Marin Mersenne‘s “Harmonie Universelle” is an encyclopedic work on the musical theory and instruments of the 17th century.
Being a mathematician, musician and theologian Mersenne took a more scientific route towards explaining the musical theory of the day, the various systems of temperament, etc.
Mersenne explains the acoustical principals behind instruments of his day, theories on selecting string gauges and other specialized information relevant to musicians and instrument makers.
Books I am drawn too are often out of print, rare, expensive or generally hard to find. I was delighted to find a version of Harmonie Universelle translated into English through my local library system.