320 



d. When the record sheet is removed from the hygrothermograph 

 each week, tabulate on suitable sheets the degrees of temperature and per- 

 centages of relative humidity which occurred in each hour (or, if more 

 convenient, each two-hour period) of each day of the week, assembling 

 them by days. From Table I, where velocity values are given 

 in numbers of developmental units per hour, take the velocity value 

 for each of these combinations of temperature and humidity. If two-hour 

 periods are used, multiply each velocity value by 2. 



TUESDAY WEDNESDAY THURSDAY 



TEMPERATURE 

 TIME 



Pig. 1. Tracings of a portion of a hygrothermograph record of weather 

 conditions at Olney, Illinois, April 13-14, 1915. The tracings in solid lines are 

 included in Table II. 



For example, refer to Fig. 1, first noting that the time of day is 

 indicated at the top for temperature and at the bottom for humidity. The 

 reading for 2 P. M. Apr. 13 is: temperature 00° F. and humidity 33 per 

 cent. Referring to Table I, we find the velocity value for that combina- 

 tion of temperature and humidity to be '^.■^ developmental units per hour, 

 which we may use as the average rate of development for two hours. We 

 thus get 15. -1 developmental units for that two-hour period. Again, the 

 reading for i P. M. is: temperature 59° and humidity 30 per cent. .A.n- 

 other reference to Table I (and Fig. 1-lB ) shows the corresponding 

 velocity value to be (>.4 developmental units per hour, which may be used 

 as the average velocity giving 12.8 developmental units for the period. 

 The time, temperature, humidity, and velocity for all two-hour jieriods of 

 the 24 hours, of which the above two readings are a part, are shown in 

 Table II. 



