Tyndall phenomenon

[tĭndl]
n.
  1. The occurrence of visible floating particles in gases or liquids that are illuminated by a ray of sunlight and are viewed at right angles to the illuminating ray.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.