Direct measurement of three-body interactions
  Three-body interactions have been measured among three charged colloidal particles in deionized solvent. Two of the particles have been confined to an optical line-trap while the third one was approached by means of a focused laser beam. The experimentally determined three-body interactions are attractive and roughly of the same magnitude and range as the pair-interactions. In addition, numerical calculations have been performed, which show good agreement with the experimental results. 
M. Brunner, J. Dobnikar, H.H. von Gr\"unberg, and C. Bechinger