218 



mercury in his barometer, he perceived^ that the 

 column sunk in an extraordinary manner. I 

 know not whether we can give credit to this as- 

 sertion ; but as it is nearly impossible to ex- 

 amine the variations of the weight of the atmo- 

 sphere during the shocks, we must be satisfied in 

 observing the barometer before or after these 

 phenomena have taken place. In the temper- 

 ate zone, the aurora borealis does not always 

 modify the variation of the needle, and the in- 

 tensity of the magnetic forces *. Perhaps also 

 earthquakes do not act constantly in the same 

 manner on the air that surrounds us. 



We can scarcely doubt, that the earth, when 

 opened and agitated by shocks, spreads occa- 

 sionally gazeous emanations through the atmo- 

 sphere, in places remote from the mouths of vol- 

 canoes not extinct. At Cumana, as we have 

 already observed, flames and vapors mixed with 

 sulphurous acid spring up from the most arid 

 soil. In other parts of the same province, the 

 earth ejects water and petroleum. At Riobamba 

 a muddy and inflammable mass, which is called 

 moya, issues from crevices that close again, and 



* I had an opportunity of observing, conjointly with Mr. 

 Oltmanns at Berlin, on the night of the 20th of December, 

 1803, a change of magnetic intensity. The point of con- 

 vergence ot the rays of the aurora borealis was determined 

 astronomically by the azimuth of a star. (Gilbert's Annalen, 

 1811, p. 274.) 



