ON THE FACTS AND THEORY OF EBARTHQUAKE PHENOMENA, 55 
laws, when once reached, must shed upon terrestrial physics. The period 
of mere cataloguing (like that of fossil-list making in the earlier geology) 
seems now past; we must give it up, and, in the words of Herschel, “we 
must now grapple with the palpable phenomena, seeking means to reduce 
their features to measurement, the measures to laws, the laws to higher 
generalizations, and so, step by step, advance to causes and theories.” 
(Address, Camb. 1845.) 
Many cases are recorded in the Catalogue of Earthquakes, of shocks 
occurring at two very distant places upon the earth’s surface, but felt simul- 
taneously, or nearly so, at both. The coincidence in time is, for all very 
distant places, rendered extremely doubtful, from errors of observation and 
of clocks, and of their reduction for difference of longitude when the places 
are not on the same meridian. 
Milne also has collected several such instances; for example— 
February 1750...England and Italy. 
March 1750...England and Italy. 
May 1750...England and Calabria. 
August 1750...England and European Turkey. 
February 1756.. England and Central France, Holland and the Rhine. 
November 1756...Scotland and Malta. 
January 1768...Shetland and Central England. 
December 1789...Edinburgh and Florence. 
February 1818...Great Britain and Sicily. 
September 1833...England and Peru. 
August 1834...Scotland and Italy. 
September 1834... England and Peru. 
In these, however, the coincidence in time cannot be assured within several 
hours ; and it must be admitted, with Mylne, that the probability of any- 
thing more than mere coincidence is extremely slight. 
In 1840-41 he found three shocks of this character: viz. 
March 1840......+.. Scotland and Germany. 
June 1841......... Terceira and St. Louis. 
Waly | L941. cases, Scotland and France. 
(Edin. Phil. Journ. xxxi. to xxxvi.) 
A few such instances, that possess a closer approximation in time and 
some additional probability of actual coincidence, have been extracted from 
the Catalogue, and have been drawn in the diagram (Plate X bis) to scale,— 
those which had horizontal components of motion in the meridians N. to 8S. 
or S. to N. being placed at the right and left sides of the great-circle section 
of the globe ; and those with horizontal movement E. and W. or W. and E., 
placed above and below. 
Right lines connecting the supposed distant points of coincident shock by 
chords of the circle, would probably pass through the origin or centre of 
disturbance common to both places on the surface. The origin might be 
deeper to any extent, and possibly somewhat nearer the surface, at least in 
the cases of the longer chords. Were any reliance to be placed upon these 
coincidences, some of them would thus give a depth of origin of about 800 
miles below the surface. None of those, however, that appear to have any 
satisfactory evidence of a real connexion in time and in origin, suggest a 
depth for the latter of even one-tenth that amount. All our other know- 
