100 Founders of Seismology.—I. John Michell. 
earthquakes should have remained, or appeared to remain, practically 
unknown for more than half a century. It was referred to in an 
article in the Edinburgh Review for February, 1818, and later in that 
year was reprinted, with notes by John Farey, sen., in the Philo- 
sophical Magazine.1 Many years after his death, full, if belated, 
justice has been done to Michell’s stratigraphical conceptions ; 
but his work, so far as it deals with earthquakes, is less well known, 
owing partly perhaps to the inaccurate account which Mallet gave 
of it in his early memoirs.” 
Leaving out of account the important section on the nature and 
trend of strata—a section which has been adequately dealt with 
by Sir A. Geikie and others—Michell’s paper may be divided into 
three parts. In the first he describes the phenomena of earth- 
quakes, in the second he explains in detail his theory of their cause, 
and in the third he gives methods for determining the position of the 
seismic focus. 
The Phenomena of Earthquakes——Like his predecessors, Michell 
begins with a summary of the phenomena which his theory must 
explain; but, unlike them, he distinguishes between certain 
phenomena which are essential to, and others which have no 
connexion with, the origin of earthquakes. The latter are what we 
now call secondary or mechanical effects of the shock, such as the 
sudden stopping and gushing out of fountains occasioned by the 
opening or contraction of fissures, the dizziness and sickness induced 
by the wave-like motion, and the disturbances sometimes occasioned 
in the direction oi the magnetic needle. These are not “‘ observed 
to be constant attendants on earthquakes, nor do they seem 
materially to affect the solution given one way or other’’. The 
phenomena which Michell regarded as essential, five in number, are 
the following :— 
(i) The same places are subject to returns of earthquakes, not only 
at small intervals for some time after any considerable one has — 
happened, but also at greater intervals of some ages. Michell thus ~ 
distinguishes between the occurrence of after-shocks and the returns 
of great earthquakes, as he shows by his reference to the 451 shocks 
felt at Lima from October 28, 1746, to February 24, 1747, and to 
the sixteen very violent earthquakes at the same place from 1582 
to 1746. 
(ii) Those places that are in the neighbourhood of burning 
mountains are always subject to frequent earthquakes, and the 
eruptions of those mountains, when violent, are generally attended 
by them. Michell refers especially to Peru and Chile, no other 
known countries, he supposes, being so subject to earthquakes and 
none so full of volcanoes. 
1 Vol. lii, 1818, pp. 186-95, 254-70, 323-40. 
* Trans. Irish Acad. (read 1846), vol. xxi, 1848, pp. 58-60, 65-7, 84-5 ; 
also Rep. Brit. Assoc., 1850, pp. 17-19. 
