Station. Jan Mayen. St Petersburg
and Pavlovsk.		 Greenwich. Kew. Parc
St Maur.		 Tiflis. Kolaba. Batavia. Mauritius. South Vic-
toria Land.
Latitude. 71° 0′ N. 59° 41′ N. 51° 28′ N. 51° 28′ N. 48° 49′ N. 41° 43′ N. 18° 54′ N.  6° 11′ S. 20°  6′ S.  77° 51′ S.
Longitude.  8° 28′ W. 30° 29′ E.  0°  0′.   0° 19′ W.  2° 29′ E. 44° 48′ E. 72° 49′ E. 106° 49′ E. 57° 33′ E. 166° 45′ E.
Period. 1882-1883. 1873-1885. 1890-1900. 1890-1900. 1883-1897. 1888-1898. 1894-1901. 1883-1894. 1876-1890. 1902-1903.
a. q. a. q. a. a. q. a. a. q. a. a. a. q.
Hour. ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′
1 − 6.6 −4.2 −1.3 −0.7 −1.4 −1.5 −0.9 −1.4 −0.7 −0.2 +0.1 +0.1 + 2.0 + 0.9
2 −10.5 −6.4 −1.2 −0.8 −1.3 −1.4 −0.9 −1.2 −0.6 −0.1 −0.1 +0.1 − 2.1 − 1.8
3 −15.2 −7.8 −1.2 −1.0 −1.3 −1.5 −1.0 −1.2 −0.6 −0.1 −0.1 +0.1 − 5.2 − 4.5
4 −16.9 −8.4 −1.4 −1.3 −1.4 −1.7 −1.3 −1.2 −0.5 −0.1 0.0 +0.2 − 9.4 − 6.8
5 −17.0 −8.1 −1.7 −1.8 −1.7 −2.1 −1.8 −1.6 −0.7 −0.1 0.0 +0.3 −12.2 − 9.0
6 −13.7 −7.0 −1.9 −2.3 −2.1 −2.4 −2.3 −1.9 −1.2 −0.6 +0.1 +0.4 −15.3 −11.7
7 − 9.3 −5.1 −2.2 −2.8 −2.4 −2.7 −2.8 −2.4 −1.9 −1.0 +0.5 +0.6 −17.2 −15.0
8 − 6.8 −3.2 −2.5 −3.2 −2.5 −2.8 −3.1 −2.7 −2.4 −1.2 +1.3 +1.1 −21.5 −17.3
9 − 3.7 −0.6 −2.3 −3.0 −1.9 −2.1 −2.5 −2.3 −2.3 −0.7 +1.7 +1.8 −23.5 −18.1
10 − 2.4 +2.1 −1.0 −1.7 −0.2 −0.3 −0.7 −0.5 −0.9 0.0 +1.5 +1.9 −21.2 −15.8
11 − 0.5 +4.6 +1.0 +0.4 +2.1 +2.2 +1.7 +2.0 +1.0 +0.9 +0.9 +1.3 −15.3 − 9.2
Noon + 2.5 +6.5 +3.1 +2.7 +4.2 +4.3 +3.9 +4.2 +2.6 +1.4 +0.1 0.0 − 9.8 − 4.9
1 + 3.7 +7.3 +4.6 +4.3 +5.1 +5.3 +4.8 +5.3 +3.3 +1.2 −0.6 −1.1 − 3.2 − 0.1
2 + 6.4 +7.1 +4.9 +4.5 +4.7 +4.9 +4.4 +4.9 +3.1 +0.6 −1.1 −2.0 + 3.8 + 5.9
3 + 7.4 +5.9 +4.1 +3.6 +3.6 +3.7 +3.1 +3.7 +2.3 +0.1 −1.3 −2.3 +11.1 + 9.5
4 + 8.5 +4.3 +2.7 +2.3 +2.2 +2.4 +1.8 +2.3 +1.3 −0.2 −1.2 −1.8 +16.6 +12.9
5 +10.6 +3.0 +1.5 +1.3 +1.1 +1.2 +0.7 +1.1 +0.6 −0.1 −0.9 −0.9 +19.9 +14.6
6 +14.2 +2.3 +0.6 +0.7 +0.3 +0.4 +0.2 +0.2 +0.2 0.0 −0.6 −0.1 +22.0 +15.5
7 +15.2 +2.2  0.0 +0.4 −0.3 −0.2 −0.1 −0.4 +0.1 +0.1 −0.4 +0.1 +22.0 +15.9
8 +15.8 +2.6 −0.4 +0.2 −0.9 −0.6 −0.3 −0.9 −0.1 +0.2 −0.2 +0.1 +19.9 +14.6
9 +13.2 +2.6 −1.0  0.0 −1.2 −1.0 −0.5 −1.3 −0.4 +0.1 0.0 +0.1 +16.0 +10.6
10 + 7.4 +2.0 −1.4 −0.2 −1.5 −1.3 −0.7 −1.5 −0.6 0.0 +0.1 +0.1 +11.6 + 7.2
11 + 1.1 +0.5 −1.6 −0.4 −1.6 −1.4 −0.8 −1.6 −0.7 0.0 +0.1 +0.1 + 7.6 + 4.2
12 − 3.6 −1.8 −1.5 −0.6 −1.6 −1.5 −0.9 −1.6 −0.8 −0.1 +0.1 +0.1 + 3.3 + 1.9
Range 32.8 15.7 7.4 7.7 7.6 8.1 7.9 8.0 5.7 2.6 3.0 4.2 45.5 34.0

