52 



Whilst this table does not bear testimony directly to cloud 

 evaporation, it still shows that the ratio of rainfall for the 

 last three months of the past year was excessive. 



"On the Recent Coloured Skies at Sunset and Sunrise," 

 by the Rev. Thomas Mackereth, F.R.A.S., F.R.Met.Soc. 



If the air were deprived of all the vapour which arises 

 from water, it is almost a certainty that the various hues 

 seen in the sky would disappear. That water is a refractor 

 of light is well known, and the beauties arising therefrom 

 appear in the marvels of the rainbow. And what is vapour 

 derived from water but the particles of water expanded by 

 heat and rarefaction ? Hence, there is no reason why the re- 

 fractive power of water may not bo maintained by its vapour 

 with a difference proportionate to the dispersive power of 

 the vapour. This is illustrated by the prismatic appearance 

 at the edges of clouds when the light of the moon is freely 

 and fully poured forth through breaks amongst them, and 

 is incident upon the edges of those of different altitudes and 

 approximate to the path of the rays. Of course the colours 

 are pale and diffused in such a case, because the light of the 

 moon is pale, and the clouds not only refract but disperse 

 the force of the liffht. 



If, therefore, the light of the sun should fall so obliquely 

 upon cloud or vapour that the refrangibility could be seen, 

 there would necessarily appear more or less of the prismatic 

 colours, but of course dispersed according to the density or 

 rarity of the vapour, or to the extent and direction of its 

 presence and diffusion. 



