tit 
’ 
ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 17 
In the first of these, the winter and spring earthquakes together are to 
the summer and autumn together 
as6: 5. 
Tn the supplemental table taken alone, however, the winter season has lost 
its preponderance, and autumn shows the smallest number. 
The number in winter and autumn together, however, still slightly ex- 
ceeds that for spring and summer, in the ratio of 9: 8. 
While this shows the usual doubtfulness of generalizations from partial data, 
the result rather tends to awaken increased attention to the very prevalent 
excess of seismic action in the winter half-year, shown by so many cata- 
logues, and here sustained, though by a supplement, that, taken alone, some- 
what departs from the principle. 
As regards direction, he finds 
INS tor Se Se SR AE CO'8Z 
N.E. ” SOW DERG SRE hee 1:08 
EE) thy, RR OS ODE IEE Oat 
Se PO NVR SS costs mk SOI aie) 1:29 
S. ” NE BAG et eee rh oean 1°29 
Saws AB e bt ane erm 0 0 
eS pg Es ek PEST OE) 189001 0-91 
N.W. ” top) op es oe SOC On ee 4s: 
and the mean general horizontal direction of resultant 
S. 72° 97' E. to N. 72° 27' W. 
Observation by no means accords with any such general mean direction. It 
has repeatedly indicated movements in Italy and Sicily in every azimuth— 
perhaps with some greater prevalence of those from north to south, and the 
reverse ; but the fact appears to be that these regions have their centre of dis- 
turbance almost directly beneath, and hence, as is the case in South America, 
and the Moluccas, Philippines and Sunda Islands, the emergence of the wave 
generally makes an extremely large angle with the horizon ; and the horizontal 
component is ill-suited to easy observation. The most fearful earthquakes 
with which this region has been visited, and whose force has reached 
France, Germany, Holland, and England, and into Africa, are said to have 
had a point within their immediate cincture where the shock was absolutely 
vertical, as in the Riobambe earthquake recorded by Humboldt. 
The memoir of Perrey on Algiers and Northern Africa is brief; and he 
laments that the want of information, and of access to sources of it not 
attainable, prevented his collecting a sufficient number to found any ge- 
neralization upon. ‘The following results alone he is able to tabulate :— 
Tasre XII.—Earthquakes of Algeria and Northern Africa. 
Earthquakes with date of Month. an 
a 
os 
=) £ a | | S38 | Total. 
E z sls |x/2l/2ia8 
a/s|4|-; z Bolo ae pes 
SiS ISLES ele) ale) Ss) ers | er 
Sleijalalisels/S /ea;alol/ala 
peajeae canna) (a \a9]%ar | ar. | ome" |)°63 
Spring Summer Autumn 
12 8 13 
