The published results of lidar observations of the atmospheric sodium layer show that may consistent change in the abundance of sodium during the night is very small, and that there is probably little change between day and night. These measurements also show that the winter increase in sodium observed at mid-latitudes occurs maninly on the bottomside of the layer. Recent 24-hour observations show that any 24-hour component in the diurnal variation in abundance is less than about 5% of the mean. At least as it stands the recently proposed meteor-ablation model, in which sodium atoms which enter the atmosphere during meteor ablation are lost by ionization and subsequent attachments of the ions to aerosols, is shown to be inconsistent with these experimental data.