1120 
MR. C. DAVISOR ON THE ANNUAL 
amplitude of the period being diminislied; while the effect of including a large 
number of slight shocks of the second class is to keep the epochs interchanged and to 
increase the amplitude, (3) With regard to the semi-annual period, the results, as a 
rule, show that strong shocks and slight shocks have the same maximum epochs, but 
that the amplitude for the latter is somewhat greater than for the former. 
Seismic Periodicity in the Northern Hemisphere. 
Northern Hemis'pliere. 
18. Pv. Mallet, “ Catalogue of Recorded Earthquakes from ,1606 b.c. to a.d. 1850,” 
‘Brit. Assoc. Rep,,’ 1852, pp. 1-176; 1853, pp, 118-212; 1854, pp, 1-326; 1858, 
pp. 46 and 57. 
Duration of record, a.d. 223-1850. Number of earthquakes, 5879. 
Mallet’s great catalogue includes several earthquakes which occurred before the 
Christian era, but the first in which the month is stated was felt in the year a.d. 223. 
It closes with the end of the year 1842, though he originally intended to bring it 
down to the end of 1850. M. Perrey’s catalogues, which rendered the continuation 
unnecessary, were, however, used by Mallet in his final discussion in his “Fourth 
Pteport.” It was found necessary to make some convention with regard to the long- 
continued series of slight shocks or tremors felt at several places (Pignerol, Comrie, 
&c.), and in these cases “ the slight shocks recorded for each month of the disturbed 
period are grouped as forming one earthquake at the locality.” It will be seen from 
Table II. that the six-monthly means for November, December and January are the 
same. I have taken the intermediate month as the date of the annual maximum. 
Period. 
Maximum. 
Amplitude. 
Annual. 
December, h 
T1 
Semi-annual . ... 
r Febrnarj, a 1 
•07 
t Augu.st, a j 
19, *'C. W. C. Fuchs, ‘ Statistik der Erdbeben,’ pp. 13-286, 315-321, 357-408. 
Duration of record, 1865-1884. Number of earthquakes, 8133 (fig. 5). 
This number includes all the earthquakes recorded by Fuchs as occurriug in the 
northern hemisphere, with tlie exception of those felt in the northern part of the 
Malay Archipelago. I have also omitted a few shocks in places which I am unable 
to identify, but the number of these is so small that it cannot possibly affect the 
result. The same remark applies to the discussion for Fuchs’ catalogues for the 
southern hemisphere. 
