I was a living historian and did Civil War reenactments for years. It's pretty hot when you're wearing a heavy wig and corset, chemise, 2 petticoats, a hoop, and a long sleeved dress.
We would have lessons in the heat of the afternoon. We called it the Shady Tree Academy. We would sit in the shade and teach young girls stitching: how to sew on buttons, to sew a hem, sew patchwork, and knit or crochet.
And we kept cool with our own secret hidden individual cooling units. We each had a big tin bowl, a foot or more in diameter. (They were pretty cheap in the kitchenware department. I think they use them in restaurants for making salads.) We put water and ice in them and then sat and slipped our bare feet in. Ooooohhhhhh.... It was cold! That really kept us cool. And no one knew, because they were hidden under our hoop skirts.
So my cooling tip is, when it's oppressive, soak your feet. And cool damp cloths on your pulse points at wrist and neck really cool you down too.