INCUBATION 
Second, the Egyptian incubator of ancient origin, which is 
a large clay oven holding thousands of eggs and warmed by 
smouldering fires of straw. 
Third, the Chinese incubator, much on the principle of the 
Egyptian hatchery, but run in the room of an ordinary house, 
heated with charcoal braziers and used only for duck eggs. 
I have no accurate information on the results of the Chinese 
method, and as it is not used for hen eggs, we will confine 
our attention to the first two processes only. 
I do not care to go into detail in discussing makes of box 
incubators, but I will mention briefly the chief points in the 
development of.our present machines. 
The first difficulties were in getting lamps, regulators, etc., 
that would give a uniform temperature. This now has been 
worked out to a point where, with any good incubator and an 
experienced operator, the temperature of the egg chamber is 
readily kept within the desired range. 
These are two principal types of box incubators now in use. 
In the earliest of these, the eggs were heated by radiation 
from a tank of hot water. These machines depended for venti- 
lation or, what is much more important, evaporation, upon 
chance air currents passing in and out of augur holes in the 
ends or bottom of the machine. 
The second, or more modern type, warms the eggs by a 
current of air which passes around a lamp flue where, being 
made lighter by the expansion due to heat, the air rises, cre- 
ating a draft that forces it into the egg chamber. There it is 
caused to spread by muslin or felt diaphragms so that no per- 
ceptible current of air strikes the eggs. This type is the most 
popular type of small incubator on the market. Its advantage 
will be more readily seen after the discussion of the principles 
of incubation. 
Hazy tales of Egyptian incubators have gone the rounds of 
poultry papers these many years. More recently some ac- 
curate accounts from American travelers and European in- 
vestigators have come to light, and as a result, the average 
poultry editor is kept busy trying to explain how such won- 
derful results can be obtained “in opposition to the well-known 
laws of incubation.” 
The facts about Egyptian incubators are as follows: They 
have a capacity of 50 to 100 thousand eggs, and are built as a 
single large room, partly underground and made of clay rein- 
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