John Henry Poynting citations

“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.”