140 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
The result in this case approximates very closely to that at Grand 
Island, if we take 00° as the minimum. As the data in reference to North 
Platte is not so positive as that in reference to the other two, we may take 
the latter as giving approximately the length of exposure to a given 
degree of temperature that is necessary to hatch the eggs in their nat- 
ural position. 
Taking the results at these two places and Mr. Riley's experiments, 
let us from them test Professor Abbe's " working basis." Mr. Riley 
found by actual experiment that at a temperature of 85°, from 28 to 33 — 
say 31 days — 744 hours were required to hatch the eggs ; that at a tem- 
perature of 75° — 42 days — 1,008 hours were required. By taking the 
number of hours at which they .were exposed, at these two places, to a 
temperature between 50° and 00°, 00° and 75°, and above 75°, to wit, 
Grand Island, 784, 988, and 240 hours, respectively, as given above, and 
Moorhead, 921, 1,411, and 3G0 hours, and reducing them by proportion 
to 50° and 00°, we obtain the following results : 
The time required to hatch the eggs at a uniform temperature of 85° 
is 31 whole days, or 744 hours ; at 75° is 42 whole days, or 1,008 hours; 
at G0° is GO whole days, or 1,440 hours; at 50° is 116 whole days, or 
2,784 hours. 
The result at G0° is precisely that given by Professor Abbe, the dif- 
ference between the two places being only one day — one 60 days, the 
other 61. The number of days at 50° in the average of 112 and 120. 
Notwithstanding the close agreement between Mr. Riley's experi- 
ments and Professor Abbe's theory, there are so many elements of uncer- 
tainty entering into the calculation that it can at most be considered 
but as a means of approximating, as Professor Abbe truly says, the fact. 
If the hatching depends entirely on the spring temperature and not 
on the sum during the time they are in the ground, then the length of 
time required is not only very brief but is by no means uniform ; but 
the results of the foregoing calculations would appear to render it cer- 
tain that thesMwis a necessary factor, and for bringing this out we must 
thank Professor Abbe ; but we must not forget that time also is a factor 
which must be considered, otherwise the southern locabties ought to 
produce two broods in the year. 
The direct influence of the temperature and winds on flights. — For the 
purpose of illustrating this we introduce here the daily records of tem- 
perature and wind during the summer of 1877. It is limited to six of 
the most important northwestern stations, and has been kindly fur- 
nished to the Commission by the Chief of the Signal Service Bureau, to 
whom we are under obbgations for numerous favors. 
