Mesons produced in association with local penetrating showers have been investigated at 11,300 ft. above sea level. The apparatus recorded delayed coincidences arising from the 2.2-μsec. decay process of $\mu$-mesons and distinguished the delayed coincidences which were associated with a local penetrating shower from those which were not. It is found that the fraction of penetrating showers which gives a delayed coincidence is in accordance with the assumption that the local penetrating showers are the typical events in which mesons are produced. The comparison of the delayed coincidences rate using carbon as the material stopping the mesons, with the rate using sulfur shows that the locally produced particles are $\pi$-mesons.

Since a recent latitude experiment on local penetrating showers indicates that the average energy of the particles producing such events is above 10 Bev, the result of the present work extends to that energy the conclusion originated from observations in photographic emulsion, that only $\pi$-mesons, and not $\mu \text{'}\mathrm{s}$ are directly created in the collision of fast particles.

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