Tables VIII. to XI. give mean diurnal inequalities derived from all the months of the year combined, the figures representing the algebraic excess of the hourly value over the mean for the twenty-four hours. The + sign denotes in Table VIII. that the north end of the needle is to the west of its mean position for the day; in Tables IX. to XI. it denotes that the element—the dip being the north or south as indicated—is numerically in excess of the twenty-four hour mean. The letter “a” denotes that all days have been included except, as a rule, those characterized by specially large disturbances. The letter “q” denotes that the results are derived from a limited number of days selected as being specially quiet, i.e. free from disturbance. In all cases the aperiodic or non-cyclic element—indicated by a difference between the values found for the first and second midnights of the day—has been eliminated in the usual way, i.e. by treating it as accumulating at a uniform rate throughout the twenty-four hours. The years from which the data were derived are indicated. The algebraically greatest and least of the hourly values are printed in heavy type; the range thence derived is given at the foot of the tables.

Table IX.—Diurnal Inequality of Horizontal Force, mean from whole year (Unit 1γ = .00001 C.G.S.)

Station. Jan Mayen. St Petersburg
and Pavlovsk.		 Greenwich. Kew. Parc
St Maur.		 Tiflis. Kolaba. Batavia. Mauritius. S. Victoria
Land.
Period. 1882-1883. 1873-1885. 1890-1900. 1890-1900. 1883-1897. 1888-1898. 1894-1901. 1883-1894. 1883-1890. 1902-1903.
a. q. a. q. a. q. a. a. q. a. a. a.
Hour.
1 −57 −22 + 4 + 5 + 4 + 4 + 5 + 3 −10 −11 − 3 −12
2 −64 −24 + 4 + 4 + 3 + 4 + 5 + 3 − 9 −10 − 1 −13
3 −74 −25 + 4 + 4 + 3 + 4 + 5 + 3 − 9 − 8 + 1 −14
4 −69 −24 + 4 + 4 + 3 + 4 + 5 + 4 − 9 − 7 + 2 −15
5 −60 −22 + 5 + 4 + 3 + 4 + 6 + 4 − 9 − 5 + 3 −15
6 −37 −19 + 4 + 4 + 1 + 2 + 4 + 4 − 7 − 1 + 4 −12
7 −15 −15 + 2 + 2 − 3 − 1 + 1 + 2 − 1 + 5 + 7 − 9
8 − 1 −13 − 3 − 4 − 9 − 7 − 5 − 3 + 8 +14 + 9 − 7
9 + 8 −12 −10 −10 −16 −13 −12 − 8 −19 +24 + 9 − 3
10 +17 −12 −16 −16 −20 −18 −17 −10 +26 +31 + 9 + 3
11 +32 −10 −19 −20 −19 −18 −16 − 7 +30 +35 + 9 + 7
Noon +49 − 4 −17 −18 −13 −12 −12 − 1 +26 +31 + 8 +12
