Of hammers and singers
“Until the 19th century, there was no concerted effort to standardize musical pitch and the levels across Europe varied widely. Even within one church, the pitch used could vary over time because of the way organs were tuned. Generally, the end of an organ pipe would be hammered inwards to a cone, or flared outwards to raise or lower the pitch. When the pipe ends became frayed by this constant process, they were all trimmed down, thus raising the overall pitch of the organ.”
From the Wikipedia article on concert pitch – concert pitch has risen over the period of the 19th century to the standardization on the A above middle C being 440Hz in 1955. The main effect has been to increase the demands on singers (more energy at higher notes). The maths in music leads naturally to geometric series and roots and surds….