Magnetic Dip. 
249 
TABLE XXIII.— Diurnal Variation of Magnetic Dip, deduced from Tables XII. and XIX. 
Gbtt. 
M. T. 
Winter 
Solstice. 
Equinoxes 
Summer 
Solstice. 
1842 and 
1843. 
Gbtt. 
M. T. 
Winter 
Solstice. 
Equinoxes. 
Summer 
Solstice. 
1842 and 
1843. 
H. 
10 
11 
12 
13 
14 
15 
16 
17 
18 
19 
20 
21 
0-499 
0-514 
0-484 
0125 
0-354 
0-207 
0-264 
0-324 
0-054 
0-000 
0-182 
0-360 
0-000 
0-509 
0-345 
1013 
0-282 
0- 468 
1- 136 
0-587 
0-623 
0- 659 
1- 147 
1-549 
0-808 
0-574 
0-379 
0-421 
0-624 
0-922 
0- 890 
1- 065 
1-563 
1- 959 
2- 118 
2-224 
0 040 
0-137 
0-008 
0-126 
0025 
0-138 
0-371 
0-263 
0-351 
0-478 
0-754 
0-982 
H. 
22 
23 
0 
1 
2 
3 
4 
5 
6 
7 
8 
9 
0-735 
0-877 
0-955 
0-733 
0-450 
0-238 
0-240 
0-235 
0-248 
0-457 
0-307 
0-389 
2-213 
2-448 
2-033 
1-476 
0-953 
0-493 
0-496 
0-573 
0-673 ■ 
0- 905 
1- 138 
0-992 
2-466 
2-416 
2-006 
1-635 
0-929 
0-899 
0-547 
0-447 
0-263 
0-000 
0-282 
0-346 
1-410 
1-518 
1-270 
0-886 
0-383 
0-148 
0-033 
0-024 
0-000 
0-060 
0183 
0-184 
In winter the principal minimum occurs at 6 h a.m., the secondary maximum about 10 h 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 op the Diurnal Variations 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. 
Range. Jan. Peb. March. April. May. June. July. Aug. Sept. Oct. Nov. Dec- 
True 0'-71 0'-62 V-26 2'T2 2'-60 2'- 79 2'93 2'-68 2'-ll l'-70 0'-76 0'"74 
Computed 0'-69 l'-09 l'-63 2'-21 2'-66 2'-87 2'78 2'-40 1''86 l'-28 0'-80 0'-57 
Thus, in the first half of the year, the true range is less tban 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 l'"75, the diurnal range of the mean for the year being l'-55. 
MAG. AND MET. OBS. 1843. 
