48 



ancy is due to the lack of circulation, the moisture given off by the wet- 

 bulb not being- dissipated fast enough to indicate the true humidity. This 

 result proves absolutely the 1906 conclusion from theoretic considerations 

 that the real humidity of an incubator is not learned by the use of the wet- 

 and dry-bulb hygrometer without fanning. Again, as fanning disturbs 

 the normal conditions within the machine, the fanned reading, while cor- 

 rect for the artificial conditions, does not represent the exact humidity 

 under normal conditions. Hence the only way to gain reliable informa- 

 tion as to the actual humidity in an incubator is by this or some other 

 ''absolute" method. 



Machines I., III., and IV., being all of the same make, with the 

 moisture provided in the same way, would be expected to have approxi- 

 mately the same humidity. From the column "actual humidity" this 

 would appear to be the case, while from "apparent humidity" I. and IV. 

 are nearly alike, but III. considerably lower. The explanation of this 

 apparent discrepancy is found in the individual readings of which 47.8 

 and 4^.8 are the averages. During the first ten days of incubation the 

 humidity in III. was low, apparent 43.4, real 35.5; difference 7.9. During 

 the remainder of the hatch it was high, apparent 56.6, real 50.8; differ- 

 ence 5.8. It so happened that for this machine two-thirds of the readings 

 for the "apparent" were taken while the humidity was low, but that three- 

 fourths of those for the "real" were taken while the humidity was high. 

 Hence the average of the "apparent humidities" is too low and of the 

 "real humidities" too high to represent the true averages for the whole 

 hatching period. The cause of the low humidity in this apparently moist 

 machine during the first ten days was not discovered.. The difference 

 between the apparent and true humidities was 7.9 during the dry period 

 and 5.8 during the moist period. In I. it was 8.8; in IV., 6.9; in VII., 

 where the moisture was provided in the form of buttermilk, the difference 

 was 7.5. Thus in the moist machines, too, we see that the humidity as 

 given by the wet- and dry-bulb hygrometer is astray, an error of 7.5 

 (average difference) on 47.5 (average real humidity) or 15.8 per cent., 

 and we again remark that for reliable information on the humidity in 

 incubators an absolute method is essential. 



The actual vapor pressure in these "moist" machines was in all cases 

 more than double that in the room at the same time, and in No. VII. it 

 was nearly three times that in the room. Hence in all these cases there 

 would be a strong tendency for the vapor to pass outwards through the 

 cracks. 



Actual Humidity in Nests. 



The same methods were applied to determining the actual humidity 

 in hens' nests. The results are given in' Table No. XVIII. : 



