xxxii 
Geneeal Results of the Makerstoun Observations. 
53. The mean yearly secular change of the horizontal force in absolute measure, 
By the observations of the bifilar magnetometer, = + 0-00446 
By the observations for the absolute force (Table 21), = + 0-00388 
Such a near agreement is, perhaps, more than could have been expected : if the observations with the small 
deflecting bar were neglected (No. 49), the agreement would be even greater. 
54. It has been shewn, No. 38, that when we deduce the yearly mean declination from the days which were 
selected as little affected by intermittent disturbances, the result is almost precisely the same as that deduced 
from the whole ordinary observations, and therefore from the days disturbed ; a similar comparison being made 
for the horizontal component, we find as follows : — 
The yearly mean of the horizontal component, as deduced from the 120 days selected as nearlyfree from disturbance, 
In 1844, is gTeater than that deduced from all the hourly observations of the year by 0'000189. 
In 1845, ' ."..0-000154. 
The effect of disturbance in both years was to diminish the mean value of the horizontal component on the 
average by 0-000172 of the whole component. It was found for 1844 (see the volume for that year, p. 365) 
that a more careful selection of 60 days (5 in each month) shewed even a greater effect of disturbance, namtlv 
0-000251 for that year. 
Table 24. — Monthly Variations of the Horizontal Component of Magnetic Force, free ft-om 
Regular Secular Change. 
Month. 
1842. 
1843. 
1844. 
1845. 
1846. 
1847. 
1848. 
1849. 
i 
1842 
to 
1845. 
1846 
to 
1849. 
1842 
to 
1849. 
1842 
to 
1847. 
Pvefix. 
0-000 
0-000 
0-000 
0-000 
0-000 
0-00 
0-000 
0-00 
0-000 
0-000 
0-000 
0-ono 
January 
-t-100 
+ 470 
+ 050 
+ 114 
+ 213 
+ 0409 
-219 
-0339 
+ 183 
+ 016 
+ 100 
+ 339 
February 
-015 
+ 232 
-003 
+ 091 
+ 204 
-0007 
-500 
-0271 
+ 076 
-143 
-034 
+ 1-25 
March 
+ 092 
-327 
-422 
-027 
+ 128 
+ 0162 
-210 
-0413 ; 
-171 
-084 
-127 
-098 
April 
-386 
-468 
-342 
-218 
+ 014 
+ 0023 
+ 007 
-0141 ■ 
-353 
-024 
-189 
-344 
May 
i + 377 
+ 224 
+ 126 
+ 139 
+ 262 
-0021 
+ 530 
+ 0462 
+ 216 
+ 308 
+ 262 
+ 277 
June 
+ 381 
+ 371 
-1-637 
+ 351 
+ 002 
+ 0619 
+ 667 
+ 1207 
+ 435 
+ 624 
+ 530 
+ 590 
July 
+ 019 
-075 
+ 561 
+ 185 
+ 257 
+ 0246 
+ 531 
+ 0667 
+ 172 
+ 425 
+ 299 
+ 298 
August 
- 189 
-239 
+ 118 
-073 
-408 
+ 0052 
+ 217 
+ 0070 
-096 
-017 
-056 
- 185 
September 
-221 
-271 
- 133 
-495 
-677 
-0171 
-472 
-0364 
-280 
-421 
-350 
-492 
October 
-083 
-356 
-384 
-205 
-544 
- 1111 
+ 081 
-0631 
-257 
-551 
-404 
-671 
1 November 
- 163 
+ 132 
-223 
+ 092 
+ 023 
-0572 
-245 
-0356 
-041 
-287 
- 164 
- 178 
j December 
+ 094 
+ 301 
+ 014 
+ 043 
+ 523 
+ 0371 
-389 
+ 0109 
+ 113 
+ 153 
+ 133 
+ 336 
55. Annual Fcnocl of the Horizontal Component. — Table 24 has been formed in the same manner as Table 3 | 
(see ]). xiii.) The secular changes employed in the reduction for each year, obtained in the same manner a* for i 
tlie magnetic declination in 1847-8 (No. 8), are as follow : — . j 
I 
1842. 1843. 1844. 1845. 1846. 1^47. 1848. It^i?. j 
Yearly increase, 0-003480 0-003804 0-002820 0-001116 0-001368 0-000768 0-001500 0-001920 
56. The mean result for the six years 1842 to 1847, given in the last column of Table 24. is prokibly to 
he most depended on for an accurate exhibition of the mean annual law, the means for 1848 and 1849 hem^ 
deduced from too few observations. The mean for the six years 1842 to 1847 shews, that the /torhoHtai 
coiapoii.ent at Makergtoim was a maximum at the .niminer solstice, and etli>o at the winter solstice ; that it wnf 
a niiniiimm shorth/ after the avtumnal, and shortly after the vernal equinox.* This result is shewn with 
* Tliis law, ns deducctl fi-oin the Jliiker.stoun Observations for 1842, was stated to the Physical Section of the British Association 
in June 1845, confirmed by a rediscussion of observations made at Toronto in 1842 : it has since been confirmed bv the observ.itions 
made in tlio successive years at Malierstoun, and, as has been shewn in the Makerstoun Observations for 1844 i^fvwt-note p. 357"! by l^r 
