PHENOMENA IN THE INTERIOR; 177 



illuminated by small electric explosions, like phos- 

 phorescent gleams confined to a single group of va- 

 pours. From this period the breeze shifts at inter- 

 vals, and for several hours, to the west and south- 

 west, affording a sure indication of the approach of 

 the rainy season, which, on the Orinoco, commences 

 about the end of April. The sky begins to be over- 

 cast, its azure colour disappears, and a gray tint is 

 uniformly diffused over it. At the same time the 

 heat of the atmosphere gradually increases, and in- 

 stead of scattered clouds the whole vault of the 

 heavens is overspread with condensed vapours.. The 

 howling-monkeys begin to utter their plaintive cries 

 long before sunrise. The atmospheric electricity, 

 which, during the period of the greatest drought, 

 from December to March, had been almost con- 

 stantly in the daytime from 1*7 to 2 lines to Volta's 

 electrometer, becomes extremely variable after 

 March. During whole days it appears null, and 

 again, for some hours, the pith-balls of the elec- 

 trometer diverge from three to four lines. The at- 

 mosphere, which in the torrid as in the temperate 

 zone is generally in a state of positive electricity, 

 passes alternately, in the course of eight or ten 

 minutes, to the negative state. The rainy season is 

 that of thunder-storms ; and yet I have found, from 

 numerous experiments made during three years, that 

 at this season the electric tension is less in the 

 lower regions of the atmosphere. Are thunder- 

 storms the effect of this unequal change of the dif- 

 ferent superimposed strata of the air 1 What pre- 

 vents the electricity from descending towards the 

 earth in a stratum of air which has become more 

 humid since the month of March 1 At this period 

 the electricity, in place of being diffused through the 

 whole atmosphere, would seem to be accumulated 

 on the outer envelope at the surface of the clouds. 

 According to M. Gay Lussac, it is the formation of 

 the cloud itself that carries the fluid towards the sur- 



