Annual Variations foe the Veetical 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 184-1 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. 
J une. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Year. 
1843 
1844 
1845 
1846 
0-00 
0210 
0271 
0440 
0181 
0-00 
0239 
0273 
0412 
0168 
0-00 
0284 
0688 
0629 
0360 
0-00 
0594 
0705 
0581 
0588 
0-00 
0302 
0516 
0432 
0606 
O'OO 
0259 
0233 
0284 
0403 
O'OO 
0289 
0298 
0293 
0776, 
0-00 
0282 
0587 
0464 
0807 
0-00 
0301 
0616 
0677 
0740 
0-00 
0297 
0702 
0365 
0863 
0-00 
0195 
0588 
0296 
0601 
0-00 
0292 
0292 
0355 
0177 
0-00 
0252 
0419 
0399 
0479 
Mean) 
of allj 
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 diflFerences 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 A^ertical 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 10124 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 thi'ee elements, that the law of the variation with season of the 
range of the hourly variations when unaftected by intermittent disturbance is as follows : — A gi'adual 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 Sinyle Observation of the Vertical Component f^-om the 
Monthly Mean at the corresponding Hour. — 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 
123 
157 
294 
224 
203 
144 
137 
172 
191 
247 
199 
123 
184 
1845, 
0-000 
192 
157 
156 
175 
174 
117 
137 
167 
210 
139 
168 
208 
167 
Mean, 
0-000 
157 
157 
225 
200 
188 
130 
137 
170 
200 
193 
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 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 
50-0 
41-9 
52-7 
