John Henry Poynting Quotes

John Henry Poynting: 2 quotes 0 likes

“When we see the havoc wrought on a sea-wall by a storm, it is easy to believe that ocean waves exert a pressure against the shore on which they beat. But it is not easy to think that the tiny ripples of light also press against every body on which they fall, to think that when a lamp is lighted waves of pressure are sent out from it—pressing against the source from which they start, pressing against every surface which they illuminate. It is a very minute pressure, far too small, even when it is strongest, to be felt by our bodies, and only to be detected by exceeding sensitive apparatus.”

John Henry Poynting

[The pressure of light, 1910, London, Society for Promoting Christian Knowledge, 9, https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t87h1gt3q;view=1up;seq=13]

Light , Sea , Thinking

“A very simple experiment shows that a black surface is a better radiator, or pours out more energy when hot, than a surface which does not absorb fully, but reflects much of the radiation which falls upon it. If a platinum foil with some black marks on it be heated to redness, the marks, black when cold, are much brighter than the surrounding metal when hot; they are, in fact, pouring out much more visible radiation than the metal.”

John Henry Poynting

[Smithsonian Report for 1904, 185–193, Radiation in the solar system, https://books.google.com/books?id=2G1xpr2w4PUC&pg=PA186] (p. 185)

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