xliv GENERAL RESULTS OF THE MAKERSTOUN OBSERVATIONS. 
3d, The mean difference, independent of sign, has the following epochs of maximum and minimum. 
Nov. Dee. Jan. Feb. March, April. May, June, July. Aug. Sept. Oct. 
Maximum, +8" pM. + 22 am. +2) pM. 11> p.m. 
Minimum, — 635 a.m. —6> a.m, to 6 p.m. —9) pM. 332 aM. 
Maximum, 10" «a.m. o00 cee seclcasinee cesses bus Pach elvdiciae we 105 a.m. 
Minimum, 3" pom. eae cee ens tee cen ee cee cce see cee cee eee 6h P.M. 
77. The opposition in the epochs of maximum and minimum is even more considerable for the 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 with season, and 
that the law for summer is nearly the reverse of that for winter. In summer, the minimum disturbance occurs 
about 8" p.t., 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, which differs little in value from the principal 
minimum; the law for autumn also differs considerably from that for spring, the least values of the disturbance 
occur in the latter between 6" a.m and 64 p.m., while the greatest values occur in the former between 8" a.m. 
and 4” pw. 
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 :— 
SPEUISy mates jeer GRPALME was GP BIMGy 5 soucnideed eee REMEe cata es af seede 0:00 0b praese see. -see on eaepeee 
Summer, ......... OBrprnc! cae OP ASMP oie Par eR REC EI Aga alo ce voeer OPO OO Sh raes-h spit caste cee eee 
‘Acutumn;: 32 ands 42 arary amdi6) wins, e.2essh cos eee cedcldes Seach s 0:0004 ..... ueies eekk ae 
Variation of the Horizontal Component with reference to the Moon's Hour-Angle.—The following Table 
has been formed from Table XXXI., 1844, p. 391, and Table XXVL., 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. oo 8.44, 1845. Mean. | 1844. 1845, || Mean. 
0-00 0-00 | 0: 5 0-00 | 0-00 0-00 0-00 0-00 
—0066 | —0018 | 2 +0050) +0039 | —0019 | +0014 | —0002 
—0132 | +0131 2 +0163 , +0091 | —0056 | +0147 | +0045 
—0059 | —0107 +0081 || +0049 | —0021 | —0019 | —0020 
— 0046 | —0046 | —0004 || —0016 | —0037 | —0026 | —0031 
+0004 | —0112 | —0182 || —0121 | —0028 | —0143 || —0085 
—0036 | —0021 2} +0029 || +0008 | —0023 | +0003 | —0010 
+0122 | +0029 | +0102 || +0093 | +0104 | +0063 || +0083 
+0099 | +0074 | 5) +0092 || +0124 | +0128 | +0083 | +0105 
—0001 | +0123 | d —0039 || —0005 | +0014 | +0049 || +0031 
+0093 | +0047 | 3 | —0102 | —0078 | +0014 | —0021 || —0003 
+0065 | —0025 2 —0130 || —0128 | —0031 | —0073 || —0052 
—0028 | —0081 | : —0055 || —0056 | —0044 | —0068 || —0056 
0 
5 
) 
5 | 
ty) 
5 
0 
79. The following are 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 may be derived from either with but little 
error in epochs; that result from the last column of the Table is as follows :— 
A maximum of the horizontal component about 1} hours after the inferior transit. 
A minimum 3 hours before the superior transit. 
A maximum .,, 2 hours after the superior transit. 
A minimum 8 hours after the superior transit. 
