504? Light not polarised by Feathers. 



solar haloes may be readily discovered, if observers would 

 accustom themselves to look steadily within a few degrees of 

 the sun, when he has risen from 1 0° to 30° ; and also when 

 he has about the same altitude in the evening (as solar haloes 

 are of very rare occurrence at mid-day), when they perceive 

 he shines faintly, and there is no appearance of cloud. Solar 

 haloes are usually the most perfectly formed, and exhibit the 

 prismatic colours the most distinctly on the vesiculce of haze 

 or thin vapour, on attenuated cirrostratus clouds, and some- 

 times on thin cirrocumulus. 



The following prognostications of falling weather of Minna 

 Troil, in the Pirate, are not only much to the purpose, but 

 would greatly assist observers: — "The morning mist lies 

 heavy upon yonder chain of isles, nor has it permitted us, 

 since day-break, even a single glimpse of Fitful Head, the lofty 

 cape that concludes yon splendid range of mountains. The 

 fowls are winging their way to the shore, and the shell-drake 

 seems, through the mist, so large as the scarf. See, the very 

 shear-waters and bouxis are making to the cliff for shelter. 

 See, the air is close and sultry, though the season is yet so 

 early, and the day so calm, that not a windelstraw moves on 

 the heath. See how heavy the clouds fall every moment ; 

 and see those weather-gaws that streak the lead- coloured map 

 with partial gleams of faded red and purple. The storm "which 

 these signs announce will be a dreadful one" — Pirate, vol. i. 

 p. 58, 59. 



Old Kent Road, August 7. 1835. 



Art. VII. Short Communications. 



Birds. — The Effect of Feathers of some Kinds on Light, 

 deemed, in p. 469, 470., that of Polarisation, is not so, but is 

 the Result of the same Principles as the Fringes in the Shadows 

 of small Objects, explained in some of the recent Works on Optics. 

 — Undulations of light come through the interstices between 

 the fibres, and produce, by their interferences, dark and white 

 spaces. Now, different colours are produced by undulations 

 of different lengths ; and these chequered lines of light and 

 shadow, being varied in the distances at which they are inter- 

 cepted, make the gay-coloured patterns. When the fibres of 

 the feather are regular, the patterns are regular also. — P. J. 

 T. London, August 7. 1835. 



" Are all Birds in the Habit of alluring Intruders from 

 their Nests f " — This question, treated of in VII. 483, 484., 



