At the time, during the manufacture of the frame doubles as a window, one of the pierced holes in the bottom of the wood frame of the outer frame. This allowed outside air to penetrate between the two windows, providing a good controlled ventilation which prevented condensation and fogging from forming. Then, there is also installed a clapait wood, which could be movable close to the holes, among other things, preventing mosquitoes from entering between the two panes of the window. more... See more text