10 BULLETIN 1328, U. S. DEPARTMENT OF AGRICULTURE 
On any particular day the magnitude of the experimental error 
depends upon the combination of factors operating on that day. 
On 89 of the 105 days on which records were taken, omitting records 
accidentally falsified by various causes, it appears that out of every 
100 of the 2,434,666 contacts formed by outgoing bees, 96.84 re- 
turns were registered. On 37 of these days the records show more 
bees coming back than were recorded as going out, and these so- 
called gains in the returns give an obvious error of at least 1.86 
per cent for the days recorded in Table 1. These 37 days were dis- 
tributed as follows, and show^ed for every 100 exits daily the fol- 
lowing average returns for each group: April, 4 days, 111.99; May, 
10 days, 104.50; June, 7 days, 104.87; July, 16 days, 104.29. These 
data give some idea of the magnitude of the daily experimental error 
which may take place. The percentage returns on these days varied 
from 100.08 to the maximum, one day in April, when they were as 
high as 127.81. 
If the days are selected on which the apparatus worked well, and 
the daily percentage of error which occurred, so far as it could be 
determined, is kept in mind, the general utility of the curves ob- 
tained from these data for such purposes as a study of the effect of 
external environmental factors is little affected by this error. For 
a study of the average duration of each flight, where a greater 
degree of accuracy is essential, a closer selection of data is necessary. 
Referring, therefore, to the outline of the problems on which it is 
hoped that such an apparatus may give some information, it is found 
that this apparatus is performing its function as regards four of 
them, one of which has been rated as the most important in this in- 
vestigation. 
FACTORS INFLUENCING THE FLIGHT 
The various activities of the colony population are so interrelated 
that in a study of any one factor, influencing any particular activity 
such as flight, it sometimes becomes exceedingly difficult to gauge 
its exact influence, or even to give the right factor the credit for the 
behavior observed. Since it is possible not only to observe the varia- 
tions in flight produced by changes in the intensity of any single 
factor throughout the course of a day, but also to gauge to a certain 
extent the gross influence of this factor on the day's flight as a whole, 
it is necessary in a study of any factor to make use of both of these 
sources of information. To ascertain the gross influence of any 
factor, a general survey of the whole period in which records were 
made is necessary. 
THE SEASONAL SURVEY 
In order to obtain a comprehensive picture of the daily flight 
activities throughout the season, it is necessary to plot a curve (fig. 
2) of the total daily exits from the hive (Table 1). As might be 
expected, this curve has several high points, representing the data 
for those days when the conditions for flight were at an o})timum for 
the period of the season in which they occur. A day that is consid- 
ered an optimum for April would very naturally be a bad flight day 
for June or fJuly; therefore in a study of any ])articular day a com- 
parison must be made between this day and another in close prox- 
imity to it, when presimuibly, or as far as can be ascertained, the 
field conditions, internal conditions of the colony, and the number of 
