Dr Brewster's account of ttvo remarkable Rainbows. 1 63 



are considerably improved and simplified, and much more ge- 

 nerally adopted, that we can look for very extended deduc- 

 tions of value in this branch of meteorological science. I am. 

 Sir, your most obedient servant, A 



Art. XXVII. — Account of two remarkable Rainbows, one of 

 which enclosed the Phenomenon of converging' Solar Beams. 

 By David Brewster, LL. D., F. R. S. Lond. and, Edin. 



On the 5th July 1828, there was seen here the most brilliant 

 rainbow that I had ever an opportunity of witnessing. Both 

 the outer and the inner bow were perfectly complete, and 

 equally luminous in all their parts ; and they continued in this 

 condition for a very considerable time. I was thus enabled to 

 verify, in every part of the two bows, the fact which I pub- 

 lished more than fifteen years ago, of the polarization of the co- 

 loured light, in planes passing through the centre of the bow, 

 or, what is the same thing, in the planes of reflection, within 

 the drops of rain. Similar portions of the inner and the outer 

 bow were thus seen to disappear simultaneously, when seen 

 through a plate of tourmaline. 



The pecuHarity in this rainbow, which has induced me to 

 describe it at present, has I believe never before been noticed. 

 On the outside of the outer or secondary bow, there was seen 

 distinctly a red arch, and beyond it a very faint green one, 

 constituting a supernumerary rainbow, analogous to those which 

 sometimes accompany the inner bow. It will be interesting 

 to ascertain, if Dr Young's ingenious theory of the common 

 supernumerary bow will apply to the present one. 



On the afternoon of Thursday, the 2d of October, a rain- 

 bow appeared in the north-east, with considerable brilliancy, 

 and was accompanied with the rare phenomenon of the converg- 

 ing of the solar beams, described in this Journal, No. iii. p. 

 136. As the point to which the solar beams converged below 

 the horizon was exactly opposite to the sun, and, therefore, 

 necessarily coincident with the centre of the rainbow, the two 

 phenomena, when thus accidentally combined, had a very re- 

 markable appearance. 



