end edges of the glass slats 50 when in the closed position thus when the glass slats 50 are in their closed position the outside perimeter of the slats 50 is effectively sealed on all sides and thus the window construction 10 is substantially fully sealed against the passage of air into the inside of or through the window construction from fig2 and 3 it may be seen that each set of levers 66 includes free ends pivotally connected to an operating bar 96 and that each operating bar 96 has one end of an actuating lever 98 pivotally connected thereto for acting upon by any suitable form of slat operating mechanism not shown with attention now invited more specifically to fig7 it will be noted that minimal clearance between the shaft 62 and the center bore 46 provides an extremely stable connection between the bearing disk 43 and the shaft 62 due to the long axial extent of the connection between the disk 43 and shaft 62 furthermore the bearing disk 43 at axially spaced locations is journalled through the openings 40 and 42 to provide even more stable support for the shaft 62 and this greater support is provided in a manner leading to a smoother operation and minimal friction.