788 Transactioxs of the American Institute 



the ground, the earth heing shaken uninterrnptedlj for upwards of a 

 quarter of an hour with such violence that they could not keep their 

 legs. 



It is much to be hoped, for the sake of science that we may have 

 full and accurate datarespecting the late South American earthquakes. 

 In general there is a great deficiency of reliable information regarding 

 such phenomena. There are very few that would have the nerve and 

 mental balance to imitate the savan Boussingault, who, in one of the 

 South American earthquakes in 1827, sat tranquilly, marine chro- 

 nometer in hand, braving the shock and calmly counting the regular 

 pulsations of the subterranean thunder, which lasted six minutes. 

 And this paucity of satisfactory observations is the more to be regret- 

 ted from the fact that, as Leyell states, " in every instance where a 

 spirit of scientific inquiry has animated the eye-witnesses of these 

 events, facts calculated to throw light on former modifications of the 

 earth's structure are recorded." 



The South American earthquake waves seem to have extended 

 over the whole zone already indicated, though with varj'ing degrees 

 of violence, varying, as we may conjecture, according to the physical 

 constitution of the crust. So far as information has come to hand, 

 the shocks appear to have been confined to the region between the 

 Andes and the Pacific, and not to have swept to the eastward of the 

 great mountain range ; but the pulsations were conveyed along the 

 bed of the ocean, (for it seems that earthquake waves are propagated 

 from place to place precisely in the same manner and according to 

 the same mechanical laws as a wave along the sea or the waves of 

 sound along the air), and made themselves felt at far distant points. 

 This is an observed and well known peculiarity of great earthquake 

 shocks. " It has been computed," says Humboldt, " that during the 

 earthquake of Lisbon on November 1st, 1755, a portion of the earth's 

 surface four times greater than the extent of Europe was simultane- 

 ously shaken. The shock was felt in the Alps and on the coast of 

 Sweden, in small inland lakes on the shores of the Baltic, in Tliurin- 

 gia, and in the flat country north of Germany. The thermal springs 

 of Toplitz dried up and again returned, inundating everything 

 with water discolored by ochre. In the islands of Antigua, Bar- 

 bados, and Martinoy, in the "West Indies, where the tide 

 usually rises little more than two feet, it suddenly rose above 

 twenty feet, the water being discolored and of an inky blackness. 

 The movement was also sensible in the £:reat lakes of Canada and on 



