487 



The earthquake, the greatest that has occurred in Italy since that 

 of 1 783, was felt over nearly the whole of the Peninsula south of 

 Terracina and Gargano. Its area of greatest destruction (the 

 meizoseismal area), within which nearly all the towns were wholly 

 demolished, was an oval whose major axis was in a direction N.W. 

 and S.E. nearly, and ahout 25 geog. miles in length by 10 geog. 

 miles in width. The first isoseismal area beyond this, within which 

 buildings were everywhere more or less prostrated and people killed, 

 is within an oval of about 60 geog. miles by 35 geog. miles ; 

 the second isoseismal is also an oval within which buildings were 

 everywhere fissured, but few prostrated and few or no lives lost. 

 The third isoseismal embraces a greatly enlarged area, within which 

 the earthquake was everywhere perceived by the unassisted senses, 

 but did not produce injury. A fourth isoseismal was partially 

 traced, within which the shock was capable of being perceived by 

 instrumental means, and which probably reached beyond Rome to 

 the northward. 



The author divides his Report into three parts. In the first he 

 has developed the methods of investigation which he pursued for 

 the purpose of finding the directions of movement of the wave of 

 shock at various points, and thence to determine 1st. The point 

 upon the earth's surface vertically over the centre of effort or focal 

 point, whence the earthquake impulse was delivered; 2nd, the 

 depth below the surface (or rather sea-level) of the focal point itself. 

 The line passing through both these points he calls the seismic 

 vertical. The author points out, that of the three elements of the 

 earthquake-wave, viz. the velocity of transit, the velocity of the 

 wave-particle (or wave itself), and the direction of motion at each 

 point of the seismic area, the first alone in other instances has 

 hitherto been attempted to be determined, the velocity of the wave 

 and that of its transit being apparently confounded, and any attempt 

 at direction confined to the apparent path on the surface. He then 

 shows that every displaced object is in fact a seismometer, and that 

 the displacement of regular bodies, such as buildings or their parts, 

 may be made, by examination of their conditions after the shock, 

 and the application of the principles of dynamics, to give precise 

 information as to the true directions- in azimuth and angles of emer- 

 gence at various points of the wave, and its velocity at those points. 



