QUESTIONS.

Bruce Herald, Volume XXXVII, Issue 4, 15 January 1901, Page 7

QUESTIONS.

What is the bast form of nightlight ? There is so much to be said in favour of the thick, dumpy form of candle, adapted to be set to burn in a saucer of water, that it is difficult to give conscientious praise to any other kind. We may, however, at least pay a tribute to the ingenuity displayed in tho construction of a little acetylene gas nightlig-ht, which is being hawked about the streets of our large towns — for the humble penny. It is a tin vessel., containing a preparation of calcium carbide, and provided with a tiny aperture. On dipping it in water, a very slow but regular evolution of illuminating gas commences, and a medest but sufficient flame subserves the purposes of the bedroom. (As our sleeping apartments should always be well ventilated, the acetylene nightlight may be said to be tolerably free from danger.) Why is rain sometimes warmer, sometimes colder than the surrounding air ? There is a perfectly definite, scientific explanation to be given of this interesting phenomenon. When the raindrops fall through an 'unsaturated' stratum of the atmosphere — that is, through relatively dry air — undergoing partial evaporation, they are cooled down (to that temperature for the time being indicated by a 'wet bulb' thermometer). This is 'cooling by evaporatin,' just like the cooling of the fevered brow by eau-de-Cologne. On the other hand, when the raindrops fall through supersaturated — very wet — air, they grow larger and they become appreciably warmer than the moist atmosphere from which they derive their increased bulk. This is 'warming by condensation/ which may be said to be the principle underlying action of ice-making machinery.