540 MR JOHN ALLAN BROUN ON THE HORIZONTAL FORCE 
vandrum differ little; while they differ little also for Hobarton and Singapore ; 
but the sum for the two former exceeds that for the two latter nearly in the ratio 
of 13 to 10. If we could assume that the differences shown in these sums are due 
to the different effect of disturbance, we should arrive at the curious result, that 
the effect is the same at Singapore on the equator and at Hobarton in 43° south 
latitude; while the difference between Trevandrum (in 8}° N.) and Makerstoun 
(in 553° N.) is also not so great as between Trevandrum and Singapore. It must 
be remembered, however, that 1844 and 1845 were years of minimum distur- 
bance, and therefore not the best fitted for this determination. 
72. It follows from these sums, that the amount of movement is wholly inde- 
pendent of the value of the magnetic inclination, since that is nearly the same at 
Hobarton and Makerstoun, and nearly zero at Trevandrum. 
73. Since the disturbance appears to affect the movements of the mean hori- 
zontal force more at Makerstoun than at the other places, we should expect that 
those months containing the greatest amount of disturbance would show the 
greatest difference in the ratio of the amounts of movement at Makerstoun, and 
at the more southern stations. The following table contains the sums of the 
positive and negative differences of daily means, from January 1, 1844, to 
December 28, 1845, for each period of four weeks :— 
TABLE XXII.—SuMs OF THE POSITIVE AND NEGATIVE DIFFERENCES OF THE SUCCESSIVE 
DAILY MEANS OF HORIZONTAL FORCE, IN FOURTEEN HUNDRED-THOUSANDTHS OF THE 
WHOLE HorRIZONTAL FORCE AT MAKERSTOUN, TREVANDRUM, SINGAPORE, AND HOBAR- 
TON, RESPECTIVELY. (1:00=0-00014 X.) 

1844. 1845. 1844-45, 
©. ¢ d s ~ iS] g 
Four WEEKS. 8 A 3 A, Four WEEKS. 3 FI 3 ey Z I $ a 
=) 3 8 S = oS 5 3 = Ss 5 3 
a 8 = a= 4 5 By = 2 5 = = 
oO 3 s 3 o s os a3 oO a s 2 
4 ie on 2 = re op 2 =| Be oo 2 
& x 2 = Ci 2 5 ° 3 2 = ° 
a = R = a a a i a a a | 







Jan. 1toJan. 28, | 28-02 32-35 |26'81 24-05 | Dee. 29 to Jan. 26, |81-95 (57-76 |39'88 [46-52 (109-97 | 90-11 |66-69 |70-57] 
Jan. 28,, Feb. 25, | 60-03 /45-46 [33-23 |27°30 | Jan. 26 ,, Feb. 23, (38°66 [33°69 [32-01 |37-81| 98-69| 79°15 165-24 [65-11 | 
Feb. 25 ,, Mar. 24, | 49:69 |38-60 |29-31 |39-49 | Feb. 23 ,, Mar. 23, |40-46 |26-49 24-19 28-07 | 90-15| 65-09 |53-50 |67-56) 
Mar. 24,, Apr. 21, |103:32 |57-95 50°21 |49-94| Mar. 23 ,, Apr. 20, |66-52 |41-06 |35°35 [37-49 [169-84 | 99-01 |85-56 [87-43] 
Apr.21,, May 19, | 55°13 /44-32 |37-48|37-71 | Apr. 20 ,, May 18, |36-78 [43-66 |31-85 [30:92 | 91-91| 87-98 |69:33 6363 
May 19, June 16, | 36°84 32°34 [26-95 |25-46 | May 18 ,, June 15, |37-83 /32-79 |22-65 31-69 | 74-67 | 65°13 |49-60 |57-15] 
June16 ,, July 14, | 38-41 [39:23 |30-99 |28-49 | June15 ,, July 13, |29-52 |31-55 25-48 /17-91| 67-93 | 70°78 |56-47 46-40) 
July 14,, Aug. 11, | 60°15 |53-71 [42-01 |37-30| July 13 ,, Aug. 10, |46-66 /45-70 [34-81 [38:31 |106-81 | 99-41 \76°82 |75:61| 
Aug.11,, Sept. 8, | 30°10 |36-17 |36-11 |32-'74| Aug.10,, Sept. 7, [51:97 |45-77 |36-55 |43-07 | 82:07 | 81-94 172-66 75-81! 
Sept. 8,, Oct. 6, | 54°70 /54:02 46-57 [52:91 | Sept. 7 ,, Oct. 5, [45-71 |60-77 |43-79 [39-60 [100-41 [114-79 |90-36 [92-51] 
Oct. 6,, Nov. 3, | 51°56 |4598 [31-26 [42:21 | Oct. 5,, Nov. 2, 170-39 |53-68 [46-74 [41:32 [121-95 | 99-66 |78-00 |83:53)_ 
Nov. 3,, Dec. 1, | 65-41 [62-78 [52-65 |50°02| Nov. 2,, Nov. 30, |53-79 |56:86 |38-89 [38-62 [119-20 |119-64 |91-54 |8S:64) 
Dec. 1,, Dec. 29, | 45°63 [42-85 [38:47 |28-97 | Nov. 30 ,, Dec. 28, |57-06 |65-29 |52-28 |44-52 |102°69 [108-14 |90-75 |73:49) 


















74. The law of the annual period will be shown better from a larger series; 
but as far as these go, all show the greatest amount of movement in the four 
weeks March 23 to April 20, and in the four weeks September 7 to October 5, or 
