Norman G. Knab, age ll, of Sarasota, Florida, for his question:

Why does the coldest weather come weeks after the shortest day?

The seasons, we are told, depend upon the sun. During the long summer days, the sun rises high in the sky and sheds more heat than during the short winter days, when the noon sun is lower. In a general way, these factors do apply to the changing seasons. But in practice this system fails to keep to a, precise schedule. In the Northern Hemisphere, we should expect December 21 to be the coldest day of the year. This is the shortest day of the year and also the day when the noon sun is lowest in the sky. With the shortest hours of daylight and also the longest, most slanting rays of sunshine from above, we surely have a right to expect less heat and more cold than on any other day of the year. True, the Christmas season may be cold and white with snow. But years of weather watching have taught us to expect the worst of the winter to arrive in late January or February.

This lag in the seasonal schedule is caused by the way our planet absorbs, holds, and releases its quota of daily sunshine throughout the year. There are time lags at the opposite side of the schedule also. The year's longest day falls on June 21 or 22. On that summer solstice day the noon sun rises to its highest peak and its scorching rays pierce directly down through a shorter layer of atmosphere. It is reasonable to expect this to be the hottest day of the year. June 21 or 22 may indeed be scorching hot, but once again, years: of weather watching lead us to expect the best of the summer's heat to arrive later in July and August. Once again, the earth is upsetting the schedule by its methods of absorbing, retaining and releasing its solar radiation. These delaying tactics of the earth's surface are aided and abetted by the gaseous blanket of atmosphere that surrounds it. The air absorbs a negligible amount of heat from sunbeams passing on their way down to the surface of the planet. Instead, solar radiations are changed into heat by the land and oceans, and the lower levels of the atmosphere are warmed by heat radiating up from these wet and dry areas. Any warm substance must share its heat with cooler substances around it. But this heat radiation takes time. It takes time to boil a pot of soup so that it stays hot while you serve it. The earth absorbs heat from every sunbeam and takes its time giving back some of its heat to the atmosphere. A summer night is too short for all the heat absorbed during the long, hot day to escape. Solar heat accumulates from day to summer's day, even though it cools at night.