202 COSMOS. 



heat, and a misty horizon are always the forerunners of this 

 phenomenon. The fallacy of this popular opinion is not only 

 refuted by my own experience, but likewise by the observa- 

 tions of all those who have lived many years in districts where, 

 as in Cumana, Quito, Peru, and Chili, the earth is frequently 

 and violently agitated. I have felt earthquakes in clear air 

 and a fresh east wind, as well as in rain and thunder-storms. 

 The regularity of the horary changes in the declination of the 

 magnetic needle and in the atmospheric pressure remained 

 undisturbed between the tropics on the days when earth- 

 earthquake, and shortly before it; on the 4th of November, 1799, I ex 

 perienced two sharp shocks at die moment of a loud clap of thunder. 

 (Relat. hist, Liv. iv. chap. 10.) The Turin physicist, Vassalli Eandi, 

 observed Volta's electrometer to be strongly agitated during the pro- 

 tracted earthquake of Pignerol, which lasted from the 2nd of April to 

 the 17th of May, 1808; Journal de Physique, t. Ixvii. p. 291. But 

 these indications presented by clouds, by modifications of atmospheric 

 electricity, or by calms cannot be regarded as generally or necessarily 

 connected with earthquakes, since in Quito, Peru, and Chili, as well as 

 in Canada and Italy, many earthquakes are observed along with the 

 purest and clearest skies, and with the freshest land and sea breezes. 

 But if no meteorological phenomenon indicates the coming earthquake 

 either on the morning of the shock or a few days previously, the influence 

 of certain periods of the year, (the vernal and autumnal equinoxes,) the 

 commencement of the rainy season in the tropics after long drought, and 

 the change of the monsoons (according to general belief) cannot be over- 

 looked, even though the genetic connexion of meteorological processes 

 with those going on in the interior of our globe is still enveloped in ob- 

 scurity. Numerical inquiries on the distribution of earthquakes through- 

 out the course of the year, such as those of von Hoff, Peter Merian, and 

 Priedrich Hoffmann, bear testimony to their frequency at the periods 

 the equinoxes. It is singular that Pliny, at the end of his fanciful 

 theory of earthquakes, names the entire frightful phenomenon, a sub- 

 terranean storm ; not so much in consequence of the rolling sound which 

 frequently accompanies the shock, as because the elastic forces, concus- 

 sive by their tension, accumulate in the interior of the Earth when they 

 are absent in the atmosphere ! " Ventos in causa esse non dubium reor. 

 Neque enim unquam intremiscunt terrae, nisi sopito mari, coeloque adeo 

 tranquillo, ut volatus avium non pendeant, subtracto omni spiritu qui 

 vehit ; nee unquam nisi post ventos conditos, scilicet in venas et cavernas 

 ejus occulto afflatu. Neque aliud est in terra tremor, quam in nube toni- 

 tnmm; nee hiatus aliud quam cum fulmen erumpit, incluso spiritu 

 luctante et ad libertatem exire nitente." (Plin. ii. 79.) The germs of 

 almost everything that has been observed or imagined on the causes of 

 earthquakes, up to the present day, may be found in Seneca, Nat. Quast., 

 vi. 4-31. 



