[1] Full statistics of the yield of income tax and other information
pertaining thereto will be found in the _Reports of the Commissioners
of His Majesty's Inland Revenue_ (published annually); those issued
in 1870 and in 1885 are especially interesting.
[2] In Appendix No. 4 to the _Report from the Select Committee on
Income Tax_ (1906), will be found a valuable list (prepared in the
Library of the London School of Economics) of references to the
graduation of the income tax and the distribution of incomes both in
the United Kingdom and in other countries.
INCORPORATION (from Lat. _incorporare_, to form into a body), in law,
the embodying or formation of a legal corporation, brought about either
by a general rule contained in such laws, e.g. as the Companies acts,
and applicable wherever its conditions are satisfied; or by a special
act of sovereign power, e.g. an incorporating statute or charter. The
word is used also in the sense of uniting, e.g. a will may incorporate
by reference other papers, which may be then taken as part of the will,
as much as if they were set out at length in it.
INCUBATION and INCUBATORS. The subject of "incubation" (Lat. _incubare_,
to brood; _in-cumbere_, to lie on), a term which, while strictly
signifying the action of a hen in sitting on her eggs to hatch them, is
also used in pathology for the development within the body of the germs
of disease, is especially associated with the artificial means, or
"incubators," devised for hatching eggs, or for analogous purposes of an
artificial foster-mother nature, or for use in bacteriological
laboratories.
Life is dependent, alike for its awakening and its maintenance, upon the
influence of certain physical and chemical factors, among which heat and
moisture may be regarded as the chief. It is therefore obvious that any
method of incubation must provide for a due degree of temperature and
moisture. And this degree must be one within limits, for while all
organisms are plastic and can attune themselves to a greater or less
range of variation in their physical environment, there is a given
degree at which the processes of life in each species proceed most
favourably. It is this particular degree, which differs for different
species, which must be attained, if artificial incubation is to be
successfully conducted. In other words, the degree of temperature and
moisture within the incubation drawer must remain uniform throughout the
period of incubation if the best results are to be reached. It is not
easy to attain these conditions, for there are many disturbing factors.
We may therefore next consider the more important of them.
The chief causes which operate to make the temperature within the
incubator drawer variable are the changes of the temperature of the
outer air, fluctuations in the pressure of the gas when that is used as
the source of heat, or the gradual diminution of the oxidizing power of
the flame and wick when an oil lamp is substituted for gas. Also, the
necessary opening of the incubator drawer, either for airing or for
sprinkling the eggs with water when that is necessary, tends to reduce
the temperature. But there is another equally important though less
obvious source of disturbance, and this resides within the organism
undergoing incubation. In the case of the chick, at about the ninth or
tenth days of incubation important changes are occurring. Between this
period and the fourteenth day the chick becomes relatively large and
bulky, and the temporary respiratory organ, the allantois, together with
its veins, increases greatly in size and extent. As a consequence, the
respiratory processes are enabled to proceed with greater activity, and
the chemical processes of oxidation thus enhanced necessarily largely
increase the amount of heat which the chick itself produces. Thus an
incubator, to be successful, must be capable of automatically adjusting
itself to this heightened temperature.
The drawer of an incubator is a confined space and is usually packed as
closely as possible with the contained eggs. The eggs are living
structures and consequently need air. This necessitates some method of
direct ventilation, and this in its turn necessarily increases the
evaporation of water vapour from the surface of the egg. Unless,
therefore, this evaporation is checked, the eggs will be too dry at the
period--from the tenth day onwards--when moisture is more than ever an
important factor. There is, according to some poultry authorities,
reason to believe that the sitting hen secretes some oily substance
which, becoming diffused over the surface of the egg, prevents or
retards evaporation from within; presumably, this oil is permeable to
oxygen. In nature, with the sitting hen, and in the "Mamal" artificial
incubating establishments of the Egyptians, direct air currents do not
exist, owing to the large size of the chambers, and consequently
incubation can be successfully achieved without any special provision
for the supply of moisture.
Artificial incubation has been known to the Egyptians and the Chinese
from almost time immemorial. In Egypt, at Berme on the Delta, the trade
of artificial hatching is traditionally transmitted from father to son,
and is consequently confined to particular families. The secrets of the
process are guarded with a religious zeal, and the individuals who
practise it are held under plighted word not to divulge them. It is
highly probable that the process of artificial incubation as practised
by the Egyptians is not so simple as it is believed to be. But as far as
the structures and processes involved have been ascertained by
travellers, it appears that the "Mamal" is a brick building, consisting
of four large ovens, each of such a size that several men could be
contained within it. These ovens are in pairs, in each pair one oven
being above the other, on each side of a long passage, into which they
open by a circular aperture, just large enough for a man to obtain
access to each. The eggs are placed in the middle of the floor of the
oven, and in the gutters round the sides the fire is lighted. The
material for this latter, according to one account, consists of camels'
dung and chopped hay, and according to another of horses' dung. The
attainment of the right degree of heat is apparently reached wholly by
the skill of the persons employed. When this has been attained, they
plug the entrance hole with coarse tow. On the tenth to twelfth days
they cease to light the fires.
Each "Mamal" may contain from 40,000 to 80,000 eggs. There are 386
"Mamals" in the country, which are only worked for six months of the
year, and produce in that time eight broods. Many more than two-thirds
of the eggs put in are successfully hatched. It is estimated that
90,000,000 eggs are annually hatched by the Bermeans.
A method of incubating that appears to have been altogether overlooked
in England--or at least never to have been practised--is that carried on
by the _Couveurs_ or professional hatchers in France. They make use of
hen-turkeys for the purpose, and each bird can be made to sit
continuously for from three to six months. The _modus operandi_ is as
follows: a dark room which is kept at a constant temperature throughout
the year contains a number of boxes, just large enough to accommodate a
turkey. The bottom of the box is filled with some vegetable material,
bracken, hay, heather, straw or cocoa-fibres. Each box is covered in
with lattice-work wire, so arranged that the freedom of the sitting bird
is limited and its escape prevented. Dummy eggs, made by emptying addled
ones and filling with plaster of Paris, are then placed in the nest and
a bird put in. At first it endeavours to escape, but after an interval
of a few days it becomes quiet, and the dummy eggs being then removed,
fresh ones are inserted. As soon as the chickens are hatched, they are
withdrawn and fresh eggs substituted. The hen turkeys are also used
successfully as foster-mothers. Each bird can adequately cover about two
dozen eggs.
Incubation as an industry in Europe and America is of recent
development. The growing scarcity of game birds of all kinds, coincident
with the increase of population, and the introduction of the
breech-loading gun, together with the marked revival of interest in
fancy poultry about the year 1870, led, however, to the production of a
great variety of appliances designed to render artificial incubation
successful.
Previously to this, several interesting attempts had been made. As long
ago as 1824, Walthew constructed an incubator designed to be used by
farmers' wives with the aid of no more than ordinary household
conditions. It consisted of a double-walled metal box, with several
pipes opening into the walled space round the sides, bottom and top of
the incubator. These pipes were connected with an ordinary kitchen
boiler. Walthew, however, constructed a fire grate, with a special
boiler adapted to the requirements of the incubator. Into the walled
space of the incubator, steam from the kitchen boiler passed; the excess
steam escaped from an aperture in the roof, and the condensed steam
through one in the floor. Ventilating holes and also plugs, into which
thermometers were placed, pierced the door of the incubator.
In 1827, J. H. Barlow successfully reared hens and other birds by means
of steam at Drayton Green, Ealing. He constructed very large rooms and
rearing houses, expending many thousands of pounds upon the work. He
reared some 64,000 game birds annually. The celebrated physician Harvey,
and the famous anatomist Hunter were much interested in his results.
To John Champion, Berwick-on-Tweed, in 1870, belongs, however, the
credit of instituting a system which, when extended, may become the
system of the future, and will rival the ancient "Mamals" in the success
of the incubation and in the largeness of the numbers of eggs incubated.
He used a large room through which passed two heated flues, the eggs
being placed upon a table in the centre. The flues opened out into an
adjoining space. The temperature of the room was adjusted by personal
supervision of the fire. This system, more elaborated and refined, is
now in use in some parts of America.
_Bird Incubators._
Owing to the great variety in the details of construction, it is
difficult to arrange a classification of incubators which shall include
them all. They may, however, be classified in one of two ways. We may
either consider the method by which they are heated or the method by
which their temperature is regulated.
In the former case we may divide them into "hot-air" incubators and into
"hot-water" or "tank" incubators. In the latter ease we may classify
them according as their thermostat or temperature-regulator is actuated
by a liquid expanding with rising temperature, or by solids, usually
metals.
In America incubators of the hot-air type with solid and metallic
thermostats are most used, while in Europe the "tank" type, with a
thermostat of expansible liquid, prevails.
For the purpose of more adequately considering the various forms which
have been in use, or are still used, we shall here divide them into the
"hot-air" and "hot-water" (or "tank") classes.
In the hot-air types the incubator chamber is heated by columns of hot
air, while in the tank system this chamber is heated by a tank of warmed
water.
(a) _Hot-Water Incubators._--In 1866 Colonel Stuart Wortley described
in _The Field_ an incubator constructed upon a novel principle, but
which appears never to have been adopted by breeders. The descriptive
article is illustrated with a sketch. Essentially the incubator
consists of four pipes which extend across the egg chamber some little
distance above the eggs. The pipes pass through holes in the side of
the incubator, which are furnished with pads, so as to render their
passage air-tight. Externally they are connected with a boiler. This
is provided with a dome through which steam escapes, and also with a
glass gauge to show the height of the water within the boiler. The
water in the boiler is kept at the boiling point, and the temperature
of the incubator is regulated by adjustment of the length of the
hot-water pipes within the egg chamber. To raise the temperature, a
greater length of the pipes is pushed into the chamber, and to reduce
it, more of their length is pulled outwards. It is claimed for this
instrument that since the temperature of boiling water at any
particular locality remains practically constant, the disadvantages
due to fluctuations in the activity of a lamp flame or the size of a
gas flame are obviated. But it has the serious disadvantage that there
is no automatic adjustment to compensate for fluctuations of
atmospheric temperature. And experiments by C. Hearson have shown that
even if the temperature of the tank or source of heat be constant,
that of the incubator drawer will nevertheless vary with fluctuations
of external temperature. Probably if the mechanical difficulties of
providing a self-regulator were overcome, it would prove an efficient
and reliable incubator. The difficulties do not seem to be
insuperable, and it appears possible that a thermostatic bar could be
so arranged as to automatically increase or decrease the length of
hot-water pipes within the incubator, and therefore the incubator
temperature.
