Based on the text and figure from Proposition XII of the “Book of the Instruments” in Harmonie Universelle by Marin Mersenne, a digital-virtual monochord (multimedia and interactive) and a real-material one (wood and gut strings) have been created to investigate and verify, both numerically and acoustically, the musical science of this natural philosopher. Mersenne's monochord is presented here as a piece of evidence in the continuity of the history of science, that is, the conclusion of some metaphysical traditions, and as prologue of what we call an-aestheticized modern science. These reconstructions help to read some chapters of the Harmonie Universelle in a multimedia way, convinced as we are that musical treatises—especially from the 17th century—have to be “heard” in order to reach a full understanding of their propositions. A fundamental link for this essay is: http://www.calderon-online.com/mersenne/monochord_mersenne.htm