The means by which the air moisture is regulated is similar to that used in up-to-date cold storage plants where the air is 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 thermostat 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 composition 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 additional cost of hatching extra chicks will be insignificant compared with the present system. The Egyptian poultryman gives four eggs for three chicks, but the American poultryman would be willing to give four eggs for one chick, as is shown by the fact that he sells eggs for from 1 to 3 cents apiece and buys day-old chicks for ten to fifteen cents. A plant with a seasonable capacity of 100,000 eggs has a basis to work upon something as follows: With a fifty per cent. hatch and chicks at 10 cents each there would be a gross income of $5,000 annually. From this we must subtract for eggs at 2 cents each, $2,000. Salary for operator $1,000, wages for helper $300. Fuel, supplies and repairs $500. Cost of delivery and sales of chicks $200. This leaves a residue of $1,000, which would pay a 20 per cent. interest on the necessary investment of $5,000. Personally, I think this is about the minimum unit of hatching that would prove worth while as independent institutions. Any increase in the percentage of the hatch would, of course, reduce the unit of size necessary for profitable operation. Upon a single poultry plant as a duck farm the cost of operation would be materially reduced, as the operator himself would take the place of the intelligent manager and the cost of gathering eggs and the delivery of the product would be eliminated.