Another early form of incubator is Brindley's, which was first in use
about 1845, and in his hands it appeared occasionally to act
successfully, but it never became generally used. The egg chamber was
lined with felt, and was placed beneath a heated air chamber, the
floor and roof of which were composed of glass. The air chamber was
heated by a number of hot-water pipes which were connected with a
copper boiler. This latter was heated by means of a lamp so
constructed as to burn steadily. The temperature of the air chamber
was regulated within certain limits by means of a balanced valve,
which could be so adjusted that it would open at any desired
temperature.
In Colonel Stuart Wortley's incubator the hot-water tubes passed
directly into the egg chamber, and in Brindley's into a chamber above
it. But in other forms of incubators in which the principle of an
external boiler connected with water tubes is adopted, the latter pass
not into the egg chamber nor into an air chamber, but open into and
from a tank of water. The floor of this tank forms the roof of the egg
chamber, so that the eggs are heated from above. This device of
warming the eggs from above was adopted in imitation of the processes
that presumably occur with the sitting hen; for it is generally
assumed that the surface of the eggs in contact with the hen is warmer
than that in contact with the damp soil or with the material of the
nest.
One of the earliest of this form of incubator is that invented by F.
Schröder, manager of the now extinct British National Poultry Company.
In this incubator the form is circular, and there are four egg
drawers, so that each one occupied the quadrant of a circle, and the
inner corner of each drawer meets in the middle of the incubator. From
the centre of the incubator a vertical chimney passes upwards and
opens out from the inner corners of the four egg drawers. This chimney
acts as a ventilator to the incubating chambers. These latter are open
above, but their floors are made of perforated zinc, and when in use
they are partially filled with chaff or similar material. Under them
is a tank containing cold water and common to all four drawers; the
slight vapour rising from the surface of the water diffuses through
the egg drawers and thus insures a sufficient degree of humidity to
the air within. Above the egg drawers is a circular tank containing
warm water. The floor of this tank constitutes the roof of the egg
drawers, while the roof forms the floor of a circular chamber above
it, the side wall of which is composed of perforated zinc. This upper
chamber is used to dry the chicks when they are just hatched and to
rear them until they are strong enough for removal. It is partially
filled with sand, which serves the double purpose of retaining the
heat in the warm-water tank beneath and of forming a bed for the
chicks. The water in the warm-water tank is heated by means of a
boiler which is external to the incubator, and in communication with
the tank by means of an inlet and an outlet pipe. There is no valve to
regulate the temperature, and the latter is measured by means of a
thermometer, the bulb of which is situated not in the incubator
drawers, but in the warm-water tank. This is a wrong position for the
thermometer, since it is now known that the temperature of the water
tank may be different by several degrees to that of the egg drawer;
for with a fall of external temperature that of the latter necessarily
tends to fall more rapidly than the former. But, none the less, in
skilful hands this incubator gave good results.
[Illustration: FIG. 1.--Christy's Improved Incubator.]
T. Christy's incubator, which we shall describe next, has passed
through several forms. We shall consider the most recent one (1894).
The incubator (fig. 1) is double walled, and the space between the two
walls is packed with a non-conducting material. In the upper part of
the incubator there is a water tank (T) divided by a horizontal
partition into two chambers, communicating with each other at the
left-hand side. Below the tank is the incubation drawer (E), which
contains the eggs and also a temperature regulator or thermostat (R).
The tank is traversed by a ventilating shaft (V), and inserted into
this is a smaller sliding tube passing up to it from a hole in the
bottom of the incubator drawer. The floor of the incubator drawer is
perforated, and beneath it is an enclosed air space which opens into
the sliding air shaft just described. Fresh air is let into the
incubator drawer from a few apertures (I) at its top. The ventilating
shaft (V) is closed externally by a cap (C), which can be raised from
or lowered down upon its orifice by the horizontal arm (H) working
upon pivot joints at (P). This arm is operated by the thermostat (R),
through the agency of a vertical rod. The water in the tank is heated
by an external boiler (B) through two pipes, one of which (T) serves
as an inlet, and the other (L) as an outlet channel from the tank.
These two pipes do not open directly into the tank, but into an outer
vessel (O) communicating with it. Communication between this vessel
and the tank may be made or broken by means of a sliding valve (S),
which is pierced by an aperture that corresponds in position with the
upper of the two in the wall of the tank when the valve is up. When
this valve is in its upper position, the tank (T) communicates with
the outer vessel (O) by two apertures (A and A´), the top one being
the inlet and the lower one the outlet. These coincide in position
with the tubes from the boiler. This latter (B) is a conical vessel
containing two spaces. The heated water is contained in the outer of
these spaces, while the central space is an air shaft heated by a lamp
flame. This particular form of the boiler results in the water at its
top part being more heated than that in its lower. As a consequence of
this, a continual circulation of water through the tank ensues. The
more heated water, being specifically lighter, passes into the outer
vessel, where it remains among the higher strata, and therefore enters
the tank through the upper aperture. In passing along the upper
division of the tank it becomes slightly cooled and sinks therefore
into the lower compartment, passes along it, and out through the
aperture A´. Hence it passes into the lower portion of the boiler,
where it becomes warmed and specifically lighter; in consequence it
becomes pushed upwards in the boiler by the cooler and heavier water
coming in behind and below it.
Should the temperature in the incubator drawer rise, the bimetallic
thermostat (R) opens out its coil and pulls down the vertical rod.
This simultaneously effects two things: it raises the cap (C) over the
ventilating shaft and allows of a more rapid flow of fresh air through
the incubator drawer, and it also lowers the slide-valve (S) so that
the tank becomes cut off from communication with the outer vessel (O)
and therefore with the boiler. The temperature thereupon begins to
fall and the thermostat, coiling closer, raises the vertical rod,
closes the ventilating shaft, and once more places the tank in
communication with the boiler.
The structure of the thermostat is given below.
The Chantry Incubator (Sheffield) is also an incubator with a
hot-water tank, the circulation of which is maintained by an outside
boiler. Its temperature is regulated by a metal regulator.
In Schröder's and Christy's incubators the hot-water pipes from the
boiler simply entered the warm-water tank but did not traverse it. In
the two incubators to be next described the hot-water pipes are made
to pass through the water in the tank, and are so arranged as to
minimize the possibility that the outside of the tank may become
colder than the centre. Both of them are also fitted with an ingenious
though slightly complex valve for maintaining an approximately
constant temperature.
Halsted's incubator was the earliest of this type. Since his original
form was constructed he has designed an improved one, and it is this
latter which will be described.
[Illustration: FIG 2.--Halsted's Incubator.]
The egg drawer (E, fig. 2) lies beneath the warm-water tank (T), and
above this is a nursery (N). The egg drawer is ventilated by two
tubular shafts (V), of which only one is represented in the
illustration; the tubes are about 2½ in. in diameter, and each one is
fitted at its upper end, where it opens into the nursery, with a
swing-valve (V´) which turns upon a horizontal axis (A), in its turn
connected, by means of cranks (C) and shafts (S), with the heat
regulating apparatus (R). A space of about 2 in. between the top of
the incubating drawer and the warm-water tank is necessary for the
insertion of this apparatus. The water in the tank (T) is heated by
means of the boiler (B); the tank and boiler are connected by the two
pipes (I) and (O), of which one is the inlet and the other the outlet
channel. The boiler consists of an inner (I´) and an outer (O)
division in communication with each other below. The latter is
cylindrical in form, while the outer wall of the former is cylindrical
and its inner wall conical. The conical wall of the inner boiler is
the surface which is heated by the lamp (L). The arrangement of the
inlet and outlet tubes is important. In the illustration, for the sake
of clearness, they are represented as one above the other. In reality
they lie in the same plane, and the fork (F) of the inlet pipe
similarly lies in the horizontal plane and not vertically as
represented. The inlet pipe not only differs from the outlet pipe in
the possession of a forked end, but it is carried to the farther end
(not shown in the diagram) of the water tank, while the outlet pipe
opens from about the middle of the tank. The inlet pipe is connected
with the inner portion of the boiler and the outlet one with the outer
portion. The result of this adjustment of the parts is that the warmer
water of the inner boiler, being specifically lighter than the cooler
water of the outer boiler, rises up and passes through the inlet pipe
(I) and is discharged into the tank through the two divergent orifices
of the fork (F). Here the water strikes the side wall of the farther
end of the tank and is reflected back along the back and front walls
towards the nearer side. Hence it is again reflected, but in the
opposite direction, and now forms a central current, which is directed
towards the centrally situated orifice of the outlet tube (O). Through
this it passes to the outer boiler, and sinking towards the bottom,
reaches the base of the inner boiler. Here it becomes heated and
lighter and consequently rises to the top, and once more passes
through the inlet pipe to the water tank. The warm water thus travels
round the outer walls of the tank and the cooled water is conducted
away along the middle portion. A more equable distribution of
temperature over the roof of the incubating chamber is thus ensured
than would be the case if the heated water were discharged either into
the centre or at any other single point only of the tank.
To a very large extent, the efficiency of this apparatus depends upon
the approximately perfect performance of the lamp. A good, steadily
burning one should be employed, and only the best oil used; for,
should the wick become fouled the flame cannot freely burn. For this
reason it is better to use gas, whenever obtainable.
The maintenance of an approximately uniform temperature is obtained by
allowing the heated air of the egg-drawer to escape through the two
ventilating shafts (V). The swing-valves of these are opened or closed
by means of the regulator (R). This latter consists of a glass bowl
prolonged into a tube, about 8 in. long and three-eighths of an inch
in diameter. The glass tube swings upon an axis (A) which is situated
as near as possible to the bowl of the regulator. The axis is
connected with a crank (C´) which is disposed so as to act as a lever
upon the vertical shaft (S), which in its turn is connected with the
upper crank (C); this works the axis (A´) of the swing-valves, and so
can open or close the apertures of the ventilating pipes. The bowl of
the regulator is filled with mercury to such an extent that at the
temperature of 100° F., and when the tube is slightly inclined upwards
from the horizontal it just flows slightly into the tube from the
bowl. On the lever-crank (C´) a weight is slung by a sliding
adjustment, and is so placed that when the temperature of the
egg-drawer is 103° it just balances the tube of the regulator when it
is slightly inclined upwards. Should the temperature of the drawer now
rise higher the mercury flows towards the distant end of the tube and,
causing it to fall down, brings about a rotation of the regulator axis
and as a consequence the opening of the ventilating valves. A
transverse stay prevents the limb of the regulator from quite reaching
the horizontal when it falls. As the temperature cools down the
mercury contracts and retraces to the nearer end of the tube and to
the bowl, and consequently results in the upward inclination of the
limb; the valves are thus closed again.
