Annual Vaeiations for the Horizontal Component of Magnetic Force, xxxv 
60. Annual Variation of the Diurnal Range of the Horizontal Component of Magnetic Force. — The means . 
for 18-44 and 1845 only, in Table 26, are comparaMe with each other. From the last line of Table 26 we find 
that the mean daily range was least in the months of December, January, and February, and less in May and 
June than in April. July, and August. These mean ranges are deduced from the ordinary daily observations. 
"VMien we seek for the absolute ranges, as obtained from all the extra observations made in the years 1844 and 
1845 (Table LX. 1844, p. 400, and Table L. p. 28 of this volume), we obtain the following numbers (prefix 
0-00) :— 
Jan. 
Feb. 
JIai-ch. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
1844. 
2943 
3811 
6193 
6234 
5088 
3802 
4538 
5319 
4538 
5134 
6556 
2965 
1845, 
5758 
3009 
4268 
6138 
4733 
4054 
4174 
5270 
5062 
3759 
2864 
3995 
Mean, 
4355 
3410 
5230 
6186 
4910 
3928 
4356 
5294 
4800 
4446 
4710 
3480 
These numbers follow the same law as those in Table 26, they are, however, considerably larger ; the in- 
crease is most marked in the winter months. From tlie means of both years we may conclude that the mean 
value of the diurnal change of the horizontal component of magnetic force at Makerstoun in years of moderate 
disturbance is about 0*0057 in April and August, and about 0-0038 at the solstices, the whole horizontal com- 
ponent being unity. 
Table 27. — Ranges of the Mean Diurnal Variation of the Horizontal Component of Magnetic Force. 
Year. 
Jan. 
Feb. 
March. 
April. 
May. 
June. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Mean. 
1843 
1844 
1845 
1846 
0-00 
0928 
0690 
1742 
1027 
0-00 
0862 
0875 
1008 
0956 
0-00 
1674 
2195 
2247 
2333 
0-00 
3209 
3378 
3585 
4099 
0-00 
3409 
3644 
3623 
5504 
0-00 
3615 
3179 
3458 
4822 
0-00 
3867 
3657 
3651 
5550 
000 
3541 
3501 
3374 
5573 
0-00 
2698 
2948 
3282 
4427 
0-00 
2203 
2313 
1877 
2395 
0-00 
1051 
1305 
1537 
2392 
0.00 
0724 
0760 
1845 
1099 
0-00 
2128 
2212 
2387 
3152 
Mean) 
of an/ 
1062 
1 
0840 
2185 
3482 
3969 
3685 
4148 
3997 
3100 
2169 
1431 
0897 
2452 
61. Annual Variation of the Ranges of the Monthly Mean Diurnal Variation. — From the last line of Table 
27, it appears that the range of the monthly mean diurnal variation is least in December, January, and February, 
and that it is less in June than in May, July, or August. The following are the diux-nal ranges of the monthly 
mean diurnal variations, as deduced from the 20 days selected as free from irregular disturbance in the 
years 1844 and 1845 : — 
Prefix. Jan. Feb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec. 
0-00 0547 0682 1833 3154 3279 3209 3417 3080 2988 2030 1291 0875 
62. When we examine the mean diurnal ranges as deduced from all the observations (extra and ordinary) made 
in 1844 and 1845, we find that the means for March and April, and for August and September, are greater 
than the means for May, June, and July ; when we deduce the mean diurnal range from the regular daily 
observations, as in Table 26, then we find only the mean for April greater than the means for May, June, and July, 
the means for July and August being greater than those for May and June. So when we consider the range of 
the monthly mean variation as in Table 27, we find the mean for June less than the means for May, July and 
August only ; and, finally, in the ranges last given, deduced from the mean variations of undisturbed days, the 
differences for the months from April to September almost altogether disappear, the excess for July being in 
all probability accidental. This result is similar to that already found for the magnetic declination, and we may 
draw from it a similar conclusion, that the excess of the diurnal range in the equinoctial months over that 
for the midsummer months is due to irregular disturbance. 
63. Annual Variation of the Mean Difference of a Single Observation of the Horizontcd Component from the 
Monthly Mean at the corresponding Hour. — The mean differences for 1844 and 1845 (from Table XXXIV., 
1844, p. 368, and Table XXX., p. 17, of this volume) are as follow (Prefix 0-000) :— 
Jan. 
Feb. 
March. 
April. 
May. 
.J une. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
Mean. 
1844, 
350 
533 
823 
770 
568 
400 
469 
645 
587 
689 
591 
521 
579 
1845, 
697 
515 
477 
650 
503 
421 
447 
577 
610 
473 
501 
699 
547 
1' Mean, 
523 
524 
650 
710 
535 
410 
458 
611 
598 
581 
546 
610 
563 
MAG. AND MET. OBS. 1845 AND 1846. 
