Definition of "radiometer" [ra•di•om•e•ter]

• A device that measures the intensity of radiant energy, consisting of a partially evacuated glass bulb containing lightweight vertical vanes, each blackened on one side, suspended radially about a central vertical axis to permit their revolution about the axis as a result of incident radiation. (noun)
• An instrument that detects electromagnetic radiation. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "They are part of my fascination with the supernatural, the otherworldly, the dark and sinister, in contrast to the radiometer, which is of the material world, and which relies on the light, rather than dark."
• "The device, called a radiometer, is based on a classical light-powered, rotating vane most often seen in mall novelty stores."
• "A few years ago, Professor Crookes, of London, having observed that light pith balls delicately suspended in a vacuous tube were under certain conditions repelled by the sun's rays, was led on from step to step until he had constructed the instrument now so well known as the radiometer, in which a delicate wheel is rapidly turned by the rays of the sun, or by the rays of any source of bright light, shining on its blackened vanes."