USES OF RADIATION.

Otago Witness, Issue 3773, 6 July 1926, Page 73

USES OF RADIATION.

During t 1 ' past frosty and snow r v weather one of the weather reports made reference to the fact that snow on the ground gave rise to such intense cold radiation that the feeble rays of the sun were unable to counteract it. Radiation of cold is a phenomenon to which refererence is not very often made, and its existence is quite unsuspected by the general public. Its effects, however, are very perceptible, although frequently unrecognised. Most people have experienced the extraordinary chill which accompanies the passage of a snow cloud across the sky. The chill is frequently put down to the presence of cold winds, but, in fact, it is due entirely to the radiation from the snow cloud. This radiation is of exactly the same nature as the radiation from the sun, but its wave lengths and other characteristics are such as to produce upon a human being a chilly effect instead of r heating effect. The snowclad ground has exactly the same result, am. in the absence of wind and bright sunshine the cold feeling due to snow on the ground is entirely due to radiation. In parts of the world where the atmosphere is clear, as, for instance, in Switzerland and other mountainous districts, the w r arm radiation from the sun, if it shines, is generally sufficient to counteract the cold radiation from the snow, with the result that it is possible, with snow covering the ground entirely, to feel almost oppressively hot. The subject is interesting, and is a commentary on some information which was published a short time back in these columns in regard to the system of warming in which radiant warmth projected from the ceilings of buildings, is used, in place of radiators distributing warm air. We understand that in the calculations which are made for the designs of systems of warming, using the ceilings or the walls as radiating surfaces, the exposed portions of the building are assumed to be sources of cold radiation, the amount and intensity of which depends on the external temperature, and the warm radiating surface is proportioned in such a way as to counteract the effect of t’ 9 cold radiating surfaces under varying conditions of weather. It is claimed that the bracing effect of a mild, sunny day is very closely imitated in this manner, and anyone who lias experienced the extraordinary comfort which is engendered by bright sunshine in a bracing atmosphere, will appreciate how valuable must be the imitation of such an effect in a building, especially in contrast with the somewhat depressing effects which are frequently obtained with the ordinary central heating apparatus. —Daily Telegrapl*-