Magnetic Dip. 



-247 



Diurnal Ranges op the Vertical Component of 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 neiu m,oon, and a maximum, about the time of full m,oon. 



Means of Groups. 



14 days to 16 days. Full Moon, 0-000381 



17 20 ... 0-000366 



21 24 ... 0-000285 



25 28 ... 0-000452 



29 days to 1 day, New Moon, 0-000337 



2 5 ... 0-000356 



6 9 ... 0-000611 



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 ... 0000384 



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 e= 



sm 



2 6 /aY aX 



0-0002909 



/aY aX \ 



V Y X ; 



where is the quantity in the tables for the vertical component, the quantity in those for the horizontal 



X X 



component, 6, 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 1' in parts of radius. 



Secular Change op 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 op Magnetic Dip. 

 From the quantities, pages 231 and 241, exhibiting the annual periods of the two components of magnetic 



