56 



DISCUSSION OF THE DIURNAL V A K I A T ION 



(K.) SoLAK-DlUKKAL RAXOB Or THE HORIZONTAL FORCE FOR EACU MoXTU OF TUB YEAR. 



1. scale. 

 0.0060 

 56 

 52 

 48 

 44 

 40 

 36 

 32 

 28 

 24 

 0.0020 



The next table contains the epochs when the mean horizontal force is reached in 

 each day, as computed by the preceding formula?. The diurnal curves intersect 

 the axis of abscissa) four times, of which the table contains only the A. M. and 

 first P. M. intersection: those later in the afternoon and near midnight occur in 

 summer, winter, and whole year at 7 P. M., 5| P. M., and 6| P. M. respectively, 

 and at 11| P. M., 12 P. M., and llf P. M. respectively. 



The above times are generally correct within two minutes (according to the 

 formulae). The morning hour of average daily horizontal force is less variable in 

 the course of a year than the afternoon hour. 



The following table contains the computed diurnal variation of the horizontal 

 force. The values have been expressed in absolute measure. It compares directly 

 with Table IV., which contains the observed values. It will be useful for the 

 interpolation of observations, or for their reduction to the mean value of the day 

 from observations taken at irregular hours. The table also forms the basis for the 

 construction of diagram G. 



