and 38 spaced inward from respective outer edge portions 26 and 30 and substantially parallel spaced apart transversely extending edges 40 and 42 also spaced inward from respective transverse outer edge portions 28 and 32 the intersection of each of longitudinally extending edges 36 and 38 and transversely extending edges 40 and 42 is slightly rounded so as to avoid the possibility of stress concentrations occurring at these points which could result in cracking of frame member 18 the spacing between edges 36 38 40 and 42 will be slightly greater than the length and width respectively of transparent member 22 so as to allow transparent member 22 to fit easily within this opening and also to allow a relatively narrow bead of a resilient sealing compound to be injected between the edge of transparent member 22 and respective edges 36 38 40 and 42 of frame member 18 frame member 18 also has a flange portion extending into opening 34 from each of edges 36 38 40 and 42 including portions 44 46 48 and 50 which are adapted to support transparent member 22 within opening 34 the inner edges of this flange portion are also provided with rounded.