484 COSMOS. 



phenomenon is known to be a consequence of refraction, 

 since, as Kepler very correctly expresses himself (Paralip. 

 Astron. pars Optica, p. 893), the Sun's rays are inflected 28 



transparence variable de la partie de 1'atmosphere travers 

 laquelle nous apercevons la Lune eclipsee. Sous les tropiques, 

 une grande serenite du ciel, une dissemination uniforme des 

 vapeurs diminuent Fextinction de la lumiere que le disque 

 lunaire nous renvoie." Humboldt, Voyage aux Regions Equi- 

 noxiales, torn. iii. p. 544 ; and Recueil d? Observ. Astrono- 

 miques, vol. ii. p. 145. u It may easily be understood that the 

 intensity of the red light does not depend solely upon the 

 state of the atmosphere which refracts more or less feebly the 

 solar rays by inflecting them into the shadow cone, but that it 

 is especially modified by the variable transparency of that 

 part of the atmosphere across which we perceive the eclipsed 

 Moon. Under the tropics a great serenity of sky, an uniform 

 dissemination of vapours, diminish the extinction of the light 

 which the lunar disc sends towards us." Arago observes : 

 " Les rayons solaires arrivent a notre satellite par 1'effet d'une 

 refraction et a la suite d'une absorption dans les couches les 

 plus bases de 1'atmosphere terrestre ; pourraient -ils avoir une 

 autre teinte que le rouge?" Annuaire for 1842, p. 528. 

 <c The solar rays reach our planet by the effect of a refraction, 

 and subsequently to an absorption (partial) in the lower 

 strata of the Earth's atmosphere. How can they have any 

 other colours than red ?" 



28 Babinet declares the reddening to be a consequence of 

 diffraction, in a memoir as to the different share of the white, 

 blue, and red lights which are produced by the inflection; 

 see his Reflections upon the Total Eclipse of the Moon on 

 the 19th of March, 1848, in Moigno's Repertoire d'Optique 

 Moderns, 1850, torn. iv. p. 1656. " La lumiere diffractee qui 

 penetre dans Fombre de la Terre, predomine toujours et 

 meme a ete seule sensible. Elle est d'autant plus rouge ou 

 orangee qu'elle se trouve plus pres du centre de 1'ombrc 

 geometrique; car se sont les rayons les moins refrangibles 

 qui se propagent le plus abondamment par diffraction, a 

 mesure qu'on s'eloigne de la propagation en ligne droite." 

 "The diffracted light which, penetrates into the Earth's 



