Mersenne’s Universal Harmony 113
clarity of their echo, did not depend on these factors. Though his monastic brethren would
have recognized his words, his intent went beyond ordinary prayer. He also refers to an
echo in the Tower of Metallus near the Aventine Hill in Rome, which (or so he recounts)
can repeat eight times the recited opening of Virgil ’ s Aeneid , Arma virumque cano qui
primus ab oris ( “ of arms and the man I sing ... ” ). Mersenne used this curious lore to
extend his calculations. He notes that this verse cannot be said clearly and distinctly
in less than two seconds, so that the eightfold repetition would take thirty-two seconds
(evidently allowing equal time between each successive echo). Based on his calculated
velocity of sound, the eight echoes traverse 1,296 toises, traveling back and forth, about
half a league (2.78 km). He speculates that this might give a way of measuring a
large distance (such as the width of a city) by measuring how far sound could be heard
across it.Figure 7.4
Mersenne ’ s “ Harmonic Tablature for the Deaf, ” showing (leftmost column) the notes of the scale, along with the
tension, size, and length of the string needed to produce these sounds.