WHY THE SKY IS BLUE.

Dunstan Times, Issue 3131, 21 August 1922, Page 8

WHY THE SKY IS BLUE.

The investigations of a French scientist incline him to the old theory that the blueness of the sky is due to the color of the atmospheric oxygen instead of to suspended dust as most authorities have held since Tyndall's celebrated experiments on the subject. The Frenchman has detailed his reasons in an interesting way. He classifies the explanation hitherto offered into two divisions: The physical type, based chiefly on the experiments of Tyndall on the illumination of vapors; and the chemical type, more rarely advanced, founded oii the intrinsic color of the components of the atmosphere. The Frenchman criticises the experiments on which the physical theory is based and which, are supported by a remarkable mathematical analysis by Kayleigh of the reflection of light from particles in turbid mediums. Such a medium may reflect an unusual proportion of waves of short lengths, so that it will appear reddish by transmitted light and bluish by reflected light. Besides this the plane of polarisation in such a . medium is situated as Tyndall's merits indicate. Now the Frenchman, by absorbing the blue rays of the sky has, it appears, demonstrated that the polarisation of the sky's light is not a sufficient proof of the optical origin of the blue, since he shows that other rays are also polarised. Payleigh's theory would rather lead us to expect a violet color for the sky, which experiments with a long tube confirm. Besides, the dust of all kinds that renders the atmosphere turbid does not rise higher than. 1000 to 2000 miles and the weight and electric: state of the air make it impossible for its particles to remain at rest and hastens their combination into flakes. Are the solar rays', then, reflected by the gaseous molecules themselves? Here enter the observations of Sbret, which prove that this hypothesis hais no foundation, neither in the case of liquids nor in that of solids. The Frenchman first mentioned has also shown its falsity for gases. Another authority hac explained the illumination of the atmosphere by attributing it to layers of different densities, which intermingle, causing reflection and refraction of light rays*. Finally, in the case of the atmosphere, the Frenchman explains, relying on a calculation based on the properties of oxygen in the liquid state, the" amount of this gas contained in the air. . without counting the ozone and other bodies, will suffice to give the medium a sufficiently intense blue coloration to explain the appearances that are observed at different heights in the: celestial vault. The variations of intensity in the blue and 1 its thinning out in certain directions would he due to the dust which was formerly thought capable of causing its colon - . The sky is really more, blue where there is less dust in the direction of the visual ray.