• WordNet 3.6
    • n actinometer an instrument for measuring the intensity of electromagnetic radiation (usually by the photochemical effect)
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Webster's Revised Unabridged Dictionary
    • n Actinometer An instrument for measuring the direct heating power of the sun's rays.
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Century Dictionary and Cyclopedia
    • n actinometer An instrument for measuring the intensity of radiation.
    • n actinometer Chemical actinometers measure the energy of radiation by its chemical effects. Bunsen measured the amount of hydrochloric acid made by sunshine from a mixture of hydrogen and chlorin; Marchand measured the amount of carbonic-acid gas liberated from a solution of perchlorid of iron and oxalic acid by the use of his antiphotypimeter. Photographic actinometers measure the intensity of the shade produced on a sensitized plate by an exposure during one unit of time. Vapor actinometers measure the volume of liquid (water, alcohol, or ether) evaporated in a unit of time. Thermal actinometers measure the heating effect of radiation by many different devices: sometimes called pyrheliometers. De Saussure used the simple hot box; Sir John Herschel, a large thermometer-bulb filled with a blue liquid; Pouillet, a measured volume of water inclosed in a blackened cylinder, the temperature of the water being given by a thermometer within it; Crova and Violle, a black-bulb thermometer within a large spherical inclosure kept at uniform temperature; Arago, as modified by Davy, a pair of bright-and black-bulb thermometers each inclosed in a plane-glass spherical envelop from which the air has been exhausted: when exposed to the sunshine the black bulb attains a higher temperature than the bright bulb, and the difference between the two is an index of the amount of heat which penetrates the glass envelop. The complete theory of this action was published by Ferrel in 1885. Langley used a fine wire coated with lamp-black, the intensity of an electric current flowing through the wire being shown by a delicate galvanometer and varying with the temperature of the wire. Hutchins, following Melloni and Tyndall, employed a delicate thermo-electric junction together with a galvanometer; Chwolson, a pair of plates one of which is exposed to the sunshine while the other is in the shade, the difference of temperature being shown by the intensity of a thermo-electric current; and Angström, in his electrically compensated actinometer, two thin strips alternately exposed and shaded, the difference of temperature being measured by the intensity of the electric current needed to bring them both to the same temperature.
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Chambers's Twentieth Century Dictionary
    • n Actinometer ak-tin-om′e-tėr an instrument for measuring the heat-intensity of the sun's rays or the actinic effect of light-rays.
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Webster's Revised Unabridged Dictionary
Gr. , , ray + -meter,
Chambers's Twentieth Century Dictionary
Gr. aktis, aktinos, ray, and Meter.


In literature:

You may sometimes find that the actinometer indicates a very different exposure from what the eye would lead you to expect.
"Scientific American Supplement, No. 492, June 6, 1885" by Various
For judging long exposures, the use of an actinometer (issued in many inexpensive forms) is helpful.
"How to Observe in Archaeology" by Various
Exposure must be judged by an actinometer.
"Photogravure" by Henry R. Blaney
It is a good plan to employ an actinometer to judge the correct exposure.
"Photographic Amusements, Ninth Edition" by Walter E. Woodbury and Frank R. Fraprie
"The Barnet Book of Photography" by Various