1 +65 + 8 −12 −13 − 7 − 7 − 7 + 4 +19 +22 + 7 +18
2 +78 +22 − 6 − 6 − 1 − 2 − 4 + 5 +10 +10 + 2 +20
3 +89 +37 0 0 + 2 + 1 − 1 + 3 + 2 − 1 − 2 +19
4 +83 +43 + 3 + 3 + 5 + 3 0 − 1 − 3 − 9 − 6 +18
5 +68 +49 + 5 + 5 + 7 + 5 + 2 − 4 − 7 −13 − 7 +15
6 +37 +43 + 6 + 6 + 9 + 7 + 4 − 6 − 8 −14 − 7 +11
7 +13 +30 + 7 + 7 +10 + 8 + 6 − 4 − 9 −15 − 7 + 5
8 −11 +15 + 8 + 8 +10 + 8 + 7 − 1 −10 −16 − 8 + 0
9 −33 + 1 + 9 + 9 + 8 + 7 + 7 + 1 −11 −16 − 8 − 4
10 −36 −10 + 8 + 9 + 7 + 6 + 6 + 2 −11 −16 − 8 − 7
11 −40 −16 + 7 + 8 + 6 + 6 + 6 + 3 −10 −15 − 7 − 9
12 −51 −20 + 6 + 6 + 5 + 5 + 6 + 3 −10 −13 − 5 −11
Range 163 74 28 29 30 26 24 15 41 51 17 35

Table X.—Diurnal Inequality of Vertical Force, mean from whole year (Unit 1γ).

Station. Jan Mayen. St Petersburg
and Pavlovsk.		 Greenwich. Kew. Parc St
Maur.		 Tiflis. Kolaba. Batavia. Mauritius. South Vic-
toria Land.
Period. 1882-1883. 1873-1885. 1890-1900. 1891-1900. 1883-1897. 1888-1898. 1894-1901. 1883-1894. 1884-1890. 1902-1903.
a. q. a. q. a. q. a. a. q. a. a. a.
Hour
1 +65 + 3 − 7 − 1 − 3 + 1   0 + 2 + 4 + 7 + 2 +13
2 +65 + 2 − 7 − 1 − 4 + 1   0 + 2 + 4 + 5 + 2 +12
3 +56 − 1 − 7 − 1 − 4   0 − 1 + 1 + 3 + 4 + 2 +10
4 +37 − 5 − 6   0 − 3   0   0 + 1 + 3 + 3 + 2 + 8
5 +16 − 7 − 5   0 − 2 + 1   0 + 2 + 5 + 2 + 2 + 3
6 − 7 − 8 − 4   0 − 1 + 1 + 1 + 3 + 7 + 1 + 2   0
7 −17 − 6 − 3   0   0   0 + 1 + 3 + 6   0 + 3   0
8 −14 − 4 − 2   0   0 − 1   0 + 3   0 − 3 + 4 − 2
9 − 9   0 − 3 − 1 − 3 − 4 − 4 − 1 − 8 −11 + 5 − 6
10 − 6 + 5 − 2 − 2 − 6 − 8 − 8 − 7 −14 −20 + 3 −13
11 − 6 +10 − 3 − 4 − 9 −11 −12 −11 −15 −26   0 −17
Noon −10 +16 − 3 − 5 −10 −11 −12 −11 −10 −27 − 4 −20
1 −13 +21 − 1 − 4 − 6 − 8 − 9 − 9 − 3 −21 − 7 −20
2 −24 +23 + 2 − 1   0 − 3 − 3 − 5 + 1 −13 − 9 −16
3 −31 +20 + 8 + 2 + 5 + 2 + 2 − 1 + 4 − 4 − 8 −12
4 −40 +13 + 9 + 3 + 8 + 5 + 6 + 1 + 3 + 4 − 5 − 6
5 −48 + 2 +10 + 3 + 9 + 6 + 7 + 3   0 +10 − 3 − 1
6 −53 − 9 +10 + 3 +10 + 7 + 8 + 4   0 +13   0 + 3
7 −47 −18 + 9 + 3 + 9 + 6 + 7 + 3   0 +14   0 + 6
8 −36 −20 + 8 + 3 + 7 + 5 + 6 + 3 + 1 +14 + 1 + 9
9 − 7 −19 + 6 + 2 + 5 + 5 + 5 + 3 + 2 +14 + 2 +11
10 +18 −13 + 3 + 2 + 3 + 4 + 3 + 3 + 3 +13 + 2 +12
11 +42 − 5 − 2   0   0 + 3 + 2 + 3 + 3 +11 + 2 +12
12 +54   0 − 5 − 1 − 2 + 2 + 1 + 2 + 3 + 9 + 2 +13
Range 118 43 17 8 20 18 20 15 22 41 14 33

