TotaL MAGNETIC ForRcE. 253 
From this table, the principal minimum occurs about 1» 10™ a.m. in the mean for the year, about midnight 
in winter, and about 2° a.m. at the equinoxes and in summer. 
The results from Table XXVI. differ little from those deduced from}Table XXV. The secondary maxi- 
mum occurs earlier in summer than at the other periods, namely, about 64 a.m. in summer, and about 85 a.m. 
in winter and at the solstices. The following are the periods for the year :— 
The principal maximum occurs at 6" p.m., | Makerstoun mean time. 
The principal minimum occurs at 15 10" a.m., ....... saastouescumebasts 
A secondary maximum occurs at 8° aM, x. sess 
A secondary minimum occurs at 10° 40™ A.M., .........ccceceeeeeeeeee 
RANGES OF THE MONTHLY MEANS OF THE DIURNAL VARIATIONS OF THE TOTAL MAGNETIC FORCE. 
It is evident, from the previous results, that the quantities in the last column of Table XXV. are not at 
all the diurnal ranges, as the minimum occurs near midnight. From Table XXVI., however, it appears that 
the range of the mean diurnal curve for the months about the winter solstice is 0-:000240, about the equinoxes 
is 0:000744, and about the summer solstice is 0:000506 ; or, that the ranges are nearly in the following ratio :— 
Winter Solstice : Summer Solstice : Equinoxes = 1 : 2: 3. 
TABLE XXVII.—Variations of the Total Force of the Earth’s Magnetism with reference to the 
Moon’s Age, Declination, and Distance from the Earth, as deduced from Tables IX. and XVI. 
Variations ' | Variations|} After | Variations} After | Variations|| Before | Variations| Before | Variations 
Moon’s of Moon’s of Moon of Moon of and of and of 
Age. | Magnetic | Age. | Magnetic || farthest] Magnetic |farthest} Magnetic || After | Magnetic | After | Magnetic 
Force. Force. || North.| Force. | North. | Force. ||Perigee.| Force. |Apogee.| Force. 
Days. 0-000 Days. 0-000 Days. 0000 Days. 0-000 Days. 0000 Days. 0-000 
15 037 0 040 0 130 14 073 7 107 7 052 
16 058 1 025 1 087 15 057 6 086 6 022 
17 073 2 066 2 146 16 033 5 164 5 051 
18 064 3 083 3 092 17 005 4 058 4 045 
19 048 4 049 4 064 18 033 3 040 3 027 
20 082 5 042 © 5 035 19 017 2 062 2 025 
21 087 6 145 6 041 20 027 1 083 1 040 
22 071 7 040 7 056 21 009 P 053 A 031 
23 076 8 067 8 066 22 015 1 056 1 000 
24 073 9 048 va) 042 23 028 2 087 2 035 
25 095 10 036 10 026 24 000 3 084 3 051 
26 084 11 053 il 043 25 060 4 076 4 094 
27 049 12 001 12 053 26 037 5 080 5 095 
28 154 13 000 13 087 27 085 6 043 6 120 
29 058 14 016 7 047 7 101 
VARIATIONS OF THE TOTAL MAGNETIC FORCE WITH REFERENCE TO THE Moon’s AGE. 
Means of Groups. 
14 days to 16 days, Full Moon, 0:000037 29 days to 1 day, New Moon, 0:000041 
17 wees 20 + 0:000067 Q vere 5 ++ 0:000060 
BALL cea aha 24. 0:000077 G6 wee eee 9... 0:000075 
25 wee e ee 28 «ss 0:000095 10 «-++- 13 + 0:000022 
From these means the total force is a minimum when the sun and moon are in opposition and in conjunction, 
and a maximum about the quadratures. The principal minimum occurs at the time of full moon. 
MAG, AND MET. oBs. 1843. 3s 
