238 



and the colors of the atmosphere of the tropics 

 enlightened by the Moon, are worthy of new 

 researches on the part of natural philosophers. 

 At Mexico, in extremely fine weather, I have 

 seen large bands % having all the colors of the 

 rainbow, spread along the vault of the sky, and 

 converging toward the lunar disk ; a curious 

 meteor, which reminds us of that described by 

 Mr. Cotes f in 1716. 



If the situation of our house at Cumana was 

 highly favourable for the observation of the 

 stars and meteorological phenomena, it obliged 

 us to be sometimes the witnesses of afflicting 



excentricity, and the small halo had only 1° 27 1 diameter. 

 These measures were taken without a telescope, and by 

 bringing with the sextant the edge of the Moon into contact 

 with the very well defined extremities of both haloes. It 

 seemed to me difficult to admit my being deceived nineteen 

 minutes with respect to the excentricity of the Moon : the 

 refraction would have rather diminished than have augment- 

 ed the extent of the halo toward the lower edge. We must 

 not confound this phenomenon, which belongs to the last 

 strata of the atmosphere, and which is observed in a clear 

 sky without any visible vapors, with those colored circles 

 which are projected on the white clouds driven by the wind, 

 before the lunar disk, and which have only seven or eight 

 hundred toises of absolute height. (See Gibbes Walker 

 Jordan, in Nicholson's Journ., 4to. ed., vol. iv, p. 141 ; and 

 Newton's Optics, 1722, p. 476.) 



* The night of the 8th of May, 1813. 

 t Smith's Optics, French translation, 1767, t. i, p. 173, 

 § 109, and p. 121, § 169. 



