reverse loop order

I’m working on a theme and I want the pages showing from my homepage to be shown backwards—I still want the n most recent posts, but I want them to show up with the oldest first.

e.g. if i make one post per month, and my index page shows four images, i want it to show:

(first page)
sept.
oct.
nov.
dec. (most recent)

(second page)
may.
jun.
jul.
aug.

etc.