22 REPORT—1845. 
after the great earthquake of 1755, and 119 days* between those at and after the 
great earthquake of 1761. 
But while such remarkable days have occurred at intervals of four lunations, others 
were mentioned as having taken place at intervals of either single lunations or some 
multiple of a lunation+; and the great earthquakes throughout Mexico on the 9th 
of March and the 7th of April last, are almost exactly one lunation from each other. 
So also, in reference to the six known} shocks of the earth and extraordinary oscilla- 
tions of the sea in Cornwall during the last century, the interval between any two of 
them is almost exactly some multiple of a lunation, The same observation applies 
to the six which have occurred in the present century, except that of the 20th of 
October 1837. With this single exception they have all happened at or near the 
moon’s first quarters. 
From the facts above noticed, it would appear that an earthquake or any very 
disturbed or extraordinary state of the atmosphere, is generally preceded or followed 
either by other earthquakes or by unusual states of the atmosphere occurring at 
intervals of single lunations, or of some multiple of a lunation ; and that the phe- 
nomena which happen at intervals of four lunations, are more striking than those at 
the shorter periods. There seems reason therefore for supposing that earthquakes and 
great atmospherical changes are in many, if not most instances, occasioned princi- 
pally by the action of the moon. 
On the Nature and Origin of the Aurora Borealis, 
By the Rev. Gzorce Fisuer, M.A., F.R.S. 
The following is an abstract of this paper, and the results which the author has 
endeavoured to establish :— 
That the principal displays of the aurora occur in the vicinity of the edge or mar- 
gin of the frozen sea, and occasionally at those places in more temperate climates, 
where humid vapours are accumulated, and by the operation of certain causes, such 
as tides, winds, &c., are brought suddenly within the influence of a cold and dry 
atmosphere, and thereby subject to congelation. That the aurora is an electrical 
phenomenon, and arises from the positive electricity developed by the congelation of 
these vapours, and the consequent induced negative electricity of the upper and 
surrounding portions of dry atmosphere. It is the accompanying indication of the 
restoration of the electrical equilibrium, which equilibrium is restored by the inter- 
vention and conducting power of minute frozen particles, which particles are rendered 
luminous by the transmission of the electricity, and thereby give rise to the various 
appearances of the phenomena. 
From the author’s observations at Winter island and at the island of Igloolik 
(the two winter stations of Capt. Parry’s second expedition to the polar regions, 
which expedition he accompanied as astronomer), he was led to the conclusion that 
those places at which the aurora took its rise, were chiefly confined to the edge or 
margin of the frozen sea. He observed at each of these places, that in the early 
part of the winter, before the sea around was frozen over, the aurora was of a ge- 
neral and diffused character, and extended through the zenith in every direction. 
As the winter advanced and the edge of the ice in consequence became more remote, 
so the aurora diminished in splendour, assumed a low-arch appearance, and was 
seen only in the direction of the open-water, fringing the upper surfaces of dark- 
masses of vapours, known by the name of ‘ Sea-blink,” which hung over and were 
apparently in contact with the exposed surface of the sea, He gives additional evi- 
dence as to this particular locality of the phenomenon from the observations of 
Captains Sir John Franklin, Beechey, Biscoe, and others; and he observes, that its 
7 
* On the last of these 119 days, when the second oscillation occurred in Mounts-bay in 
1761, a very violent thunderstorm happened there in the evening, distant thunder having 
been heard occasionally all the day, and the weather very sultry and calm.—PAil, Trans., 
vol. lii. p. 507. 
+ These haye since been inserted in Jameson’s Edinburgh Philosophical Journal for 
October 1845, pp. 386-389. 
+ The dates are given in the Transactions of the Geological Society of Cornwall, 1843, 
p- 111, and 1844, p. 209. 
