I write this as I'm listening on a Sunday morning to a rather lovely Schubert composition on Radio 3: his A minor Sonata for fortepiano and arpeggione.
No, I hadn't heard of the arpeggione either. It enjoyed a brief vogue in Vienna in the 19th century, and is vaguely like a cello, but with six strings tuned and fretted like a guitar. Here's a photo: [Sorry - the original photo referenced in this article has been deleted by its owner]
Although the instrument doesn't have the depth or richness of a modern cello, it's still very lovely, and with an extra dimension given by the added range. And it set me thinking. Every school concert I've ever been to has been a painful experience when listening to the string section, because kids find it so difficult to get keep anything close to correct intonation when playing fretless instruments. They can play quite complex runs of notes, bow the notes nicely, control difficult dynamics, keep in time - but it still sounds horribly out of tune, and I grit my teeth when being a dutiful and polite parent who says how lovely everything was.