Principal Forbes, also, as we have seen, is of opinion that the opalescent vapour occurs " perhaps conversely during evaporation," as well as condensation. This we aro able to confirm from our own observations, made long before he had enabled us to understand them. It may be proved by a ready experiment. If a plate or a saucer be plunged into nearly boiling water and withdrawn, it will be covered with a film of water, which the beat acquired by the porcelain will immediately convert into vapour, rendering the plate dry. If, on withdrawing it from the water, it be immediately held up to the light, a pink blush, as it were, will be seen, momentarily, before the steam cloud resulting from entire condensation. During evaporation in nature the same phenomenon must of course take place : it may readily be observed on Derwentwater, looking northward, on a summer morning, when Skiddaw and the adjacent mountains may be seen through a transparent mist, having a pale pink or rose-coloured hue; the evaporating water below constantly supplying opalescent vapour, the appearance is persistent so long as the sun is acting and the atmospheric circumstances are unaltered, notwithstanding the perpetual resolution of the opalescent into invisible vapour above. This connects the sub
ject with the colours of the sky and the prognostics of the weather derivable from them. A part of this subject, also, is considered in the article just referred to. In the article on OPALESCENT Vermin itself we have expressed our dissent from Principal Forbes as to the process by which the colours of the morning sky are produced, deeming it to be merely the reverse of that occurring in the evening. We think it might be shown " that the Slowly progressive transition of vast masses of air through the temperature of the dew-point " must occur at sunrise as well as at sunset ; of thin, the "beautiful rosy tint, shooting far up into the heavens," described as preceding the dawn, when observed from Mont Blanc, is one of many examples that might be mentioned in evidence, according entirely with the facts already noticed, winch the distinguished physicist whose views we have been considering first recognised in their due importance. [CLIMATE; Messonosoov.]