yi the Horizontal Component of Magnetic Force. 375 

 Tablk No. II. 



184U-44. 



w 



Nov. 

 Dec. 



Normal. 

 676-3- 



76M 







si? 



To obtain the regular solar diurnal variation for each month 

 and season of the year, we subtract the numbers in table I. from 

 their respective monthly and season and yearly mean values 

 given in table 11. After converting these numbers into parts 

 of the absolute horizontal force, table No. III. of the memoir 

 shows the results, the significant numbers being expressed in 

 units of the sixth place of decimals and the sign + indicating a 

 value greater than the mean, and the sign - one less than the 

 niean. Three decimals 0*000 are placed at the side of the table. 

 This table is omitted in the present abstract. 



Table No. IV. shows the results obtained in table III, con- 

 verted into absolute measure by multiplying by 4 176 the abso- 

 lute horizontal force. Two places of decimals O'OO are placed 

 ^^ the side of the table and are to be understood as preced- 

 ing each number. 



The annual inequality in the daily variation of horizontal 

 force as derived from table No. IV, is shown in diagram A. 

 The annual mean shows a maximum value about 6 A. M., a mini- 

 ^'iin about 11 a. M., a secondary maximum about 3^ P. M. and a 

 secondary minimum about 9 P. M. The maximum at 6 a. m. 

 ;s stationary throughout the year. The morning minimum is 

 lower during the summer when the sun's declination is north, 

 ^nd the afternoon maximum is higher, thus increasing the daily 

 range. The converse takes place in winter. The average sum- 

 Qier range is 00046, and the average winter range 00025. The 

 average range between the morning maximum and the morning 

 »>ini.num in summer is 0-0045 and in winter 0-0036. 



The half yearlv change is better represented in the annexed 

 diagram (B) derived from (A) by straightening out the annual 

 *urve and usino- it as an axis of abscissa, upon which to lay off 

 the differences between the values of the same hours for the 

 year, and for the summer and winter. The comparison of this 

 <iiagram with the corresponding one in Part II. tor the annual 

 change in the diurnal variation of the declination is of consid- 

 erable interest. . , „, 



At 6 A. M. there is scarcely any change during the year. The 

 Maximum change occurs about 9 A. M., the range being about 



