MEAN DIURNAL INEQUALITY OF EARTH'S FORCE. 205 



graphic records during a year, the mean value of the 

 ordinate at each individual hour, and having compared 

 that number for each hour with the mean of all the 

 similar numbers for the 24 hours, we obtain the dis- 

 turbance at each hour; in westerly force, or in northerly 

 force, or in vertical force, as the case may be. Now if 

 we lay down in a left-hand ordinate the westerly dis- 

 turbance at each hour, and in an upright ordinate the 

 northerly disturbance at each hour, we produce a curve 

 of the singular form represented in Figure 62. The 



Fig. 62 



small figures on the curve give the solar hours. And 



