432 EARTHQUAKE PHENOMENA. 



of pestilences, failure of crops, &c, in relation to earthquakes, while 

 they must be received with caution, should not be disregarded. 



Any changes of permanent level of sea and land that accompanied 

 former earthquakes that are on record should be obtained, with their 

 particulars; whether the same points have been affected in successive 

 earthquakes and by successive upheavals; whether the same or differ- 

 ent volcanoes were in action during successive earthquakes; and 

 whether the area of disturbance in habitual earthquake regions seems 

 to enlarge in successive shocks. — (Humboldt, " Cosmos.") 



Upon maps of the country in which the shock was felt, coseismal 

 and meizoseismal curves may be finally laid down, upon which also 

 the cotidal lines of the great sea-waves on a long coast-line may be 

 marked. Maps of fissures formed in relation to the coseismal lines, 

 and generally sketches of all visible remarkable effects of the earth- 

 quake 'on natural or artificial objects, should be made. Photography 

 affords precious facilities for preserving the appearances of shattered 

 buildings and the relations or alterations of natural features, &c. The 

 effects of earthquakes on the lives of men and animals; statistics of 

 mortality; modes of entombment by the convulsion, as bearing on 

 future organic remains; burying of objects of human art — are all 

 worthy of notice. 



It sometimes happens that a shock of earthquake is felt at sea at 

 great distances from land, and over profound depths; a sudden blow 

 is felt as if the ship had struck a rock. — (See " Comptes Rendus, " 

 vol. vi, pp. 302 and 512, 1853.) 



The earth-wave coming from an origin probably in most cases nearly 

 vertically beneath is here transferred to the ocean, through which it 

 passes upwards as an elastic wave, with the same speed as the sound- 

 wave through the sea. When such an event occurs in a smooth sea, 

 and circumstances are favorable, we should look out for and note the 

 direction of the passage almost immediately in form of a single, low 

 swell, of the great sea-wave, which may be formed directly over the 

 origin, at no very great distance off. Immediate attention should be 

 given to the particulars of any objects that may have been displaced 

 on board. Compasses are thrown out of the gimbals, shot dislodged 

 from their seats round the hatchway coamings, or other places; a mast 

 has even been unstepped. The relation observed between the extent 

 of lateral and of vertical displacement will give some notion of the 

 deviation of the line of shock from the vertical, and of its elope in 

 azimuth. This found, a cruise about may be made in search of pumice, 

 discoloration, or other indications upon the surface of the sea, <fcc, 

 of the orgin under the sea bottom. Where the depth of water is 

 great it is improbable that any indications of the convulsion below 

 will reach the surface. Efforts, however, should be made to reach the 

 bottom with the armed lead line and to obtain two lines of soundings 

 at equal intervals for some miles, running both in latitude and longi- 

 tude, and to bring up specimens of the bottom at each throw of the 

 line. The origin may be found to be a newly-emerging volcano, an 

 object always of great interest ; the observation when in deep water 



