This isn’t a folk song; it’s got a known author (Robert Burns) and date of composition (1783), and it’s written in fluent eighteenth-century poetic-ese (“to muse upon my charmer”, indeed). The original title is “Song composed in August”; the first lines are
Now westlin winds and slaught’ring guns
Bring Autumn’s pleasant weather
I’m putting it up this week in time for the 12th.
I haven’t got much else to say about this, except that it’s one of the most beautiful poems in the language, and works beautifully with this (slightly metrically irregular) tune. I feel quite privileged to sing it. I could explain what’s so great about it as a poem, but I’d rather you just listened to it, read the words and listened to it again (there are lots of other versions around if you get tired of the sound of my voice).