xliv 
General Results of the Makeestoun Observations. 
3d, The mean difference, independent of sign, has the following epochs of maximum and minimum. 
Maximum, 
Minimum, 
Maximum, 
Minimum, 
Nov. Dec. Jan. 
+ 8"^ P.M. 
- A.M. 
lO*' A.M. 
3" P.M. 
Feb. March, April. 
+ 2^ A.M. 
— A.M. to 6^ P.M. 
May, .June, July. 
+ 2^ P.M. 
-9^ 
P.M. 
Aug. Sept. Oct. 
Ill' p.j^_ 
311^ A.M. 
10^ A.M. 
P.M. 
77. The opposition in the epochs of maximum and minimum is even more considerable for tlie mean dif- 
ference than for its positive and negative elements. We find, as has already been found for the magnetic 
declination. No. 45, that the diurnal law of disturbance of the horizontal component varies vritb season, and 
that the law for summer is nearly the reverse of that for winter. In summer, the minimum disturbance occurs 
about 8^ P.M., which is the hour of the maximum disturbance in winter ; in summer, the maximum disturbance 
occurs about 3^ p.m., which is the hour of a minimum in winter, w^hich differs little in value from the principal 
minimum ; the law for autumn also difiFers considerably from that for spring, the least values of the disturbance 
occur in the latter between 6^ a.m and 6^ p.m., while the greatest values occur in the former between 8** a.m. 
and 4^ p.m. 
78. Probable Error of Observations of the Horizontal Component. — At Makerstoun, in years of moderate 
disturbance, the probable error of an observation of the horizontal component from the monthly mean for the 
hour of observation has its least values as follow : — 
Winter, between 4^^ a.m. and 4^' p.m., the probable error being less than 0-0004 of the whole component. 
Spring, e'^A.M. ... e^^p.M 0-0005 
Summer, 8'^ p.m. ... 81^ a.m 0-0003 
Autumn, 3^ and 4'' a.m. and e'' p.m 0-0004 
Variation of the Horizontal Component with reference to the Moo7i^s Hour-Angle. — The following Table 
has been formed from Table XXXI., 1844, p. 391, and Table XXVI., p. 15, of the present volume. 
Table 37. — Variations of the Horizontal Component of Magnetic Force with reference to the Moon's 
Hour- Angle for the Winter and Summer Lunations, and for all the Lunations of the Years 1844 
and 1845. 
Moon 's 
Winter Lunations. 
Summer Lunations. 
All the Lunations. 
Hour 
Angle. 
1844. 
1845. 
Mean. 
1844. 
1845. 
Mean. 
1844. 
1845. 
1 
l^Iean. 
h . m. 
0-00 
0-00 
0-00 
0-00 
0-00 
0-00 
0-nn 
0-00 
0-00 
0 0 
-0066 
-0018 
-0042 
+ 0029 
+ 0050 
+ 0039 
-0019 
+ 0014 
-0002 
2 25 
-0132 
+ 0131 
0000 
+ 0021 
+ 0163 
+ 0091 
-0056 
+ 0147 
+ 0045 
4 20 
-0059 
-0107 
-0083 
+ 0018 
+ 0081 
+ 0049 
-0021 
-0019 
-0020 
6 15 
-0046 
-0046 
-0046 
-0028 
-0004 
1 -0016 
-0037 
-0026 
-0031 
8 10 
+ 0004 
-0112 
- 0054 
-0060 
-0182 
-0121 
- 0028 
-0143 
-0085 
10 5 
-0036 
-0021 ' 
-0028 
-0012 
+ 0029 
+ 0008 
-0023 
+ 0003 
-0010 
12 0 
+ 0122 
+ 0029 
+ 0075 
+ 0086 
+ 0102 
+ 0093 
+ 0104 
+ 0063 
+ 0083 
13 55 
+ 0099 
+ 0074 
+ 0086 
+ 0157 
+ 0092 
+ 0124 
+ 0128 
+ 00S3 
+ 0105 
15 50 
-0001 
+ 0123 
+ 0061 
+ 0030 
-0039 
-0005 
+ 0014 
+ 0049 
+ 0031 
17 45 
+ 0093 
+ 0047 
+ 0070 
-0053 
-0102 
-0078 
+ 0014 
-002] 
-0003 
19 40 
+ 0065 
-0025 
+ 0020 
-0126 
-0130 
-0128 
-0031 
-0073 
-0052 
21 35 
-0028 
-0081 
-0054 
-0056 
-0055 
-0056 
-0044 
-0068 
-0056 
79. The following arc the conclusions from Table 37- 
There are four independent results in this Table, two for the winter lunations of 1844 and 1845. and two 
for the summer lunations of the same years ; the other columns are derived from these : of the four results 
three give the same law so nearly, that the result for the two years nuiy be derived from either witli but little 
error in epochs ; that result from the last column of the Table is as follows : — 
A maximum of the horizontal component about \\ hours after the inferior transit. 
A minimum 3 hours before the superior transit. 
A maximum '1 homs after the su]ierior transit. 
A minimum 8 hours after the suiierior transit. 
