from Vapours, fogs, Ml/Is, &c. 341 



fey, if the picture is brilliant; for, though thofe fog banks 

 often appear in dark or cloudy weather, the reflection is im- 

 perfect, and reprefcnts only confufed images of rocks, moun- 

 tains, and capes. Though diflant objects are reflected, thofe 

 immediately under or behind will be refracted. Thus in 

 %. 2. if a vapour reds upon an horizontal plane AB, the 

 point B will be refracted to a, when the plane will reprefent 

 a hill to a fpe&ator at I. The fccnery may alfo be repre- 

 fented by refraction only ; for, if the fog or vapour fhould 

 contain two fmooth furiaces oppofite to each other, in the 

 manner of a double concave lens, objects will be feen re- 

 fracted, though much diminiihed in apparent magnitude ; 

 and if one or both of the concave furfaces fhould be com- 

 posed of different inclined planes, a fmgle object will be va- 

 rioufly multiplied and transformed. Thus let AB (fig. 3.) 

 reprefent a vapour, whofe furfaces are concave and tranfpa- 

 rent, but of different faces, as CD, DE, and EF, the object 

 M will be feen by a fpectator at G fmall and at a great di- 

 ftance beyond M, and multiplied as at PQ. And this cafe 

 was exhibited from a bog vapour in the county of Kildare in 

 the year 1787. About eleven o'clock in the morning, the fun 

 mining clear, a hill appeared, about a mile diftant, covered 

 with trees and houfes, where it was known there was only 

 a plain field ; the phoenomenon being caufed by a houfe and 

 garden refracted through a denfe and racetwife concave vapour 

 arifing from the bog. 



Thefe phenomena are alfo frequently caufed by the light 

 refracted through the cryftailine parts of the vapour, without 

 any of the adjacent objects being either refracted or reflected. 

 For the vapour, being formed into different parts, the light 

 refracted through them caufes the confufed appearance of 

 ruins, houfes, woods, lawns, &c. in the fame manner as a 

 board covered in an irregular manner with black and white 

 fpots mixed with lines, will at a certain diftance refemble a 

 jandfcape with woods, ruins, houfes, trees, caftles, &c, and 

 under luch impomig forms as to appear real reprefentations. 

 Of this fpecies of the fata morgana feem to be thofe feen at 

 Youghal in 1801 before fpoken of: but in whatever manner 

 the reprefentations from vapours and fogs are formed, the 

 weather mult be calm and ferene, otherwife the vapours will 

 be broken and difperfed by the wind. 



Y3 3LVI. An 



