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seventh violet. These stripes do not glare ; but the 

 eye passes from one to the other by gradations or 

 shades. 



The rays which bear the highest colours, as the red, 

 orange, and yellow, are those that refract or curve the 

 least in the prism. They are also such as reflect the 

 first on inclining the instrument. 



From thence it follows, that each ray has its fixt de- 

 gree of refrangilillty. Make one of these rays pass 

 through several prisms at the same time, it will afford you 

 no new colours ; but it will constantly retain its primi- 

 tive colour, which is ail invincible proof of its immuta.- 

 lility. Present a lens to seven rays divided by the 

 prisrn, you will reunite them into a single ray, which 

 will afford you a round image of a shining white. Take 

 only five or six of these rays with the lens, you will 

 have but a dusky white. Only reunite two rays, you 

 will make a colour that will partake of both. A stream 

 of light then is a cluster of seven rays, whose reunion 

 forms white, and the division of which produces seven 

 principal and immoveable colours ! 



What is now the source of that infinite diversity of 

 colours, which embellishes every part of our abode? 

 The particles whtclf compose the surface of bodies, are 

 so many liUle prisms, variously inclined, which break 

 the light, and reflect different colours. Gold, divided 

 into very thin plates, appears blue when opposed to 

 broad day-light. The greater or less thickness of the 

 plates contributes then to the diversity of colours. 

 Whence proceeds that beautiful azure which tinges the 

 canopy of heaven ? The ground of the heavens is black : 

 this ground viewed through the body of air which sur- 

 rounds us, must appear blue to us. Whence proceeds 

 this "smiling verdure which adorns our fields? The 

 lamellae of <he surface of plants are disposed in such a 

 manner, that they remit only green rays, whilst they 

 afford a free passage to others. If green pleases our 

 sight, it is bi ' aus it hoKls precisely a medium between 

 th; -'.-ven principal colours. -But who can remain 1 in- 

 , sensible of the cave which NATURE has taken to depart 



