6 BULLETIX 1080, U. S. DEPARTMEXT OF AGRICULTURE. 
first year could be compiled and studied it became evident that 
humidity could play little, if any, part in the killing of the eggs. 
As stated elsewhere, the factor responsible for nonhatch acts during 
the cold months of December. January, and February, during which 
the amount of moisture in any giyen space is yery low. This in 
itself would hardly be proof, as low humidity might have some 
eifect. There was no appreciable difference, however, between the 
humidity records from the three points, two of which showed non- 
hatch while none was obtained from the third. Humidity records 
for succeeding years have only served to substantiate those obtained 
the first year. 
Temperature lines for the three points followed one another 
closely until December, but as soon as severe cold weather set in 
the difference became very marked. 
At the point which had never yielded nonhatch the coldest days 
found the mercur}' little below zero, while at the other two. tempera- 
tures of from —20° F. to —30° F. were recorded, and during most 
of the time they were from 15° to 25° colder than the first point. 
The two exceptions to this were during December. 1917, and Febru- 
ary, 1920, when the temperature at the warmest point fell to —15° 
and —16° F., respectively, for the only times during the four years 
that records have been taken. These resulted in many eggs failing 
to hatch. 
Temperature records obtained from the instruments during four 
consecutive winters show that the cold weather comes from the last 
part of December to the first of March, with the lowest drops in 
January and February. The first winter, 1916-17, was only moder- 
ately cold, with the greatest drop coming in February. The next 
winter, 1917-18, was extremely cold in December, January, and 
February, and folloAving this came the unusually mild winter of 
1918-19 with hardly a drop below zero. This in turn was followed 
by another extremely cold winter which made conditions almost 
ideal for our experiments. The mild winter of 1918-19; coming as 
it did between two that were very cold, made comparison of the 
records of all three seasons very valuable. 
The "Weather Bureau office at Boston obtains records regularly 
from 50 substations in the o-ipsy-moth area. A study of these rec- 
ords shows that in general the drops in temperature become lower as 
one goes northward. Along the coast, however, due to the modify- 
ing effect of the ocean, the cold is nowhere nearly as severe as it is 
farther inland. Also, one may find small areas having much lower 
temperatures than the surrounding countr3% due to the topography 
which induces that phenomenon known as air drainage, the cold air- 
flowing down into the lowest spot and settling there. 
RESULTS OBTAINED FROM EXPERIMENTS. 
Monthl}^ collections, as stated on page 3, were made at five chronic 
nonhatch points and one control point Avhere no nonhatch had ever 
been found. Three of these had weather instruments, so that it was 
possible to check results against temperature records. 
