THOSE of us old enough to have lived before the dawn of" central heating remember the "ferns" of ice that used to form on the insides of our bedroom window panes on cold, frosty winter mornings. "Jack Frost's garden", as it was sometimes called, is a phenomenon unfamiliar to our children - the temperature inside a modern house is rarely, if ever, allowed to fall low enough for it to happen.
On a cold frosty night, the temperature of the inside surface of a window pane in an unheated house may fall well below the zero mark. Moreover, in the case of bedrooms, the moisture exuded through the night by the occupants increases the humidity, often to the point of saturation. As the temperature falls, the air seeks to rid itself of its excess moisture by depositing it in the form of ice crystals, to form delicate patterns on the freezing glass.
The crystals are usually shaped like columns or plates and, like snow, they have hexatgonal cross sections that, singularly and in combination, are very pleasing to the eye.
The beautiful jewel like shape, incorporating clusters of "rosettes" or "ferns", grow outwards in all directions from the point of first formation, creating intricate branches as they creep across the frozen surface of the glass. The individual crystals, if examined under a microscope, do not have the perfect symmetry found in the snow crystals that form in free air. But, indeed, it is this very lack of symmetry that allows the patterns to take on such a great variety of magical, surreal shapes.
The alleged author of these icy logos, Jack Frost, was an imaginary elf like character in the folklore of many countries, whose artistry was also evident earlier in the circle of the year when he turned the leaves from green to brown with the approach of winter. He is supposed to be of Scandinavian origin in Norse mythology, Kari, god of the winds, and had a son who was variously known as Jocul, meaning "icicle", or Frosti, meaning "frost": it is Jocul Frosti, we are told, who performs this secret ministry on winter nights.
But then, as so often happens, in other countries there are quite different explanations. In Russia, the icy artist is a white, old man called Father Frost in Japan the Frost Man is the slightly malevolent brother of the Mist Man and in Germany, the agent of the patterns is a woman - a somewhat cold, austere figure that children know as Old Mother Frost.