= ae 
ANNUAL VARIATIONS FOR THE VERTICAL COMPONENT OF 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. 
0-00 0-00 0-00 0-00 0-00 0-00 0-00 0:00 0-00 0-00 0-00 0-00 | 0-00 
1843 || 0210 | 0239 | 0284 | 0594 | 0302 | 0259 | 0289 | 0282 | 0301 | 0297 | 0195 | 0292 | 0252 
1844 || 0271 | 0273 | 0688 | 0705 | 0516 | 0233 | 0298 | 0587 | 0616 | 0702 | 0588 | 0292 || 0419 
1845 || 0440 | 0412 | 0629 | 0581 | 0432 | 0254 | 0293 | 0464 | 0677 | 0365 | 0296 | 0355 || 0399 
1846 0181 | 0168 | 0360 | 0588 | 0606 | 0403 | 0776 | 0807 | 0740 | 0863 | 0601 | 0177 | 0479 
| | 
aa 0250 | 0258 | 0540 | 0716 | 0522 | 0257 | 0412 | 0608 | 0666 | 0561 | 0363 | 0269 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.) Jan. Feb. March. April. May. June, July. Aug. Sept. Oct. Nov. Dec. Year. 
0-00 | 0124 0124 0180 0186 0228 02388 0196 0190 0257 0209 0167 0182 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 winter 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 Howr.—The following mean differences have been obtained from Table L. 
1844, p. 389, and Table XLI. p. 23 of this volume :-— 
Year. Prefix. Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. ; Mean. 
1844, 0-000 1230) Mapmeeoteee 4.) 20a tad tes, y 172) 191842471 5199). 1235) 184 
1845, 0-000 192 ts7 56 175. 174 117, 137,167 210 139 168 208 | 167 
Mean, 0-000 157 157 225 200 188 130 187 170 200 1938 183 165 | 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 Howrs.—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 57-7 498 52:5 55-7 55:4 52:0 55:0 50:0 465 40-7 | 51-5 
1845, 55:7 549 558 59:3 548 515 543 574 506 56:3 53:5 43:2 | 53:9 
Mean, 544 52:2 56°7 545 536 536 548 54:7 52: 531 50:0 41:9 | 52:7 
