From Glossary of Meteorology
(Also called reflecting nephoscope, cloud mirror.) A nephoscope in which the motion of the cloud is observed by its reflection in a mirror.
A representative instrument consists of a black mirror disk, engraved with special concentric circles calibrated in degrees, and mounted on a tripod stand fitted with leveling screws. An eyepiece is arranged so that it can be rotated about the center of the mirror and adjusted to various distances above the mirror surface. The observer orients the mirror so that its zero corresponds to true north, and then adjusts the eyepiece until the cloud is observed at the center of the mirror. The cloud's direction of motion is indicated by the azimuth at which the image leaves the mirror.