INCUBATION 
The hair hygrometers commcnly sold to incubator operators 
are known by scientists to be absolutely unreliable. The range 
between the wet and dry bulb thermometers was found in the 
Ontario experiments to give readings with and without fanning 
that varied 15 to 20 per cent. in relative humidity which, at the 
temperature of an egg chamber, would amount to a varia- 
tion of three to four hundred of vapcr pressure units, which, 
with the forced draught plan, would ruin a hatch of eggs in 
a few hours. The sling psychromeier as used by the U. S. 
Weather Bureau should, in the hands of an expert, give re- 
sults making possible measurements accurate to two or three 
per cent. of relative hum‘ ‘ty or forty to sixty units of vapor 
pressure. In contrast with these blundering instruments we 
now have available an instrument with which the writer has 
frequently determined vapor pressure accurately to within a 
range of two or three vapor pressure units and the instru- 
ment is capable of being constructed for even finer work. 
As it is only by means <f air with the moisture content 
absolutely controlled that the use of a large room becomes 
possible, we can now see why this type of hatching remained 
so long undeveloped. By neans of such vapor pressure con- 
trol the large egg chamber is not only feasible but the rate of 
evaporation at once becomes subject to the control of the oper- 
ator and we achieve a perfection in artificial incubation hith- 
erto unattained. 
The means by which the air moisture is regulated is similar 
to that used in up-to-date cold storage plants where the air 
ig made moist by sprinkling and dried with deliquescent salts. 
The regulation of vapor pressure, like that of temperature, 
may be by electrically moved dampers which switch a greater 
or less proportion of the incoming current to the sprinkler 
or dryer as the case may be. The ordinary incubator ther- 
mostat gives the necessary impulse for the control of the 
temperature dampers, while the instrument above referred to 
is used for the vapor pressure control. 
As the entire air circuit is closed, the chemical composi- 
tion of the air may also be regulated at will. This results in a 
reduction of the quantity of heat required to a minimum; in 
fact, with the incubator in full swing, the air will, at times, 
need cooling rather than warming. 
The question of the cost of incubation by this method, or 
of profit of such a hatchery operated for the public is almost 
wholly one of the size of operations. Where sufficient eggs 
may be obtained and sufficient demand exists for the chicks to 
make it profitable to operate, the aaHonal cost of hatching 
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