4td 



Singular Appearance of a Rainbow. 



The difference of temperature between the earth and atmo- 

 sphere increases more rapidly than I should have anticipated. 

 How near these results and assumptions may approximate to 

 truth, future observations must determine. Meantime, I 

 should feel much indebted to any one for additional inform- 

 ation on this subject. 



Ditton Marsh, July, 1834. 



Art. XI. Facts and Arguments in Relation to the Causes of a 

 singular Appearance of a Rainbou), of an unusual Appearance 

 of the Sky, of Mirage, of Devo, and of Hoar-Frost. By A 

 Subscriber. 



Along with B. (IV. 79.), I have been looking for an 

 explanation, from some correspondent, of the phenomenon 

 described in III. 544., under the head of " Notice of a sin- 

 gular Appearance of the Rainbow, by E. G. ;" and, with a view 

 of recalling attention to the subject, I beg to submit the fol- 

 lowing extracts from Sir D. Brewster's treatise on Optics, in 

 Lardner's Cyclopedia, p. 269, 270. : — 



" Many peculiar rainbows have been seen and described. 

 On the 1 0th of August, 1665, a faint rainbow was seen, at 

 Chartres, crossing the primary rainbow at its vertex. It was 

 formed by reflection from the river." 



To save a new cut, I have altered the letters of reference 

 in the next passage, to make them correspond with the dia- 

 gram in III. 544. 

 E, --v^ [which we here repeat 



(fg- 57.)].^ In ad- 

 dition to which, it will 

 be necessary to sup- 

 pose that the segment 

 E F reaches to a ; and 

 that there is a similar 

 ^' ^^' B j> segment on the left 



side, which I shall call e' f' : the arch f' e' e f thus being the 

 remaining part of the circle of which the primary bow a b is 

 a portion. 



