A New Method of Treating [april, 



of the amount by which the temperature exceeds a given 

 base temperature and the length of time during which the 

 excess is maintained. The unit of measurement is the day- 

 degree, a day-degree signifying i° F. of excess above the base 

 continued for 24 hours or any other number of degrees con- 

 tinued for an inversely proportional number of hours. As 

 base temperature 42 0 F. is adopted, this being regarded as the 

 limit above which temperature is mainly effective in promoting 

 the growth of plants in a climate such as that of the British 

 Isles. 



The meaning of the term may be most easily understood 

 from the diagram, Fig. 2, in which the central curve represents 



KEW. March 



TUESDAY S™ WEDNESDAY 9th THURSDAY IOth 



50* 



30* 



M 



>r 6 No 



0N 6 M 



DT 6 Hi 





or 6 N 



DON 6 M 







L 











— 













A 









L 





\ 





I 



r 





r y 













—J 





N 





' / 













__ 





1 



J 



• 















B 



FIG. 2. 



a thermograph record at Kew for a period of three days. The 

 thickened line AB is the base line 42 0 . That portion of the 

 area bounded by the thermometer record and the base line, 

 which lies above the base line, represents the accumulated 

 temperature above 42 0 . In the figure it has been shaded. 



" Coldness " is estimated by accumulated temperature 

 below 42 0 . The unit of measurement is, as before, the day- 

 degree. In the figure the cross-ruled area lying below the 

 base line and between it and the thermometer record represents 

 accumulated temperature below 42 0 . 



In practice the accumulated temperature above and below 

 42 0 is calculated, in accordance with a set of rules drawn up 

 by Sir Richard Strachey, from readings of maximum and mini- 

 mum thermometers taken once a day. These rules are given 

 in the preface to the Weekly Weather Report ; a full account 



