C—la

12

Seasonal Diurnal Variation of H, 1922. (Coefficients of the first four terms.)

The summer months taken are January, February, November, December ; equinoctial months taken are March, April, September, October ; winter months taken are May, June, July, August. As regards the amplitudes of these harmonics, a general seasonal graduation shows itself in the first three terms, the amplitude being greatest in summer-time; but in P 4 the reverse is the case, the amplitude being greatest in winter and very small in summer; but there seems no reason to doubt that it is well determined, so that some significance attaches to its phase angle differing by very approximately 90° between summer and winter. Significant also is the fact that in the third and fourth components the winter phase angle is f of the summer angle phase, very nearly. In A 2 the summer angle is practically -| of the winter value, so that in these harmonics the summer angle is -f of the winter angle for A 2 and f- of the winter angle for A 4 and A~. There seems to be more evidence than usual of the non-independence of the harmonic constituents. This may be looked upon as worthy of consideration, and perhaps attributable to our latitude. The origin of the averages must be remembered, for the summer data are the means for two intervals of two months each, separated by ten months ; for the equinoctial data the separation is six months ; for the winter data, really two months ; and the mean values from the three means is this year appreciably different, being — 11, summer months.. .. .. .. .. .. 0-222209 C.G.S. H, equinoctial .. .. .. .. .. .. 0-222125 H, winter .. .. .. .. .. .. 0-222162 Year .. .. .. .. .. .. 0-222165 The winter value is very near the arithmetical mean for the year.

Coefficients of the First Four Terms in Fourier Series, of the Main Seasonal Diurnal Variation, for Year 1922 and for Greenwich Civil Mean Day, at Christchurch, N.Z.

The phase angles are as at Oh. G.C.M.T. The four summer months comprise January, February, November, December; the equinoctial months, March, April, September, October; and the four winter months, May, June, July, August. In the horizontal force it is noticeable that the amplitude of the diurnal wave P t in summer seems to determine all the amplitudes during the equinoctial months ; and in the same way the amplitude of the diurnal wave in equinox seems to determine all the amplitudes in the winter months. This is possibly dependent upon the consideration that the amplitude of Pj depends upon a generally effective cause. Such cause may be expected to have an effect upon the amplitude of the constituent waves P., I'.,, P 3 , l'i in the ratio I, \, y, -}. And taking the resolved equinoctial amplitudes in H, we find 9-78 + i' (4-94) + £ (3-14) + { (0-55) = 9-78 + 2-47 + 1-05 + 0-14 = 13-44r, which is the value of Pj in summer. Similarly, for the winter months, in H, we find 7-30 + J (3-01) + |- (1-97)

P.. A,. J>2A,. PaA,. P*. A 4 . Four summer months Four equinoctial months Four winter months 7 .. 13-43 .. 9-78 .. 7-30 o 291 257 208 f 7 37 8-86 00 4-94 55 3-01 O 299 275 224 32 19 19 7 ' 4-52 3-Id 1-97 O 303 285 202 / 43 34 42 7 0-35 0-59 1-17 O / 276 55 218 43 186 19

P,. A t . P 2 . A,. P 3 . A 3 . P,. A 4 . Magnetic Horizontal Force (unit ly). or or O / O / Pour summer months Four equinoctial months Four winter months Year .. 13-43 291 37 8-86 299 32 4-52 .. 9-78 257 00 4-94 275 19 3-14 .. 7-30 208 55 3-01 224 19 1-97 .. 8-61 261 51 5-02 282 23 5-84 303 285 202 334 i 43 34 42 06 0-35 262 57 0-55 272 14 1-17 186 19 0-57 226 16 261 51 5-02 282 23 5-84 334 06 0-57 226 16 Magnetic Declination: (unit 1'). metic Declination: (unitT). 0-16 43 45 0-25 332 12 0-27 289 15 0-17 329 06 Four summer months Four equinoctial months Four winter months Year .. 2-59 14 09 2-19 357 48 0-20 .. 1-28 35 23 1-83 339 46 0-79 .. 5-06 170 54 0-97 328 54 0-43 .. 1-36 32 01 1-63 345 33 0-84 14 09 2-19 357 48 0-20 22 35 23 1-83 339 46 0-79 347 170 54 0-97 328 54 0-43 338 22 347 338 00 39 58 16 39 58 16 33 0-16 43 45 0-25 332 12 0-27 289 15 0-17 329 06 32 01 1-63 345 33 0-84 00 33