Diurnal Variations for the Total Magnetic Force. 



Ixvii 



142. Diurnal Variation of the Total Magnetic Force. — Table 62 has been computed from Tables 31 and 

 48. The following are the approximate epochs of maxima and minima in apparent time, distinguishing those 

 of the principal maximum by + , and of the principal minimum by — . 





.Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 





h. m. 



h. m. 



b. m. 



b. m. 



h. m. 



b. m. 



h. m. 



h. m. 



h. m. 



h. m. 



b. m. 



h. m. 



Max. 



+ 5 35 



+ 50 



+ 55 



+ 5 55 



+ 5 45 



+ 6 30 



+ 5 35 



+ 5 35 



+ 4 55 



+ 3 40 



+ 6 25 



+ 6 20 



Min. 



-14 5 



-14 



-13 45 



-13 



-14 35 



14 15 



14 40 



-14 5 



-13 35 



-16 15 



-12 45 



-14 45 



Max. 



19 5 



19 15 



19 30 



19 



18 40 



18 35 



18 30 



18 35 



18 50 



19 45 



18 50 



19 5 



Min. 



22 



21 55 



22 30 



22 45 



-22 45 



-23 



-22 45 



22 20 



21 35 



22 35 



-22 50 



-22 15 



The principal maximum of the total magnetic force occurs between S** 40"i and 6*^ 30™ p.m. in each 

 month of the year ; it occurs latest in June and November ; it occurs earliest in February and March, of the 

 first six months, and in October and. September of the last six months of the year. The principal minimum 

 occurs near 2^ a.m. in each month, with the exceptions of June and July, in which months it occurs near 11*^ 

 A.M. ; in May, November, and December, the two minima are nearly equal. The secondary maximum occurs 

 between Q^^ and 1^^ a.m., and it is best marked in the months of March, April, and May, August, and Sep- 

 tember. 



Table 63. — Diurnal "Variations of the Total Magnetic Force for Different Periods, deduced from 



Table 62. 





Dec. 











Six Months. 





Mak. 



March. 



May. 



July. 

 Aug. 



Sept. 







Twelve 



Mean 

 Time. 



Jan. 

 Feb. 



April. 



June. 



Oct. 

 Nov. 



Sept. 

 to 



March 



to 



Months. 















Feb. 



Aug. 





h. m. 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



0-00 



12 13 



-0091 



-0236 



-0123 



-0154 



-0180 



-0135 



-0171 



-0154 



13 13 



-0094 



-0249 



-0168 



-0190 



-0192 



-0143 



-0202 



-0173 



14 13 



-0135 



-0288 



-0180 



-0218 



-0198 



-0166 



-0229 



-0198 



15 13 



-0109 



-0207 



-0166 



-0197 



-0182 



-0145 



-0190 



-0168 



16 13 



-0085 



-0180 



-0124 



-0158 



-0169 



-0127 



-0154 



-0141 



17 13 



-0064 



-0125 



-0089 



-0148 



-0132 



-0098 



-0121 



-0110 



18 13 



; -0045 



-0067 



-0059 



-0117 



-0096 



-0070 



-0081 



-0076 



19 13 



-00,37 



-0046 



-0065 



-0120 



-0075 



-0056 



-0077 



- 0067 



20 13 



1 -0041 



-0066 



-0116 



-0160 



-0085 



-0063 



-0114 



-0089 



21 13 



-0061 



-0111 



-0178 



-0202 



-0114 



-0087 



-0164 



-0126 



22 13 



-0075 



-0151 



-0230 



-0223 



-0124 



-0099 



-0201 



-0151 



23 13 



-0050 



-0148 



-0230 



-0219 



-0095 



-0072 



-0199 



-0136 



13 



; -0021 



-0102 



-0163 



-0148 



-0001 



-0011 



-0138 



-0074 



1 13 



+ 0033 



0000 



-0060 



-0021 



+ 0098 



+ 0065 



-0027 



+ 0019 



2 13 



+ 0085 



+ 0130 



+ 0051 



+ 0106 



+ 0184 



+ 0134 



+ 0096 



+ 0115 



3 13 



+ 0133 



+ 0236 



+ 0167 



+ 0258 



+ 0285 



+ 0209 



+ 0220 



+ 0214 



4 13 



j +0144 



+ 0305 



+ 0236 



+ 0361 



+ 0313 



+ 0228 



+ 0301 



+ 0264 



5 13 



1 +0152 



+ 0408 



+ 0358 



+ 0441 



+ 0313 



+ 0232 



+ 0402 



+ 0317 



6 13 



\ +0161 



+ 0399 



+ 0373 



+ 0441 



+ 0284 



+ 0222 



+ 0404 



+ 0313 



7 13 



: +0142 



+ 0325 



+ 0356 



+ 0378 



+ 0209 



+ 0175 



+ 0353 



+ 0264 



8 13 



i +0107 



+ 0210 



+ 0264 



+ 0265 



+ 0114 



+ 0110 



+ 0246 



+ 0178 



9 13 



+ 0056 



+ 0074 



+ 0141 



+ 0097 



+ 0020 



+ 0038 



+ 0104 



+ 0071 



10 13 



-0020 



-0045 



+ 0048 



+ 0018 



-0055 



-0037 



+ 0007 



-0015 



11 13 



-0074 



-0074 



-0038 



-0096 



-0121 



-0097 



-0069 



-0084 



143. The means for groups of months having been obtained, as for the other magnetic elements, we find 

 the approximate epochs for the mean diurnal variation in apparent time as follow : — 



Maximum, 

 Minimum, 

 Maximum, 

 Minimum, 



Dec. Jan. Feb. 

 + 6^ lOm P.M. 

 -2h lOra A.M. 

 1^ 10™ A.M. 



9^ 55™ A.M. 



March, April. 

 + 5^ 25™ P.M. 

 — 2^ 10™ A.M. 

 7^ 5™ A.M. 



lO'' 35™ A.M. 



MAG. AND MET. OBS. 1845 AND 1846. 



May, June. 



+ 5*" 45™ P.M. 



1'' 45™ A.M. 



6^ 35™A.M. 



_10b 45™ A.M. 



July, Aug. 



+ 5'' 35™ P.M. 



— 2'^ 10™ A.M. 

 Q^ 35™ A.M. 



-10»i 35™ A.M. 



Sept. Oct. Nov. 

 + 4h 50™ P.M. 



— 2^ 20™ A.M. 



7^ 35™ A.M. 

 lOli 20™ A.M. 



