Table I.—Magnetic Elements and their Rate of Secular Change for January 1, 1901.

Place. Absolute values. Secular change.
D. I. H. D. I. H.
° ′ ° ′ ′ ′ γ
Pavlovsk 0 39.8E 70 36.8N .16553 − 4.1 −0.8 + 7
Ekatarinburg 10  6.3E 70 40.5N .17783 − 4.6 +0.5 −13
Copenhagen 10 10.4W 68 38.5N .17525
Stonyhurst 18 10.3W 68 48.0N .17330 − 4.0 +22
Wilhelmshaven 12 26.0W 67 39.7N .18108 − 4.1 −2.1 +20
Potsdam 9 54.2W 66 24.5N .18852 − 4.2 −1.6 +16
Irkutsk 2  1.0E 70 15.8N .20122 + 0.5 +1.6 −14
de Bilt 13 48.3W 66 55.5N .18516 − 4.4 −2.2 +14
Kew 16 50.8W 67 10.6N .18440 − 4.2 −2.2 +25
Greenwich 16 27.5W 67  7.3N .18465 − 4.0 −2.2 +23
Uccle 14 11.0W 66  8.8N .18954 − 4.2 −2.1 +23
Falmouth 18 27.3W 66 44.0N .18705 − 3.8 −2.7 +26
Prague 9  4.4W .19956 − 4.4 +20 +20
St Helier 16 58.1W 65 44.1N − 3.5 −2.7
Parc St Maur 14 43.4W 64 52.3N .19755 − 4.0 −2.2 +23
Val Joyeux 15 13.7W 65  0.0N .19670
Munich 10 25.8W 63 18.1N .20629 − 4.8 −2.7 +21
O’Gyalla 7 26.1W .21164 − 4.8 +13
Pola 9 22.7W 60 14.5N .22216 − 4.0 +23
Toulouse 14 16.4W 60 55.9N .21945 − 3.9 −2.5 +25
Perpignan 13 34.7W 59 57.6N .22453
Capo di Monte 9  8.0W 56 22.3N − 5.2 −2.3
Madrid 15 39.0W
Coimbra 17 18.1W 59 22.0N .22786 − 3.7 −4.3 +34
Lisbon 17 15.7W 57 53.0N .23548
Athens 5 38.2W 52  7.5N .26076
San Fernando 15 57.5W 55  8.8N .24648
Tokyo 4 34.9W 49  0.3N .29932
Zi−ka−wei 2 23.5W 45 43.5N .32875 + 1.5 −1.5 +37
Helwan 3 39.7W 40 30.8N .30136 − 7.0 −0.4 − 7
Hong−Kong 0 17.5E 31 22.8N .36753 + 1.8 −4.3 +45
Kolaba 0 23.2E 21 26.5N .37436 + 2.2 +7.0 − 9
Manila 0 52.2E 16 13.5N .38064 + 0.1 −5.3 +47
Batavia 1  7.3E 30 35.5S .36724 + 3.0 −7.3 −11
Mauritius 9 25.2W 54  9.4S .23820 − 4.7 +4.6 −39
Rio de Janeiro 8  2.9W 13 20.1S .2501 +10.4 −2.3
Melbourne 8 25.6E 67 24.6S .23295

The rate of movement of the needle to the east at London—and throughout Europe generally—fell off markedly subsequent to 1880. The change of declination in fact between 1880 and 1895 was only about 75% of that between 1865 and 1880, and the mean annual change from 1895 to 1900 was less than 75% of the mean annual change of the preceding fifteen years. Thus in 1902 it was at least open to doubt whether a change in the sign of the secular change were not in immediate prospect. Subsequent, however, to that date there was little further decline in the rate of secular change, and since 1905 there has been very distinct acceleration. Thus, if we derive a mean value from the eighteen European stations for which declination secular changes are given in Tables I. and II. we find

mean value from tableI.−4.18
”   ”   ”   ”II.−5.21

The epoch to which the data in Table II. refer is somewhat variable, but is in all cases more recent than the epoch, January 1, 1901, for Table I., the mean difference being about 5 years.

§ 10. At Paris there seems to have been a maximum of easterly declination (about 9°) about 1580; the needle pointed to true north about 1662, and reached its extreme westerly position between 1812 and 1814. The phenomena at Rome resembled those at Paris and London, but the extreme westerly position is believed to have been attained earlier. The rate of change near the turning point seems to have been very slow, and as no fixed observatories existed in those days, the precise time of its occurrence is open to some doubt.

Perhaps the most complete observations extant as to the declination phenomena near a turning point relate to Kolaba observatory at Bombay; they were given originally by N. A. F. Moos,[11] the director of the observatory. Some of the more interesting details are given in Table IV.; here W denotes movement to be west, and so answers to a numerical diminution in the declination, which is easterly.

Prior to 1880 the secular change at Kolaba was unmistakably to the east, and subsequent to 1883 it was clearly to the west; but between these dates opinions will probably differ as to what actually happened. The fluctuations then apparent in the sign of the annual change may be real, but it is at least conceivable that they are of instrumental origin. From 1870 to 1875 the mean annual change was −1′.2; from 1885 to 1890 it was +1′.5, from 1890 to 1895 it was +2′.0, while from 1895 to 1905 it was +2′.35, the + sign denoting movement to the west. Thus, in this case the rate of secular change has increased fairly steadily since the turning point was reached.

Table V. contains some data for St Helena and the Cape of Good Hope,[12] both places having a long magnetic history. The remarkable feature at St Helena is the uniformity in the rate of secular change. The figures for the Cape show a reversal in the direction of the secular change about 1840, but after a few years the arrested movement to the west again became visible. According, however, to J. C. Beattie’s Magnetic Survey of South Africa the movement to the west ceased shortly after 1870. A persistent movement to the east then set in, the mean annual change increasing from 1′.8 between 1873 and 1890 to 3′.8 between 1890 and 1900.