Moisture is generated in any hive by the life of the animals and by the evaporation of nectar. There is also stale air resulting from animal respiration.
This stale, humid air is warm when it is in the cluster of bees and thus it tends to rise. Reaching the top of the hive, it does not cool down quickly, because the top of the hive is always warm, and because the walls of the People's Hive are never very cold, due to the shorter distance between them and the bee cluster. This stale air will continue to occupy the top of the hive, but the cloth lets it pass and be taken into the quilt. This escape of stale air draws in fresh air through the hive entrance. As this escape of air is continuous and under the control of the bees, the fresh air enters only slowly but continuously, to renew the air in the hive and without making the bees uncomfortable.
In other hives this ventilation does not take place in the same manner. The stale air is quickly stopped by the oilcloth or crown boards and continues to surround the bees, for in hives bigger than the People's Hive, the bees are closer to the top.
This stale air extends as far as the walls and condenses on contact with them as they are further away from the bee cluster and thus cooler than the walls of the People's Hive. Having condensed, the moist air passes down the walls and the outer combs and produces moisture and mould. However big the entrance may be, the fresh air does not enter the hive because it is not drawn in by the departure of the stale air. Ventilation in such hives is insufficient or absent.