WCP472

[1]¹

Ardenlea

Falkirk

27 March [18]99

Dr. A.R. Wallace

Dear Sir

I have yours of the 24^th inst. and have much pleasure in sending you a copy of paper on The Colour of Sea Water². You will notice it is an abstract, the complete paper was never published[.]

I do not know of any complete work on the Colour [2] of Sea & Sky, & nothing final has been given on the latter. Almost every new substance discovered in the atmosphere has been in turn been given credit for the blue of the sky, & when oxygen has shown to be blue in its liquid condition it also got credit for the colour. It is very evident however that no transparent blue medium can be the cause, because if it were [3] the sun's light would come to us blue & ^be bluer at sunset than at midday, owing to it passing through more air at sunset than at midday. Whereas the sun's light is yellow and yellower at sunset. Showing that the blue light is stopped by something in the air, & it seems highly probable that it is the very small particles in suspension in the air that scatter the blue light & make the sky blue, while they are so small they allow the larger waves of the red end of the spectrum to pass[.] [4] This seems probable now that the <dust counter> has shown the existence of very fine particles at all elevations yet tested. If the blueness were due to a blue medium we would require the presence of some light-reflecting surfaces outside our atmosphere. Further the blue of the sky is polarized light which points to its origin having undergone reflection from very small particles. If it were reflected from larger particles & coloured blue by a blue medium, then the higher we ascend the poorer the blue would become, whereas it gets deeper in accordance with the very small particle theory.

Yours truly | John Aitken [signature]