INTENSE HEAT THUNDER. 175 



a temperature of 126'5°, at two in the afternoon. 

 The thermometer, raised eighteen inches above the 

 sand, indicated 109° : and at six feet, 101*7°. The 

 temperature of the air in the shade was 97°. These 

 observations were made during a dead calm, and 

 when the wind began to blow, the heat increased 

 three degrees. 



On the 28th March, Humboldt and his companion, 

 being on the shore at sunrise, heard the thunder 

 rolling all around, although as yet there were only- 

 scattered clouds, advancing in opposite directions 

 towards the zenith. Deluc's hygrometer was at 53°, 

 the thermometer stood at 74*7°, and the electrome- 

 ter gave no particular indication. As the clouds 

 mustered, the blue of the sky changed to deep azure, 

 and then to gray ; and when it was completely over- 

 cast the thermometer rose several degrees. Al- 

 though a heavy rain fell, the travellers remained 

 on the shore to observe the electrometer. When 

 it was held at the height of six feet from the 

 ground, the pith-balls generally separated only a few 

 seconds before the lightning was seen. The sep- 

 aration was four lines. The electric charge re- 

 mained the same for several minutes, and there were 

 repeated oscillations from positive to negative. To- 

 wards the end of the storm the west wind blew with 

 great impetuosity, and when the clouds dispersed 

 the thermometer fell to 71*6°. 



Humboldt states, that he enters into these details 

 because Europeans usually confine themselves to a 

 description of the impression made on their minds 

 by the solemn spectacle of a tropical thunder-storm ; 

 and because, in a country where the year is divided 

 into two great seasons of drought and rain, it is in- 

 teresting to trace the transition from the one to the 

 other. In the valleys of Aragua, he had from the 

 18th February observed clouds forming in the even- 

 ing, and in the beginning of March the accumulation 

 of vesicular vapours became visible. Flashes of 



