Magnetic Dip. 



393 



TABLE LVI. — Variations of Magnetic Dip, with reference to the Moon's Hour- Angle, as deduced 



from Tables XXXI. and XL VII. 



Moon's 

 Hour- 

 Angle. 



Lunations. 



Moon's 

 Hour- 

 Angle. 



Lunations. 



Moon's 

 Hour- 

 Angle. 



Lunations. 



Winter. 



Summer. 



Year. 



Winter. 



Summer. 



Year. 



Winter. 



Summer. 



Year. 



h. 

 

 1 

 2 

 3 

 4 

 5 

 6 

 7 



0-202 

 0-138 

 0-228 

 0-141 

 0-056 

 01 96 

 0-107 

 0114 



0-192 

 0-241 

 0-196 

 0-255 

 0-206 

 0-240 

 0-278 

 0-249 



0134 

 0-126 

 0-149 

 0-135 

 0-068 

 0155 

 0-129 

 0119 



h. 

 8 

 9 

 10 

 11 

 12 

 13 

 14 

 15 



0-000 

 0143 

 01 47 

 0-187 

 0-023 

 0119 

 0-127 

 0-164 



0-356 

 0-219 

 0-272 

 0-248 

 0-216 

 0-081 

 0000 

 0-202 



0-115 

 0-118 

 0-146 

 0152 

 0056 

 0-036 

 0000 

 0120 



h. 



16 

 17 

 18 

 19 

 20 

 21 

 22 

 23 

 24 



0-247 

 0-226 

 0-171 

 0-032 

 0151 

 0076 

 0-213 

 0-112 

 0-107 



0-233 

 0-300 

 0-369 

 0-291 

 0-404 

 0-386 

 0-358 

 0-304 

 0-297 



0-176 

 0-200 

 0-207 

 0099 

 0-215 

 0-168 

 0-222 

 0-145 

 0139 



The following are the means at nearly two-hourly intervals 



Groups, h m 



Winter, 0'-15 



Summer,... 0'-24 



Year 1844, 0'-13 



2 h 25- 



4 h 20- 



6hl5m 



8h 10m 



K)h5m 



12b Qm 



13 b 55-" 



15i 50'" 



17h 45 m 



19 h 40" 



211" 35- 



0'-18 



0'13 



0'-ll 



0'-07 



. 0'-17 



0'-07 



0'-14 



0'-24 



0'-l0 



0'-ll 



0'-l6 



0'-22 



0'-22 



0'-26 



0'-29 



0'-26 



0'-15 



0'-10 



0'-27 



0'-33 



0'-39 



0'-33 



0'-14 



0'-ll 



0'-12 



0'-12 



0'-15 



0'-05 



0'-06 



0'-19 



0'-15 



0'-19 



0'-18 



In the winter group — 



The principal maximum of dip occurs about 4 hours after the moon's inferior transit. 

 The principal minimum occurs 4 hours before and at the inferior transit. 

 A secondary maximum occurs about 2 hours after the superior transit. 

 A secondary mininrum occurs about 6 hours before the superior transit. 



There is a secondary maximum 2 hours before the inferior transit, which is perhaps accidental. 



In the summer group the law of variation is most distinct — 



The principal maximum occurs 4 hours before the moon's superior transit. 

 The principal minimum occurs about 2 hours after the inferior transit. 

 The secondary maximum occurs about 4 hours before the inferior transit. 

 The secondary minimum occurs about 3 hours after the superior transit. 



In the mean for the year the secondary maximum and minimum are not well marked — 



The principal maximum occurs about 6 hours after the inferior transit. 

 The principal minimum occurs about 1 hour after the inferior transit. 

 The secondary maximum occurs about 2 hours before the inferior transit. 

 The secondary minimum occurs about 6 hours before the inferior transit. 



The whole range of these variations is very small, the greatest range is that for the summer group, which 

 is 0'-4, this however is equivalent to a range of l'-2 for the declination : if we examine the similar discussion 

 for the magnetic declination, p. 342, it will be seen that the greatest range is that for the winter group, which 

 is l'*5 ; so that the diurnal range of the variation due to the moon is nearly the same for the magnetic declina- 

 tion in winter as it is for the magnetic dip in summer. 



If we determine the variations from those for the horizontal and vertical components after Tables XXXI. 

 and XL VII., from which the large disturbances have been removed, we have for the variations of dip for the 

 year — 



h m 



2 h 25- 



4 h 20 m 



6» 15- 



8b 10m 



10 h 5- 



12 h 0- 



13i> 55- 



15b so- 



17b 45 m 



19h 40 m 



21b 35m 



0'104 



0'-087 



0'-030 



0'-062 



0'045 



0'-068 



0'-001 



0'-000 



0'134 



0'-087 



0'-157 



0'080 



These quantities give nearly the same law as that obtained above, 



MAG. AND MET. OBS. 1844. 



5g 



