238 LETTERS ON NATURAL MAGIC. 



says Baron Humboldt, " on which we lay, is one 

 of those where travellers on the Orinoco have 

 heard from time to time, towards sunrise, sub- 

 terraneous sounds resembling those of the organ. 

 The missionaries call these stones loxas de musica. 

 'It is witchcraft,' said our young Indian pilot. 

 We never ourselves heard these mysterious sounds 

 either at Carichana Vieja or in the upper Orinoco : 

 but from information given us by witnesses 

 worthy of belief, the existence of a phenomenon 

 that seems to depend on a certain state of the 

 atmosphere cannot be denied. The shelves of rock 

 are full of very narrow and deep crevices. They 

 are heated during the day to about 50. I often 

 found their temperature at the surface during the 

 night at 39, the surrounding atmosphere being 

 at 28. It may easily be conceived that the 

 difference of temperature between the subterra- 

 neous and the external air attains its maximum 

 about sunrise, or at that moment which is at the 

 same time farther from the period of the maximum 

 of the heat of the preceding day. May not these 

 sounds of an organ, then, which are heard when 

 a person sleeps upon the rock, his ear in contact 

 with the stone, be the effect of a current of air 

 that issues out through the crevices ? Does not 

 the impulse of the air against the elastic spangles 

 of mica that intercept the crevices contribute to 

 modify the sounds ? May we not admit that the 

 ancient inhabitants of Egypt, in passing in- 

 cessantly up and down the Nile, had made the 

 same observation on some rock of the Thebaid, 

 and that the music of the rocks there led to the 

 jugglery of the priests in the statue of Memnon ?" 

 This curious case of the production of sounds 



