294 r LETTERS ON NATURAL MAGIC. 



we must seek some natural cause for the phenomena 

 similar to that suggested by Dussaulx. It is curious to 

 observe how the study of nature gradually dispels the 

 consecrated delusions of ages, and reduces to the level of 

 ordinary facts what time had invested with all the 

 characters of the supernatural. And in the present case 

 it is no less remarkable that the problem of the statue of 

 Memnon should have been first solved by means of an 

 observation made by a solitary traveller wandering on the 

 banks of the Orinoco. " The granitic rock," says Baron 

 Humboldt, " on which we lay is one of those where 

 travellers on the Orinoco have heard from time to time, 

 towards sunrise, subterraneous 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 subterraneous 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 con- 

 tribute to modify the sounds ? May we not admit that 



