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MAGNETISM, TERRESTRIAL

363

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

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