Akin to Newton's law of gravitation on a microscopic scale, it is proportional to the quotient of the mirror area and separation distance to the fourth power, and it may be thought of as the attractive force between two parallel plates in a vacuum.  
Predicted in 1948 when van der Waals forces did not properly explain experimental measurements on colloids, it was successfully measured in 1997 by Steve Lamoreaux.  Akin to Newton's law of gravitation on a microscopic scale, it is proportional to the quotient of the mirror area and separation distance to the fourth power, and it may be thought of as the attractive force between two parallel plates in a vacuum.  FTP, this effect named for a Dutch scientist that results in an attractive force between two plates in the absence of other forces.
Predicted in 1948 when van der Waals forces did not properly explain experimental measurements on colloids, it was successfully measured in 1997 by Steve Lamoreaux.  
Casimir effect