Ixviii NOTES. 



Ventos iu causa esse non dubium reor. Neque enim unquam intremiscnnt 

 terree, nisi sopito mari cocloque adeo tranquillo, ut volatus avium non 

 pendeant, subtracto omni spiritu qui vehit ; nee unquam nisi post ventos con- 

 ditos, scilicet in venas, et cavernas ejus occulto afflatu. Neque aliud est in 

 terra tremor, quam in nulie tonitruum ; nee hiatus aliud quam cum fulmen 

 erumpit, incluso spiritu luctante et ad libertatem exire nitente (Plin. ii. 79). 

 We find in Seneca (Nat. dusest. vi. 4 31), the germ of all that has been 

 observed or imagined up to very recent times regarding the causes of 

 earthquakes. 



( 185 ) p. 193. In my Relation historique, T. i. p. 311 and 513, I have 

 given evidence that the horary march of the barometer continues undisturbed 

 both before and after the occurrence of earthquake shocks. 



( 186 ) p. 194. Humboldt, Rel. hist. T. i. p. 515517. 



( 187 ) p. 196. On the "bramidos" of Guanaxuato, see my Essai polit. 

 snr la Nouv. Espagne, T. i. p. 303. The town of Guanaxuato is situated 

 6420 French feet above the level of the sea. The subterranean thunder was 

 not accompanied by any sensible shock either in the deep mines or at the 

 surface : it was not heard on the neighbouring plateau, but only in the 

 mountainous part of the Sierra, from the Cuesta de los Aguilares, not far 

 from Marfil, to the north of Santa Rosa. The waves of sound did not reach 

 detached portions of the Sierra situated 24 to 28 miles north-west of 

 Guanaxuato, in the neighbourhood of the thermal spring of San Jose de 

 Comangillas beyond Chichimequillo. Measures of extraordinary severity were 

 adopted by the magistrates of the city, when the panic caused by the sub- 

 terranean thunder was at the highest. The flight of a family was punished by 

 a fine of 1000 piastres or by two months' imprisonment, and the militia were 

 commanded to arrest and bring back thfc fugitives. The most curious circum- 

 stance, however, was the confidence which the authorities, " el cabildo," 

 seemed to have reposed in their own superior knowledge, saying, in a proclama- 

 tion of the period, which I had an opportunity of seeing "the magistracy in 

 their wisdom (en su sabiduria) will be well aware of the period of real and 

 imminent danger, should it arise, and they will then give orders for flight ; 

 but for the present it is sufficient to continue the processions." A famine 

 ensued, as the inhabitants of the tabb lands were prevented by their feara 

 from bringing corn to the town. The ancients were acquainted with tiie pirn:- 

 nomenon of subterranean noises unaccompanied ly earth aake : see Arislot. 

 Meteor, ii. p. 802 ; and Plin. ii. 80. The singular noiso which was heard in 



