance of land. As usually construed it amoimts to a contract of indemnity, securing the grantee against loss by reason of any incumbrance which may exist upon the land at the time of the con- veyance. See Cot:xaxt. INCUNAB'UXA (Lat, cradles). A name applied to printed books published before 1500. Specimens of such works are generally rare, and sought after for their historical bearing on the art of printing, and. as in first editions of Greek and Latin classics, for their scientific value. The number of incunabul.a is variously estimated, but is probably upward of 20.000. Among the works on the subject are: Hain's Repertorium liibliographicum (Stuttgart. 1828-38) and Ber- nard. De I'origine et des debuts de I'imprimerie en Europe (Paris. 1S53), besides a number of later treatises.