When comparing results from different stations, it must be remembered that the disturbing forces required to cause a change of 1′ in declination and in dip vary directly, the former as the horizontal force, the latter as the total force. Near a magnetic pole the horizontal force is relatively very small, and this accounts, at least partly, for the difference between the declination phenomena at Jan Mayen and South Victoria Land on the one hand and at Kolaba, Batavia and Mauritius on the other. There is, however, another cause, already alluded to, viz. the variability in the type of the diurnal inequality in tropical stations. With a view to illustrating this point Table XII. gives diurnal inequalities of declination for June and December for a number of stations lying between 45° N. and 45° S. latitude. Some of the results are represented graphically in fig. 6, plus ordinates representing westerly deflection. At the northmost station, Toronto, the difference between the two months is mainly a matter of amplitude, the range being much larger at midsummer than at midwinter. The conspicuous phenomenon at both seasons is the rapid swing to the west from 8 or 9 a.m. to 1 or 2 p.m. At the extreme southern station, Hobart—at nearly equal latitude—the rapid diurnal movement is to the east, and so in the opposite direction to that in the northern hemisphere, but it again takes place at nearly the same hours in June (midwinter) as in December. If, however, we take a tropical station such as Trivandrum or Kolaba, the phenomena in June and December are widely different in type. At Trivandrum—situated near the magnetic equator in India—we have in June the conspicuous forenoon swing to the west seen at Toronto, occurring it is true slightly earlier in the day; but in December at the corresponding hours the needle is actually swinging to the east, just as it is doing at Hobart. In June the diurnal inequality of declination at tropical stations—whether to the north of the equator like Trivandrum, or to the south of it like Batavia—is on the whole of the general type characteristic of temperate regions in the northern hemisphere; whereas in December the inequality at these stations resembles that of temperate regions in the southern hemisphere. Comparing the inequalities for June in Table XII. amongst themselves, and those for December amongst themselves, one can trace a gradual transformation from the phenomena seen at Toronto to those seen at Hobart. At a tropical station the change from the June to the December type is probably in all cases more or less gradual, but at some stations the transition seems pretty rapid.

Table XI.—Diurnal Inequality of Inclination mean from whole year.

