THE CAUSE.
Scientists will tell you that the reason a window sweats is because there is an uneven temperature on the opposite sides of the window pane. The cold air outside chills the pane, which condenses the moisture in the warm air inside as it strikes the glass, and the moisture is deposited in the form of “sweat” upon the inner surface of the glass. It then freezes, producing “frost.” Occasionally, when there is moisture in the outer air, a deposit is also made upon the outer surface of the glass, but in either case the frost arises from the uneven temperature of the air inside and outside the window glass.