Monthly Vaeiations for the Horizontal Component. 



XXXVll 



Table 29. — Diurnal Range of the Horizontal Component of Magnetic Force, with reference to the 



Moon's Age and Declination. 















After 













Moon's 













Moon 













Age. 



1843. 



1844. 



1845. 



1846. 



Mean. 



farthest 

 North. 



1843. 



1844. 



1845. 



1846. 



Mean. 



a. d. 



0-00 



0-00 



0-0(1 



0-00 



0-00 



d. d. 



0-00 



0-00 



O'OO 



0-0(1 



000 



14—16 



3105 



4710 



3683 



4906 



4101 



27— 1 



3527 



3267 



3686 



4209 



3672 



17—20 



2846 



4235 



3959 



5489 



4132 



2— 5 



3792 



4481 



4429 



4285 



4247 



21—24 



2504 



3127 



3685 



4634 



3487 



6— 8 



3031 



4115 



4019 



4197 



3840 



25—28 



3282 



2936 



2986 



4510 



3428 



9—12 



2907 



3401 



3615 



5377 



3825 



29— 1 



2771 



3436 



3920 



4434 



3640 



13—15 



2998 



3248 



3491 



5394 



3783 



2— 5 



2792 



3058 



4492 



4429 



3693 



16—19 



2634 



3546 



4712 



4080 



3743 



6— 9 



3792 



3874 



4076 



4729 



4118 



20—22 



2795 



3682 



3290 



5271 



3759 



10—13 



3145 



4982 



3706 



4370 



4051 



23—26 



2665 



4311 



3137 



4620 



3683 



Variation of the Diurnal Mange of the Horizontal Component with reference to the Moon's Age and De- 

 clination. — Table 29 has been formed from-the Tables in former volumes, and the Tables pages 12 and 33 of 

 this volume. 



67. The conclusions from Table 29 are : — 



\st, That the diurnal range of the horizontal component is greatest about the time of opposition, and 

 least about the time of conjunction ; in the mean of the 4 years the range varies little from the time that the 

 moon is 6 days till it is 20 days old ; it also varies little during the remaining half lunation, but the value for 

 the former is considerably greater than for the latter. 



2d, In the mean of the 4 years the diurnal range is a maximum about 4 days after the moon has attained 

 its greatest north declination; it is a minimum when the moon is farthest north. The means for 1844 and 

 also for 1845 indicate a minimum, both when the moon was farthest north and when farthest south, with 

 maxima during the intermediate periods ; this result seems to deserve the greatest value, agreeing as it does 

 with the conclusion deducible from a comparison of the laws of mean values and ranges, namely, that the 

 range of the horizontal component is a maximum when its mean value is least, and vice versa. 



Table 30. — Mean Difference of a Single Observation of the Horizontal Component of Magnetic 

 Force from the Monthly Mean, at the corresponding Hour, with reference to the Moon's Age and 

 Declination. 













After 











Moon's 









Varia- 



Moon 









Varia- 



Age. 



1844. 



1846. 



Mean . 



tions. 



farthest 

 North. 



1844. 



1845. 



Mean. 



tions. 



d. d. 



0-00 



0-00 



0-00 



0-00 



d. d. 



0-00 



O'OO 



0-00 



0-00 



14—16 



0668 



0498 



0583 



+ 0018 



27— 1 



0533 



0519 



0526 



-0036 



17—20 



0682 



0591 



0636 



+ 0071 



2— 5 



0655 



0643 



0649 



+ 0087 



21—24 



0441 



0578 



0509 



-0056 



6— 8 



0588 



0577 



0582 



+ 0020 



25—28 



0484 



0539 



0511 



-0054 



9—12 



0510 



0536 



0523 



-0039 



29— 1 



0539 



0571 



0555 



-0010 



13—15 



0519 



0484 



0501 



-0061 



2- 5 



0497 



0568 



0532 



- 0033 



16—19 



0560 



0647 



0603 



+ 0041 



6— 9 



0605 



0556 



0580 



+ 0015 



20—22 



0570 



0472 



0521 



-0041 



10—13 



0731 



0493 



0612 



+ 0047 



23—26 



0675 



0507 



0591 



+ 0029 



68. Variation of the Mean Difference of a, Single Observation from, the Monthly Mean for the correspondinc/ 

 Hour with reference to the Moon's Age and Declination. — The results for two years 1844 and 1845 from Table 

 XXXV., 1844, p. 369, and Table XXIX., p. 16 of this volume, are given in Table 30. The conclusions from 

 this Table, which are nearly the same as those from Table 29, are as follow : — 



Isi, The departure of the horizontal component from its monthly mean value for the corresponding hour, 

 is greatest about the time of opposition, and least about the time of conjunction ; the actual epochs are imme- 



