II. Robert Mallet. — 243 
was writing his British Association reports on the facts of earth- 
quake phenomena, determining the velocity of earth-waves in sand 
and solid rock, and compiling his catalogue of recorded earthquakes. 
In 1859 he wrote a valuable paper on the coefficients of elasticity and 
rupture in wrought iron, and at about the same time worked out 
the results of his investigation of the Neapolitan earthquake of 
1857, and made further experiments on the velocity of earth-waves 
at Holyhead. 
In 1861, engineering work becoming scarce in Ireland, Mallet 
moved to London, where he set up as a consulting engineer and 
edited the Practical Mechanic's Journal. After an active and healthy 
life his eyes began to fail during the winter of 1871-2, and he was 
practically, though not quite, blind during the last seven years of 
his life. He died on November 5, 1881. 
“In scientific thought, Robert Mallet was remarkable for the 
originality of his ideas, and for the broad grasp he took of every 
subject that engaged his attention ; in private and social-life he was 
beloved for. the kindness, geniality and humour of his disposition, 
for his readiness in conversation and uniform good temper.”2 
Until he was about 35 years old, Mallet, like Michell, had 
apparently given no thought to earthquakes. His attention was 
drawn to them, not by a great disaster, but almost by accident. He 
had noticed in Lyell’s Principles the well-known diagram of a pair 
of pillars, the upper parts of which had been twisted, without being 
overthrown, by one of the Calabrian earthquakes. He saw at once 
the flaw in the usual statement that, under each pillar, there must 
have existed an independent vorticose movement. His practical 
training suggested a simple mechanical explanation. If the centre 
of adherence of the base of the twisted portion were to lie outside 
the vertical plane containing its centre of gravity and the direction 
of the motion, the result might be the observed rotation.2 The 
problem is one of minor importance. Its interest lies chiefly in the 
fact that its solution led Mallet to the views on the nature of earth- 
quake-motion which he described in his memoir on the dynamics 
of earthquakes.$ 
In this memoir, in addition to the discussion of the problem 
referred to, Mallet considers the nature of the earthquake-motion 
in the earth’s crust, the nature and origin of seismic sea-waves 
and of earthquake sounds, the need and use of observations on the 
* Roy. Soc. Proc., vol. xxxiii, 1882, pp. xx. For the above biographical 
details I am chiefly indebted to notices in Hngineering, vol. lii, 1881, 
pp. 352-3, 371-2, 389-90 ; and Min. of Proc. of Inst. of Civ. Eng., vol. lxviii, 
1882, pp. 297-304. 
* Other, and perhaps more probable, explanations of the movement are 
given in Trans. Seis. Soc. Japan, vol. i, pt. ii, 1880, pp. 31-5, and GEOL. 
MAG., 1882, p. 264. 
* “On the Dynamics of Earthquakes; being an attempt to reduce their 
observed phenomena to the known laws of wave motion in solids and fluids’? 
(read February 9, 1846): Trans. Irish Acad., vol. xxi, 1848, pp. 51-105. 
