48 Eighteenth Report State Entomologist of Minnesota — 1920 



first day. adding the sixth, placing the average for these days after 

 the fourth day, and so on. This is given in column 5, Table II. The 

 daily catch was then computed as a percentage of the normal catch, 

 a catch of 100 being normal. This method practically eliminates the 

 emergence curves, replacing them by a smoothed normal curve, from 

 which variations are taken. The remaining columns are self-explana- 

 tory. The weather data were obtained as follows : The temperature 

 represents the mean between 9 p. m. and 5 a. m., obtained by integrat- 

 ing the curve of a thermograph exposed in the field. By this method 

 a better measure of the temperature is obtained than by averaging 

 maximum and minimum ( Hartzell. 5). The relative humidity repre- 

 sents the 7 p.m. observation taken at the Minneapolis United States 

 Weather Bureau station, and is used in default of any observations 

 taken in the field. This does not represent the actual night conditions 

 in the field, the humidity on any night actually becoming much higher 

 before morning; but it is a good index of conditions on successive 

 nights, when considered in connection witli the temperature. A 7 p.m. 

 humidity of 54 per cent at a temperature of 70 degrees F. indicates a 

 dew point of about 51 degrees F., which would probably not be reached 

 during the night. Normally the temperature falls constantly during 

 the night, reaching its lowest value about 6 a. m. in the summer. The 

 records of pressure and precipitation are also from the records of the 

 Minneapolis station, the precipitation being correlated with field notes 

 taken by the writer, and the pressure being integrated from the station 

 record from 9 p. m. to 5 a. m. 



