The size distribution of secondary particulate matter, formed from condensing vapors in meteoric trains in the meteoric evaporating zone, was calculated. The diameters of the particles were found to be approximately proportional to the size of the meteor. The particles were calculated to be below 100 A in diameter, and the median volume diameters ranged from 4.5 to 80 A one min after evaporation. The average concentration of secondary particles formed from meteoric showers was found to be higher than the concentration from the steady-state influx of sporadic meteors. From these results, the majority of the freezing nuclei in Bowen's hypothesis might be interpreted to be connected with the secondary particles formed in meteoric trails. If these particles serve as freezing nuclei, then freezing nuclei should be of similar chemical composition. The presence of larger secondary particles in the wakes of very bright meteors may contribute to the formation of noctilucent clouds. Bowen's hypothesis shou... Abstract The size distribution of secondary particulate matter, formed from condensing vapors in meteoric trains in the meteoric evaporating zone, was calculated. The diameters of the particles were found to be approximately proportional to the size of the meteor. The particles were calculated to be below 100 A in diameter, and the median volume diameters ranged from 4.5 to 80 A one min after evaporation. The average concentration of secondary particles formed from meteoric showers was found to be higher than the concentration from the steady-state influx of sporadic meteors. From these results, the majority of the freezing nuclei in Bowen's hypothesis might be interpreted to be connected with the secondary particles formed in meteoric trails. If these particles serve as freezing nuclei, then freezing nuclei should be of similar chemical composition. The presence of larger secondary particles in the wakes of very bright meteors may contribute to the formation of noctilucent clouds. Bowen's hypothesis shou...