EARTHQUAKES. 201 



apparently much less intense injure low reed cottages. The 

 natives, who have experienced many hundred earthquakes, 

 believe that the difference depends less upon the length or 

 shortness of the waves, and the slowness or rapidity of the 

 horizontal vibrations,* than on the uniformity of the motion 

 in opposite directions. The circling rotatory commotions are 

 the most uncommon, but at the same time the most dangerous. 

 Walls were observed to be twisted, but not thrown down ; 

 rows of trees turned from their previous parallel direction ; 

 and fields covered with different kinds of plants found to be 

 displaced in the great earthquake of Riobamba, in the pro- 

 vince of Quito, on the 4th of February, 1797, and in that of 

 Calabria, between the 5th of February and the 28th of March, 

 1783. The phenomenon of the inversion or displacement of 

 fields and pieces of land, by which one is made to occupy the 

 place of another, is connected with a translatory motion or 

 penetration of separate terrestrial strata. When I made the 

 plan of the ruined town of Riobamba, one particular spot 

 was pointed out to me, where all the furniture of one house 

 had been found under the ruins of another. The loose earth 

 had evidently moved like a fluid in currents, which must be 

 assumed to have been directed first downwards, then hori- 

 zontally, and lastly upwards. It was found necessary to 

 appeal to the Audiencia, or Council of Justice, to decide upon, 

 the contentions that arose regarding the proprietorship of 

 objects that had been removed to a distance of many hundred 

 toises. 



In countries where earthquakes are comparatively of much 

 less frequent occurrence, (as, for instance, in southern Europe,) 

 a very general belief prevails, although unsupported by the 

 authority of inductive reasoning,! that a calm, an oppressive 



* " Tutissimum est cum vibrat crispante aedificiorum crepitu; et cum 

 intumescit assurgens alternoque motu residet, innoxium et cum concur- 

 rentia tccta contrario ictu arietant ; quoniain alter motus alter! renititur^ 

 [Jndantis inclinatio et fluctus more quaedam volutatio infesta est, aut 

 cum in unam partem totus se motus impellit." Plin., ii. 82. 



t Even in Italy they have begun to observe that earthquakes are un- 

 connected with the state of the weather, that is to say, with the appear- 

 ance cf the heavens immediately before the shock. The numerical 

 results of Friedrich Hoffmann (Hinterlassene Werke, bd. ii. 366-375) 

 exactly correspond with the experience of the Abbate Scina of Palermo. 

 I have myself several times observed reddish clouds onjthe day of aa 



