In this apparatus, light from a sodium lamp falls on the glass plate, inclined at 45 degree to the horizontal, get reflected, and then falls normally on the convex lens placed over the glass plate. A system of bright and dark concentric circular rings are observed through a microscope, arranged vertically above the glass plate. The microscope is properly focused so that alternate bright and dark concentric circular rings are observed more clearly. Measurements are taken from a micrometer driven traveling microscope, which is integrated with this apparatus. The two interfering beams, derived from a monochromatic source satisfy the coherence condition for interference. Ring shaped fringes are produced by the air film existing between the convex surface of a long focus planoconvex lens and the plane of glass plate. Consists of a  microscope tube which can be raised or lowered and clamped at any desired position. The eyepiece, which can be focused using rack & pinion arrangement, having 30x magnification approx. ,and a rotatable cross-line which makes it easy to use.

    The microscope saddle moves linearly along an inlaid Stainless Steel scale on a smooth inter-ground carriage. The motion is controlled using a micrometer drum which is capable of reading accurately up to 0.001 cm.  The platform below the microscope tube has a plano-convex lens arrangement housed in a protective metal case. A reflector plate is also incorporated in the unit which can be adjusted to clearly observe the interference fringes. The unit also has an arrangement for a condensing lens placed between the external light source and the lens, which corrects the path of the light wave and ensures it is optically straight at the time of incidence with the reflector plate. Supplied in a sturdy wooden box.