as PHILOSOPHICAL TRANSACTIONS. [aNNO 1672, 



And yet this light, with which they are ilkiminated, cannot possibly be uniform, 

 because if the rays, which at their entrance are of divers colours, do in their 

 progress through the room suffer any alteration to be reduced to a uniformity ; 

 the glass would not in the remotest parts of the room appear of the very same 

 colour, which it does when the spectator's eye is very near it: nor would the 

 rays, when transmitted into another dark room through a little hole in an oppo- 

 site door or partition wall, project on a paper the species or representation of the 

 glass in its proper colours. 



And by the by, this seems a very fit and cogent instance of some other parts 

 of my theory, and particularly of the 13th proposition. For in this room all 

 natural bodies whatever appear in their proper colours. And all the phaenomena 

 of colours in nature, made either by refraction or without it, are here the same 

 as in the open air. Now the light in this room being such a dissimilar mixture, 

 as I have described in my theory, the causes of all these phaenomena must be 

 the same that I have there assigned. And I see no reason to suspect, that the 

 same phaenomena should have other causes in the open air. 



The success of this experiment may easily be conjectured by the appearances 

 of things in a church or chapel, whose windows are of coloured glass; or in the 

 open air, when it is illustrated with clouds of various colours. 



There are yet other ways by which I have produced whiteness ; as by casting 

 several colours from two or more prisms upon the same place; by refracting a 

 beam of light with two or three prisms successively, to make the diverging co- 

 lours converge again; by reflecting one colour to another; and by looking 

 through a prism on an object of many colours ; and (which is equivalent to the 

 above-mentioned way of mixing colours by concave wedges filled with coloured 

 liquors,) I have observed the shadows of a painted glass window to become white, 

 where those of many colours have at a great distance interfered. But yet, for 

 further satisfaction, the animadversor may try, if he please, the effects of four or 

 five of such wedges, filled with liquors of as many several colours. 



Besides all these, the colours of water bubbles, and other thin pellucid sub- 

 stances, afford several instances of whiteness produced by their mixture; with 

 one of which I shall conclude this particular. Let some water, in which a con- 

 venient quantity of soap or wash-ball is dissolved, be agitated into froth, and, 

 after that froth has stood a while without further agitation, till you see the bub- 

 bles of which it consists begin to break, there will appear a great variety of 

 colours all over the top of every bubble, if you view them near at hand; but if 

 you view them at so great a distance, that you cannot distinguish the colours one 

 from another, the froth will appear perfectly white. 



Thus much concerning the design and substance of the animadversor's con- 



