OF THE HORIZONTAL FORCE. 



55 



The extreme variation in the epoch of the A. M. maximum is therefore 2 h 15 m ; 

 the variation for the A. M. minimum is l h 55 m ; for the P. M. maximum it is 2 h 30 m , 

 and for the secondary afternoon minimum between 3 and 4 hours. In all cases, the 

 earlier hours occur in the summer season. 



Table IX. shows the diurnal range, expressed hi scale divisions, parts of the 

 horizontal force and in absolute measure. In the second column the range between 

 the A. M. maximum and minimum is given; in the third column that between the 

 A. M. minimum and the P. M. maximum. These two amplitudes for A. M., and 

 for A. M. and P. M., are further illustrated in diagram F, which shows the curve 

 to be double crested, with maxima near the time of the equinoxes, and the greater 

 of these near the autumnal equinox. 