The egg-drawer (E) is specially constructed so as to imitate as nearly
as possible the natural conditions that exist under a sitting hen. The
drawer is of wood and contains a zinc tray (Z) into which cold water
is placed. Fitting into the zinc tray is another zinc compartment, the
floor of which is made of a number of zinc strips (X) transversely
arranged and placed in relation to each other like the limbs of an
inverted V. The limbs are so disposed that those of one series do not
touch the adjacent ones, and in fact a space is left between them.
Thus a number of parallel troughs are formed, each of which opens
below into the moist air chamber of the cold water tray beneath. In
practice these troughs are covered with flannel which is allowed to
dip into the water of the tray. Thus the eggs lie in a series of damp
troughs and their lower surfaces are therefore damper and colder than
their upper ones. This incubator, if carefully worked and the
necessary practical details observed, has the reputation of being an
efficient machine.
Somewhat similar to the Halsted incubator, but differing from it in
the nature of the boiler and in the temperature regulator, is the
Graves incubator, made in Boston, U.S.A. The incubator itself (fig. 3)
consists of an incubating or egg-drawer (E) heated from above by a
warm-water tank (T). Below the egg-drawer is a tank containing cold
water, the vapour of which passes through the perforated floor of the
former and keeps the air of the egg-chamber slightly humid. Above the
warm-water tank is an air chamber (AC) to serve as a non-conducting
medium and to prevent therefore undue loss of heat. Above this is a
nursery or drying chamber (N), closed in, with a movable lid.
The warm-water tank is heated by means of a simple boiler (B) from
which an inlet tube (I) carries heated water to the tank; the tube
traverses the length of the tank and discharges at its farther end
(not shown in the diagram). From the nearer end of the tank an outlet
tube (O) passes out and opens into the boiler at a slightly higher
level than the inlet one. The boiler is heated by an evenly burning
lamp below, of special construction. The rectangular tube through
which the wick passes is bevelled at its outer end, and upon this
bevelled edge a metal flap (F) is allowed to rest more or less
closely, according as the flame is to be smaller or larger
respectively. The wick is, of course, bevelled to correspond to the
form of its tube. The metal flap is raised or depressed by means of
levers connected with the heat-regulator. When it is depressed upon
the wick the flame is lessened; and it becomes proportionately bigger
as the flap is raised more and more.
[Illustration: FIG. 3.--Graves's Incubator.]
The heat-regulator consists of a glass tube (T) which runs the whole
width of the incubation chamber and lies in contact with the floor of
the warm-water tank; it is filled with alcohol. Externally to the
incubator this tube is connected with a U-shaped one containing
mercury. The free limb of the U-tube contains a piston (P) which rests
upon the surface of the mercury in that limb. From the piston a piston
rod (PR) passes vertically upwards and is connected with a lever (L)
which operates, through the agency of a second lever (L´) the
movements of the ventilating valve (V) inserted over the orifice of
the ventilating shaft (A) which opens from the roof of the incubator
drawer. The lever (L) is further connected with a spiral spring (S)
which works the metal flap of the lamp already described. The height
of the piston in the U tube can be so adjusted, by varying the
quantity of mercury in the tube, that when the temperature of the
incubation drawer is 103° F., the ventilating valves are closed and
the wick is burning to its full extent. Should the temperature rise,
the alcohol in the glass tube (T) expands and causes the mercury in
the free limb of the U tube to rise. This carries with it the piston,
and this movement brings about the opening of the ventilating valves,
and at the same time, through the agency of the lever (L) and the
spiral spring (S) the metal flap is brought down upon the wick,
cutting off more or less of the flame. Should the temperature then
fall to 103° or lower, the contraction of the alcohol reverses these
movements, the valve closes, and the wick once more burns to its full
extent.
In practice, the boiler and the temperature regulator are duplicated,
there being a set on both sides of the incubator. Any slight
irregularity on the one side may be thus compensated for by the other
side.
Graves's incubator has the reputation of being a good machine.
[Illustration: FIG. 4.--Hearson's Incubator.]
Among the most recent type of incubators made in England is that of
Charles Hearson. This differs from any of those described in the
simplicity and ingenuity of the heat regulator, and in that the tubes
which traverse the water tank are hot-air flues, carrying the air
heated by the flame and not warm water. Consequently a further
simplification is introduced inasmuch as no boiler is required.
The essential features of this incubator are shown in fig. 4. The
internal parts of the incubator are insulated by a double wall, the
interspace being packed by a non-conducting material, which is not
shown in the figure. The incubation or egg-drawer (E) is heated by the
warm-water tank (T). Beneath the egg-drawer is a zinc tray (Z), so
constructed that in the central part the floor is raised up into a
short cylinder. Around the raised cylinder is a wide trough containing
water and into this dips a canvas cloth which is stretched out over a
perforated zinc support (F). By this means an extended moistened
surface is produced which allows of a rapid evaporation. The floor of
the incubator, which is raised by short feet from the table on which
it stands, is perforated in the central portion by a number of holes,
and which are so situated that they lie beneath the raised cylinder of
the cold-water tray (Z). The incubation-drawer is thus supplied
continuously by a slow current of moistened air because the air in the
upper part of the drawer, i.e. in contact with the floor of the
warm-water tank, is the warmest and lightest. It therefore tends to
diffuse or pass through the narrow slits between the drawer and the
walls of the incubator, and also through the aperture in the front
wall of the egg-drawer, through which a thermometer is laced. To
replace the air thus lost, fresh air passes in through the holes in
the bottom of the incubator, and on its way must pass through the
pores of the damp canvas which dips into the water in the zinc tray
(Z).
The warm-water tank is heated by an inlet (I) and outlet (O) flue
which are, however, continuous. The inlet flue opens out from a
vertical chimney (C), the air in which is heated either by a gas flame
or that of an oil lamp. The outlet or return flue passes back through
the width of the tank and opens independently to the exterior. The
vertical chimney (C) is capped by a lid (L) capable of being raised or
lowered upon its orifice by the lever (L´). When the cap is resting
upon the chimney all the heated air from within the latter passes
through the flues and heats the water in the tank. If the cap is
widely raised, practically all the heated air passes directly upwards
through the chimney and none goes through the flues. If the cap be but
slightly raised, part of the heated air goes through the flues and
part directly escapes through the aperture of the chimney. The
movement of the lever (L´) which raises the cap (L) is determined by
the thermostatic capsule (S), situated within the egg-drawer.
The principle upon which this capsule is designed is that the boiling
point of a liquid depends not only upon temperature but also upon
pressure. A given liquid at ordinary atmospheric pressure will boil at
a certain degree of temperature, which varies for different
substances. But if the pressure be increased the boiling point of the
liquid is raised to a higher degree of temperature. A liquid when it
boils passes into a gaseous condition and in this state will occupy a
very much larger volume--some two or three hundred times--than in the
liquid condition. If, therefore, a hermetically sealed capsule with
flexible sides be filled with some liquid which boils at a given
temperature, the sides of the capsule will distend when the
temperature of the air round the capsule has been raised to the
boiling point of the liquid within it. The distension of this capsule
can be used to raise the lever (L´). The thermostatic capsule is
placed on a fixed cradle (F) and is filled with a mixture of ether and
alcohol, the proportions being such that the boiling point of the
mixed liquid is 100° F. Between the capsule and the lever (L´) is a
vertical rod (V), articulating with the lever as close as possible to
its fulcrum (M). The articulation with the lever is by means of a
screw, so that the necessary nice adjustment between the height of the
rod (V), the thickness of the capsule and the position of rest of the
damper (L) upon the chimney, can be accurately made. The temperature
at which it is desired that the liquid in the capsule shall boil can
be determined by sliding the weight (W) nearer or farther to the
fulcrum of the lever (L´). The farther it is moved outwards, the
greater is the pressure upon the thermostatic capsule and consequently
the higher will be the boiling point of its contained liquid. By means
of the milled-head screw (A), the height of the lever at its outer end
can be so adjusted that when the liquid of the capsule is not boiling
the damper (L) closes the chimney, but that when it does boil the
damper will be raised sufficiently high from it. If the weight is
pushed as far as it will go towards the fulcrum end of the lever, the
temperature of the egg-drawer will never rise more than 100° F.
because at this temperature and under the pressure to which it is then
subjected, the liquid in the capsule boils, and consequently brings
about the raising of the damper. It matters not, therefore, how high
the flame of the gas or lamp be turned, the temperature of the
egg-drawer will not increase, because the extra heat of the enlarged
flame is passing directly outwards through the chimney, and is not
going through the flues in the tank. In order to raise the temperature
within the incubation chamber to 102° or 103°, or any other desired
degree, the weight (W) must be moved outwards along the lever (L´),
about 1 in. for every degree of temperature increase desired. This
thermostatic capsule works admirably, and the incubator will work for
months at a time and requires no adjustment, however much, within the
limits of our climate, the external temperature may vary. The capsule,
like all other thermostats in which the expansible substance is a
liquid, is, however, dependent upon external pressure for the point at
which its contained liquid boils and therefore, for the degree of
temperature prevailing within the incubator drawer. It is therefore
responsive to variations in atmospheric pressure, and as the barometer
may fall 1 or 2 in., this may possibly make a difference of two or
three degrees in the fluctuation of temperature within the egg-drawer.
It is not, of course, often that such large oscillations of the
barometer occur, and as a matter of practical experience, under
ordinary conditions, this incubator will work for months together
without attention with only half a degree variation round the point at
which it was set.
