Transparency cassette and viewer or projector

A viewer and a cassette, which cassette includes planar upper and lower walls and is in the general form of a parallelepiped and which includes two compartments, each compartment having a cross-section corresponding to the dimensions of slides adapted to be received therein and adapted for holding stacks of slides, each compartment having an end wall and a separate box-shaped structure interposed between and connecting the two compartments and having at least one open end, passages at the top and bottom of said connecting structure communicating with both said compartments, the lower wall of said cassette being provided centrally with a first opening of a size corresponding to a slide to be projected, said box-shaped connecting structure also provided with an opening aligned with said lower wall cassette opening, said viewer having a housing provided with a light source, a condenser lens and a focusing lens, a protruding, hollow supporting element provided on said housing and removably entering said open end of said box-shaped connecting structure and supporting said cassette, with said openings optically aligned with said condenser lens and said focusing lens.