ON THE FACTS OF EARTHQUAKE ΡΗΦΝΟΜΕΝΑ. 73 
a distance through the earth, and having their origin in very distant earth- 
quakes. Such must have been the cause of the simultaneous movements 
of the magnetometers of Arago at the Observatoire, and of Biot at the Col- 
lége de France some years since. Indeed it was found that at the moment 
a slight shock had been felt in Switzerland and southern France. Capocci, 
Director of the Observatory at Naples, relates that at the eruption of Vesu- 
vius of Jan. 1st, 1839, the declination-needle was moved. (Poggend. Annal., 
b. 1. p. 192; Comptes Rendus, t. ix. p. 735.) It is questionable, however, 
in all such cases, whether the motion be due to magnetism or to pulses com- 
municated to the needle through the shaken ground; and hence special in- 
struments would be desirable, formed to make the distinction. 
“In many instances,” says Von Hoff, “in which an opportunity of ob- 
serving the magnetic needle during an earthquake has presented itself, an 
alteration in its direction for the time has been observed. The usual peri- 
odical oscillations (Abweichungs-Schwingungen) are quicker, or take place 
in a different direction, or are altogether interrupted. It is only in very 
modern times that great and regular attention has been devoted to the 
observation of the magnetic needle; consequently good observations of it 
made during earthquakes are as yet but few in number. The suddenness 
and unexpectedness of earthquake phenomena certainly render it difficult to 
obtain accurate observations made at the place where the earthquake occurs, 
if even the necessary preparations for such observations should be ready, 
which is to be expected from very few places. The greatest care and the 
most perfect and accurate instruments also are required for magnetical ob- 
servations made at the place of the earthquake; the more especially since 
the shock itself, in proportion to its violence, may mechanically put the 
needle in motion, which motion is quite independent of that produced by 
magnetism. 
* More remarkable however are the changes in the direction of the dip- and 
variation-needles, which take place at a distance from the place where the 
earthquake was observed, and at a place where the shock itself is not per- 
ceptible; as, for instance, in Paris, on the 19th of February and 31st of May 
1822, simultaneously with an earthquake which occurred in Savoy and some 
of the southern parts of France. If this observation should be established 
by others carefully made, the existence could not be denied of a connexion 
between terrestrial vulcanism (Erd-vulcanismus) and terrestrial magnetism.” 
(Gescb. Veran. Erdober, Th. iv.) It may be here remarked, that without 
self-registering seismometers and magnetometers, any correct or sustained 
observation of a connexion between these forces is impracticable. 
8th. The Wind. 
“The opinion, that surprising calms precede earthquakes, is also sup- 
ported by some evidence, as in the earthquakes of 1704 in England, 1754 
in Asia Minor, 1759 at Aleppo, and several others noted. But, on the 
other hand, earthquakes are sometimes preceded by high wind and tem- 
pestuous weather; and with respect to this also no law can be laid down. 
Violent storms, which raged at the same time with earthquakes, are men- 
tioned as having occurred in the year 359 in Asia Minor; in 1703 at 
Rome; 1827, 30th of November; 1828, 21st and 23rd of March; 1829, 
13th of April. Storms burst forth immediately after earthquakes, in 893 in — 
India; 1703, at Abruzzo; 1824, 26th of October; 1829, 23rd of April ; 
1833, 9th of October; 1836, 18th of November; 1837, 24th of January. 
The few instances here adduced, laboriously sought for out of such a long 
period of time, during which innumerable earthquakes occurred, at least 
