298 Charles Davison—British Earthquakes. 
Breage, Budock, Camborne, Gwennap, Gwinear, Gwithian, Hayle, 
Lannarth, Leedstown, Mabe, Manaccan, Marazion, Mawgan-in- 
Meneage, Mawnan Swith, Penryn, Perran-ar-Worthal, Phillack, 
Praze, Redruth and St. Ives; III. at Mullion, Penzance and Truro. 
These observations enable us to draw the isoseismal of intensity 
IV. with some accuracy. The area inclosed by this curve is: 
20 miles long and 15 miles broad, and contains about 224 square 
miles. The centre of this area is indicated on the map by the star 
marked B. The direction of the longer axis is approximately east 
and west. 
Outside this area we have observations from only seven places, 
and not more than four of these are of much value in determining 
the boundary of the area over which the earthquake was perceptible. 
Some guide is however given by the position of several places where 
the shock was not felt, inquiries having been made from many 
persons in each place. It is clear that the accuracy of the outer line 
cannot be depended upon, but it is no doubt sufficiently close to the 
correct position to support the inferences that will be afterwards 
made about the origin of the shock. As drawn upon the map, the 
area enclosed by this line is 29 miles long and 22 miles broad, and, 
including the part covered by the sea, contains about 480 square 
miles. The centre of the area is indicated on the map by the star 
marked C. 
Nature of the Harthquake-Phenomena.— Of the accounts given 
below, the first group come from places lying close to the shorter 
axis of the disturbed area :— 
Helston (Observer, Rev. W. Jeffery).—A distant rumble heard, 
gradually increasing in intensity until it became a violent thunder- 
ing sound, at which instant everything in the room was perceptibly 
shaken, the sound dying away after the shock with the same rumble 
as before. Duration of shock, two to three seconds. 
Redruth.—(1. Observer, Mr. T. Carhart.) Two vibrations, the 
first the stronger; preceded and followed by tremulous motion ; 
vertical motion perceptible, downward first and then upward. A 
roaring sound heard, preceding the shock by about five seconds, 
and ending several seconds after it. Duration of the shock, about 
four seconds.—(2. Observer, Mr. W. K. Wilton). A continued 
trembling, consisting of several vibrations, the strongest shortly 
after the first, then dying away; direction, apparently from the 
south-west; duration, less than ten seconds. A sound like that 
of an explosion in a distant part of a mine but more prolonged. 
The next three places are close to the longer axis of the disturbed 
area, the first two near the eastern end :— 
Penryn (Observer, Mr. J. Blamey, M.R.C.S.).—Two distinct 
vibrations of equal intensity, each accompanied and followed, but 
not preceded, by a tremulous motion. Hach vibration also was 
accompanied by a sound of the same kind and intensity, like the 
crash of a heavy weight on the floor above, and followed by a 
rumbling sound like that of a waggon roaring along the street, con- 
tinuing after the tremulous motion and dying away in the distance. 
Duration of shock, three or four seconds. 
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