Annual Vaeiations for the Vertical Component or Magnetic Force, xlix 



Annual Variation of the Ranges of the Monthly Mean Diurnal Variation of the Vertical Component. — 

 In the previous Table we have given the monthly means of the diurnal ranges observed for each day, the follow- 

 ing Table contains the diurnal range of the hourly means for each month, those for 1844 and 1845 only being 

 comparable with each other. 



Table 44. — Ranges of the Mean Diurnal Variation of the Vertical Component of Magnetic Force. 



Year. 



Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



1843 

 1844 

 1845 

 1846 



Mean) 

 of aUj 



0-00 



0210 

 0271 

 0440 

 0181 



0250 



0-00 



0239 

 0273 

 0412 

 0168 



0258 



0-00 



0284 

 0688 

 0629 

 0360 



0540 



0-00 



0594 

 0705 

 0581 

 0588 



0716 



0-00 



0302 

 0516 

 0432 

 0606 



0522 



0-00 



0259 

 0233 

 0284 

 0403 



0257 



0-00 



0289 

 0298 

 0293 

 0776 



0412 



0-00 



0282 

 0587 

 0464 

 0807 



0608 



0-00 



0301 

 0616 

 0677 

 0740 



0666 



0-00 



0297 

 0702 

 0365 

 0863 



0561 



0-00 



0195 



0588 

 0296 

 0601 



0363 



0-00 



0292 

 0292 

 0355 

 0177 



0269 



0-00 



0252 

 0419 

 0399 

 0479 



0422 



92. The last line of Table 44, which is deduced from observations for the four years, as in Table 48, shews 

 the law already obtained from Table 43, but in a more marked manner. In the corresponding discussions for the 

 declination (No. 14) and for the horizontal component (No. 62), it was found that in the combination of four 

 years' observations, the differences between the diurnal range at the summer solstice, and for the preceding and 

 succeeding months, was considerably diminished ; this is not the case for the vertical component ; the range at 

 the equinoxes of the hourly mean variation is nearly three times the range at the solstices. When, however, 

 we consider the ranges of the hourly mean variation, as deduced from days selected nearly free from disturbances, 

 we obtain a result similar to that for the other elements. The following are the ranges of the hourly means for 

 each month deduced from the selected days in 1844 and 1845 (see 1844, p. 379, and p. 21 of this volume) : — 



Prefix. I Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. Year. 



0-00 I 0124 0124 0180 0186 0223 0238 0196 0190 0257 0209 0167 0132 0136 



From these it appears, that the diurnal range of the mean variation, when unaffected by intermittent disturb- 

 ance, varies little from March to October, the irregularities in the values being due in all probability to dis- 

 turbance remaining in the selected days. 



93. On the whole it is evident for all the three elements, that the law of the variation with season of the 

 range of the hourly variations when unaffected by intermittent disturbance is as follows : — A gradual increase 

 from the winter solstice till the vernal equinox, little variation from the vernal till the autumnal equinox, and 

 a gradual decrease from thence till the winter solstice. Intermittent disturbances increase the diurnal range 

 greatly at the equinoxes, and more at the vrinter solstice than at the summer solstice. 



94. Annual Variation of the Mean Difference of a Single Observation of the Vertical Component from the 

 Monthly Mean at the corresponding Hour. — The following mean differences have been obtained from Table L. 

 p. 389, and Table XLI. p. ~" " ' " 



1844, p. 389, and Table XLI. p. 23 of this volume :— 



Year. Prefix. 



1844, 0000 



1845, 0-000 

 Mean, 0-000 



Jan. Feb. March. April. May. June. July. Aug. Sept. 



123 157 294 224 203 144 137 172 191 



192 157 156 175 174 117 137 167 210 



157 157 225 200 188 130 137 170 200 193 183 165 



Oct. 



Nov. 



Dec. 



Mean 



247 



199 



123 



184 



139 



168 



208 



167 



175 



These numbers give the same law as has already been obtained for the other two elements. The mean 

 difference of an observation of the vertical component is greatest at the equinoxes, and least at the solstices 

 (see No. 16). 



95. Annual Variation of the Number of Observations of the Vertical Component which were greater than the 

 Monthly Means for the corresponding Hours. — The numbers in 100 observations for each month of the years 

 1844 and 1845 are as follow : — 





Jan. 



Feb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Mean. 



1844, 



53-0 



49-5 



57-7 



49-8 



52-5 



55-7 



55-4 



52-0 



55-0 



50-0 



46-5 



40-7 



51-5 



1845, 



55-7 



54-9 



55-8 



59-3 



54-8 



51-5 



54-3 



57-4 



50-6 



56-3 



53-5 



43-2 



53-9 



Mean, 54-4 52-2 56-7 54-5 53-6 53-6 54-8 54-7 52-8 531 500 41-9 



52-7 



