liv 



General Results of the Makeestoun Observations. 



the latter occurring about 7^ a.m., which is nearly the epoch of a maximum in the other months : in the months 

 from March to September the diurnal curve is double, the maxima having nearly the same value in each 

 month, and the minima also being nearly equal ; the form of the diurnal curve from March to September is 

 nearly constant ; in October the morning maximum becomes less marked, and it wholly disappears in Novem- 

 ber. In June the minima occur almost exactly at apparent midnight and noon, that at the latter time being 

 on the whole best marked ; the maxima occur when the sun is near the prime vertical. 



102. Diurnal Variation of the Efcct of Disturbance on the Mean Vertical Component. — The following 

 Table contains the mean effect of disturbance upon the hourly means in each group of months, the assumption 

 being made that the effects of disturbance upon the means of the groups of months are zero ; it will be seen 

 from Nos. 89 and 85 that the means of the days selected as free from disturbance, are rather greater 

 than the means for all the days ; while this difference may be partially due to regular laws, it is also so small, 

 compared with the actual differences in the following Table, that the epochs for the zero of effect would 

 be little altered if it were taken into account. It will be seen also that the epochs for each group vary little, 

 though the effect of disturbance, as found No. 89, differs considerably in the different groups ; thus, for the 

 group December to February, the mean for all the selected days is 0"000005 greater than the mean for all the 

 (lays, while the mean of the selected days in March and April is 0-000061 less than the mean for all. 



Table 51. — Differences of Disturbed and Undisturbed Diurnal Variations of the Vertical Com- 

 ponent of Magnetic Force, as deduced from Tables 49 and 50, exhibiting the effect of Irregular 

 Disturbance on the Hourly Mean Positions. 



Mak. 

 Mean 



Dec. 

 Jan. 









c;„„4. 



Six Months. 





March. 



May. 



July. 



Jsept. 

 Oct. 



Sept. 



March 



Twelve 



Time. 



Feb. 



April. 



June. 



Aug. 



Nov. 



to 

 Feb. 



to 

 Aug. 



Months. 



li. m. 



0-00 



0-00 



0-00 



0-00 



(MO 



000 



0-00 



0-00 



12 13 



-0057 



-0205 



-0080 



-0127 



-0122 



-0090 



-0137 



-0114 



13 13 



-0052 



-0183 



-0121 



-0137 



-0141 



-0096 



-0147 



-0123 



14 13 



-0073 



-0217 



-0139 



-0162 



-0144 



-0108 



-0173 



-0141 



15 13 



-0067 



-0185 



-0149 



-0163 



-0153 



-OHO 



-0166 



-0138 



16 13 



-0059 



-0152 



-0124 



-0151 



-0150 



-0105 



-0142 



-0124 



17 13 



-0055 



-0119 



-0107 



-0141 



-0120 i 



-0087 



-0122 



-0105 



18 13 



-0038 



-0088 



-0066 



-0119 



-0080 



-0059 



-0091 



-0075 



19 13 



-0022 



-0056 



-0037 



-0077 



-0044 



-0033 



-0056 



-0046 



20 13 



-0021 



-0031 



-0020 



-0034 



-0023 



-0022 



-0028 



-0026 



21 13 



-0011 



-0018 



+ 0001 



-0008 



+ 0001 



-0005 



-0008 



-0007 



22 13 



-0010 



-0001 



+ 0014 



0000 



+ 0023 



+ 0006 



+ 0004 



+ 0004 



23 13 



+ 0001 



+ 0033 



+ 0026 



+ 0010 



+ 0035 



+ 0018 



+ 0023 



+ 0021 



13 



+ 0006 



+ 0073 



+ 0032 



+ 0034 



+ 0082 



+ 0043 



+ 0046 



+ 0045 



1 13 



+ 0014 



+ 0076 



+ 0031 



+ 0064 



+ 0090 



+ 0052 



+ 0057 



+ 0054 



2 13 



+ 0024 



+ 0110 



+ 0042 



+ 0093 



+ 0098 



+ 0061 



+ 0082 



+ 0072 



3 13 



+ 0051 



+ 0148 



+ 0082 



+ 0132 



+ 0141 



+ 0096 



+ 0121 



+ 0108 



4 13 



+ 0062 



+ 0157 



+ 0101 



+ 0164 



+ 0157 



+ 0110 



+ 0141 



+ 0125 



5 13 



+ 0094 



+ 0235 



+ 0123 



+ 0196 



+ 0163 



+ 0129 



+ 0185 



+ 0157 



6 13 



+ 0109 



+ 0247 



+ 0128 



+ 0206 



+ 0163 



+ 0136 



+ 0194 



+ 0165 



7 13 



+ 0096 



+ 0204 



+ 0126 



+ 0190 



+ 0119 



+ 0107 



+ 0173 



: +0141 



8 13 



+ 0068 



+ 0117 



+ 0095 



+ 0123 



+ 0043 



+ 0055 



+ 0112 



+ 0084 



9 13 



+ 0022 



+ 0008 



+ 0047 



+ 0023 



-0015 



+ 0003 



+ 0026 



+ 0015 



10 13 



-0019 



-0079 



+ 0011 



-0019 



-0058 



-0039 



-0029 



' -0034 



11 13 



-0050 



-0075 



-0016 



-0088 



-0076 



-0063 



-0060 



; -0062 



103. The following are the conclusions from Table 51. 



\st, The greatest effect of disturbance in increasing the vertical component occurs 



In 

 About 



Dec. Jan. Feb. 



Q^ 15°^ P.M. 



March, April. 

 Q^ Qm P.M. 



May, .June. 



Q^ 30^ P.M. 



July, Aug. 



Q^ 0^ P.M. 



.Sept. Oct. Nov. 



5*' 30«» P.M. 



