324 



The Use of Tempekatuke Data Alone. 



a. Maximum and minimum temperatures. Daily maximum and 

 minimum temperatures cannot be used to give accurate results, as the rate 

 of development often varies too much from hour to hour. 



b. Thermograph Records. If it is desired to use temperature alone 

 (i. e., without data on humidity, etc.), thermograph records are necessary. 

 For rough approximations for estimating the progress of the first genera- 

 tion in southern Illinois localities, use Table I as follows : Draw a straight 

 line from T. 45°. H. 80% to T. 63°, H. 77%, continuing this line to 

 T. 90°, H. 43%. Make a list of the velocity values lying nearest to this 

 line and use them for their corresponding temperatures from the thermo- 

 graph records for one-hour or two-hour periods. This applies to the first 

 generation pupae and eggs. For the second and third generation pupae 

 and eggs, draw the line from 45°, Si)% to 70°, 89% and continue to 90°, 

 60% ; and use the velocity values lying nearest to this line for their corre- 

 sponding temperatures. The results by this method will not be reliable 

 but will probably serve as well as, or better than, summing temperatures 

 in "degree-days". 



c. Sling Psychrometer Readings at / A.M. and 7 P.M. \\^here 

 hygrograph records are not available, as is often the case in working over 

 old data, it will probably give fair results to use thermograph records for 

 hourly or bihourly temperatures if sling readings are available for humidi- 

 ties at 7 A. M. and 7 P. M. The values on Table I may then be read by 

 using a celluloid triangle as a guide for getting the probable march of 

 temperature and humidity from the 7 A. M. value to the value at the 

 maximum temperature for the day. To make this triangle, draw a line 

 on Table I from the temperature-humidity combination at 30° and 95%, 

 for example (assuming that to be true for 7 A. M.), to the combination 

 at 50° and 73% (which is the probable combination* at the time of maxi- 

 mum temperature on such a day in our climate) ; measure the angle 

 formed by this line with a vertical line along the side of the Table ; then 

 cut the triangle to fit this angle, making it a right triangle for convenience 

 in keeping its base parallel with lines running across the Table. Use the 

 humidities crossed by this line drawn on the table (which line is now the 

 hypothenuse of the triangle), with the corresponding temperatures from 

 the thermograph sheet, up to the maximum temperature. For all clear 

 days, read along the hypothenuse of the triangle made on the basis of the 

 example, for all rising temperatures, beginning with the 7 A. M. combina- 

 tion for the day. For all falling temperatures, follow back across the 

 Table from this maximum along a straight line to the 7 P. M. temperature- 

 humidity combination for that day. (The triangle is not needed here.) If 

 practicable, consider periods when it is raining as having 95 per cent 

 humidity. 



• This probable combination was derived from data on the average daily march 

 of temperature and humidity, obtained by an analysis of many hygrothermograph 

 records. 



