AT KEW OBSERVATORY, 1898 TO 1912. 



149 



curve, and but for the desirability of having the three seasons equal, February might 

 have been included under equinox and April under summer. 



When the type of the diurnal inequality varies but little with the season the range 

 usually gives a very fair idea of how the intensity of the forces to which the regular 



J F M A M' J' j" X S N D 





1-5 



1-0 

 05 



1-5 

 1-0 



0-5 



I -5 

 1-0 

 05 



Z-0 

 15 



1-0 

 (J5 



1-5 



1-0 

 0-5 



M A M' J" j" A' S 

 Fig. 4. Annual variation. 



. A.D. 



Mean 



potential 



gradient. 



Range 



diurnal 



inequality. 



N D 





diurnal changes are due vary throughout the year. An exception to this may arise 

 when the curves are of a sharply peaked type, unless the times of daily maximum and 

 minimum happen to fall very close to exact hours. Peaked curves are, however, 

 unusual in the diurnal inequalities of natural phenomena. 



If the type varies much, a better idea of the activity of the forces is derived from 



