The observation of correlated pairs of mesons associated with high energy stars is suggestive of a strong attractive interaction between pairs of $\pi$-mesons. If such an interaction exists, it should appear in a relatively simple manner in the production of pairs of mesons by protons or $\gamma$-rays near the energetic threshold. The observation of a marked correlation in energy and angle between the mesons of a pair produced in a single event should lead to quantitative information concerning the meson-meson interaction.

• Received 18 April 1952

DOI:https://doi.org/10.1103/PhysRev.87.621