ON THE FACTS AND THEORY OF BARTHQUAKE PHENOMENA. 7 
elastic wave. A considerable number of shocks, recorded in Scotland, have 
been stated to have had a horizontal direction more or less from west to east; 
and this is by no means incompatible with the general prevalent direction from 
south to north already mentioned ; nor has it been unnoticed elsewhere, that 
long ranges of hills of hard elastic rocks, with deep intervening valleys, change 
the general horizontal course of the wave of shock reaching their fanks into 
one mainly felt along the line of the chain. The little shocks for long 
periods almost continuously felt in and about Comrie in Scotland, have all 
had a general direction from west to east ; but these, like the similar phe- 
nomena long carefully observed by Prof. Merian at Basle in Switzerland, 
those at East Haddam in Massachusetts and elsewhere, I omit from consi- 
deration here, as very doubtfully belonging to the class of earthquakes 
proper at all, and perhaps no more than tremors, more or less forcible 
at the surface, due to the fracturing of rocky masses below, by the gradual 
processes of elevation or depression of the land. Excluding these, our 
records, so far as they go, point to the south-to-north general direction 
as given. 
Milne has discussed, with reference to period of the year, the circumstances 
of 139 Scottish and 116 English earthquakes ; and the result squares pretty 
closely with Perrey’s. 
The following is Milne’s Table :— 
TABLE V. 
Scotland. England. Total. 
JAtitiary-ci.inee.; 14 ages sifeoes, LI 
Hebruaty .crccasel PA) issasesdscs 13 +74. Winter months. 
March ..... Sucaed f RAS vecdccaet 10 
10 
4 +44, Spring months. 
9 
5 
9 $58. Summer months. 
15 
October sssssvvee 14  sesvcessssse J] 
November,....... polls cdepteecesst 12+79. Autumn months. . 
December.... i: sis AG > caseee ceases 
139 1l 
He notices also the fact, which we shall find has not escaped Perrey (‘ Me- 
moir on France’), that the period of the year at which seismic action appears 
to be greatest, is that when both the actual height of the barometric column 
is the minimum, and the range of its oscillations the greatest in the year ; 
and he has put with clearness the enornious total effect in the increase or 
diminution of pressure over large areas, due to such changes in atmospheric 
pressure, as a possible (he deems a certainly) connected cause in the produc- 
tion of earthquakes. 
Proceeding now to the Spabish Peninsula, comprehending all west of the 
Pyrenees and the ocean washing the shores of Portugal, the following are 
Perrey’s results :— 
