RESEAKCH METHODS IN STUDY OF FOREST ENVIRONMENT. 31 



Readings. 



All readings of soil thermometers should be in degrees and tenths. 

 Where suspended soil thermometers are used the readings should 

 be made with the greatest possible speed after removing the ther- 

 mometer from its seat, and care should be exercised not to expose 

 the thermometer bulb to the sun, even though it be encased. Ther- 

 mometers on the surface of the soil should be read, if possible, 

 without frequent disturbance of their contact with the soil. 



With standardized thermometers the correction may best be ap- 

 plied before recording the reading; but if centigrade readings must 

 be transposed to Fahrenheit, or the reverse, it may be best to make 

 the instrumental correction and the transposition in the office simul- 

 taneously. 



Tabulation. 



The daily observations may be tabulated on the "Soil Tempera- 

 tures' 1 form. Where two observations are made in one day, both 

 should be entered on the line for the day, with the mean for the day 

 computed from each, and the average of the two computed means in 

 a separate column. Where more than two observations are made, it 

 will be best to enter all at their respective hours on the "Hourly 

 (Air, Soil, or Actinograph) Temperatures" form, and to enter on 

 the "Soil Temperatures' 1 form the mean of all readings without 

 any corrections, provided the three or more readings are distributed 

 well between the times of maximum and minimum temperatures. 



Hourly Soil Temperatures. 



Whenever the soil thermograph is used, or when eye observations 

 are made at frequent intervals, the hourly values should be tabulated 

 on the "Hourly (Air, Soil, or Actinograph) Temperatures ' ; form. 

 With the complete record, the means by hours as well as by day- 

 should be computed for any period covered. 



In addition, from the hourly record the maximum, minimum, and 

 mean for each day (midnight to midnight) may be transferred to the 

 "Soil Temperatures" form, in order that the mean may be compared 

 with that obtained from thermometer readings, and that the daily 

 range may be shown. 



The application of corrections to the soil thermograph trace can 

 not follow the same rules as are used with air thermographs, because 

 of the difficulty of making corrections of the maxima and minima at 

 the time. If the correction of the soil thermograph trace varies con- 

 siderably in amount from day to day, the amount of the correction 

 at any hour should be determined by its position with respect to the 

 preceding and following correction hours. If the correction at, say, 

 9 a. m. is about the same from day to day, one correction may be 



