Ix 
General Results of the Makeestoun Observations. 
The variations of each of these groups of years exhibit a law which may be thus stated : — The magnetic dip 
is greatest near the eqinoxes, and it is least near the solstices. The variations for the years 1842—5 are perhaps 
least affected by disturbances ; for these years the two maxima have nearly equal values, but the minimum at 
the summer solstice is greater than that at the winter solstice : in the variations for the years 1843-6 the two 
minima have nearly equal values, but the two maxima are unequal, the maximum at the autumnal equinox 
being greatest (See Plate VI.) : and in the variations for the years 1842—7, both, maxima and minima are 
unequal ; the greatest maximum occurring at the autumnal equinox, and the greatest minimum at the summer 
solstice. The same results are to be obtained for the annual period of the horizontal component, the differences 
depending upon the amount of disturbance in the different groups of years. 
123. When we deduce the monthly means of magnetic dip from the observations of the two component mag- 
netometers, made on the days selected as nearly free from irregular disturbance, in the years 1844 and 1845, 
we find the means from all the houi'ly observations in those years greater ( + ) or less ( — ) than the former by the 
following quantities. (See Nos. 57 and 59.) 
.Ian. fcb. March. April. May. June. July. Aug. Sept. Oct. N'ov. Dec. 
+ 0'-i58 + 0'-294 +0'-258 + 0'-196 -0'-037 -0'-026 -0'-032 + 0'-060 +0'-038 4 0-348 +0'-150 +0'-356 
The effect of disturbance on the monthly mean magnetic dip is negative in the three months May to July, 
and is positive in the remaining months. If these means be subtracted from those for the corresponding 
months in Table 56, it \vi\l be found that the annual period from the undisturbed days has the same epochs 
as that from the disturbed days. (See No. 58.) 
124. Annual Variation of the Ranges of the Monthlij Mean Variation of Dip. — The follo^ving are the 
ranges of the mean variation for each month, from four years' observations, as obtained from Table 57. 
.Tan. Feb. March. April. May. June. July. Aug. Sept. Oct. Xov. Dec. 
r-10 0'-72 2'-06 3'-26 3'-82 3'-71 4'-04 3'-88 2'-92 2'-39 l'-46 I'-Ol 
The range of dip was least in February, and in the three months December, January, and February; it was 
greatest in July, and in the months from May to August, the range for June being slightly less than for 
May, July, and August. The following are the i-anges of the mean variation, obtained ft-om the obseiwatious 
on the selected days of 1844 and 1845. 
.Jan. Feb. March. April. May. .June. July. Aug. Sept. Oct. Xov. Dec. 
0'-53 0'-62 l'-85 3''27 3'-25 3'-26 3'-04 3'-23 3'-10 l'-94 l'-38 l'-05 
The range of the nearly undisturbed mean diurnal variation is least in January, and it is nearly constant 
in the months from April to September. (See No. 93.) 
125. Variations of the Daili/ Mean Magnetic Dip ivith reference to the Moon's Age. — The follo-»ving num- 
bers, the means for groups of days from four years' observations, are obtained from the last column of the first 
parts of Tables 28 and 45. 
Moon's Age. 16^ 17'i— 20>i 21'i— 2-i'i 25<i— 28'^ 29>'— 2<i— e^— 9'* lO-i— 13'i 
Variations, + 0'-069 + 0'-147 + 0'-034 - 0'-137 - 0'-123 - 0'-088 + 0'-012 + 0'-085 
Tliese numbers shew that the magnetic dip was greatest immediately after opposition, and that it was least 
immediately before conjunction. 
126. Variations of the Daily Mean Magnetic Dip with reference to the Moon's Declination. — The follow- 
ing numbers, also derived from four years' observations, are obtained from the last columns of Table 28 and 45. 
Day after Moon | 27^— 2-'— .'J'l 6>i— 8'i 9'i— 12'i 13->— lo>i 
farthest North. J 
Variations, - ()'-043 + 0'-003 + 0'-n72 + 0'-0()4 - 0'-051 
It appears therefore, that a minimum of magnetic dip occurred when the moon was farthest north, another 
minimum occurred when it was farthest south, and maxima occurred when the moon was near the equator. 
This law is exactly the same as that for the annual variations. No. 122. 
127. JSlonthlji Variations of the Ra)igc of Dip. — Those and tlio analogous results tor tlio moan difference 
cannot be derived from Tables 29, 30, and 46, 47, but ro<piire the oonvorsion of all tho hourly observations 
Itjd — i9d oQd — 03J — 26* 
- 0'-027 + o'-oni + 0'-038 
