OF THE EARTH’S MAGNETISM. 539 
Makerstoun ; at the other places, a diminution of force was then experienced. 
Considering that the disturbances affect the dip as well as the intensity, the 
rarity of this opposition is not a little extraordinary. Some of the differences to 
be found on careful comparison, are probably due to accidental causes; such as 
spiders (of which Trevandrum, February 18 to 23, 1844, is probably an example). 
69. The amounts of movement also do not appear much different. When we 
take the differences from day to day, for each of the two years, subtracting the 
difference of the first daily mean of each year from the last of the corresponding 
year, to eliminate the effects of secular change, we obtain the amounts of move- 
ment at the respective places, as follows :— 
TABLE XX.—Soums oF PosiItTIVE AND NEGATIVE DIFFERENCES OF SUCCESSIVE DAILY 
MEANS OF HoriIzonvTAL Force. (1:00=0:00014 X.) 

STATIONS. 1844. 1845. Lena ge ueno mately 
Makerstoun, . ; 4 664:44 644-00 130800 1-42 
Trevandrum, . é : 578-66 576-12 1154-78 1-25 
Singapore, . : 78:44 448-62 927-06 1:01 
Hobarton, F , : 466°96 45366 920-62 1:00 

70. The differences of amounts has evidently no relation to the value of the 
horizontal force at each place, since Trevandrum and Singapore have each X=7:9 
nearly, whereas at Hobarton the value is only 45, and at Makerstoun 3-4. It 
would be easy to show that the inequality of the movements is chiefly due to 
large disturbances; for if we omit the differences due to only three daily means, 
namely, those for March 29, 1844, January 9, and April 13, 1845, we obtain the 
following differences of movements :— 
TABLE XXI.—Soums or TABLE XX. DIMINISHED BY OMITTING THREE LARGE 
DISTURBANCES. 
STATIONS. 1844, 1845, 1844-45, aa seen aed 
Makerstoun, . , ; 610-22 574:36 1184'58 1:33 
Trevandrum, . é 3 570:42 593'°13 1123°25 1°26 
Singapore, i * 4 469-42 429:58 899-00 1:01 
Hobarton, i P ; 452-23 435:°48 887:71 1:00 

71. It thus appears, that the sums of the differences for Makerstoun and Tre- 
VOL. XXII. PART III. 62 
