INCUBATION 
perhaps, with some fancied resemblance of felt diaphragms to 
hen feathers, has resulted in the widespread use of this type 
of machine. " 
The latest effort along the lines of reducing evaporation is 
the sand tray machine that followed in the wake of the On- 
tario investigation. This device simply gives a greater evap- 
orating surface to the water and hence a greater addition to 
the vapor pressure. The results in practice I had given me by 
a man who last year hatched sixty-five thousand chicks and 
as many more ducklings. 
He said: “The sand tray early in the season gave the best 
hatches and most vigorous chicks we had, but later on things 
got too wet and the chickens drowned.” No nicer demonstra- 
tion of science in practice could be desired. 
In the present-day incubator of either type we are wholly 
at the mercy of sudden climatic changes of vapor pressure. 
For the slower changes from season to season some control by 
greater and less amounts of supplied moisture, or by venti- 
nor slides is available, but little understood and seldom prac- 
ticed. 
It will certainly be of interest to my readers to know the 
actual hatches obtained with the prevailing type of box incu- 
bator. By actual hatches we mean the per cent. of live chicks 
taken out of the machine to the per cent. of eggs put in. 
The ordinary published hatches, based on one per cent. of fer- 
tile hatches, are a delusion and a snare. When eggs are tested 
out many dead germs come out with them and the separation 
of microscopic dead germs from the infertile egg is, of course, 
impossible. Such padded and show hatching records do not 
interest us. 
Where incubators are run on top of the ground I have found 
the results to be poor and to improve, the bigger and deeper 
and damper and warmer and less ventilated the cellar is made. 
The reason for this is plain. In such a cellar the vapor 
pressure of the air is not only greater but is less influenced by 
the shifting vapor pressure of the outside air. In a good cel- 
lar the operator, though his knowledge of the factors with 
which he deals is greviously deficient, learns, through long 
and costly experience, about what addition of moisture or 
about what rate of ventilation will give him the best results. 
In the room more subject to outside influences, the conditions 
are so constantly changing that uniformity of practice never 
gives uniform results, and hence the operator is without guid- 
ance, either intelligent or blind, and the results are wholly 
a@ product of chance. 
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