WHY THE SKY IS BLUE.

Hauraki Plains Gazette, Volume XXXIV, Issue 4639, 17 December 1923, Page 4

WHY THE SKY IS BLUE.

(By G.F.S. in the Overseas' Daily Mail) The blue colour of the sky is a matter that has given scientists far more trouble than is generally. Among the early scientists, Leonardo da Vinci put forward the interesting theory that the blue is in reality a speckled mixture of white light from the, atmosphere with the black of space. In .this connection one may refer to the Blue Andalusian fowl, which is a cross between a black and a white, the two colours being blended in the feathers to produce a blue,effect. Sir Isaac Newton believed that the blue .was produced by the interference rays reflected from the front and rear surfaces of water drops, in the same way as colours are produced in soap bubbles. This theory held ground for 175 years. Then it was discovered that such drSplets as Newton required would cause the heavenly bodies to appear magnified, and to get over this difficulty hollow droplets were invented. '.• It ■ was* found that . sky light is partially polarised (vibrations in one discovery instead of in all directions), and this discovery laid Newton’s theory open to attack from the mathematicians, who-proved that the observed angle of polarisation did not agree with what shodld be produced by. reflection from water. The modern theory is that .the blue colour is produced by “scattering ’ of light. Under the influence of sunlight the molecules' of the air and other particles such as dust motes give out a light of their own. Physicists haveshown that when the particles in a •meiium through which light passes are very .small the light produced in this manner is of short wave-length or belonging to the blue en'd of the spectrum. The smoke that rises freshly from the end of a cigar is blue from this same cause, and so also isi that from a '•igarette, but during inhalation the smoke particles become agglutinated together and on. exhalation they are too large to produce the blue light. Thus the exhaled smoke is usually white. ' ■