Greenwood's incubator (fig. 5), named the Bedford, resembles Pearson's
in that hot-air flues (F and F´) and not hot-water pipes, traverse the
water tank (T). And the method of regulation of the temperature is
much the same, i.e. a thermostat (V) operating upon a lever which
raises a cap (C) from off the aperture of the main flue (F) and thus
allows all the heat of the flame to pass directly outwards, without
passing through the series of flues (F) which horizontally traverse
the water-tank. Fresh air enters through a wide circular aperture (A)
which surrounds the main flue, and it thus becomes partially warmed
before entering the egg-chamber. The eggs are placed upon a perforated
floor (E) lying over water baths (B). The water tank (T) lies in the
centre of the incubation chamber and is traversed through its central
axis by the main hot-air flue (F). From this, four horizontal flues
pass outwards through the water and open into small vertical flues,
which in their turn communicate with the exterior.
[Illustration: FIG. 5.--The Bedford (Greenwood's) Incubator.]
The thermostat (V) consists of a glass tube of peculiar form. This is
closed at the end of its short limb and open at its other extremity on
the long limb. The bent portion of the tube is filled with mercury and
between the mercury column and the closed end is a small quantity of
ether. The thermostat is lodged in a box (G), which forms part of the
lever (L). At one end this lever is pivoted to a fixed arm, and at the
other to the vertical rod which operates the ventilating cap (C). If
the temperature should rise, the ether in the thermostat expands and
pushes the mercury column up along the inclined long limb. This
disturbs the equilibrium of the lever (L), and it descends downwards,
pulling with it the vertical rod, and thus raising the cap over the
main flue. If the temperature falls the reverse series of changes
occur. The temperature at which the cap will be raised can be adjusted
within limits by the position of the weight (W) and by the adjustment
of the degree of inclination of the thermostat.
The Proctor incubator, made at Otley, is apparently, in its main
features, similar to the Greenwood.
[Illustration: FIG. 6.--The Winchcombe Incubator.]
Somewhat similar, in certain features, to the Greenwood is the
Winchcombe. Its improved form, in which metal replaces the wood
casing, is named the Gladstone. In it there is a combination of the
hot-air and the water-tank systems of warming the incubation chamber.
The wall of the incubator is double, and the space between the outer
and inner wall is packed with a non-conducting material. The
incubation chamber is heated above by a water-tank (fig. 6 T) which is
traversed by a main vertical flue (F) and four subsidiary horizontal
ones which discharge externally. The main flue, however, in passing up
to enter the water tank traverses the egg-chamber, and therefore
serves to warm it, as in the hot-air type of incubator, by the heat of
the flue itself. Around the lower half of the flue is a water vessel
consisting of two concentric containers (C), holding water. In the
space between these concentric containers, fresh air passes in through
the aperture (A), and before it reaches the egg-chamber it passes
through coarse canvas which dips into the water in the containers, and
is therefore kept permanently moist. The containers are filled from a
water tank (S) outside the incubator. Air passes out from the
egg-chamber through the aperture (O). The temperature is regulated by
a bimetallic thermostat (see below), which operates two levers, that
by their arrangement can raise or depress the cap (D) over the main
flue (F). The temperature at which this occurs will be determined,
within limits, by the position of the adjustable weight (W).
Tomlinson's incubator, designed in 1880, is novel in principle. It
possesses a very large water tank, holding 15 gallons for every
hundred eggs. Through this tank there pass two hot-air horizontal
flues, lying in the same plane. The novelty of the construction lies
in the great volume of water used and in the disposition of the flues
towards the top of the tank. It is said that very little circulation
of water takes place beneath the flues, because warmed water rises
instead of falling. The great body of water below the flues will
therefore only take up heat relatively slowly, and will, on account of
its bulk and its physical properties, but slowly lose it. Should the
flame fall in power, or even go out for ten or twelve hours, it is
claimed that no serious loss of efficiency of the apparatus will
result.
Regulation of the temperature is by means of an air tube, the air in
which expanding bulges out an india-rubber diaphragm and this moves a
lever. The lever operates a valve which allows more or less of the
heated air to escape from the egg-drawer.
[Illustration: FIG. 7.--Hillier's Incubator.]
(b) _Hot-air Incubators._--W. H. Hillier's Incubator (fig. 7) is
circular in form and is constructed of a double-walled metal case. The
space between the two walls is packed with a non-conducting material.
The incubation or egg-chamber (C) is warmed by a circular heating box
(H), and the air in this is heated by a lamp. The roof of this box
forms part of the floor of the incubation chamber and from it a main
flue (F) and four smaller ones (F´) pass upwards through the roof of
the incubator and discharge to the exterior. Fresh air passes in to
the incubator through two tubular channels (A and A´) on either side
of the heating box and escapes through a hole in the roof, which
serves at the same time as a passage for one of the rods (D) in
connexion with the temperature regulating apparatus.
This apparatus (T) consists of a glass tube of ½ in. bore, and which
is bent into the form of a circle of 5 in. diameter. The tube is
fastened to a wooden disk, which rotates upon a pivot and in so doing
operates a vertical rod (D), which in its turn works the cap (V) which
covers the orifice of the main flue. The tube is partly filled with
mercury and is closed at one end. At this end there is contained some
spirit. As the temperature rises, this expands and pushes the mercury
column farther along the tube. The equilibrium of the position of rest
is thus disturbed, and the wooden disk consequently rotates, carrying
with it the vertical arm, the downward movement of which raises the
cap (V) of the flue. The temperature at which it is desired that this
valve shall uncover the flue, can be adjusted within the necessary
limits by sliding the weight (W) along the horizontal arm and by the
amount of mercury present in the bent tube. The air of the incubation
chamber is rendered sufficiently moist by the evaporation of water in
the vessel (G).
In the Cornell incubator (New York) more personal attention is
required than in other forms, since the ventilation of the egg-chamber
is not wholly automatic but is regulated according to the results of
observation. The great difficulty in ventilation is the proper
combination of fresh air and moisture. The Cornell Incubator Company
has endeavoured to obviate this difficulty by carrying out a series of
observations on the rate at which evaporation occurs in incubating
eggs under natural conditions. The rate of evaporation is measured by
the size of the air-space within the egg-shell at successive days.
This they have ascertained, and with their incubators they furnish a
book of instructions in which diagrams showing the size of the air
space on the 1st, 5th, 10th, 14th and 18th days are given. Examination
of the eggs should therefore be made every two or three days, and the
result compared with the diagrams. The incubator is provided with an
adjustable ventilator and this should be so arranged that evaporation
is neither too great nor too little. The ventilator should never be
wholly closed, and if when closed to its minimum evaporation is still
too great, then water should be placed in the moisture pans. In all
cases lukewarm water should be placed in these on the 18th day and the
ventilating slide opened wide.
It will thus be seen that in this machine there is an attempt to do
away with the addition of water to the incubator drawer during the
greater part of the period of incubation, and to rely upon the aqueous
vapour naturally present in the atmosphere. This attempt is based upon
the fact that water vapour is lighter than air, and will therefore
rise to the top in any enclosed volume of air. If the direction of the
ventilating current is downwards in the incubation chamber, and if it
is slow enough, it is thought that the water vapour will be sifted out
and tend to accumulate to a sufficient extent in the chamber. In the
Cornell incubator consequently the ventilating current passes first
upward through an external heater in order to warm it, whence it is
then deflected downwards into the egg-chamber and diffuses through its
perforated bottom. Then it passes along a space beneath the chamber
into a space in the left-hand wall of the incubator and out to the
exterior through an adjustable and graduated ventilating slide.
These incubators are hot-air machines, and the hot-air chamber is
situated above the egg-drawer and is traversed by several flues
opening out from a main one. The temperature regulating apparatus
appears to be similar to that of Hearson's machine and operates by a
thermostat, which through the agency of levers opens or closes a valve
over the main flue.
The Westmeria incubators (Leighton Buzzard) are of two patterns. One
type is built on the hot-air principle and the other on the hot-water
system. In both forms the heated air from the heating surfaces is
deflected down on the eggs and escapes through the perforated bottom
of the egg-drawer. The inlet air is first warmed by contact with the
main flue. The thermostat is similar to that in the Hillier machine
(fig. 7) and consists of a coil mounted on an axis, round which it can
rotate. The coil is filled with mercury and is closed at one end.
Between this end and the mercury column is a short column of air. By
expansion of the air under a rising temperature, the mercury column is
displaced and brings about a rotation of the disk to which the coiled
tube containing it is attached. This rotation raises the cap over the
main flue.
All the incubators so far described have been constructed with the
idea of obtaining as nearly as possible a uniform temperature. But in
E. S. Renwick's incubator (America) no attempt is made to obtain
uniformity in temperature. On the other hand, it is designed to give a
periodical oscillation from one extreme to the other of a limited
range, about 3°, of temperature. This is accomplished by means of a
thermostatic bar made of plates of brass and vulcanite fastened
together. This is connected with a clockwork and detent arrangement,
which simultaneously opens a valve and actuates the lamp flame. The
temperature falls to the lower limit of its range before the
thermostatic bar is sufficiently bent to set the clockwork arrangement
operating in the reverse direction, by which the valve is closed and
the lamp flame increased. The temperature then rises to the higher
limit, when the bending of the thermostatic bar again releases the
detent and the clockwork opens the valve and reduces the flame.
The incubator is said to succeed well. It also possesses a mechanical
arrangement by which all the eggs can be periodically turned on
rollers at once.
_Size._--The incubators which have been described are of relatively
small size, and the numbers of eggs which they can incubate are
strictly limited. For commercial purposes, however, operations of a
much larger magnitude are desirable and necessary. And there can be no
doubt that for these purposes the incubators of the future will be of
great size and will contain from 15,000 to 30,000 eggs or more at a
time. Already, at Aratoma Farm, Stamford, New York State, there is
established a large incubation room, containing several thousands of
eggs, and in which the heat regulation is controlled in part by the
personal efforts of attendants. It constitutes almost a complete
return, with added accessories, to the methods of the Egyptians, and
to those of John Champion.
_Bacteriological Incubators._
These differ from bird Incubators in that the heating surface of the
incubation chamber generally surrounds all sides of it and there is, as
a rule, no special arrangement for bringing about a more or less humid
condition of the contained air. In some forms there is an arrangement to
ensure a continuous supply of fresh and moist air, but in the majority
the incubation chamber obtains its supply of fresh air vicariously. In
some forms the chamber of the incubator is heated by a warm water tank
of a simple kind, which extends round all its sides. But in other forms
a series of tubes or flues passes through the water in this tank and
thus simulates in principle the tube boiler. This latter form utilizes
the heat of the flame to a greater degree than the former kind. In yet
other forms the incubation chamber is heated by warm air chambers which
surround it or flues which traverse it. Most bacteriological incubators
are square or rectangular in form, but some bacteriologists prefer
cylindrical forms, presumably on account of the ratio of volume to
surface in connexion with the water tank.
