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363
MAGNETISM, TERRESTRIAL

TABLE IX.-Diurnal Inequality of Horizontal Force, mean from whole year (Unit 1-yE~0o0o1 C.G.S.) Station. ]anMayen. Greenwich. Kewl St Ili/?;;, . Tiflis. Kolaba. Batavia. Mauritius. S']Y;§ 1§ Tna Period. 1882-1883. 1873-1885. 1890-1900. I8QO 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 + + 4 + + 5 + 3 -10 - II - 3 -12 V 2 -64 -24 + 4 + + 3 + + 5 + 3 - 9 -10 - 1 -13 3 74 25 +4 + +3 + +5 +3 9 8 +I I4

4 69 24 +4 + +3 + +5 +4 -9 -7 + -15

5 60 22 +5 + +3 + +6 +4 9 5 + -15

6 37 19 +4 + +1 + +4 +4 7 I + I2

7 15 15 +2 + 3 +I +2 I +5 + 9

3 l 13 3 9 S 3 +3 +14 + 7

9 + 8 -12 -I0 - -16 - -12 - 8 +19 +24 + - 3 I0 +17 -12 -16 - -20 - -17, -10 +26 +31 + + 3 II +32 -10 -19 - -19 - -16 - 7 +30 -I-35 + + 7 Noon +49 - 4 -17 - -13 - -I2 - 1 +26 +31 + +12 1 +65 + 8 -12 7 7 + 4 +19 +22 + +18 2 +78 +22 - 6 - - 1 - - 4 + 5 +10 +10 + +20 3 +89 +37 o +2 + -1 +3 +2 -1 - +19

4 +33 +43 +3 + +5 + 0 I 3 9 +18

5 +68 +49 + 5 + + 7 + + 2 4 7 13 +15 6 +37 +43 + 6 + + 9 + + 4 6 8 -14 - +11 7 +13 +30 + 7 + +10 + + 6 4 9 15 1 + 5 8 -II +15 + 8 + +10 + + 7 - 1 -10 -16 - + o 9 33+1 +9 + +8 + +7 +I -11 16 4

IO -36 -10 + 8 + + 7 + + 6 + 2 -11 -16 - - 7 II -40 -16 + 7 + + 6 + + 6 + 3 -10 -15 - - 9 I2 -51 -20 + 6 + + 5 + + 6 + 3 -10 -13 - -II Range 163 74 28 29 30 26 24 15 41 51 17 35 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, Le. 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. When com aring results from different stations, it must be remembered tiiiat 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 Ian 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 north most 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 0 a.m. to TABLE X.-Diurnal Inequality of Vertical Force, mean from whole year (Unit 17). S r ' -

Station. ]anMayen. a, §§ £1§§ f, i;,)3S1§ Greenwich. Kew. Pl?/E3-F Tifiis. Kolaba. Batavia. Mauritius. §§ :;hL;;fd le

Period. 1882-1883. 1873-1885. 1890-1900. 1891-1900. 1883-1897. 1888-1898. 1894-1901. 1883-1894. 1884-1890. 1902-1903. 4; a. q. a. q. a. q. a. a. q. a. a. a. I Hour

1 +65+3 7 3 + 0 +2 +4 +7 + +13

2 +65+2-7 - -4 + 0 +2 +4 +5 + +12

3 +56-1-7 - -4 -1 +1 +3 +4 + +10

4 +37 5 6 3 0 + 1 + 3 + 3 + + 8

5 +16 7 5 2 + 0 + 2 + 5 + 2 + + 3

6 - 7 - 8 - 4 ~ 1 + + 1 + 3 + 7 + 1 + 0 7 -17 - 6 - 3 0 + 1 + 3 + 6 0 + 'o

1 8 -14 - 4 - 2 o - 0 + 3 0 - 3 + - 2 9 -9'o-3 - -3 - -4 -1 -8 -11 + -6

10 -6+5 -2 - -6 - -8 -7 -14 -20 + -13 Il - 6 +10 - 3 - - 9 - -12 -11 -15 -26 -17 Noon -IO +16 - 3 - -10 - -12 -11 -10 +27 - -20 1 -13 +21 - 1 - - 6 - - .9 - 9 - 3 -21 - -20 2 +24 +23 + 2 - 0 - - 3 - 5 + 1 -13 - -16 3 -31+2o +8 + +5 + +2 -1 +4 -4 - -12

4 4<>+13+9 + +8 + +6 +1 +3 +4 6

5 48 +2 +10 + +9 + +7 +3 o +10 - -I

6 -53 - 9 +10 + +10 + + 8 + 4 0 +13 + 3 7 47 18 +9 + +9 + +7 +3 o +14 +6

8 -36-20 +8 + +7 + +6 +3 -|-1 +14 + +9 9 7-19+6 + +5 + +5 +3 +2 +14 + +11

I0 +18 -13 + 3 + + 3 + + 3 + 3 + 3 +13 + +12 Il +42 - 5 - 2 0 + + 2 + 3 + 3 +11 + +12 I2 +54 0-5 - -2 + +I +2 +3 +9 + +13

Range 118 43 17 8 20 18 . 20 15 22, 41 14 33