596 Catife if the "Colours of Natural BoJitf, 



and the conclufion to which it evidently leads, may be transferred to the colours of natural 

 Ixxiies, as fcen by reflexion ? For, the parts being fpecular and fpherical, each will form 

 an image of the luminous body ; and by the pofilion of the fides of the neighbouring ones, 

 any fix of the colours may be ftopped while the feventh emerges; and if this happens in one 

 part it will happen in all, fince, that the texture and fize of the parts is the fame throughout 

 has never been called in qiieftion. But it will be alked, How are the panicles to reflcd a 

 mixture of different colours ? We anfwer, That a particle having its fide concave and front 

 convex will produce the effeft ; for the colours will be thus mixed in a proportion deter- 

 mined by the pofition of the others. How can whitenefs and blackncfs be produced I M 

 the particles be large, then the whole light incident on each will be reflciSted and feparated^ 

 and all the images being compounded and mixed together, a confufed fenfation, or a fcn- 

 fation of white, will be the refult. For, the parts being tranfparent, and the images formed 

 by the convex furface of the fecond rowr of particles, thefe will be larger in proportion to 

 the thicknefs of the particles or plates through which they have to pafs before they meet 

 with obflruftion, and confequently will not be flopped by other particles; and in like manner 

 the colour will be red if the particles are a little lefs, and fo on. If the particles be very 

 fniall, the light will be feparated into images alfo fmall ; with which and with one another 

 the particles interfering, the light by many reflexions and obftru£lions will be totally loft. 

 How do bodies appear of their proper colours, though no luminous body be fliining whofe 

 image may be formed by a reflexion ? They refleG images of the clouds which refle£l the 

 fun's white light ; for if we hold between our eye and a liolc in the window illuminated by 

 the light of the clouds a refle£tir>g body, as a pin, &c. coloured images are formed of the hole 

 diftcnded, like thofe of the fun, as I have often found ; and the fame holds of inflexion. 

 Why does cutting a body to pieces not alter its colours ? This only changes the pofition of 

 mafTes of particles, not of the particles themfelves ; but if by bruifuig them we change 

 their magnitude and pofition, we change alfo their colonr : thus the leaves of vegetables 

 bruifed in a mortar, many paints powdered, &c. Why do many bodies change colours 

 when viewed in different pofitions ? Becaufe they reflect two colours or more of each image 

 to different quarters; and it matters not whether their pofition with refpe£t to us, or our 

 pofition with refpeft to them, be changed. How do bodies become coloured by tranf- 

 niitfcd light ? Becaufe the foregoing reafonings apply alfo to the flexion of the rays in their 

 paflage through the parts of bodies. Thefe obfervations appear to me to furnifh a very 

 fimple folution of the problem. 1 fhall endeavour in a future communication to confirm 

 what has been faid by other remarks and experiments ; for it would be tedious, and per- 

 haps fuperfluous, to illuftratc what has been faid by figures and demonftrarions *. 



Purfuant to thefe remarks, it will not be difiicult to account for the rings of colours of 

 thin plates by reflexion, as we before did thofe of thick plates by flexion f. Indeed, thofc 

 formed in the experiment of the two lenfes, fuppofed by Newton to be owing to the platej 



♦ It is obviens that the different refrangibility of the rays will not aceount for the bright and diftiuft colour 

 nf bodies. If the refracting angle of a prifm be continually diminilhcd, till, for example, it is equal to one of a 

 minute, the refr.nilion will produce no fcnfiblc colour. Indeed, almoft every piece of plane glafs has its fides in a 

 fmaTi degree inclined to one another, and yet no colours are formed. Much lefs then will rcfra£lion through 

 the infinitely finaller parts of bodies produce reparation of the rays. 



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