OF THE EARTH’S MAGNETISM. 523 
24. It ought to be remarked, that the part of the secular variation which is 
due to the movement of the poles of force will depend not only on the amount of 
that movement and its direction, but also on the angle which the isodynamic 
lines make at the place with the direction of motion of the poles. 
TABLE X.—Montuiy MEAN VALUES OF HORIZONTAL FORCE (minus A CONSTANT) AT 


















x 
SINGAPORE, 1842-45, 1 00 = 70000 
Monthly Means. (Monthly minus Yearly Means) plus 5:00. 
MONTHS. 
1842. 1843. 1844. 1845. 1842. 1843. 1844. 1845. | Means. 
January, : : 5:63} 21°36] 23:91} 30:03; 10:09; 11-45] 6:58 | 3-88 | 8-00 
February, . ‘ 4:09 | 17:32| 24:47] 33:42) 7:34] 6-61] 6-24 | 653 | 668 
March, : : 5:40| 15:°57| 22°58) 33:66| 7:44) 4:26] 3-58 | 6:00 | 5:32 
April, A ‘ 3'°32| 14:24] 22-29] 33:04; 3:10| 2:38} 2°55 | 4:51 | 3:13 
May, . , ; 7:94| 14:21) 24-70| 34:06] 6:14] 1:81) 4:46 | 4:55 | 4:24 
June, . : b 7:76! 16°60} 28:10} 37:10} 4:63) 3-79] 7:27 | 6-79 | 5-62 
July, . 5 A 5°73) e700)! 28°97) 37-3 1:06| 3-94) 7:51 | 6:20 | 4-68 
August, : : 9:65| 17-46| 26:94] 36-61| 3-77) 4:02] 4:86 | 4:70 | 4:34 
September, . : 10°74) 17:20) 27°20) 36:06) 3°88) 3:21) 4:28 | 3:35 | 3°68 
October, : : 13:37 | 19:94| 26°67] 38:36} 5:-64| 5:27] 2°84 | 4:85 | 4:65 
November, . A 15°48} 22:16| 27°76| 39:59| 7:03) 6-79] 3-09 5:28 | 5:55 
December, . } 19:12| 22-13) 30°79] 88:15| 10:04| 5:78] 5:37 | 3:04 | 6:06 



25. SINGAPORE.—The movement is a gradual and slight increase of force from 
the commencement to the end of 1845, being most rapid in the end of 1842, as in 
the other places. Maxima are generally shown near the solstices, and minima 
near the equinoxes. 
26. TrevANDRUM.—The movement resembles on the whole that at Singapore, 
the force diminishing, however, in 1843, and then increasing more slowly than at 
Singapore. The appearances of maxima near the solstices and minima near the 
equinoxes are also evident as at Singapore. 
27. On the whole, the movements at Trevandrum and Singapore confirm each 
other: it must be remembered, however, that the observations at both places have 
undergone several corrections for accidental errors, spiders and movement of tele- 
scope at Trevandrum, and unknown causes, perhaps movement of telescope, at 
Singapore. The means for these two places are therefore not wholly trustworthy ; 
the limits of error are probably small, but there is no doubt that there are several 
errors due to spiders and movement of telescope uncorrected at Trevandrum, and 
probably also at Singapore. 
28. Stm~A.—The movement at Simla for 1842 resembles much that at Singa- 
pore and the Cape, being nearly a mean between the two. ‘The dotted line (Plate 
XXIII.) is a mere approximate correction, the temperatures having been obtained 
VOL. XXII. PART III. 6T 
