Magnetic Dip, 



249 



TABLE XXIII.— Diurnal Variation of Magnetic Dip, deduced from Tables XII. and XIX. 



Gott. 



Winter 





Summer 



1842 and 



Gott. 



Winter 





Summer 



1842 and 



M. T. 



Solstice. 



Equinoxes 



Solstice. 



1843. 



M. T. 



Solstice. 



Equinoxes. 



Solstice. 



1843. 



H. 



10 



0-499 



0-000 



0-808 



0-040 



H. 



22 



0-735 



2-213 



2-466 



1-410 



11 



0-514 



0-509 



0-574 



0-137 



23 



0-877 



2-448 



2-416 



1-518 



12 



0-484 



0-345 



0-379 



0-008 







0-955 



2-033 



2-006 



1-270 



13 



0125 



1-013 



0-421 



0-126 



1 



0-733 



1-476 



1-635 



0-886 



14 



0-354 



0-282 



0-624 



0025 



2 



0-450 



0-953 



0-929 



0-383 



15 



0-207 



0-468 



0-922 



0-138 



3 



0-238 



0-493 



0-899 



0-148 



16 



0-264 



1-136 



0-890 



0-371 



4 



0-240 



0-496 



0-547 



0-033 



17 



0-324 



0-587 



1065 



0-263 



5 



0-235 



0-573 



0-447 



0-024 



18 



0-054 



0-623 



1-563 



0-351 



6 



0-248 



0-673 



0-263 



0-000 



19 



0-000 



0-659 



1-959 



0-478 



7 



0-457 



0-905 



0-000 



0-060 



20 



0-182 



1-147 



2-118 



0-754 



8 



0-307 



1-138 



0-282 



0-183 



21 



0-360 



1-549 



2-224 



0-982 



9 



0-389 



0-992 



0-346 



0-184 



In winter the principal minimum occurs at 6^ am., the secondary maximum about 10^ p.m. The means 

 are too irregular in the other periods to give the times of the secondary maximum and minimum ; in other re- 

 .spects they agree with those in Table XXII. 



Ranges op the Monthly Means of the Diurnal Vaeiations op Magnetic Dip. 



The annual variation of the diurnal ranges seems to bear a similar relation to the sun's declination, as the 

 annual variation of atmospheric temperature does to it ; this will be seen distinctly if we place under the ranges 

 of the diurnal variation of magnetic dip the ranges computed on the assumption that one degree of the sun's 

 altitude is equivalent to a diurnal range of 0'-05 of dip. 



Kange. 



Jan. 



Peb. 



March. 



April. 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



True 



0'-71 



0'-62 



V-26 



2'- 12 



2'-60 



2'-79 



2'-93 



2'-68 



2'- 11 



l'-70 



0'-76 



0'-74 



Computed 



0'-69 



r-09 



r-63 



2'-21 



2'- 66 • 



2'-87 



2'-78 



2'-40 



r-86 



l'-28 



0'-80 



0'-57 



Thus, in the first half of the year, the true range is less than the computed, but in the second it is greater. 

 If this similarity to the mean monthly increase of temperature should be found to hold for succeeding years, it 

 is probable that no other connection will be found to exist ; a glance at the mean temperatures for each month 

 in 1843, in the succeeding abstracts, will shew that there is no distinct relation between range and temperature 

 for that year ; there will, however, be evidence of some cause of retardation of the solar influence which produces 

 the diurnal motion of the needle. 



The diurnal variation of dip is about 0'-7 in winter, and four times as great in summer ; the mean of all 

 the monthly ranges is I'-'Jb, the diurnal I'ange of the mean for the year being l'-55. 



MAG. AND MET. OBS. 1843. 



3 B 



