ToraL Magnetic Force. 251 
VARIATIONS OF MaGnetic DIP, WITH REFERENCE TO THE Moon’s DISTANCE FROM THE EARTH.’ 
Means of Groups. 
6 days after Apogee to 6 days before Perigee, 0’-119 6 days after Perigee to 6 days before Apogee, 0-197 
5 days to 2 days before Perigee, . : 0'-297 5 days to 2 days before Apogee, . 0°176 
1 day before to 1 day after Perigee, : 0"201 1 day before to 1 day after Apogee, : 0°125 
2 days to 5 days after Perigee, ; 0°163 2 days to 5 days after Apogee, : F 0162 
TOTAL MAGNETIC FORCE. 
The following results are deduced from the variations of the horizontal and vertical components by means 
of the formula 
AU Bey, AW, = ( DONG BAX 
— cos 76 ) 
(Rie EY he i XC 
where a is the quantity in the following tables, — and * the quantities in the tables for the vertical and 
horizontal components respectively, and 6 the magnetic dip = 71° 18. 
SECULAR CHANGE OF THE TOTAL MAGNETIC ForRCE. 
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 1848, = 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 
foree (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. July. Aug. Sept. Oct. Nov. Dee. 
0-000 | 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 equinozes. 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 XI. and XVIII. 
Period. 
January 
February 
March 
April 
May 
June 
July 
August 
September 
284 | 205 081 284 
