Its a swamp cooler
I have one for my 48 Plymouth.
You fill them with ice and water. they hang on the window and as you drive, they scoop air (like a ram air thing), air flows through them, over the ice and water, and out of the outlet into the car. There is a rope you pull that rotates a drum inside of it that soaks up the cold water that the air flows through. So, as you move down the road, cool moist air flows out of it, and when the drum dries, you just pull the cord to rotate it through the ice water again then more cool air comes out. Ya have to pull the cord every few minutes or so to keep the air cool coming out of it. They are kinda cool, old technology.. I love em..