Argument

Infrared

Overview

electromagnetic radiation with longer wavelengths than those of visible light

Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).

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The spectrum extends beyond the range of visible light, both into the infra-red and into the ultra-violet. In the latter direction, it extends right into the region of X-rays, which are only ultra-ultra-violet light.
Bertrand Russell, Philosophy
States what Infrared is.
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Much of the evidence is supposed to imply that this evolution of light, like the evolution of heat, is consequent on oxidation of the tissues or of matters contained in them. Light, like heat, is the expression of a raised state of molecular vibration: the difference between them being a difference in the rates of vibration. Hence it seems inferable that by chemical action on substances contained in the organism…
Herbert Spencer, The Principles of Biology, Volume 1
States what Infrared is.
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The effects in question are concerned with the radiation of light from a molecule which has been excited by some collision. Light consists of waves of vibration in the electromagnetic field. After a complete wave has passed a given point everything at that point is restored to its original state and is ready for the next wave which follows on.
Alfred North Whitehead, Science and the modern world
States what Infrared is.
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