ATMOSPHERIC ELECTRICITY. 113 



of the Orinoco, in the Kio Atabapo* Did they penetrate 

 into the centre of equinoctial America from the mouth of 

 the Amazon, by the communication of that river with the 

 Rio Negro, the Cassiquiare, and the Orinoco ? They are 

 found here at all seasons, and nothing seems to denote 

 that they make periodical migrations like salmon. 



While the thunder rolled around us, the sky displayed 

 only scattered clouds, that advanced slowly toward the 

 zenith, and in an opposite direction. The hygrometer of 

 Deluc was at 53, tne centigrade thermometer 23'7, and 

 Saussure's hygrometer 87*5. The electrometer gave no 

 sign of electricity. As the storm gathered, the blue of the 

 sky changed at first to deep azure and then to grey. The 

 vesicular vapour became visible, and the thermometer rose 

 three degrees, as is almost always the case, within the 

 tropics, from a cloudy sky which reflects the radiant heat of 

 the soil. A heavy rain fell. Being sufficiently habituated 

 to the climate not to fear the effect of tropical rains, we 

 remained on the shore to observe the electrometer. I held 

 it more than twenty minutes in my hand, six feet above the 

 ground, and observed that in general the pith-balls separated 

 only a few seconds before the lightning was seen. The 

 separation was four lines. The electric charge remained 

 the same during several minutes ; and having time to deter- 

 mine the nature of the electricity, by approaching a stick of 

 sealing-wax, I saw here what I had often observed on the 

 ridge of the Andes during a storm, that the electricity of 

 the atmosphere was first positive, then nil, and then ne- 

 gative. These oscillations from positive to negative were 

 often repeated. Tet the electrometer constantly denoted, a 

 little before the lightning, only E., or + E., and never E. 

 Towards the end of the storm the west wind blew very 

 strongly. The clouds dispersed, and the thermometer sunk 

 to 22 on account of the evaporation from the soil, and the 

 freer radiation towards the sky. 



I have entered into these details on the electric charge 

 of the atmosphere because travellers in general confine 

 themselves to the description of the impressions produced 

 on a European newly arrived by the solemn spectacle of a 

 tropical storm. In a country where the year is diyidod into 



