It is interesting to remember that equal temperament was not the tuning system of choice until the 1840s (pianos) and 1850s (organs)*. A reliable, standardized method for tuning ET wasn’t devised until 1917 by the acoustical engineer William Braid White. Before that time tuners, while paying lip service to ET, were really achieving something that was well tempered.
These days, ET is firmly entrenched in the western art music world. But I think we still yearn for pure intervals – at the very least, pure major thirds. Don’t get me wrong – I play in a wonderful piano trio – but maybe some of our neuroses as string players are rooted in a lingering, almost unrecognized ideal for ‘in tune’ that is at odds with ET. Ah – we live in a conflicted universe….
*These dates are for Great Britain.