and Extraordinary Agitations of the Sea. 205 
with thunder, but no shock; the wind and storm returned for 
five or six days at the same hour, almost at the same minute: 
and he states that such diurnal periodicities have been often 
observed at Cumana, and by M. Arago and himself at Paris.* I 
have observed periodicities equally striking, although the inter- 
vals, instead of being days, are lunations (293 days each) or mul- 
tiples of a lunation, and generally at the moon’s first quarter. 
As these, as well as those observed by Humboldt, resulted pro- 
bably from changes in the magnetic or electric state of the 
earth or atmosphere, which is periodically varying not only each 
day, but also according to the positions of the sun and moon in 
respect of the earth, it seems probable that at the end of each 
lunation, when the circuit is completed, and the sun, moon, and 
earth have returned to nearly the samerelative positions as they 
had at the beginning, the magnetic or electric states of the 
earth and atmosphere, and the weather consequent thereon, 
would also be nearly the same at the end as at the beginning, 
subject only to such modifications as other intervening influ- 
ences would occasion. These intervening influences are no 
doubt so considerable as to render it difficult to determine 
whether the examples referred to are merely accidental, or 
whether they depend in some measure on the relative positions 
of the sun, moon, and earth, and the locality of the observer. 
The very numerous examples, however, of lunar periodicities 
which I have given in the British Association Report for 1850 
(Sections), p. 32, cannot, I think, be merely accidental. These 
are exclusively remarkable maxima of the thermometer. 
Other tables of remarkable lunar periodicities I have given in 
the British Association Report for 1845 and elsewhere, con- 
sisting sometimes of maxima and sometimes of minima, and 
sometimes of the barometer and sometimes of the thermo- 
meter, and it might therefore be objected that the proof of 
lunar influences would have been more satisfactory had the 
examples been all maxima or all minima of the same instru- 
ment, But it must be borne in mind that the weather being 
at all times dependent on the ever-changing electric or mag- 
netic state of the atmosphere, must be very different in most 
respects immediately after a discharge (visible or invisible) 
* Personal Narrative, vol. iii., p. 319. 
NEW SERIES.—-VOL. XIV. NO. 11.—ocT. 1861. 2D 