One of the best known and most generally used of the cylindrical and
water-tank kind is that of Dr d'Arsonval. It consists of two copper
cylinders (fig. 8 C and C´), each terminating in a cone below. Between
the cylinders is a wide interspace, in order that a large volume of
water may be contained. This interspace therefore constitutes the
water-tank of the incubator. The upper orifice of the inner cylinder
is closed by a movable double lid, which contains an interspace filled
with water. The outer cylinder has an oblique form at its upper end
and is permanently closed. The result attained by this slope of the
lid of the outer cylinder is that the water tank, which is fed from
the highest point, becomes completely filled. The aperture at the
highest point of the outer cylinder is plugged with a caoutchouc plug
and through a perforation in this a glass tube (T) is placed. In the
side of the outer cylinder below this, there is a wide and rimmed
aperture, to which a gas regulator of special construction is fixed.
[Illustration: FIG. 8.--D'Arsonval Incubator.]
This regulator was designed by Théophile Schloesing, and consists of a
brass box, supplied with a rim (L) which fits on to the corresponding
rim (L´) on the aperture of the incubator. Stretching across the
orifice thus connecting the brass box of the regulator with the
water-tank of the incubator is a thin india-rubber diaphragm (D). At
its outer end a perforated cap (R) screws on to the brass box. Through
the perforation the inlet gas tube passes (I); the outlet gas tube (O)
leaves the brass box below and passes direct to the gas burners. The
inlet gas tube is fitted at its inner end with a sliding flanged
collar (F), which is kept pressed against the rubber diaphragm by a
spiral spring. Just behind the collar the inlet tube is perforated by
a small hole, so that the gas supply is never wholly cut off, even
though the rubber diaphragm completely occludes the inner aperture of
the pipe.
The mode of working of the regulator is as follows: when the water
tank of the incubator is filled with distilled or rain water at the
temperature required, it presses upon the india-rubber diaphragm with
a certain degree of pressure. By screwing the inlet pipe in or out, as
required, it can be so adjusted that the diaphragm does not occlude
its inner aperture, and consequently the full volume of gas can pass
through to the burners below. The temperature of the water in the
water-tank therefore begins to rise, and in consequence the volume of
the water to increase. This results in the water rising up into the
tube (T), and therefore the dynamical pressure which is exercised by
the water upon every part of the two cylinders of the incubator and
consequently also upon the india-rubber diaphragm of the regulator is
increased. As this pressure increases, the diaphragm becomes bulged
outwardly and reduces the volume of gas passing through the aperture
of the inlet pipe. At a certain point, of course, the diaphragm
completely occludes the aperture, and the gas supply is wholly cut
off, except for the very small hole, forming a by-pass, in the pipe,
behind the collar. This hole is just sufficiently big to allow the
minimum amount of gas requisite to keep the flames burning to pass
through. The temperature will, therefore, begin to fall, the volume of
water to decrease with its resulting descent from the glass tube (T)
and consequent decrease in the dynamical pressure of the water upon
the diaphragm. The latter therefore retracts away from the aperture of
the inlet tube, and more gas consequently passes through; the flames
again increase in size and the temperature rises once more. And as
soon as the volume of water, owing to the rising temperature, has
increased to the extent correlated with the temperature at which the
apparatus has been set to work, it will have risen once more in the
tube (T), and the gas will be again cut off. The three burners are
placed upon a support that can be moved vertically up or down along
one of the legs of the incubator. The flames are protected from
draughts by mica chimneys. Ventilation is provided by an adjustable
valve (V´) in the cylindrical termination of the incubator at its
lower end, and by tubular orifices, also fitted with valves (V) in the
lid above.
The incubator is very reliable and may be worked within very narrow
limits of variation, provided that the gas-supply be regulated by a
gas-pressure regulator, that the height of the water in the tube (T)
is maintained by daily additions of a few drops of distilled water,
and that the incubator itself be protected from draughts.
Another form of d'Arsonval incubator has a glass door in the side of
it and a slightly modified form of the heat regulator.
Other cylindrical forms of incubators are made by Lequeux of Paris. In
one of these the heat regulator is a bimetallic thermostat, the
movements of which are enlarged by a simple series of levers, so that
a valve can be automatically adjusted to allow more or less heat from
the flame to pass through the heating flue.
In another form there is a movable interior, and an arrangement for
keeping the air in the incubation chamber saturated. It is governed by
a bimetallic thermostat of the Roux type.
In Dr Hüppe's improved form of his incubator, which is approximately
square in form, the double-walled water tank is completely surrounded
externally by an air chamber, which is heated by the passage through
it of the products of combustion of the two flames. The heated gases
escape through an adjustable aperture at the top. In the earlier form
the water tank was traversed by a number of hot-air flues, and there
was consequently no external hot-air chamber. There is an arrangement
of tubes for ventilation, which allow fresh air to enter the lower
part of the incubation chamber and to leave it at the top. The
incoming air is warmed before it enters. The walls are made of
lead-coated steel, and externally the incubator is covered with
linoleum. In the more expensive forms the inner chamber is of copper.
The temperature may be controlled by any of the simpler mercury
thermostats described below.
Dr Babes' incubator is somewhat similar, but the water tank is not
surrounded by a hot-air chamber. Instead it is traversed by a number
of vertical flues through which the heated gases from the flames pass.
Ventilation is provided for and there is an apparatus for controlling
the humidity of the air in the incubation chamber. As in Hüppe's
incubator, the bottom is conical in form. The walls of the incubator
are of lead-coated steel, and externally they are covered with
linoleum; there are two doors, an inner one of glass and an outer one
of metal. The temperature may be controlled as in Hüppe's incubator.
Hearson has designed several forms of bacteriological (biological)
incubators, made by Chas. Hearson & Co., Ltd. Some are heated by a
petroleum lamp and others by a gas flame. In the form heated by a
lamp, for which, however, gas can be substituted, the incubation
chamber is surrounded by a water tank (fig. 9, A) and the lowest part
of this is traversed by an in-going (L) and an out-going flue. The
mode of regulation of the temperature is by means of a thermostat
which operates the movements of a cap (F) over the main flue (V), and
it is identical in its chief features with the method employed in the
chicken incubator. The thermostat (S) is situated in the upper part of
the incubation chamber.
[Illustration: FIG. 9.--Hearson's Bacteriological Incubator. (Heated
by a petroleum lamp.)]
In the other form (fig. 10) for which gas is used exclusively, there
are no flues traversing the water tank. This latter is heated from its
conical floor by a burner beneath the incubator. The heat regulation
is controlled by a thermostat of the same nature as in the form of
incubator just described, but instead of operating by lowering or
raising a cap over a main flue, so as to direct the heated gases
either through the water tank if the temperature is falling, or
through the main flue directly to the exterior if it is rising, it
actuates a gas-governor, so that the flame itself is increased or
diminished in size according to the needs of the incubator. The
gas-governor (fig. 11) is fixed to the roof of the incubator. The
horizontal arm (D) is the same that raises the cap (fig. 9, F) over
the flue in the other form of incubator, but in this case it simply
acts as the bearer of the sliding weight. Beyond its fulcrum (fig. 11,
G) it is continued into a detent-like spur (B) which pushes down upon
a button attached to a rubber diaphragm, when the thermostat within
the incubator is expanded by a rise in temperature. The button thus
forced down, more or less completely closes the inlet gas aperture,
and so reduces or cuts off the gas supply to the flame. There is a
by-pass to prevent the flame from going out completely, and the size
of this can be adjusted by the screw (S). Hearson's incubators have
the reputation of very accurate performance and practically need no
attention for months, or even years.
Schribaux's incubator is a hot-air form. Its walls are of metal, but
it is cased externally with wood, which serves as the insulating
material. Against the inner metal wall of the incubator, and upon its
internal surface, there are disposed a number of vertical tubes, which
open through the roof above into a common discharging funnel. Below,
at the bottom of the incubator they receive the heated gases of
several burners, which as they pass through them radiate their heat
evenly throughout the incubation chamber. In each side wall, at the
bottom of the chamber, is an adjustable ventilating valve.
[Illustration: FIG. 10.--Hearson's Bacteriological Incubator (heated
by a gas flame).]
[Illustration: FIG. 11.--Gas-governor.]
Inside the incubation chamber, and situated against its left-hand
wall, is a U-shaped bimetallic thermostat of the Roux design,
described below. This very accurately controls the temperature of the
incubator.
(c) _Cool Incubators._--In bacteriological laboratories there are two
standards of temperature, one chiefly for the culture of
non-pathogenic organisms and the other for the pathogenic forms. The
first standard of temperature lies between 18° and 20° C., and the
second between 35° and 38° C. But in hot countries, and even in
temperate regions during the summer, the external temperature is much
higher than the former of these two standards, with the result that
many cultures, especially the gelatine ones, are spoiled. The
difficulty is often partially overcome by running cold water through
the incubator.
Hearson, however, has constructed a "cool biological incubator," in
which by an ingenious device the expansion or contraction of the
thermostatic capsule deflects a horizontal pipe (C) (fig. 12), through
which cold water from an ordinary tap is kept running, in one of two
directions. If it is deflected so as to open into the tube (D), the
cold water passes into the tank (F), where it is warmed by a gas
flame, and thence it passes into the water-jacket of the incubator. If
it is deflected so as to open into the pipe (E), it then runs through
the ice tank (B), containing broken ice, before passing through the
water-jacket of the incubator. If it poured into neither of these
pipes it then simply passes out through the pipe (H) to the waste pipe
(N). By this device the temperature of the incubator can be kept
constant at any desired point, even though it may be some 30° to 40°
C. below that of the external air.
Dr Roux has also designed an incubator which can be maintained at a
constant temperature below that of the surrounding air. This also
depends upon the principle of carrying water through an ice-safe,
which then traverses a pipe within the incubator chamber before
passing into the water-jacket of the machine. The heat-regulating
apparatus is a bimetallic thermostat. The incubator is made by Lequeux
of Paris.
