Ixviii 



General Results of the Makerstoun Observations. 



m 



In the disturbed diumal variation of total magnetic force, the principal maximum occurred latest in the 

 quarter December to February, and earliest in the quarter September to November : the epoch of the 

 after-midnight minimum varied little, being slightly nearer midnight in May and June than in the other 

 groups ; the secondary maximum occurred earliest in May and June, and latest in September to November ; 

 and the forenoon minimum occurred earliest in the quarter December to February, and latest in May and June. 

 In May and June, therefore, the one minimum occurred nearest noon, the other nearest midnight. (See 

 the Continuous Curves, Plate V.) 



Table 64. — Diurnal Variations of the Total Magnetic Force for Different Periods, deduced from 

 Days selected as free from Irregular Disturbances, in the Years 1844 and 1845. 



Mak. 

 Mean 

 Time. 



Dec. 

 Jan. 

 Feb. 



March. 

 April. 



May. 

 June. 



July. 

 Aug. 



Sept. 

 Oct. 

 Nov. 



Six Months. 



Twelve 

 Months. 



Sept. to 

 Feb. 



March 



to Aug. 



h: m. 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



000 



0-00 



12 13 



-0016 



-0029 



-0031 



-0032 



-0051 



-0033 



-0031 



-0034 



13 13 



-0037 



-0043 



-0039 



-0047 



-0059 



-0048 



-0043 



-0045 



14 13 



-0041 



-0027 



-0034 



-0049 



-0049 



-0045 



-0037 



-0040 



15 13 



-0038 



-0023 



-0014 



-0027 



-0042 



-0040 



-0021 



-0030 



16 13 



-0031 



-0025 



+ 0011 



+ 0003 



-0032 



-0031 



-0004 



-0018 



17 13 



-0022 



-0004 



+ 0021 



+ 0010 



-0022 



-0022 



+ 0009 



-0007 



18 13 



-0022 



+ 0010 



+ 0012 



+ 0009 



-0023 



-0022 



+ 0010 



-0006 



19 13 



-0023 



+ 0009 



-0016 



-0030 



-0024 



-0023 



-0012 



-0018 



20 13 



-0025 



-0019 



-0077 



-0103 



-0063 



-0044 



-0066 



-0055 



21 13 



-0045 



-0080 



-0162 



-0169 



-0107 



-0076 



-0137 



-0106 



22 13 



-0061 



-0151 



-0229 



-0204 



-0146 



-0103 



-0195 



-0149 



23 13 



-0056 



-0182 



-0251 



-0218 



-0125 



-0090 



-0217 



-0154 



13 



-0028 



-0181 



-0200 



-0176 



-0089 



-0058 



-0186 



-0122 



1 13 



+ 0017 



-0100 



-0105 



-0084 



-0002 



+ 0007 



-0096 



-0044 



2 13 



+ 0053 



-0005 



-0024 



+ 0013 



+ 0075 



+ 0064 



-0005 



+ 0029 



3 13 



+ 0071 



+ 0069 



+ 0064 



+ 0108 



+ 0126 



+ 0098 



+ 0080 



+ 0089 



4 13 



+ 0075 



+ 0113 



+ 0139 



+ 0157 



+ 0152 



+ 0113 



+ 0136 



+ 0125 



5 13 



+ 0069 



+ 0143 



+ 0201 



+ 0196 



+ 0140 



+ 0104 



+ 0180 



+ 0142 



6 13 



+ 0059 



+ 0145 



+ 0215 



+ 0197 



+ 0126 



+ 0092 



+ 0186 



+ 0139 



7 13 



+ 0048 



+ 0137 



+ 0199 



+ 0176 



+ 0103 



+ 0075 



+ 0171 



+ 0123 



8 13 



+ 0039 



+ 0105 



+ 0160 



+ 0145 



+ 0086 



+ 0062 



+ 0137 



+ 0099 



9 13 



+ 0032 



+ 0080 



+ 0106 



+ 0086 



+ 0051 



+ 0041 



+ 0091 



+ 0066 



10 13 



+ 0016 



+ 0050 



+ 0045 



+ 0042 



+ 0016' 



+ 0016 



+ 0046 



+ 0030 



11 13 



-0014 



+ 0008 



0000 



-0004 



-0036 



-0025 



+ 0001 



-0012 



144. When we consider the diumal variation, as deduced from days selected as nearly free from intermit- 

 tent disturbance, and as exhibited in Table 64, and in the dotted curves, Plate V., we find the approximate epochs 

 in apparent time as follow : — 



Maximum, 

 Minimum, 

 Maximum, 

 Minimum, 



Dec. Jan. Feb. 



4"^ 0™ P.M. 



Ih 40m A.M. 



5^ 35m A.M. 

 10** 35m A.M. 



March, April. 

 + 5'' 40m p,M. 



Ih IQmA.M. 



6'' 45m A.M. 

 _llh 45m A.M. 



+ 



May, June. 



6^ Qm P.M. 



1^ 30m A.M. 



b^ 15™ A.M. 



- lO*" 55m A.M. 



July, Aug. 

 + 5^ 35m P.M. 



l^* 40m A.M. 



5^ 35m A.M. 

 — 101» 55m A.M. 



Sept. Oct. Nor. 

 + 4'' 15m P.M. 



l*" 25m A.M. 



6*> 20m A.M. 

 -lOh 30'° A.M. 



The undisturbed diurnal variation of the total magnetic force differs considerably from that affected by dis- 

 turbances, as may be seen at a glance in Plate V. ; the whole variations of the epochs of maxima and minima, 

 with season, are different from those obtained, No. 143. In each group of months, the forenoon minimum is 

 the principal, and the after-midnight minimum is quite secondary. The principal maximum occurs earliest in 

 winter, about 4'' p.m., and latest in May and June, about 6*^ p.m. ; the principal minimum occurs earliest 

 in the six months, September to February, and latest in March and April : the secondary maximum occurs 

 nearest noon, and the secondary minimum nearest midnight, in the equinoctial months. 



