INCUBATION 
may be, should be decidedly superior to those on either side. 
That they are better, has already been shown. But they are 
far from what they should be. An explanation is not hard to 
find. The correct content of moisture is not the only essential 
to the chick’s well being at the moments of hatching, but dur- 
ing the whole period of incubation. Under our present system 
of incubation, the chick is immediately subject to the chang- 
ing evaporation of American weather conditions. The data 
for that fact, picked at random, will be of interest. The fol- 
lowing table gives the vapor pressure at Bune N. Y., for 
twenty consecutive days in April: 
April) Vacs ives sa scaviaed 170° | April’ (The scecwewae ences 342 
Docs 'e-Syacagasa ya auaneo-a aness 130 Wivscis access owew.s 286 
SD afat gah Suave steht x cout ate 95 NO a leorcsaeeiane sa Wes 219 
Ah ial oiarecoke oselations Seta 103 146 aston vnwes a alates 248 
Diss a civene es weiss a aien 110 LD sierarees Oaew e etere S 217 
Cie oe een we eee Fetes 106 1G 5 setae bo Fen. 193 
Micsi.8G SousbacdSusuauetaraaysas 154 DT a wiousee ie wrsuee-slaveveces 241 
8 cere chellersteveravenew ea 183 18), esse a wigaees anne 306 
Das vats gotta es aie 245 1 ei cecaus ‘aicteveds oa creee + 261 
NO ena +-sveraure < areas ako 311 20's spate 5-0 averse os aie é 204 
Supposing a hatch to be started at the beginning of the 
above period, by the end of the first week, with the excessive 
evaporation, due to a low vapor pressure, the eggs would all 
be several per cent. below the normal water content; the fact 
that the next week was warm and rainy, and the vapor pres- 
sure rose until the loss was entirely counterbalanced, would 
not repair the injury, even though the eggs showed at the end 
of incubation exactly the correct amount of shrinkage. A man 
might thirst in the desert for a week, then, coming to a hole 
of water fall in and drown, but we would hardly accept the 
report of a normal water content found at the post-mortem 
examination as evidence that his death was not connected 
with the moisture problem. 
The change of evaporation, due to weather conditions, is, 
under hens, less marked than in incubators. This is because 
there are no drafts under the hen, and because the hen’s moist 
body and the moist earth, if she sets on the ground, are 
separate sources of moisture which the changing humidity of 
the atmosphere does not affect. Among about forty hens set 
at different times at the Utah Station and the loss of moisture 
of which was determined at three equal periods of six days 
each, the greatest irregularity I found was as follows: Ist 
period, 5.81 per cent.; 2d period, 3.86 per cent.; 3d period, 6.15 
per cent. Compare this with a similar incubator record at the 
S 85 
