490 



azimuth, and their close concurrence at the seismic vertical, the 

 position of all the points of observation, and the axial lines of the 

 great mountain ranges. The map B gives the physical features of 

 the country, and the four first isoseismal curves ; distinguishing the 

 injuries done to the numerous cities and towns, &c. by separate 

 colours. Upon both maps the probable horizontal form of the focal 

 cavity is marked, which coordinates with the existing lines of dis- 

 location of the country in a remarkable manner. The map C gives 

 the whole of the isoseismals for this earthquake, and compares them 

 with the corresponding seismal curves (so far as these can be obtained 

 from the narratives), for a number of the greatest earthquakes on 

 record which have occurred in the Italian Peninsula, including that 

 of 1783. 



d. The effects of the physical configuration of the surface and 

 formations beneath, on the progress of the wave of shock, are dis- 

 cussed, and the peculiar oval forms and the directions of the major 

 axes accounted for. 



e. The effects are pointed out, of the form and position of the 

 focal cavity in modifying the distance of transmission of the wave of 

 given effort in different directions. 



f. Applies the results to showing the actual conformity of the 

 isoseismal curves to the principles enunciated. 



g. Under this head the author explains the nature of the separate 

 system of wave-paths for Naples City, and the surrounding district, 

 which only received the shock by transmission of refracted and trans- 

 versal waves passed through the Monte St. Angelo range of moun- 

 tains, with entire change of direction. 



h. Colligates the facts ascertained as to the sounds heard with the 

 shock at various points round the seismic vertical, and points out the 

 remarkable relations that the prolongation of the sound more or less 

 at different points bears to the direction in length and in depth of 

 the focal cavity, and generally the causes of the diversity of sounds 

 heard at various points around earthquake centres. 



*. Discusses and points out the nature and correspondence with 

 the dynamic laws of wave motions, of the tremors that preceded and 

 followed the great shock, and generally the causes inducing such in 

 all earthquakes. 



k. Refers to the ascertained phenomena of reiterated or double 