The most recent forms of all kinds of incubators, made by Hearson of
London, Lequeux of Paris and Lautenschläger of Berlin are both heated
and regulated by electricity. The heating is accomplished by electric
radiators.
[Illustration: FIG. 12.--Hearson's Cool Biological Incubator.]
In Hearson's machines the regulation of the temperature is brought
about by the breaking or making of the electric current, through the
lifting or depression of a platinum contact, actuated by the expansion
or contraction of the thermostatic capsule.
In Roux's apparatus, made by Lequeux, the make and break is attained
by the movement of one limb of a bimetallic thermostat, and in some
forms a resistance coil and rheostat are placed in the circuit.
At the Pasteur Institute in Paris, and at other large laboratories in
France, the bacteriological incubator is raised to the dimensions of a
room. In the centre of this room is a large boiler heated by
gas-burners, the fumes from which pass through a large flue to the
outside. The flame of the burners is regulated by a bimetallic
thermostat. The gas by-pass can be regulated by an attendant. The
cultures are contained in vessels placed on shelves, which are ranged
round the side of the room.
_Human Incubators._
[Illustration: FIG. 13.--Tarnier's Incubator.]
The first incubator designed for rearing children who are too weak to
survive under normal conditions, or who are prematurely born, is that of
Dr Tarnier. It was constructed in 1880 and was first used at the Paris
Maternity Hospital. Its form is that of a rectangular box measuring 65 ×
30 × 50 centimetres (fig. 13). It is divided into an upper and lower
chamber; the former contains the infant, while the latter serves as a
heating chamber, and in reality is simply a modified water-tank. The
partition (P) which divides the incubator into two chambers does not
extend the whole length of it, so that the upper and lower chambers are
at one end of the apparatus in communication with each other. It is
through this passage that the heated air from the lower chamber passes
into the upper one containing the infant. The narrow bottom chamber C
serves to prevent loss of heat from the base of the water-bottles. The
outside air is admitted into the lower chamber at the opposite end,
through an aperture (A), and passing over a series of bottles (B)
containing warm water, becomes heated. The air is rendered adequately
moist by means of a wetted sponge (S) which is placed at the entrance of
the lower chamber into the upper. The warmed and moistened air is
determined in its direction by the position of the outlet aperture (O),
which is situated above and just behind the head of the infant. It
contains a helix valve (H) and the rotation of this is an indication
that the air is circulating within the incubator.
The child is kept under observation by means of a sliding glass door (G)
situated in the upper or roof wall of the incubator. Immediately beneath
this, and attached to one of the side walls, is a thermometer (T) which
records the temperature of the air in the infant-chamber. The
temperature should be maintained at 31° to 32° C. The precise limit of
temperature must of course be determined by the condition of the child;
the smaller and weaker it is, the higher the temperature must be.
The warm water vessels contain three-quarters of a pint of water and
four of them are sufficient to maintain the required temperature,
provided that the external air does not fall below 16° C. The vessels
are withdrawn and replaced through an entrance to the lower chamber, and
which can be opened or closed by a sliding door (D).
The walls of the incubator, with the exception of the glass sliding
door, are made of wood 25 millimetres thick.
The apparatus appears to have been successful, if by success is
understood the indiscriminate saving of life apart from all other
considerations, since the mortality of infants under 2000 grammes has
been reduced by about 30%, and about 45% of children who are prematurely
born are saved.
Dr Tarnier's apparatus requires constant attention, and the water in the
warm water vessels needs renewing sufficiently often. It is not provided
with a temperature regulator and consequently fluctuations of internal
temperature, due to external thermal variations, are liable to occur.
[Illustration: FIG. 14.--Hearson's "Thermostatic Nurse."]
In Hearson's Thermostatic Nurse these drawbacks are to a large extent
obviated. This "Nurse" consists fundamentally of an application of the
arrangements for heating and moistening the air and for regulating the
temperature of Hearson's chick incubator to Dr Tarnier's human
incubator. As in this latter form, there are two chambers (fig. 14), an
upper (A) and a lower (B), connected with each other in the same way as
in Tarnier's apparatus. The upper chamber contains the infant, but the
lower is not a heating but a moistening chamber. Through apertures (M)
in the bottom of the lower chamber, the external air passes through, and
as in the chick incubator it then passes through perforations in the
inner cylinder of a water tray (O) and thence over the surface of the
water in the tray, through a sheet of wet canvas, to the chamber itself.
Hence it passes to the infant chamber and ultimately leaves this through
a series of perforations round the top. The air in both chambers is
heated by a warm-water tank. This tank forms the partition which divides
the incubator into upper and lower chambers and is made of metal.
Through the water contained in it, an incoming (R) and an outgoing (R)
to the left flue, continuous with each other, pass. These two flues are
related to each other as in the chick incubator (see above) and the
inlet flue is heated in the same way and the outlet flue discharges
similarly. The heat-regulating apparatus is identical with that in the
chick incubator, and the thermostatic capsule (S) is placed in the upper
chamber, near the head of the infant.
The child is placed in a basket which has perforated walls, and is open
above. The basket rests upon two shallow supports (D) situated on the
upper surface of the water-tank partition. The child is kept under
observation through a glass door in the upper or roof-wall of the
incubator.
In Great Britain this apparatus is in use at various hospitals and
workhouses throughout the country, and provided there is no great
fluctuation of barometric pressure, it maintains a uniform temperature.
_Thermo-Regulators or Thermostats._
Certain special forms of thermo-regulators, adapted to the requirements
of the particular incubators to which they are attached, have already
been described. It remains now to describe other forms which are of more
general application. Only those kinds will be described which are
applicable to incubators. The special forms used for investigations in
physical-chemistry are not described. There are various types of
thermo-regulators, all of which fall into one of two classes. Either
they act through the expansion of a solid, or through that of a liquid.
They are so adjusted, that, at a certain temperature, the expansion of
the material chosen causes the gas supply to be nearly completely cut
off. The gas flame is prevented from being wholly extinguished by means
of a small by-pass.
[Illustration: FIG. 15.--Page's Thermostat.]
We will first describe those which act through the expansion of a
liquid. A very efficient and cheap form is that described by F. J. M.
Page in the _Journal of the Chemical Society_ for 1876. The regulator
consists of a glass bulb (fig. 15 B), continuous above with a tubular
limb (L). At the upper part of the limb is a lateral tubular arm (A)
which bends downwards and constitutes the outlet pipe. At the upper
extremity of the limb there is a short and much wider tube (T), the
lower end of which slides upwards or downwards along it. The upper end
of this wider tube is closed by a cork and through a perforation in
this a very small glass tube (G) passes downwards into the limb of the
regulator to a point a short distance below the exit of the outlet
tube. The exact height of the lower aperture of the small tube can be
varied by sliding the wider tube up or down along the limb. The
by-pass (P) consists of a transverse connexion between the inlet and
outlet gas pipes, and the amount of gas which travels through the
short circuit thus formed is regulated by means of a stopcock. The
by-pass, however, can be formed, as suggested by Schäfer (_Practical
Histology_, 1877, p. 80), by making an extremely small hole in the
small inlet tube, a little way above its lower extremity. But unless
this hole be small enough, too much gas will be allowed to pass, and a
sufficiently low temperature therefore unattainable. The regulator is
filled with mercury until the top of the column reaches within ½ in.
of the exit of the outlet tube, the bulb is placed in the incubator
chamber, and gas is allowed to pass through it. By pushing down the
inner inlet tube (G) until its aperture is immersed beneath the
mercury, the gas supply is cut off, with the exception of that passing
through the by-pass. The stopcock is now turned until only the
smallest flame exists. The inlet pipe is then raised again above the
mercury, and the flame consequently increases in size. The temperature
of the incubator gradually rises, and when the desired degree is
reached, the inlet tube is pushed down until the end is just beneath
the surface of the mercury. The gas supply is thus cut off at the
desired temperature. If the temperature of the incubator falls, the
mercury contracts, the aperture of the inlet tube is uncovered, the
gas supply is renewed and the flame increased. The temperature will
then rise until the required point is reached, when the gas supply
will again be cut off. A uniform temperature which oscillates within a
range of half a degree is thus attained.
[Illustration: FIG. 16.--Reichert's Thermo-Regulator.]
Reichert's Thermo-regulator (fig. 16) is another simple and also an
earlier form. The stem (S) of the regulator is enlarged above and
receives a hollow T-piece (P), the vertical limb of which fits
accurately into the enlarged end of the stem, and one end of the
cross-limb receives the inlet gas pipe; the other end is closed. The
vertical limb of the T-piece is narrowed down at its lower extremity
and opens by a small aperture. Above this terminal aperture is a
lateral one of the smallest size. From the enlarged end of the stem
there passes out a lateral arm (A) which is connected with the outlet
pipe to the burner, and lower down another arm (L), which is closed at
its outer extremity by a screw (R), is also attached. The stem and
lower arm are filled with mercury and the bulb of the stem is placed
in the incubator chamber, and gas allowed to pass. When the desired
temperature is reached, the mercury in the stem is forced upwards
until it closes the aperture of the T-piece, by screwing in the screw
(R) of the lower lateral arm (L).
There are several modifications of Reichert's original form. In one of
these the screw arrangement in the lower arm is replaced by a piston
rod working in a narrow bore of a vertically bent limb of the arm. In
another form, the other end of the cross bar of the T-piece is open
and leads through a stopcock to a third arm, which opens into the
enlarged upper end of the stem opposite to the outlet arm (A); this
modification acts as an adjustable by-pass and replaces the minute
aperture in the side of the vertical limb of the T-piece.
In Babes' modification the gas supply is cut off, not by the occlusion
by the rising mercury of the aperture of the T-piece, but by a
floating beaded wire-valve. The aperture of the vertical limb of the
T-piece (P) is traversed by a fine wire which is enlarged at both ends
into a bead-like knob. The wire fits loosely in the aperture and not
only therefore works easily in it, but allows gas to freely pass. When
the lower bead-like knob, however, is raised by the expansion of the
mercury, the gas supply is cut off by the bead being carried up
against the orifice.
[Illustration: FIG. 17.--Cuccatti's Thermo-Regulator.]
