II. Robert Mallet, 249 
the first instant of the motion, for, afterwards, the later vibrations of 
the condensational wave and the earlier vibrations of the distortional 
wave may coalesce—a precaution which lies at the root of Galitzin’s 
method.! It is one thing, however, to suggest a method, and a very 
different matter to apply it ; and few, I think, will be found to deny 
that, if any name is to be associated with these methods, it should 
be that of Robert Mallet. 
Study of the Neapolitan Earthquake of 1857.—Owing to his long 
residence in Ireland—a typical aseismic country—Mallet had no 
direct acquaintance with earthquakes until 1852. On November 9 
of that year he was awakened. by a strong shock, one that is perhaps 
unique among British earthquakes in having affected all four 
portions of the United Kingdom. It failed, however, to give him the 
materials that he required, and five years more had to pass before 
they were provided by the Neapolitan earthquake of December 16, 
1857. Leaving Naples on February 10, he spent several weeks 
visiting the ruined towns and villages of the meizoseismal area, 
heedless of the many discomforts of a camp life during the wet and 
cold of winter, convinced that in fractured walls and overthrown 
pillars he had ‘‘ the most precious data for determining the velocities 
and directions of the shocks that produced them ’’, inspired by the 
thought that for the first time the depth of the seismic focus was 
being “ measured in miles and yards with the certainty that belongs 
to an ordinary geodetic operation’. Sixty years have passed since 
then ; the certainty of 1858 may have given way to doubt ; yet, as 
one reads the account of his work at Polla and Vietri di Potenza, 
when he realized that at last he had found the point vertically above 
the origin of the shock and could state, as a first approximation, that 
the depth of the focus was 5°64 geographical miles, one cannot but 
sympathize with his confidence that he was showing the way to a 
true intelligence of ‘‘ the viewless and unmeasured miles of matter 
beneath our feet ”’. 
Mallet’s report on the Neapolitan earthquake is the first of a long 
series of monographs on shocks of special strength or interest, and 
for forty years, until the Assam earthquakes of 1897, it remained 
without a rival. His map of the earthquake marks an epoch in 
seismology. For the first time isoseismal lines were drawn on such 
amap. There are four of these. The first surrounds the meizoseismal 
area, within which the towns were for the most part prostrated ; 
the second includes places in which large parts were thrown down 
and persons were killed ; the third those in which slight damage to 
buildings occurred without any loss of life ; while the fourth bounds 
the area within which the shock was perceived by the unaided 
senses. 
On this map Mallet also depicted the lines of wave-path at different 
places, taking the most probable mean direction when more than 
one was measured. The majority of the observations he found to 
1 Rep. Brit. Assoc., 1847, pp. 82-3. 
