makers of scientific instruments. It will suffice if we describe two
forms, one of which (that of Buddicom) can be made by a laboratory
attendant of average intelligence.
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| Fig. 20.—Buddicom’s Gas Regulator. |
In R. A. Buddicom’s gas regulator (fig. 20) the inlet (I) and outlet (O) gas pipe open into a metal bell (B), the lower and open end of which is immersed beneath water contained in a metal tray (T). The bell is suspended upon the arm of a balance (B) and the other arm is poised by a weight (W). This weight may be made of any convenient material. In the original apparatus a test-tube partially filled with mercury was used. The weight dips into one limb of a U-shaped glass tube (U), which contains mercury. Into the other limb of this tube the gas from the meter enters through a glass tube (G) which is held in position by a well-fitting cork. The internal aperture of the tube (G) is very oblique, and it rests just above the level of the mercury when the instrument is finally adjusted. This adjustment is better made in the morning when the gas pressure in the main is at its lowest. Just above the internal aperture of the tube (G), a lateral tube (L) passes out from the limb of the U and is connected with the inlet pipe (I) of the bell. If the gas pressure rises, the bell (B) is raised and the counter-poising weight (W) is proportionately lowered. This forces the mercury up in the other limb of the U-tube and consequently diminishes the size of the oblique orifice in the tube (G). Some of the gas is thus cut off and the pressure maintained constant. Should the pressure fall, the reverse processes occur, and more gas passes through the orifice of G and consequently to the burner by the outlet tube (O).
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| Fig. 21.—Moitessier’s Gas Regulator. |
Moitessier’s regulator (fig. 21) is more complex, and needs more skilled work in its construction. It consists of an outer and closed cylinder (O), which is filled about half-way up with a mixture of acid-free glycerine and distilled water in the proportion of two to one respectively. Within the cylinder is a bell (B), the lower and open end of which dips under the glycerine-water mixture. From the top of the bell a vertical rod (R) passes up through an aperture in the cover of the outer cylinder, and supports the weighted dish (D). The inlet (I) and outlet (O) pipes enter the chamber of the bell above the level of the glycerine-water mixture. The outlet tube is a simple one; but the inlet tube is enlarged into a relatively capacious cylinder (C), and its upper end is fitted with a cover which is perforated by an aperture having a smooth surface and concave form. Into this aperture an accurately fitting ball- or socket-valve (V) fits. The ball-valve is supported by a suspension thread (T) from the roof of the bell (B). The apparatus should be adjusted in the morning when the pressure is low, and the dish (D) should be then so weighted that the full amount of gas passes through. The size of the flame should then be adjusted. Should the pressure increase, the bell (B) is raised and with it the ball-valve (V). The aperture in the cover of the inlet cylinder is consequently reduced and some of the gas cut off. When the pressure falls again, the ball-valve is lowered and more gas passes through. The relative pressure in the inlet and outlet pipes can be read off on the manometer (M) placed on each of these tubes.
Levelling screws allow of the apparatus being horizontally adjusted. The friction engendered by the working of the vertical rod (R) through the aperture in the collar of the cylinder cover is reduced to a minimum by the rod being made to slide upwards or downwards on three vertical knife-edge ridges within the aperture of the collar.
Authorities.—Charles A. Cyphers, Incubation and its Natural Laws (1776); J. H. Barlow, The Art and Method of Hatching and Rearing all Kinds of Domestic Poultry and Game Birds by Steam (London, 1827); and Daily Progress of the Chick in the Egg during Hatching in Steam Apparatus (London, 1824); Walthew, Artificial Incubation (London, 1824); William Bucknell, The Eccaleobin. A Treatise on Artificial Incubation, in 2 parts (published by the author, London, 1839); T. Christy, jun., Hydro-Incubation (London, 1877); L. Wright, The Book of Poultry (2nd ed. London, 1893); A. Forget, L’Aviculture et l’incubation artificielle (Paris, 1896); J. H. Sutcliffe, Incubators and their Management (Upcott Gill, London, 1896); H. H. Stoddard, The New Egg Farm (Orange Judd Co., New York, 1900); Edward Brown, Poultry Keeping as an Industry (5th ed., 1904); F. J. M. Page, “A Simple Form of Gas Regulator,” Journ. Chem. Soc. i. 24 (London, 1876); V. Babes, “Über einige Apparate zur Bacterienuntersuchung,” Centralblatt für Bacteriologie, iv. (1888); T. Hüppe, Methoden der Bacterienforschungen (Berlin, 1889). For further details of bacteriological incubators and accessories see catalogues of Gallenkamp, Baird & Tatlock, Hearson of London, and of the Cambridge Scientific Instrument Company, Cambridge; of P. Lequeux of Paris; and of F. & M. Lautenschläger of Berlin. That of Lequeux and of the Cambridge Company are particularly useful, as in many instances they give a scientific explanation of the principles upon which the construction of the various pieces of apparatus is based. (G. P. M.)
