The moisture problem to the small incubator operator presents itself as follows: If left to the mercies of chance and the weather, the too great or too little evaporation from his eggs will yield hatches that will prove unprofitable. In order to regulate this evaporation, he must know and be able to control both vapor pressure and the currents of air that strike the eggs. Now he does not know the amount of vapor pressure and has no way of finding it out. The so-called humidity gauges on the market are practically worthless, and even were the readings on relative humidity accurately determined, they would be wholly confusing, for their effect of the same relative humidity on the evaporation will vary widely with variations of the out-of-door temperature. If the operator knows or guesses that the humidity is too low, he can increase it by adding water to the room, or the egg chamber, but he cannot tell when he has too much, nor can he reduce the vapor pressure of the air on rainy days when nature gives him too much water. As to air currents he is little better off--he has no way to tell accurately as to the behavior of air in the egg chamber and changes in temperature of the heater or if the outside air will throw these currents all off, since they depend upon the draft principle. Taking it all in all, the man with the small incubator had better follow the manufacturer's directions and trust to luck. The writer has long been of the conviction that a plan which would keep the rate of evaporation within as narrow bounds as we now keep the temperature, would not only solve the problem of artificial incubation, but improve on nature and increase not only the numbers but the vitality or livability of the chicks. With a view of studying further the relations between the conditions of atmospheric vapor pressure, and the success of artificial incubation, I have investigated climatic reports and hatching records in the various sections of the world. The following are averages of the monthly vapor pressures at four points in which we are interested: Buffalo, St. Louis, San Fran- Cairo Month N.Y. Mo. cisco. Egypt January 87 98 311 279 February 81 94 310 288 March 138 224 337 287 April 171 283 332 311 May 301 423 317 328 June 466 550 345 365 July 546 599 374 413 August 496 627 382 435 September 429 506 389 372 October 285 327 342 365 November 271 225 285 321 December 143 133 243 397