Station. Jan Mayen. St Petersburg
and Pavlovsk.		 Greenwich. Kew. Parc
St Maur.		 Tiflis. Kolaba. Batavia. Mauritius. South Vic-
toria Land.
End Dipping North. North. North. North. North. North. North. South. South. South.
Period. 1882-1883. 1873-1885. 1890-1900. 1891-1900. 1883-1897. 1888-1898. 1894-1901. 1883-1894. 1884-1890. 1902-1903.
a. q. a. q. a. q. a. a. q. a. a. a.
Hour ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′ ′
1 +4.6 +1.5 −0.5 −0.3 −0.4 −0.3 −0.3 −0.1 +0.6 +0.9 +0.3 +0.6
2 +5.0 +1.6 −0.5 −0.3 −0.3 −0.2 −0.3 −0.1 +0.6 +0.8 +0.2 +0.7
3 +5.6 +1.6 −0.5 −0.3 −0.3 −0.2 −0.3 −0.1 +0.5 +0.6  0.0 +0.7
4 +5.0 +1.5 −0.4 −0.3 −0.3 −0.2 −0.4 −0.2 +0.5 +0.5 −0.0 +0.7
5 +4.2 +1.4 −0.5 −0.3 −0.2 −0.2 −0.4 −0.2 +0.7 +0.3 −0.1 +0.7
6 +2.4 +1.2 −0.4 −0.3 −0.1 −0.1 −0.3 −0.1 +0.8 +0.1 −0.2 +0.5
7 +0.7 +0.9 −0.2 −0.1 +0.2 +0.1  0.0  0.0 +0.5 −0.2 −0.3 +0.4
8 −0.1 +0.8 +0.1 +0.3 +0.6 +0.4 +0.4 +0.3 −0.2 −0.8 −0.4 +0.3
9 −0.7 +0.8 +0.6 +0.6 +1.0 +0.8 +0.7 +0.5 −1.2 −1.7 −0.4 +0.1
10 −1.2 +0.9 +1.0 +1.0 +1.1 +1.0 +0.9 +0.3 −1.9 −2.7 −0.5 −0.2
11 −2.2 +0.8 +1.2 +1.2 +1.0 +0.9 +0.7  0.0 −2.1 −3.3 −0.6 −0.4
Noon −3.4 +0.4 +1.1 +1.1 +0.6 +0.6 +0.4 −0.5 −1.6 −3.1 −0.7 −0.7
1 −4.5 −0.2 +0.7 +0.7 +0.3 +0.2 +0.2 −0.6 −0.8 −2.4 −0.8 −0.9
2 −5.6 −1.2 +0.4 +0.4 +0.1 +0.1 +0.2 −0.5 −0.2 −1.3 −0.6 −1.0
3 −6.3 −2.2 +0.2 +0.1  0.0  0.0 +0.2 −0.3 +0.3 −0.2 −0.3 −1.0
4 −6.1 −2.9  0.0 −0.1 −0.1 −0.1 +0.2 +0.1 +0.3 +0.7 +0.1 −0.9
5 −5.1 −3.2 −0.1 −0.3 −0.2 −0.2 +0.1 +0.4 +0.2 +1.3 +0.4 −0.7
6 −3.1 −2.9 −0.2 −0.3 −0.3 −0.3  0.0 +0.5 +0.2 +1.5 +0.5 −0.5
7 −1.7 −2.2 −0.3 −0.4 −0.4 −0.4 −0.2 +0.4 +0.3 +1.6 +0.5 −0.2
8 +0.3 −1.3 −0.3 −0.5 −0.4 −0.4 −0.3 +0.2 +0.4 +1.6 +0.6  0.0
9 +2.0 −0.3 −0.4 −0.6 −0.4 −0.4 −0.3 +0.1 +0.5 +1.6 +0.6 +0.2
10 +2.5 +0.5 −0.5 −0.6 −0.4 −0.3 −0.3  0.0 +0.6 +1.5 +0.6 +0.4
11 +3.0 +1.0 −0.5 −0.6 −0.4 −0.3 −0.3  0.0 +0.6 +1.4 +0.5 +0.5
12 +4.0 +1.3 −0.5 −0.4 −0.4 −0.3 −0.3 −0.1 +0.6 +1.2 +0.4 +0.6
Range 11.9 4.8 1.7 1.8 1.5 1.4 1.3 1.1 2.9 4.9 1.4 1.7

Table XII.—Diurnal Inequality of Declination (+ to West).