1.50 O?* COLOUKS OF THIN PELLICLES. 



It 1$ taitich to be rei^retted, that tliia great man did not 

 treat the subject of inflexion as extensively as he did that of 

 coloured rings ; or even that he did not atteiid to the devia- 

 tion of light in the vicinity of bodies, before he examined its 

 changes of direction by the action of their surfaces: as un- 

 questionably he would have deduced new and very valuable 

 consequences from it. 

 A great analo- In fact the greatest analogy subsists between the pheno- 

 fhese pheno- ^^^^ of inflexion round a minute body, and those of re- 

 inena. flexion or transmission by thin substances : for the coloured 



Coloured fringes in one case appear to follow the same law as the co- 



loure^H ^\!^p:^°' l^ured rings in the other. And if this be not very sensible 

 follow the with respect to the fringes adjacent to the shadow of a body 

 same aw. ^^ small diameter received into a dark chamber, it is more 

 evident in the fringes produced by the light that passes be- 

 tween two bodies very near together ; it is still more in the 

 series of coloured images formed between the plumes of a 

 feather, when looking at a candle through them ; and it is 

 very manifest likewise in the bars seen by the eye, when a 

 piece of linen, or a series of wires very near together, is 

 placed between it and the light, as in the experiments of 

 Mr. Rittenhouse. 

 Method of I have found a method of rendering this resemblance still 



rendering this Ytiove conspicuous. For this purpose I employ black crape, 

 more obvious. ,„ , , i ,, if. i i , , i 



If the eye be covered thus, and irom a dark place you look 



at a light a little distant, you will perceive the light sur- 

 rounded by a series of very apparent rings, the colours of 

 which are very vivid, and of the same tints as those of the co- 

 louTred rings of thin plates. 

 Candle seen If the flame of a candle be placed in the midst of a pret- 



through va- ^y abundant aqueous smoke, or so that it can be seen only 

 ^°^^' through this smoke, the flame will appear surrounded by 



perfectly analogous rings. I can imitate them likewise very 

 conveniently by tarnishing a glass with breathing on it, and 

 immediately looking at the image of a luminous body either 

 through it or reflected from it. Those rings, which are some- 

 times seen surrounding the sun or moon very closely, are 

 probably phenomena of the same kind. 

 Newton speaks On the other hand Newton speaks of undulations like 



of berpentine ^Uq^q of an eel, which he suspects are produced in the rays, 

 undulations, x * v 



when 



