A NEW THEORY OF LIGHT AND COLOURS. 469 



but yet with this difference, that they are most brisk and vivid in the 

 light of their own day-light colour. Minium appears there of any 

 colour indifferently, with which it is illustrated, but yet most luminous 

 in red; and so bise appears indifferently of any colour with which it 

 is illustrated, but yet most luminous in blue. And therefore minium 

 reflects rays of any colour, but most copiously those indued with red; 

 and consequently when illustrated with daylight, that is, with all 

 sorts of rays promiscuously blended, those qualified with red shall 

 abound most in the reflected light, and by their prevalence cause it 

 to appear of that colour. And for the same reason bise, reflecting 

 blue most copiously, shall appear blue by the excess of those rays in 

 its reflected light; and the like of other bodies. And that this is the 

 entire and adequate cause of their colours, is manifest, because they 

 have no power to change or alter the colours of any sort of rays, 

 incident apart, but put on all colours indifferently, with which they 

 are enlightened. 



These things being so, it can be no longer disputed, whether there 

 be colours in the dark, nor whether they be the qualities of the objects 

 we see, no nor perhaps whether light be a body. For since colours 

 are the qualities of light, having its rays for their entire and immediate 

 subject, how can we think those rays qualities also, unless one quality 

 may be the subject of and sustain another; which in effect is to call 

 it substance. We should not know bodies for substances, were it 

 not for their sensible qualities, and the principal of those being now 

 found due to something else, we have as good reason to believe that 

 to be a substance also. 



Besides, whoever thought any quality to be a heterogeneous aggre- 

 gate, such as light is discovered to be. But, to determine more abso- 

 lutely what light is, after what manner refracted, and by what modes 

 or actions it produces in our minds the phantasms of colours, is not 

 so easy. And I shall not mingle conjectures with certainties. 



Eeviewing what I have written, I see the discourse itself will lead 

 to diverse experiments sufficient for its examination, and therefore I 

 shall not trouble you further, than to describe one of those which I 

 have already insinuated. 



In a darkened room make a hole in the shut of a window, whose 

 diameter may conveniently be about a third part of an inch, to admit 

 a convenient quantity of the sun's light; and there place a clear 

 and colourless prism, to refract the entering light towards the further 

 part of the room, which, as I said, will thereby be diffused into an 

 oblong coloured image. Then place a lens of about three feet radius 

 (suppose a broad object glass of a three- foot telescope,) at the distance 

 of about four or five feet from thence, through which all those colours 

 may at once be transmitted, and made by its refraction to convene 



