The instrument has a dual function: it allows the enlarged image of a microscopic specimen to be projected onto a screen or observed directly.

It is composed of two parts, the light source and two optical tubes. The light source is mounted on a brass plate that would have been fixed to an attachment; it consists of a frame to which is attached a movable mirror that serves to collect sunlight and direct it inside the optical tube. One of the two optical tubes is equipped with a perforated specimen-holder that allows the passage of light to the lens, thus allowing the projection of an enlarged image. The other optical tube is equipped with a mirror that can be tilted to reflect light onto the specimen, which may be observed directly.

Instrument on display.