AMERICAN 
f 
JOURNAL OF SCIENCE AND ARTS. 
[SECOND SERIES.] 
Art. IL—Theory of Earthquakes; by Professor ALEXIS PERREY, 
of Dijon, France.’ 
ARTHQUAKEs arte a complex phenomenon. It is difficult to 
refer them to One cause alone, The shocks or series of shocks 
in a given region may have a special or local cause. Ve may 
distinguish 2 Number of such special causes acting independently 
of the pees cause whose general action they modify. More- 
over, these secondary causes may be modified in their action by 
the principal cause, the latter manifesting itself only through a 
differential result. 
: the phenomena, it is difficult to distinguish those 
which are the effects of the principal cause from those of special 
or local causes, The first aim of investigation should be to 
determine that differential result in which the gag ae 
disappear; oF, in other words, the influence of the principal 
cause is brought into strong relief, the differential action making 
lt manifest, : 
There is a periodicity as to times of occurrence in earthquakes, 
as in other Cosmical and meteorological phenomena. When 
? Translated for this Journal from a memoir communicated by the author entitled 
. itions sur lex Zremblements de terre et les Volcans ; formulées M. Avexis 
Penney, Professeur 4 la Faculté des ciences ijon, adressées 4 M. Lamé, Mem- 
bre de l'Institut; 36 p- 8vo. Paris, 1863. Mallet-Bachelier, Quai des Augustins, 55. 
Only the part on Hurthquakes is here | 
Am. Joun. $cl.~QgcoNp Seigss, Vor. XXXVIL, No. 109.—Jan., 1864. 
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