518 PHYSICAL GEOGRAPHY. 



occur. Awful as these manifestations are occasionally in our temperate climate, they are 

 but as a skirmishing of outposts to the general engagement of armies, when compared 

 with inter-tropical displays. In Hindustan, in the Indian Ocean, along the African coast 

 off Cape St. Verde, and in Central America, there is often a scene exhibited, which seems 

 a rehearsal of the day " when the heavens being on fire shall pass away with a great 

 noise." Humboldt, during his residence at Cumana, witnessed a coincident development 

 of electrical action, peculiar atmospheric phenomena, and terrestrial disturbance, during 

 what is called the winter of that region. From the 10th of October to the 3rd of Novem- 

 ber, a reddish vapour rose in the evening, and in a few minutes covered the sky. The 

 hygrometer gave no indication of humidity; the diurnal heat was from 82'4 to 89*6. 

 The vapour disappeared occasionally in the middle of the night, when brilliantly white 

 clouds formed in the zenith, extending towards the horizon. They were sometimes so 

 transparent, that they did not conceal stars even of the fourth magnitude, and the lunar spots 

 were clearly distinguishable through the veil. The clouds were arranged in masses at 

 equal distances, and seemed to be 'at a prodigious elevation. From the 28th of October 

 to the 3rd of November, the fog was thicker than it had been before ; and the heat at 

 night was stifling, though the thermometer indicated only 78*8. There was no evening 

 breeze. The sky appeared as if on fire, and the ground was everywhere cracked and 

 dusty. About two o'clock in the afternoon of November 4th, large clouds of extraordinary 

 blackness enveloped the mountains of the Brigantine and Tataraqual, extending gradually 

 to the zenith. About four, thunder was heard overhead, but at an immense height, and 

 with a dull and often interrupted sound. At the moment of the strongest electric explosion, 

 two shocks of an earthquake, separated by an interval of fifteen seconds, were felt. The 

 people in the streets filled the air with their cries. Boupland, who was examining plants, 

 was nearly thrown upon the floor, and Humboldt, who was lying in his hammock, felt the 

 concussion strongly. A few minutes before the first, there was a violent gust of wind 

 followed by large drops of rain. The sky remained cloudy, and the blast was succeeded 

 by a dead calm, which continued all night. The sunset was a scene of great magnificence. 

 The dark atmospheric shroud was rent asunder close to the horizon, and the sun appeared at 

 12 of altitude on an indigo ground, his disc enormously enlarged and distorted. The clouds 

 were gilded on the edges, and bundles of rays reflecting the most brilliant prismatic colours 

 extended over the heavens. About nine in the evening, there was a third shock, which, 

 though much slighter, was evidently attended with a subterranean noise. In the night 

 between the 3rd and 4th of November, the red vapour before mentioned had been so thick, 

 that the place of the moon could only be distinguished by a beautiful halo, 20 in 

 diameter. The vapour ceased to appear on the 7th ; the atmosphere then assumed its 

 former purity; and the night of the llth was cool and extremely lovely. This account, 

 with similar details from other observers, seems to indicate a more intimate relation 

 than is generally admitted between the interior of the earth, and its external atmo- 

 sphere. 



Among the regions peculiarly subject to electric phenomena is the country around the 

 estuary of the Rio Plata. In the year 1793, one of the most destructive thunder-storms 

 perhaps on record, happened at Buenos Ayres, when thirty-seven places in the city were 

 struck by the lightning, and nineteen of the inhabitants killed. It is an observation of Mr. 

 Darwin, founded on statements in books of travels, that thunder-storms are very common 

 near the mouths of great rivers ; and he conjectures that this may arise from the mixture 

 of large bodies of fresh and salt water disturbing the electrical equilibrium. "Even," he 

 remarks, " during our occasional visit to this part of South America, we heard of a ship, 

 two churches, and a house, having been struck. Both the church and the house I saw 

 shortly afterwards. Some of the effects were curious : the paper, for nearly a foot on 



