312 Dr. J. Hancock's Observations on l Heat Lightning] 



M. Volney, speaking of the combination and disunion of 

 water and caloric, observes, " Hence the violent showers which 

 follow loud claps of thunder, and which happen, generally, 

 at the end of storms, the igneous matter being then expended. 

 Sometimes the particles of fire being combined with the air 

 only, it melts like nitre; and this it is, doubtless, which pro- 

 duces those lightnings when no thunder is heard, called fires 

 of the horizon (feux a" horizon). But is this igneous matter 

 distinct from the electric? Does it observe peculiar laws and 

 affinities in its combinations and detonations? This I shall 

 not take upon me to examine. These researches are not 

 suited to a narrative of travels," &c. — Travels in Syria, vol. i. 

 p. 354. Such were the sentiments of this philosophical tra- 

 veller, who, for sound judgement and unaffected science, had 

 few superiors. 



From what I have seen, and heard from the inhabitants re- 

 specting those luminous appearances which " haunt the moun- 

 tain summits," I am confident that they are in general no other 

 than the usual development of electric matter from thunder- 

 clouds. A mountain up the Sibaroni is (doubtless from the 

 same cause,) reputed to be volcanic: some peaks, indeed, seem 

 to attract the lightning more than others ; to this, both their 

 form and composition may contribute, and perhaps even their 

 vegetable covering. It is said that the Mora tree (a large 

 species of Mimosa,) attracts the lightning more than any other 

 tree in Guiana. 



I have found from numerous trials (by counting seconds 

 after the flash,) that thunder is seldom heard at a greater di- 

 stance than 20 miles ; indeed, I have rarely heard it when 

 more than 15 miles distant, and the electric stream, in this 

 case, is seen at a considerable elevation above the horizon. 



Great guns are heard much further than thunder, or at 

 nearly double the distance: the 8-o'clock gun at Demerara is 

 often heard at Cape Batave, on the west coast of Essequibo, 

 a distance of 40 miles. In respect to the intensity of sound, 

 however, there is nothing we are acquainted with, that can 

 bear a comparison with the explosions of volcanos. On the 

 bursting forth of Mount Soufriere, in the Island of St. Vin- 

 cent, on the night of the 1st of May 1812, the explosions 

 were heard in this colony (Demerara) like reports of cannon, 

 more than 500 miles from the island. To this fact many peo- 

 ple here can testify as well as myself. We are told, indeed, 

 that these explosions were heard even at Cayenne, and the 

 Rio Negro, a distance of about 300 nautical leagues. Of this 

 I was assured by the natives, as well as by Captain Orosco, 

 then commandant of the Fort of Rio Negro. The island of 



