1921 .] 
Departmental Reports. 
197 
period part of the inequalities are due to variations which may be expected 
to change their phase through 180° at the solstices, which introduces a 
minor complication that cannot be disregarded. 
The possibility is also introduced that the solar variations that are 
themselves of long period— e.g., sun-spot variability and “ solar constant 55 
variability—may be themselves the product of harmonic solar variations of 
shorter period, probably of variations occurring in the various complete 
multiples of the periods of solar rotation. It seems probable that, in the 
case of a fluid rotating body such as the sun losing heat by radiation, 
under the influence of even minute tide-generating forces small tides or 
seiches will be generated, which will be probably persistent if their period 
is a multiple of the rotation-period, and by their disturbance of radiation 
their effects may be communicated to our earth. In this connection it 
would be unwise to forget that given any kind of “ valve ” action, with 
an immense reservoir of energy such as the sun, an immense magnification 
of effect may be possible. 
The Recent Magnetic Storm, 14th to 17th May, 1921. 
By H. F. Skey, B.Sc., Director of the Magnetic Observatory, Christchurch,, 
(Communicated by the Surveyor-General). 
Plates I and Ia. 
The storm commenced suddenly at 12 h. 38 m. a.m., 14th May, N.Z.S.T. 
The recognized sudden commencement occurred some hours before there 
was any departure from the ordinary type of slightly disturbed day 
(figs. 1, 2, and 3). It usually occurs just before the large amplitudes of the 
oscillations. 
The commencement was characterized by— 
(1.) A very sudden decrease of (— 3') declination, which much less 
rapidly reversed to -f- 4', the declination then gradually returning 
to initial value in twenty minutes (fig. 1). 
(2.) A very rapid seven-stepped sudden increase of the horizontal force, 
amounting to 120 y at 1 h. 38m. a.m., 14th May, followed (fig. 2), 
(3.) A second much slower swing, opposite to the preceding, about two 
and a half hours after the sudden commencement. 
(4.) A less well-defined and still slower swing about five hours after (3), 
and followed by large storminess. 
(5.) About the time of (1) the vertical force increased suddenly about 
12 y, decreasing again thereafter to previous value (fig. 3). 
From 9.30 a.m. to 11.30 a.m., 15th May, the oscillations of the horizontal 
force were too rapid to be recorded, and again from 2.30 p.m. to 4.30 p.m., 
15th May (fig. 5 and Plate Ia). 
The range of the horizontal force was over 750 y, and the declination 
over 170", or about 3°. 
Large oscillations of the horizontal force continued to 1 a.m., 16th May. 
A marked oscillation very like a reversal of the sudden commencement 
occurred at 1 h. 5 m. a.m., 16th May (Plate Ia). 
On the 16th a recrudescence of effects occurred from 1 p.m., but on this 
day the effects were milder, the horizontal force generally decreasing up to 
