246 Dr. C. Davison—Founders of Sersmology— 
the sand, and the passage of the waves at a distance of half a mile 
was detected by the tremors on the surface of a mercury bath. In 
Dalkey Island the ranges were of less than half this length (1021- 
1155 feet), the granite in one set being of a more fissured or shattered 
character than that in the other. The mean of eight measurements 
in sand, six in the fissured granite and three in the other, gave the 
following velocities, after all corrections were applied :— 
Sand. : : : : . 825 feet per second. 
Discontinuous granite. 5 3) WA ZOG He at aah Time 
More solid granite . ; : HL OOD ise se Nee han ces 
The second series of measurements were made at Holyhead from 
1856 to 1861, large masses of rock being dislodged from the Govern- 
ment quarries by the explosion of from one to five or more tons of 
gunpowder in mines. The ranges (six in number) varied from slightly 
less than a mile to about a mile and a quarter, crossing different 
lengths of quartz rock, slates, and schists. The velocities varied 
from 954 to 1,289 feet per second, the average of all six measure- 
ments being 1,089 feet per second.! 
Catalogue of Recorded Earthquakes—In the compilation of his 
earthquake catalogue, as well as in the experiments described 
above, Mallet was assisted by his eldest son, the late J. W. Mallet. 
The catalogue forms his third report on earthquake-phenomena, 
and occupies nearly six hundred pages in the reports of the British 
Association. The discussion of the catalogue and the description 
of the seismic map of the world are contained in the fourth report.” 
Though based on several earlier catalogues—especially those of 
Von Hoff, Cotte, Hoffman, Merian, and Perrey—Mallet regarded 
his catalogue as probably the first attempt to include all recorded 
earthquakes. The labour involved in its preparation must have 
been immense. From scattered sources—books of travel, British, 
French, and German newspapers and scientific journals—the number 
of entries obtained amounted to about one-half the total number. 
The details relating to each earthquake are given in tabular form 
under the six headings: time of occurrence, area chiefly affected, 
the direction, duration, and number of the shocks, great sea-waves, 
etc., meteorological and secondary phenomena, and the authorities 
for the records. The first entry is under the date 1606 B.c., and 
Mallet originally proposed that the catalogue should end with the 
year 1850. It was found, however, that the completeness of Perrey’s 
annual catalogues rendered its extension beyond the year 1842 
unnecessary, but the earthquakes of the eight omitted years are 
included in the discussion of the fourth report. The total number 
1 Rep. Brit. Assoc., 1851, pp. 272-317; Phil. Trans., 1861, pp. 655-79 ; 
1862, pp. 663-76. The above velocities are given to the nearest foot per second. 
Mallet expresses them to three places of decimals. Such detail, however, is 
meaningless, for an error of one-hundredth of a second in the time of transit 
at Killiney Bay involves an error of more than 2 feet per second in the velocity. 
2 Rep. Brit. Assoc., 1852, pp. 1-176 ; 1853, pp. 118-212; 1854, pp. 1-326 ; 
pp p 
1858, pp. 1-136. 