Cuccatti's thermo-regulator (fig. 17) is an exceedingly simple and
ingenious form. The stem (S) of the regulator is enlarged below into a
bulb, while above it divides into a V. The two limbs of the V are of
course traversed by a canal and they are connected above by a tubular
cross bar (C). In the middle of this there is a stopcock situated
between the two points where the bar joins the limbs of the V. One end
of the cross-tube serves as an inlet and the other as an outlet for
the gas. The stopcock serves as an adjustable by-pass. About an inch
below the point where the two limbs of the V join the stem, the bore
of the latter is enlarged, and it leads into a lateral arm (A),
containing a screw (R), similar to the corresponding arm in Reichert's
regulator. When the mercury in the bulb and stem expands, it rises,
and reaching the point when the two limbs of the V meet occludes the
orifice to both and thus cuts off the gas supply, except that which is
passing through the by-pass of the stopcock. The temperature at which
this occlusion will take place can be determined by the screw in the
lateral arm. The more this is screwed in, the lower will be the
temperature at which the gas becomes cut off, and vice versa.
Bunsen's, Kemp's and Muenke's regulators are in reality of the nature
of air-thermometers, and act by the expansion and contraction of air,
which raises or lowers respectively a column of mercury; this in its
turn results in the occlusion or opening of the gas aperture. Such
forms, however, are subject to the influence of barometric pressure
and an alteration of 0.5 in. of the barometer column may result in the
variation of the temperature to as much as 2°.
Lothar Meyer's regulator is described in the _Berichte of the German
Chemical Society_, 1883, p. 1089. It is essentially a liquid
thermometer, the mercury column being raised by the expansion of a
liquid of low boiling-point. The liquid replaces the air in Bunsen's
and other similar forms. The boiling-point of this liquid must be
below the temperature required as constant.
The solid forms of thermostats are constructed upon the same principle
as the compensation balance of a watch or the compensation pendulum of
a clock. This depends upon the fact that the co-efficient of expansion
is different for different metals. It therefore results that if two
bars of different metals are fastened together along their lengths
(fig. 18, Z and ST) with the same rise of temperature one of these
will expand or lengthen more than the other. And since both are
fastened together and must therefore accommodate themselves within the
same linear area, it follows that the compound rod must bend into a
curved form, in order that the bar of greater expansion may occupy the
surface of greater length, i.e. the convex one. Conversely, when the
temperature falls, the greater degree of contraction will be in the
same bar, and the surface occupied by it will tend to become the
concave one. If, then, one end of this compound rod be fixed and the
other free, the latter end will describe a backward and forward
movement through an arc of a circle, which will correspond with the
oscillations of temperature. This movement can be utilized by means of
simple mechanical arrangements, to open or close the stopcock of a gas
supply pipe.
[Illustration: FIG. 18.--Dr Roux's Thermostat (straight bar).]
In the construction of this type of thermostat it is obvious that the
greater the difference in the co-efficient of expansion of the two
metals used, the larger will be the amplitude of the movement
obtained. Steel and zinc are two metals which satisfy this condition.
The co-efficient of steel is the lowest of all metals and is
comparable in its degree with that of glass. Substances which are not
metals, such as vulcanite and porcelain, are sometimes used to replace
steel, as the substance of low co-efficient of expansion.
[Illustration: FIG. 19.--Dr Roux's Thermostat (U-shaped bar).]
The bimetallic thermostat most commonly employed is one of the two
forms designed by Dr Roux. In one of these forms the compound bar is
straight (fig. 18) and in the other it is U-shaped (fig. 19). In the
former type the bar itself is enclosed in a tube (T) of metal, the
wall of which is perforated. Towards the open end of this tube the gas
box or case (C) is fixed. In the U-shape form it is attached to the
outer surface (zinc) of one limb of the bar. The gas box is capable of
adjustment with respect to its distance from the bar, by means of a
screw (S) and a spiral spring (SP), which moves the box outwards or
inwards along a rod (R). This adjustment enables the degree of
temperature at which it is desired that the gas shall be cut off to be
fixed accurately, and within a certain more or less extended range.
The inlet and the outlet pipe are disconnected from each other in the
gas box by means of a piston-like rod (P) and valve (V), which slides
backwards and forwards in the tubular part (T) of the box, from which
the outlet pipe emerges. When the valve (V) rests upon the edge of
this box, the gas is completely cut off from passing through the
outlet pipe, with the exception of that which passes through an
exceedingly small aperture (B), serving as a by-pass. This is just
large enough to allow sufficient gas to pass to maintain a small
flame. The piston-like rod and valve, when free, is kept pressed
outwards by means of a spiral spring. This ensures that the valve
shall follow the movements of the compound bar. When this bar bends
towards the gas box owing to a fall of temperature, the valve is
pushed back away from the orifice and gas in increasing quantity
passes through. The temperature of the incubator begins then to rise,
and the zinc bar (Z) expanding more than the steel one (ST), the bar
bends outwards and the valve once more cuts off the gas supply.
(d) _Gas-Pressure Regulators._--The liquid form of thermo-regulators
especially work with a greater degree of accuracy if they are combined
with some apparatus which controls the variations in gas pressure.
There are various forms of these regulators, most of which are figured
and sometimes partially described in the catalogues of various 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.
[Illustration: 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).
[Illustration: 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 belong to the 16th century. On the
other hand Dr Copinger's _Supplement_ had hardly appeared before
additional lists began to be issued registering books unknown both to
him and to Hain, and the new _Repertorium_, begun in 1905, under the
auspices of the German government, seemed likely to register, on its
completion, not fewer than thirty thousand different incunabula as
extant either in complete copies or fragments.
In any attempt to estimate the extent to which the incunabula still in
existence represent the total output of the 15th-century presses, a
sharp distinction must be drawn between the weightier and the more
ephemeral literature. Owing to the great religious and intellectual
upheaval in the 16th century much of the literature previously current
went out of date, while the cumbrous early editions of books still read
were superseded by handier ones. Before this happened the heavier works
had found their way into countless libraries and here they reposed
peacefully, only sharing the fate of the libraries themselves when these
were pillaged, or by a happier fortune amalgamated with other
collections in a larger library. The considerable number of copies of
many books for whose preservation no special reason can be found
encourages a belief that the proportion of serious works now completely
lost is not very high, except in the case of books of devotion whose
honourable destiny was to be worn to pieces by devout fingers. On the
other hand, of the lighter literature in book-form, the cheap romances
and catchpenny literature of all kinds, the destruction has been very
great. Most of the broadsides and single sheets generally which have
escaped have done so only by virtue of the 16th-century custom of using
waste of this kind as a substitute for wooden boards to stiffen
bindings. Excluding these broadsides, &c., the total output of the
15th-century presses in book form is not likely to have exceeded forty
thousand editions. As to the size of the editions we know that the
earliest printers at Rome favoured 225 copies, those at Venice 300. By
the end of the century these numbers had increased, but the soft metal
in use then for types probably wore badly enough to keep down the size
of editions, and an average of 500 copies, giving a possible total of
twenty million books put on the European market during the 15th century
is probably as near an estimate as can be made.
Very many incunabula contain no information as to when, where or by whom
they were printed, but the individuality of most of the early types as
compared with modern ones has enabled typographical detectives (of whom
Robert Proctor, who died in 1903, was by far the greatest) to track most
of them down. To facilitate this work many volumes of facsimiles have
been published, the most important being K. Burger's _Monumenta
Germaniae et Italiae Typographica_ (1892, &c.), J. W. Holtrop's
_Monuments typographiques des Pays-Bas_ (1868), O. Thierry-Poux's
_Premiers monuments de l'imprimerie en France au XV^e siècle_ (1890), K.
Haebler's _Typographie ibérique du quinzième siècle_ (1901) and Gordon
Duff's _Early English Printing_ (1896), the publications of the Type
Facsimile Society (1700, &c.) and the _Woolley Facsimiles_, a collection
of five hundred photographs, privately printed.
In his _Index to the Early Printed Books at the British Museum_ Proctor
enumerated and described all the known types used by each printer, and
his descriptions have been usefully extended and made more precise by Dr
Haebler in his _Typenrepertorium der Wiegendrucke_ (1905, &c.). With the
aid of these descriptions and of the facsimiles already mentioned it is
usually possible to assign a newly discovered book with some certainty
to the press from which it was issued and often to specify within a few
weeks, or even days, the date at which it was finished.
As a result of these researches it is literally true that the output of
the 15th-century presses (excluding the ephemeral publications which
have very largely disappeared) is better known to students than that of
any other period. Of original literature of any importance the
half-century 1450-1500 was singularly barren, and the zeal with which
15th-century books have been collected and studied has been criticized
as excessive and misplaced. No doubt the minuteness with which it is
possible to make an old book yield up its secrets has encouraged
students to pursue the game for its own sake without any great
consideration of practical utility, but the materials which have thus
been made available for the student of European culture are far from
insignificant. The competition among the 15th-century printers was very
great and they clearly sent to press every book for which they could
hope for a sale, undaunted by its bulk. Thus the great medieval
encyclopaedia, the _Specula_ (_Speculum naturale_, _Speculum
historiale_, _Speculum morale_, _Speculum doctrinale_) of Vincent de
Beauvais went through two editions at Strassburg and found publishers
and translators elsewhere, although it must have represented an outlay
from which many modern firms would shrink. It would almost seem, indeed,
as if some publishers specially affected very bulky works which, while
they remained famous, had grown scarce because the scribes were afraid
to attempt them. Hence, more especially in Germany, it was not merely
the output of a single generation which came to the press before 1500,
but the whole of the medieval literature which remained alive, i.e.
retained a reputation sufficient to attract buyers. A study of lists of
incunabula enables a student to see just what works this included, and
the degree of their popularity. On the other hand in Italy the influence
of the classical renaissance is reflected in the enormous output of
Latin classics, and the progress of Greek studies can be traced in the
displacement of Latin translations by editions of the originals. The
part which each country and city played in the struggle between the old
ideals and the new can be determined in extraordinary detail by a study
of the output of its presses, although some allowance must be made for
the extent to which books were transported along the great trade routes.
Thus the fact that the Venetian output nearly equalled that of the whole
of the rest of Italy was no doubt mainly due to its export trade.
