536 MR JOHN ALLAN BROUN ON THE HORIZONTAL FORCE 
in the two months; that is to say, if six deflections were made in February and 
six in March 1848, the change, February to March, had a value of twelve.* 
58. The following are the changes with their values :— 
TABLE XVIII.—Montuty CHANGES OF HorIZzONTAL FORCE aT HOBARTON, FROM 
OBSERVATIONS OF ABSOLUTE INTENSITY, 1846-50. 

MONTHS. : : ; ; 5 Resulting 
















Value.| Change. |Value.| Change. /Value.| Change. | Value.| Change, | Value.| Change. iw 
Jan. to Feb, . 3 |+-0144) 3 |-—-0033|] 12 | + -0034 18 |+-0003/ 18 |—-0053 | —-0005 
Feb. ,, Mar., 3 |--0133| 3 |—-0044| 12 |—-0043}) 16 |—-0020! 16 |—-0016 | —-0032 
Mar. ,, April, 3 |-—-0019| 9 |—-0022| 12 —-0022] 16 |+-0006/} 18 |+-0013 | —-0013 
Apr. ,, May, 3 |+-0004| 12 0000} 12 |+-0018] 18 |—-0016| 16 |+-0004 0000 
May ,, June, . 3 |—-0046| 12 |+-0007} 12 |—-0009; 18 |+-0003| 14 |+-0012)|+-0001 
June, July, . 3 |+-0045/ 12 |—-0002) 12 |—-0025/ 16 |+-0017| 18 |+-0032);+4+-0011 
July ,, Aug:, 3 |—-0008/ 12 |+-0010; 12 |+-0025} 18 |—-0022} 18 |—-0036| —-0016 
Aug. ,, Sept., 3 |—-0003) 12 |—-0014} 12 ,+-0048] 18 |—-0004| 16 |+-0023 | +-0012 
Sept. 3) Oct; 3 |+-0014| 12 |—-0001|) 12 |—-0051} 18 |+-0013} 18 |—-0025| —-0013 
Oct. ,, Nov. 3 {+-0002| 12 |—-0004| 16 |+-0012; 18 |+-0002| 18 |+-0013| +-0006 
Nov ,, Dec., 3 |4+-0006; 12 |+-0018) 18 |+-0029) 16 |+-0005; 18 |+-0010 rage a 

59. Considering the value for January as ‘0040, we obtain the following vari- 
ations: — 
TABLE XIX.—MontTHLY VARIATIONS DEDUCED FROM TABLE XVIII. 



MonrTH. Mean. Month. Mean. 
January, . : : -0040 July, . ? : 3 -0028 
February, : ( 0035 August, ; : E ‘0012 
March, : A : 0003 September, : 4 0024 
April, : : : ‘0000 October, . : - 0011 
May, . : . : 0001 November, . : : 0017 
June, . $ : - 0012 December, . : 4 0032 

General SaBineE finds the secular change (giving the month’s equal values) for 
twelve months =—-0006. The yearly means (excepting that for 1846, which 
depends on only twelve observations) would give about +-0004. So that in any 
case we may neglect the secular change as small. 
60. Treating the preceding quantities for the equation of sines, we obtain— 
X=4'5025 + 0:0011 sin (6+ 133°) + 0:0018 sin (20+83°);  . : : (11.) 
* This is the same as if each whole observation had a value, since each complete observation 
was made up of two deflections, excepting in 1846, and January to March 1847, when three deflec- 
tions were made to complete the observation. 

