Search for Charge13eand23eQuarks in Cosmic Radiation near Sea Level

A large-area (3.35 ${\mathrm{m}}^2$) scintillation-counter telescope consisting of six scintillation counters and four widegap spark chambers was arranged to detect single particles with charge $\pm \frac{1}{3}e$ or $\pm \frac{2}{3}e$ which might be present in the cosmic radiation near sea level. Upper limits to the vertical intensities of such particles are 9.8×${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ for charge $\pm \frac{1}{3}e$ and 1.6×${10}^{-10\mathrm{}}$ ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sr}}^{-1\mathrm{}}$ for charge $\pm \frac{2}{3}e$ at a 90% confidence level.