What experiment did Marin Mersenne conduct to find the speed of sound?

Marin Mersenne measured the speed of sound through an experiment with echoes! The experiment went as follows: he stood in front of a large wall (a reflecting surface for sounds) saying the words "benedicam dominum" while using a pendulum to measure the time it takes for the sound to come back. If he measures the distance L to this surface, he can calculate the speed of sound by dividing 2L (the total distance traveled by the echo) by t (the time it took for him to hear the echo since the start of his phrase).That is exactly what he did. The beginning of the echo was heard just as he had finished pronouncing his phrase, which took him one second (making t equal to roughly one second). The distance L was measured to be around 485 royal feet (159 meters). Finally, the speed of sound calculated by him was close to 318 m/s (the accepted value today is approximately 343 m/s). He was very close to the correct value, a remarkable feat for that time (seventeenth century)!
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