ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 35 
she is at her greatest distance: then, in order to compare the results, he has 
taken the difference of the totals thus obtained and divided it by their sum, 
. . . . 1 1 1 1 1 1 1 . 
which has given him the quotients 53 a’ Ge Gav’ ise’ 2a 1073’ Which are 
all greater than = and the last almost equal to >: 
“The apparent result from this is, that the difference between the unequal 
attraction exercised by the moon at her greatest and nearest distance has a 
sensible influence over the oceurrence of earthquakes, In the note on the 
‘occurrence of Earthquakes in connexion with the passing of the Moon 
over the Meridian,’ which he presented to the Academy January 2, 1854, 
M. Alexis Perrey discusses the question, whether the division of the shocks 
of earthquake during a lunar day is, like the tides, connected with the 
passage of the moon over the superior and inferior meridian. For this 
method of investigation he could only avail himself of the 824 shocks felt at 
Arequipa, which are registered with day and hour in the above-mentioned 
table of M.de Castelnau. By means of proportional calculations, which 
must have occupied a considerable time, he has calculated to which hour 
after the passage of the moon over the meridian, each of these shocks cor- 
responds. He thus formed a lst table (which he afterwards changed by 
dividing it into sixteen equal portions, grouped side by side, to form eighths) 
containing the 24 hours 50 minutes and a half of which a lunar day gene- 
rally consists. 
“ By these two methods (notwithstanding some marked anomalies which 
could not but exist in so limited a number of facts as 824), the results 
obtained in both arrangements manifest the existence, in the length of a lunar 
day, of two periods of maaximum for the occurrence of shocks, and two of 
minimum, The two periods of maximum occur at the hours of the passing 
of the moon oyer the superior and inferior meridians ; and the periods of 
minimum fall about the middle of the intervals. 
“ M. Alexis Perrey has thus succeeded, by the simple analysis of catalogues 
which he had previously drawn up, in proving, by three different and inde- 
pendent methods, the influence which the moon possesses in the production 
of earthquakes ;— 
“1st. That earthquakes occur more frequently at the Syzygies, 
2nd. That their frequency increases at the Perigee, and diminishes at 
the Apogee of the moon. 
“ $rd, That the shocks of earthquake are more frequent when the moon 
is near the meridian than when she is 90 degrees away from it, 
* But the numerical tables from which these three propositions are derived, 
present some anomalies; and the author has omitted nothing to endeavour to 
account for them, and to prove the law which is revealed at their first in- 
spection. He first conceived the idea of constructing graphically the num- 
bers contained in the tables, so as to obtain by the usual method a poly- 
_gonal line analogous to those by which barometrical observations are usually 
represented, in which the eye catches at once the general course of pheno- 
mena in the midst of anomalies which tend to conceal it. We are tempted 
to regret that he has not further developed this graphical part of his work, 
which would have had the great advantage of displaying at a glance the 
direct result of his researches; and that he has not even annexed to his me- 
moir any of the lines which he constructed. But M. Alexis Perrey con- 
sidered that he would obtain still more certain results by employing caleu- 
lation ; and to this arduous task he devoted the 2nd Chapter of his principal 
- paper, and the Second Part of his note of the 2nd January, 1834, It would 
be difficult for us to follow the author step by step in these analytical discus- 
D2 
