282 LETTEKS ON NATURAL MAGIC, 



pistol also is fired. Dr. Plot mentions an echo in Wood- 

 stock Park which repeats seventeen syllables by day 

 and twenty by night. An echo on the north side of 

 Shipley Church in Sussex repeats twenty-one syllables. 

 Sir John Herschel mentions an echo in the Manfroni 

 palace at Venice, where a person standing in the centre 

 of a square room about twenty -five feet high, with a 

 concave roof, hears the stamp of his foot repeated a great 

 many times, but as his position deviates from the centre, 

 the echoes become feebler, and at a short distance entirely 

 cease. The same phenomenon, he remarks, occurs in the 

 large room of the library of the museum at Naples. 

 M. Genefay has described as existing near Eouen a 

 curious oblique echo which is not heard by the person 

 who emits the sound. A person who sings hears only 

 his own voice, while those who listen hear only the echo, 

 which sometimes seems to approach, and at other times 

 to recede from the ear ; one person hears a single sound, 

 another several sounds, and one hears it on the right and 

 another on the left, the effect always changing as the 

 hearer changes his position. Dr. Birch has described 

 an extraordinary echo at Eoseneath in Argyleshire, which 

 certainly does not now exist. When eight or ten notes 

 were played upon a trumpet they were correctly repeated, 

 but on a key a third lower. After a short pause another 

 repetition of the notes was heard in a still lower tone, 

 and after another short interval they were repeated in a 

 still lower tone. 



In the same manner as light is always lost by reflection, 

 so the waves of sound are enfeebled by reflection from 

 ordinary surfaces, and the echo is in such cases fainter 

 than the original sound. If the reflecting surface, how- 

 ever, is circular, sound may be condensed and rendered 

 stronger in the same manner as light. I have seen a fine 

 example of this in the circular turn of a garden wall 