INCUBUS (a Late Latin form of the classical incubo, a night-mare,
from incubare, to lie upon, weigh down, brood), the name
given in the middle ages to a male demon which was supposed
to haunt women in their sleep, and to whose visits the birth
of witches and demons was attributed. The female counterparts
of these demons were called succubae. The word is also
applied generally to an oppressive thing or person.
INCUMBENT (from Lat. incumbere, to lean, lie upon), a general
term for the holder (rector, vicar, curate in charge) of an ecclesiastical
benefice (see Benefice). In Scotland the title is generally
confined to clergy of the Episcopal Church. The word in this
application is peculiar to English. Du Cange (Glossarium, s.v.
“Incumbens”) says that the Jurisconsulti use incumbere in
the sense of obtinere, possidere, but the sense may be transferred
from the general one of that which rests or is laid on one as a duty
which is also found in post-classical Latin; to be “diligently
resident” in a parish or benefice, has also been suggested as
the source of the meaning.
INCUNABULA, a Latin neuter-plural meaning “swaddling-clothes,”
a “cradle,” “birthplace,” and so the beginning of
anything, now curiously specialized to denote books printed in
the 15th century. Its use in this sense may have originated
with the title of the first separately published list of 15th-century
books, Cornelius a Beughem’s Incunabula typographiae (Amsterdam,
1688). The word is generally recognized all over Europe
and has produced vernacular forms such as the French incunables,
German Inkunabeln (Wiegendrucke), Italian incunaboli, though
the anglicized incunables is not yet fully accepted. If its original
meaning had been regarded the application of the word would
have been confined to books printed before a much earlier date,
such as 1475, or to the first few printed in any country or town.
By the end of the 15th century book-production in the great
centres of the trade, such as Venice, Lyons, Paris and Cologne, had
already lost much of its primitive character, and in many countries
there is no natural halting-place between 1490 and 1520 or
later. The attractions of a round date have prevailed, however,
over these considerations, and the year 1500 is taken as a halting-place,
or more often a terminus, in all the chief works devoted
to the registration and description of early printed books. The
most important of these are (i.) Panzer’s Annales typographici
ab artis inventae origine ad annum MD., printed in five volumes
at Nuremberg in 1793 and subsequently in 1803 carried on to
1536 by six additional volumes; (ii.) Ham’s Repertorium
bibliographicum in quo libri omnes ab arte typographica inventa
usque ad annum MD. typis expressi ordine alphabetico vel simpliciter
enumerantur vel adcuratius, recensentur (Stuttgart, 1826–1838).
In Panzer’s Annales the first principle of division is
that of the alphabetical order of the Latin names of towns in
which incunabula were printed, the books being arranged under
the towns by the years of publication. In Hain’s Repertorium
the books are arranged under their authors’ names, and it was
only in 1891 that an index of printers was added by Dr Konrad
Burger. In 1898 Robert Proctor published an Index to the Early
Printed Books in the British Museum: from the invention of
printing to the year MD., with notes of those in the Bodleian Library.
In this work the books were arranged as far as possible chronologically
under their printers, the printers chronologically under
the towns in which they worked, and the towns and countries
chronologically in the order in which printing was introduced
into them, the total number of books registered being nearly
ten thousand. Between 1898 and 1902 Dr W. Copinger published
a Supplement to Hain’s Repertorium, described as a collection
towards a new edition of that work, adding some seven
thousand new entries to the sixteen thousand editions enumerated
by Hain. From the total of about twenty-three thousand
incunabula thus registered considerable deductions must be
made for duplicate entries and undated editions which probably
