JF Ptak Science Books Quick Post
A: When it is a triangularly-based monochord called the “Trumpet of Marigni”. It was designed 500 years ago to sound like a trumpet by virtue of the single string and the tremulations of the bridge. I’m not so sure what it sounds like (though it sounded like a trumpet) but it certainly is a beautiful thing seen in profile.
This appears in A Course of Lectures on Natural Philosophy and the Mechanical Arts, by the encyclopedic polymath, Thomas Young.
An 1845 version of the work and the engravings is available online–I’m using the engravings from the first edition that I have in hand, which are much cleaner than the later reprint. (I should say that the text is the same for the description of the illustrations so far as I can tell, though position and so on is different.)