26 PHILOSOPHICAL TRANSACTIONS. [aNNO l672i 



A beam of the sun*s light behig transmitted into a darkened room, if you illu- 

 minate a sheet of white paper by that light, reflected from a body of any colour, 

 the paper will always appear of the colour of that body by whose reflected light 

 it is illuminated. If it be a red body, the paper will be red; if a green body, 

 it will be green, and so of the other colours. The reason is, that the fibres or 

 threads, of which the paper consists, are all transparent and specular; and such 

 substances are known to reflect colours without changing them. To know, 

 therefore, to what species of colour a grey belongs, place any grey body (sup- 

 pose a mixture of painters colours) in the said light, and the paper, being illu- 

 minated by its reflection, shall appear white. And the same thing will happen, 

 if it be illuminated by reflection from a black substance. 



These therefore are all of one species; but yet they seem distinguished, not 

 only by degrees of luminousness, but also by some other inequalities, whereby 

 they become more harsh or pleasant. And the distinction seems to be, that 

 greys and perhaps blacks are made by an uneven defect of light, consisting as it 

 were of many little veins or streams, which differ either in luminousness, or in 

 the unequal distribution of diversely coloured rays; such as ought to be caused 

 by reflection from a mixture of white and black, or of diversely coloured cor- 

 puscles. But when such imperfectly mixed light is by a second reflection from 

 the paper more evenly and uniformly blended, it becomes more pleasant, and ex- 

 hibits a faint or shadowed whiteness. And that such little irregularities as these 

 may cause these differences is not improbable, if we consider how much variety 

 may be caused in sounds of the same tone by irregular and uneven jarrings. 

 And besides, these differences are so little that I have sometimes doubted, whe- 

 ther they be any at all, when I have considered that a black and white body 

 being placed together, the one in a strong light and the other in a very faint 

 light, so proportioned that they might appear equally luminous, it has been dif- 

 ficult to distinguish them, when viewed at a distance, unless when the black 

 seemed more bluish, and the white body in a light still fainter, has in compari- 

 son of the black body, itself appeared black. 



This leads me to another way of compounding whiteness, which is, that if 

 four or five bodies of the more eminent colours, or a paper painted all over, in 

 several parts of it, with those several colours in a due proportion, be placed in 

 the said beam of light, the light reflected from those colours to another white 

 paper, held at a convenient distance, shall make that paper appear white. If it 

 be held too near the colours, its parts will seem of those colours that are nearest 

 them; but by removing it further that all its parts may be equally illuminated 

 by all the colours, they will be more arid more diluted, until they become per- 

 fectly white. And you may further observe, that if any of the colours be in- 



