Thin film interference with mercury light on mica sheets.

Thin film interference with sodium light on mica sheets. Monochromatic yellow sodium light from a sodium arc lamp shines down upon a frosted-glass diffuser-plate. The light from the plate in turn illuminates a large sheet of clear mica framed with a cardboard mount. The mounted mica rests on black paper (for greater visibility of the fringes).The thin parallel sheets of mica are separated by microscopically thin layers of air, and the interference fringes from the sodium light can be clearly seen superimposed on the mica.These fringes can best be seen by moving the head slowly left or right while viewing the mica surface.