Accounts of Books. i^^ 



The only true principles of explanation of thefe phaenomena, are to be found among 

 thofe new obfervations concerning trie inflexions of light before fpoken of. 



When two bodies approach one another in a folar beam, the paffing light between their 

 edges is divided and diftributed on both fides into two complete fets of fringes. Vide 

 Journal, Obfervation f, page 8 1. Each of thefe fets of fringes beginning from the central 

 diftance between the bodies, and advancing towards either of the bodies, is compofed of 

 the fame colours and orders of colours as the obferved irides. Of thefe the blues are leaft, 

 the reds mod bent, the blues furtheft from, the reds neareft to the body. 



Whenever therefore two globules of water in a cloud or vapour approach near each other, 

 the light palling between them will be diftributed into Cmilar fringes, and the union of 

 thefe fringes from between different drops, will produce all around the luminary circles, 

 and orders of colours, fuch as by obfervation are really found to be exhibited. 



The nearer to, or more remote the two bodies of the experiment are froni each other, 

 the more or lefs broad will be the fringes, and therefore the breadths alfo of the irides will 

 depend upon, and vary with the diftanees of the globules, and thence the obferved varia- 

 tions of breadth are eafily accounted for. The breadths are varied alfo, and more efpecially 

 in vapours of confiderable extent or thicknefs, by the aftions of the fucceeding feries of 

 globules, for although not in the fame plane, bodies, and confequently thefe globules, a£l 

 upon the light paffing between them, and form fringes. Vide Journal, Obfervation v[y 

 page 8 1. 



Thefe principles being applied to explain the various phjenomena of lights and coloured 

 circles, exhibited in various fituations by the fun and moon through the vapours of the 

 atmofphere, they are next extended to all fimilar pha:nomena obferved round other lumi- 

 nous objeds as well as thefe. The flames of candles and lamps feen through fteam, through 

 the exhiufted receiver, through thin flocks of wool or cotton, through ftulFs of cotton, 

 linen, Ok, or wool, through the glaflts of coach windows, on which fmall drops of water 

 are precipitated from the breath of the inclofcd pcrfons, are furrounded with coronae pro- 

 duced in a fimilar manner. Tapers are feen to burn blue by an eye charged with femi- 

 pellucid .humours arifing from injury, watchfulnefs, and other caufes producing rings of 

 colours, fometimes one of dufky blueifh green, faintly terminated with yellow and red ; 

 and fometimes a fecond of duflcy green and red. A phaenomenon of this fort occurred to 

 Des Cartes. A hole in a window fliutter will alfo, under fimilar circumftances, produce 

 . fimilar appearancts. 



Thefe obfervations are illuftrated by figures of reference, and may further be confirmed 

 by viewing a candle at the diftance of ten feet or more through a thin flock of wool, or by 

 breathing on a pane of window-glafs, and looking at the image of a candle refle£ted ob- 

 liquely from the glafs through the precipitated drops of moifture, when a fingle halo, 

 compofed of the firft order of colours terminated with yellow and red, will be diftindly 

 feen. 



All 



