This particular instrument is Meteorological Office Pattern Mark IIIC and was designed to be used in temperate latitudes. The Casella catalog indicates that it is usable from 45 to 65 degrees latitude (north or south). The adjustable latitude scale on the instrument ranges from 0 to 65 degrees and was probably used on other models as well. The instrument is exposed by pointing it due south (in the Northern Hemisphere). A time calibrated heat-sensitive card is placed in the curved chart holder, one per day of recording, and the refracted beam of sunlight burns a record in the strip of the duration of sunshine.

Campbell Stokes instruments were not widely used in the USA, where different designs were preferred (the Marvin electrical sunshine recorder, later replaced by the Foster sunshine switch), but they found extensive use in the rest of the world and may be found in use today. This particular example was found in Quebec City (46.8 degrees N). The instrument was found with the set screw adjusted to 50 degrees N.

Model 6100 is shown in the 1958 and 1963 Casella catalogs on this website, but not in the 1948 catalog. So this instrument probably dates from the 1950s or newer. The glass sphere is 4 inches in diameter. The entire instrument weighs 12 pounds.

An instruction sheet for the Casella Campbell Stokes Sunshine Recorder may be downloaded below (2 pages):

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