VOL. VII.] PHILOSOPHICAL TRANSACTIONS. 27 



tercepted, the paper will no longer appear white, but of the other colours which 

 are not intercepted. Now, that this whiteness is a mixture of the severally co- 

 loured rays, falling confusedly on the paper, I see no reason to doubt; be- 

 cause if the light became uniform and similar before it fell confusedly on the 

 paper, it must much more be uniform when at a greater distance it falls on the 

 spectator's eye, and so the rays, which come from several colours, would in no 

 qualities differ from one another, but all of them exhibit the same colour to the 

 spectator, contrary to what he sees. 



Not much unlike this instance it is, that if a polished piece of metal be so 

 placed, that the colours appear in it as in a looking-glass, and then the metal 

 be made rougl^i, that by a confused reflection those apparent colours may be 

 blended together, they shall disappear, and by their mixture cause the metal 

 to look white. 



But further to enforce this experiment, if instead of the paper, any white 

 froth, consisting of small bubbles, be illuminated by reflection from the afore- 

 said colours, it shall to the naked eye seem white, and yet through a good mi- 

 croscope the several colours will appear distinct on the bubbles, as if seen by 

 reflection from so many spherical surfaces. With my naked eye, being very 

 near, I have also discerned the several colours on each bubble: and at a greater 

 distance, where I could not distinguish them apart, the froth has appeared en- 

 tirely white. And at the same distance, when I looked intently, I have seen 

 the colours distinctly on each bubble ; and yet by straining my eyes as if I would 

 look at something far off beyond them, thereby to render the vision confused, 

 the froth has appeared without any other colour than whiteness. And what is 

 here said of froths may easily be understood of the paper or metal in the fore- 

 going experiments. For their parts are specular bodies, like these bubbles; 

 and perhaps with an excellent microscope the colours may be also seen inter- 

 mixedly reflected from them. 



In proportioning the severally coloured bodies to produce these effects, there 

 may be some niceness ; and it will be more convenient to make use of the co- 

 lours of the prism, cast on a wall, by whose reflection the paper, metal, froth, 

 and other white substances, may be illuminated. And I usually made my trials 

 this way, because I could better exclude any scattering light from mixing with 

 the colours to dilate them. 



To this way of compounding whiteness may be referred that other, by mixing 

 light after it has been trajected through transparently coloured substances. For 

 mstance, if no light be admitted into a room but only through coloured glass, 

 whose several parts are of several colours in a pretty equal proportion ; all white 

 things in the room shall appear white, if they be not held too near the glass. 



£ 2 



