A sash window is a sliding window with one or two sashes that slide vertically in front of each other.
The English double-hung sash windows have wires and balancing weights built into the jambs that allow the lower sash to be easy lifted, lowered or kept open in any position in between.
The sash window was developed in France around 1550 and improved with the system of balancing weights by the English architect Robert Hooke in the 1660s.