Venetian books penetrated everywhere, and the skill of Venetian printers
in liturgical books procured them commissions to print whole editions
for the English market. From the almost complete absence of scholarly
books in the lists of English Incunabula it would be too much to
conclude that there was no demand for such books in England. The demand
existed and was met by importation, which a statute of Richard III.'s
expressly facilitated. But that it was not commercially possible for a
scholarly press to be worked in England, and that no man of means was
ready to finance one, tells its own tale. The total number of incunabula
printed in England was probably upwards of four hundred, of which Caxton
produced fully one-fourth. Of the ten thousand different incunabula
which the British Museum and Bodleian library possess between them,
about 4100 are Italian, 3400 German, 1000 French, 700 from the
Netherlands, 400 from Switzerland, 150 from Spain and Portugal, 50 from
other parts of the continent of Europe and 200 English, the proportion
of these last being about doubled by the special zeal with which they
have been collected. The celebration in 1640 of the second centenary (as
it was considered) of the invention of printing may be taken as the date
from which incunabula began to be collected for their own sake, apart
from their literary interest, and the publication of Beughem's
_Incunabula typographiae_ in 1688 marks the increased attention paid to
them. But up to the end of the 17th century Caxtons could still be
bought for a few shillings. The third centenary of the invention of
printing in 1740 again stimulated enthusiasm, and by the end of the 18th
century the really early books were eagerly competed for. Interest in
books of the last ten or fifteen years of the century is a much more
modern development, but with the considerable literature which has grown
up round the subject is not likely to be easily checked.
The chief collections of incunabula are those of the Bibliothèque
Nationale at Paris, Royal library, Munich, and British Museum, London,
the number of separate editions in each library exceeding nine
thousand, with numerous duplicates. The number of separate editions at
the Bodleian library is about five thousand. Other important
collections are at the University library, Cambridge, and the John
Rylands library, Manchester, the latter being based on the famous
Althorp library formed by Earl Spencer (see BOOK-COLLECTING).
(A. W. Po.)
INDABA, a Zulu-Bantu word, formed from the inflexional prefix _in_ and
_daba_, business, news, for an important conference held by the
"indunas" or principal men of the Kaffir (Zulu-Xosa) tribes of South
Africa. Such "indabas" may include only the "indunas" of a particular
tribe, or may be held with the representatives of other tribes or
peoples.
INDAZOLES (BENZOPYRAZOLES), organic substances containing the ring
system
/\/ CH \
| | \ NH.
\/\ N /
The parent substance indazole, C7H6N2, was obtained by E. Fischer
(_Ann._ 1883, 221, p. 280) by heating ortho-hydrazine cinnamic acid,
/CH = CH·COOH
C6H4 / = C2H4O2 + C7H6N2.
\ NH·NH2
It has also been obtained by heating ortho-diazoaminotoluene with acetic
acid and benzene (F. Heusler, _Ber._, 1891, 24, p. 4161).
/ CH3
C6H4 / = C7H7NH2 + C7H6N2.
\ N:N NHC7H7
It crystallizes in needles (from hot water), which melt at 146.5° C. and
boil at 269°-270° C. It is readily soluble in hot water, alcohol and
dilute hydrochloric acid. Nitrous acid converts it into nitrosoindazole;
whilst on heating with the alkyl iodides it is converted into alkyl
indazoles.
A series of compounds isomeric with these alkyl derivatives is known,
and can be considered as derived from the ring system
/\/ NH \
| | \ N.
\/\ CH //
These isomers are called _isindazoles_, and may be prepared by the
reduction of the nitroso-ortho-alkylamino-acetophenones with zinc dust
and water or acetic acid. The indazoles are weak bases, which
crystallize readily. Phenyl indazole, on reduction with sodium and
absolute alcohol, gives a dihydro derivative (K. L. Paal, _Ber._, 1891,
24, p. 963).
For other derivatives, see E. Fischer and J. Tafel, _Ann._ 1885, 227,
p. 314.
INDEMNITY (through Fr. _indemnité_, Lat. _indemnis_, free from damage or
loss; _in_-, negative, and _damnum_, loss), in law, an undertaking,
either express or implied, to compensate another for loss or damage, or
for trouble or expense incurred; also the sum so paid (see CONTRACT; and
INSURANCE: _Marine_). An act of indemnity is a statute passed for the
purpose either of relieving persons from disabilities and penalties to
which they have rendered themselves liable or to make legal transactions
which, when they took place, were illegal. An act or bill of indemnity
used to be passed every session by the English parliament for the relief
of those who had unwittingly neglected to qualify themselves in certain
respects for the holding of offices, &c., as, for example, justices,
without taking the necessary oaths. The Promissory Oaths Act 1868
rendered this unnecessary.
INDENE, C9H8, a hydrocarbon found in the fraction of the coal tar
distillate boiling between 176° and 182° C., and from which it may be
extracted by means of its picrate (G. Kramer, A. Spilker, Ber., 1890,
23, p. 3276). It may also be obtained by distilling the calcium salt of
hydrindene carboxylic acid, C6H4(CH2)2·CH·COOH. It is an oil which boils
at 179.5°-180.5°, and has a specific gravity 1.04 (15° C.). Dilute
nitric acid oxidizes it to phthalic acid, and sodium reduces it in
alcoholic solution to _hydrindene_, C9H10. A. v. Baeyer and W. H. Perkin
(Ber., 1884, 17, p. 125) by the action of sodiomalonic ester on
ortho-xylylene bromide obtained a hydrindene dicarboxylic ester,
C6H4(CH2Br)2 + 2CHNa(CO2C2H5)2 = 2NaBr + CH2(CO2C2H5)2
+ C6H4:[CH2]2:C(CO2C2H5)2;
this ester on hydrolysis yields the corresponding acid, which on heating
loses carbon dioxide and gives the monocarboxylic acid of hydrindene.
The barium salt of this acid, when heated, yields indene and not
hydrindene, hydrogen being liberated (W. H. Perkin, _Jour. Chem. Soc._,
1894, 65, p. 228). Indene vapour when passed through a red hot tube
yields chrysene. It combines with nitrosyl chloride to form indene
nitrosate (M. Dennstedt and C. Ahrens, _Ber._, 1895, 28, p. 1331) and it
reacts with benzaldehyde, oxalic ester and formic ester (J. Thiele,
_Ber._, 1900, 33, p. 3395).
On the derivatives of indene see W. v. Miller, _Ber._, 1890, 23, p.
1883; Th. Zincke, _Ber._, 1887, 20, p. 2394, 1886, 19, p. 2493; and W.
Roser and E. Haselhoff, _Ann._, 1888, 247, p. 140.
INDENTURE (through O. Fr. _endenture_ from a legal Latin term
_indentura_, _indentare_, to cut into teeth, to give a jagged edge, in
_modum dentium_, like teeth), a law term for a special form of deed
executed between two or more parties, and having counterparts or copies
equal to the number of parties. These copies were all drawn on one piece
of vellum or paper divided by a toothed or "indented" line. The copies
when separated along this waved line could then be identified as
"tallies" when brought together. Deeds executed by one party only had a
smooth or "polled" edge, whence the name "deed poll." By the Real
Property Act 1845, § 5, all deeds purporting to be "indentures" have the
effect of an "indenture," even though the indented line be absent. The
name "chirograph" (Gr. [Greek: cheir], hand, [Greek: graphein], to
write) was also early applied to such a form of deed, and the word
itself was often written along the indented line (see further DEED and
DIPLOMATIC). The term "indenture" is now used generally of any sealed
agreement between two or more parties, and specifically of a contract of
apprenticeship, whence the phrase "to take up one's indentures," on
completion of the term, and also of a contract by labourers to serve in
a foreign country or colony (see COOLIE).
INDEPENDENCE, a city and the county-seat of Jackson county, Missouri,
U.S.A., 3 m. S. of the Missouri river and 10 m. E. of Kansas City. Pop.
(1890) 6380, (1900) 6974 (937 negroes); (1910) 9859. The city is served
by the Missouri Pacific, the Chicago & Alton, and the Kansas City
Southern railways, and by an electric line and fine boulevard to Kansas
City. It is situated about 1000 ft. above the sea, and is surrounded by
a fertile agricultural district. The city has a small public square
(surrounding the court-house) and a public library, and is the seat of
St Mary's Academy, under the control of the Sisters of Mercy. Among its
manufactures are farming implements, flour and lumber. The municipality
owns its electric lighting plant. Independence was laid out as a town
and chosen as the county-seat in 1827, first chartered as a city in 1849
and made a city of the third-class in 1889. About 1500 Mormons,
attracted by the "revelation" that this was to be a Zion, settled in and
about Independence in 1831 and 1832. They contemplated building their
chief temple about ½ m. W. of the site of the present court house, but
in 1833 (partly because they invited free negroes to join them) were
expelled by the "gentile" inhabitants of Independence. In 1867 a
settlement of about 150 Hedrickites, or members of the "Church of Jesus
Christ" (organized in Illinois in 1835), came here and secretly bought
up parts of the "Temple Lot." The heirs of the settlers of 1831-1832
conveyed the lot by deed to the Reorganized Church of Jesus Christ of
Latter Day Saints (with headquarters at Lamoni, Iowa), which brought
suit against the Hedrickites, but in 1894 the U.S. Circuit Court of
Appeals decided the case on the ground of laches in favour of the
Hedrickites, who fifteen years afterwards had nearly died out. In
1867-1869 a few families belonging to the Reorganized Church of Jesus
Christ of Latter Day Saints (monogamists) settled in Independence, and
in 1908 their church here had about 2000 members. Besides a large church
building, they have here a printing establishment, from which is issued
the weekly _Zion's Ensign_ (founded in 1891), and the "Independence
Sanitarium" (completed in 1908). The faithful Mormons still look to
Independence as the Zion of the church. In 1907 a number of Mormons from
Utah settled here, moving the headquarters of the "Central States'
Mission" from Kansas City to Independence, and founded a periodical
called _Liahona, the Elder's Journal_. From about 1831 to 1844, when its
river landing was destroyed by flood, Independence was the headquarters
and outfitting point of the extensive caravan trains for the Santa Fé,
Oregon and Old Salt Lake trails. During the Civil War about 300 Federals
under Lieut.-Colonel D. H. Buel, occupying the town, were captured on
the 16th of August 1862 by Colonel Hughes in command of 1500
Confederates, and on the 22nd of October 1864 a part of General Sterling
Price's Confederate army was defeated a few miles E. of Independence by
General Alfred Pleasonton.