[33] The French observers have also applied a method depending on the time of occurrence of the shock. Joining places where the recorded times were the same, they notice that the perpendicular bisectors of these lines intersect within an area which agrees practically with that determined by the azimuths. The inaccuracy of the time-records must, however, lessen the significance of this result. [34] Dr. Agamennone points out that, according to the Italian report, the difference in distance is 22 kms. (or 13-3/4 miles), leading to a velocity of about 3.6 kms., or 2.3 miles per second. [35] It should be remembered that it is not improbable that there were two detached epicentres, coinciding roughly with the two foci of this curve. [36] Only eight are recorded during the night of December 25-26. On several occasions during April and May 1885, groups of slight shocks were felt; but as their individual times are not given, they are regarded as equivalent to one shock each in the above totals. [37] The boundary, as drawn in this figure, differs slightly from that given in Fig. 20. CHAPTER V. THE CHARLESTON EARTHQUAKE OF AUGUST 31ST, 1886. The Charleston earthquake stands alone among the great earthquakes described in this volume, and indeed among nearly all great earthquakes, in visiting a region where seismic disturbances were almost unknown. Calabria and Ischia, the Riviera and Andalusia, Assam and the provinces of Mino and Owari in Japan, are all regions where earthquake-shocks are more or less frequent and occasionally of destructive violence. But, from the foundation of Charleston in 1680 until 1886, that is, for more than two centuries, it is probably not too much to say that few counties in Great Britain were so free from earthquakes as the State of South Carolina.[38] The practical isolation of the earthquake of 1886 left its trace on the character of the investigation. Not only were the observers untrained, but the investigators themselves were unprepared. For instance, the scale of intensity used in drawing the isoseismal lines was not adopted until after the first letters of inquiry were issued. On the other hand, nothing could exceed the energy and ability with which the epicentral tracts were examined by Mr. Earle Sloan and the collection of time-records made by Mr. Everett Hayden. To them, and to Major C.E. Dutton, whose valuable monograph supersedes all other accounts, we are indebted for the two chief additions to our knowledge resulting from the study of the Charleston earthquake. These are the determination of the double epicentre, and the measurement of the velocity with which the earth-waves travelled. DAMAGE CAUSED BY THE EARTHQUAKE.