XXX1l GENERAL 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, 
By the observations for the absolute force (Table 21), 
+ 0:00446 
+ 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 nearly free from disturbance, 
In 1844, is greater than that deduced from all the hourly observations of the year by 0-000189. 
Damn BD ccsstepereraasc interstate sof sia\niats elaiorernicate sorte ote oicteia Ye etetetaLaatede a eTat's ssn jn(nln olseib ab iomclesaie(acriefoir=tantare 0-000154. 
The effect of disturbance in both years was to diminish the mean value of the horizontal component on the 
average by 0000172 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, namely 
0-000251 for that year. 
TABLE 24.—Monthly Variations of the Horizontal Component of Magnetic Force, free from 
Regular Secular Change. 
| 
| | 1846 
Month. | 1842. . | 1845. | 1846. to 
| 1849. 
3 
Prefix. 0-000 | 0:000 leant |] 0° 0-000 
January || + 100 |+114 | +213 
February | —015 +091 | + 204 | 
March +092 5 — 027 \|+128 
April | — 386 —218 |+014 
May | +377 +139 |+262 
June +381 +351 +002 
July +019 | [+185 |-+257 
August | 189 |—073 |—408 
September — 221 —495 |—677 
October — 083 | — 205 |—544 | 
November | —163 +092 | +023 
December | +094 +043 |-+523 
| | 
55. Annual Period of the Horizontal Component.—Vable 24 has been formed in the same manner as Table 3 
(see p. xiii.) The secular changes employed in the reduction for each year, obtained in the same manner as for 
the magnetic declination in 1847-8 (No. 8), are as follow :— 
1842. 1843. 1844. 1845, 1846. 1847. 1848. 1849. 
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 probably to 
be most depended on for an accurate exhibition of the mean annual law, the means for 1848 and 1849 being 
deduced from too few observations. The mean for the six years 1842 to 1847 shews, that the horizontal 
component at Makerstoun was a maximum at the summer solstice, and also at the winter solstice ; that it was 
a minimum shortly after the autumnal, and shortly after the vernal equinor.* This result is shewn with 
* This law, as deduced from the Makerstoun 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 by the observations 
made in the successive years at Makerstoun, and, as has been shewn in the Makerstoun Observations for 1844 (foot-note p. 357), by Dr 
