Magnetic Dip. 
247 
Diurnal Ranges of the Vertical Component op Magnetic Force, with reference to the 
Moon's Age. 
The general aspect of the partial means is exactly similar to that of the means for the horizontal com- 
ponent, Table XIV., and, with similar exceptions, namely, of the means for the 28th, 6th, and 7th days, the 
result is the same, or a minimum about the time of new moon, and a maximum about the time of full moon. 
Means of Groups. 
14 days to 16 days, Full Moon, 0-000381 29 days to 1 day, New Moon, 0-000337 
17 20 ... 0-000366 2 5 ... 0-000356 
21 24 ... 0-000285 6 9 ... 0-000611 
25 28 ... 0-000452 10 13 ... 0-000455 
Diurnal Variations of the Vertical Component of Magnetic Force, with reference to 
the Moon's Declination. 
Means of Groups. 
27 days to 1 day, Moon farthest North, 0-000482 
2 5 ... 0-000537 
6 8 ... 0-000419 
9 12 ... 0-000346 
13 days to 15 days, Moon farthest South, 0-000453 
16 19 ... 0-000344 
20 22 ... 0-000314 
23 26 ... 0 000384 
These means shew the same result as that already obtained for the horizontal component (Table XIV.), 
namely, maxima about the periods of greatest north and south declination, and minima near the periods when 
the declination is zero ; the maximum at the period of greatest south declination is better marked than for the 
horizontal component ; the principal minimum occurs when the moon is moving northwards. 
Magnetic Dip. 
The following results are deduced from the variations of the horizontal and vertical components by means 
of the formula 
A 0_ h sin 2 0 / A Y _ A X\ 
A "0-0002909 \ Y X/ 
where is the quantity in the tables for the vertical component, the quantity in those for the horizontal 
x X 
component, 0, the magnetic dip assumed to be 71° 18', A 6 the variations of dip given in the following tables, 
and 0-0002909 the value of F in parts of radius. 
Secular Change of Magnetic Dip. 
From the mean secular changes for the two components of magnetic force, pages 235 and 245, we obtain 
Mean Secular Change of Magnetic Dip 1842 to 1843 = - 4'-92. 
Annual Period of Magnetic Dip. 
From the quantities, pages 231 and 241, exhibiting the annual periods of the two components of magnetic 
