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What Is a Cloud Direction Indicator?

A cloud direction indicator, or nephoscope, is an instrument that uses measurements of speed and direction to track the direction, velocity and altitude of cloud movement. The first recorded use of the word "nephoscope" is in 1881, but the exact date and first inventor of the tool is not known. There are three main types of nephoscopes in use today - the comb, grid and mirror nephoscopes.
  1. Nephoscope Origins and Alternative Forms

    • L. Besson invented the comb nephoscope at an unknown date before 1918. Willis L. Moore's 1908 book, "Descriptive Meteorology," describes an anonymous Swedish metereologist using a mirrored nephoscope around 1888. Other nephoscope forms include Vettin's cloud camera from the late 1850s, Mohn and Lettry's altazimuths, Clayton's mirror with attachments and Fornioni's nephodoscope were invented at some point before 1889.

    Comb Nephoscope

    • A description of the comb nephoscope from the 1942 edition of the Meteorological Observer's Handbooks lists a brass "comb" mounted by rings and clamps on a tall, freely rotatable upright brass rod about 9 feet long. The instrument contains a 3.5-foot crosspiece and six equidistant vertical spikes. Observers can adjust the instrument's height so that a fixed mark on the rod is at eye level. A cloud can be viewed along the same line as the central spike. Without moving themselves, observers turn the crosspiece until the cloud follows the line of spikes in the arrow's direction. The cloud's direction can be read on a graduated circle.

    Grid Nephoscope

    • The grid nephoscope is a variation on the comb nephoscope. Like the comb, the grid is a direct-vision nephoscope with a freely rotating bar grid placed horizontally at the end of a vertical column. The observer rotates the grid and moves around until the cloud in question moves along the grid's major axis. The cloud direction is the azimuth angle at which the grid is set.

    Mirror Nephoscope

    • The mirror nephoscope, also known as the cloud mirror or reflecting nephoscope, was invented by Finemann. It uses a cloud's reflection in a mirror to observe the cloud's motion. A description of the mirror nephoscope in the Negretti &Zambra catalog from what is thought to be the late 1930s, describes a disc of black glass mounted on a tripod stand with three leveling screws. The catalog also mentions a vertical pointer with adjustable height attached to a collar that can be rotated independently of the mirror.


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