CAUSE OF EARTHQUAKES—HOBBS 259 
therefore, a sort of safety valve for pent up gas imprisoned within 
the earth, which following the Aristotelian view, he believed to be 
the cause of earthquakes. 
Modern dress of Aristotle's doctrine, Mallet, 1862—The ancient 
view that earthquakes originate within a cavity or focus wherein 
gases are confined, was given a modern dress as a scientific theory by 
an Irishman, Robert Mallet, who had invented a new type of mortar 
and had also made investigations upon the life of guns. These 
studies had brought him much renown and had been of the greatest 
service to the Allies during the Crimean War of 1854-55. When, 
therefore, in 1857 an earthquake devastated the kingdom of Naples, 
Mallet applied to the Royal Society for a grant of money for the 
purpose of making a study of this earthquake. Apparently under 
the impression that an expert upon explosives was by his training 
best qualified to study an earthquake, the society readily granted his 
request, and the results of his study were later published in two 
massive volumes bearing the title, “ The Neapolitan Earthquake of 
1857.” When Mallet undertook this study the science of physics had 
recently been much advanced by the Dutch physicist Huygens, who 
had introduced a new method for following the progress of harmonic 
disturbances traveling through media such as light through glass 
or sound through air. Mallet adapted this scientific method to a 
study of the progress of earthquakes through the outer layers of the 
earth, and he further supplied technical names which have been 
widely employed even since his theory has been discredited. The 
supposed cavity or focus within which the shocks were supposed to 
originate, Mallet called the “centrum,” and the point upon the 
earth’s surface directly above it he named the “epicentrum,” at 
which point the shocks were believed to arrive first and to be of 
the greatest intensity. This scientific dress applied to Aristotle’s 
theory accounted for its retention by scientists as orthodox doctrine 
for another 50 years, or until early in the twentieth century. 
THE UNIQUE FAULT THEORY 
Japanese earthquake of 1891, Koto, 1893.—Scientists are now well 
agreed that gases imprisoned within the earth are not the cause of 
the devastating earthquakes, though they may perhaps in part ex- 
plain the relatively insignificant shocks which occur in connection 
with eruptions of certain volcanoes. Students of earthquakes 
are also in accord in believing that earthquake shocks are in some 
way connected with the formation of breaks and resulting displace- 
ments of the rocks at and near the surface of the earth. This change 
of viewpoint has come about from studies of earthquakes which 
have occurred within the last third of a century. 
