Total Magnetic Force. 



251 



Variations op Magnetic Dip, with reference to the Moon's Distance prom the Earth. ' 



Means of Groups. 



6 days after Apogee to 6 days before Perigee, 0'-119 

 5 days to 2 days before Perigee, . . 0'-297 



1 day before to 1 day after Perigee, . 0''201 



2 days to 5 days after Perigee, . . 0'-163 



6 days after Perigee to 6 days before Apogee, 0'-197 



5 days to 2 days before Apogee, . . 0'-176 



1 day before to 1 day after Apogee, . 0'-125 



2 days to 5 days after Apogee, . . 0'-162 



Total Magnetic Force. 



The following results are deduced from the variations of the horizontal and vertical components by means 

 of the formula 



A R 



A Y 



— COS 



•0 



/ A Y aX\ 



where -^^- is the quantity in the following tables, . and -=r- the quantities in the tables for the vertical and 

 horizontal components respectively, and 6 the magnetic dip =: 71° 18'. 



Secular Change op the Total Magnetic Force. 



From the mean secular changes for the two components of magnetic force, pages 235 and 245, we obtain 

 Mean Secular Change of the Total Force, 1842 to 1843, = 0-001587. 



Annual Period of the Total Magnetic Force. 



From the quantities, pages 231 and 241, exhibiting the annual periods of the two components of magnetic 

 force (the secular change being eliminated), the following quantities have been obtained, which shew the varia- 

 tions of the total magnetic force for the different months of the year. 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



Jiily. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



0-000 1 406 



358 



127 



000 



036 



257 



248 



227 



058 



156 



313 



395 



These quantities indicate maxima of the total force about the periods of the solstices, and minima about the 

 periods of the equinoxes. One minimum occurs after the vernal euqinox, and the maximum at the winter solstice 

 is greater than that at the summer solstice. 



TABLE XXV. — ^Diurnal Variations of the Total Force of the Earth's Magnetism, deduced from 



Tables XL and XVIII. 



Period. 



ISi-. 



20". 



221'. 



23i>. 



01". 



2i>. 



41". 



eh. 



8h. 



lOi". 



Range. 





0-000 



0-000 



0-000 



0-000 



0-000 



0-000 



•000 



0-000 



0-000 



0-000 



0-000 



January 



000 



052 



032 





058 



114 



121 



150 



159 



144 



159 



February 



000 



078 



031 





025 



069 



152 



194 



219 



156 



219 



March 



063 



107 



063 





000 



071 



187 



304 



325 



206 



325 



April 



034 



076 



045 





000 



117 



340 



658 



494 



250 



658 



May 



151 



168 



085 





000 



119 



296 



434 



471 



182 



471 



June 



144 



171 



070 





000 



074 



247 



385 



411 



309 



411 



July 



057 



105 



041 





000 



155 



379 



450 



455 



271 



455 



August 



095 



136 



082 





000 



194 



339 



459 



417 



288 



459 



September 



000 



089 



048 





006 , 



150 



278 



284 



205 



081 



284 



