50 
most prominent colour ; but if at regular distances, which is probably 
meant, it is gray or darkish white. 
" I liad therefore," he observes, " a problem to solve, the com- 
plicated data of which, at first, seemed not to promise a simple solu- 
tion ; yet, after various attempts, 1 obtained my object, as will be seen. 
First, I considered that both the nature and quantity of red, green 
and violent rays, which I suppose to be the sole element of light, are 
absolutely unknown ; but I could likewise conceive them trans- 
formed into coloured matters of such intensity or condensation, that 
the mixture of an equal quantity of each should produce exactly 
white." I will take the liberty to say that it will be whitest when 
most spread as common light, and darkest when most condensed : 
thus they are naturally lost, either way, to our senses, and my 
figures will show what is meant. 
In another place it is observed, that " a pencil of very decided 
blue, being well formed, on white cloth, a green phial was placed be- 
fore the hole, when the light of the spot was immediately much 
weakened, and its colour changed to green." Certainly a very na- 
tural result, as green passed over blue, or mixed with it, makes it yel- 
lowish or bluish green, according to the quantity of either yellow or 
blue in the combination, as in material colours : see the triangle, 
&c. The yellow would be green with a blue phial, and orange with 
a red one, and blue and red would become violet or purple. 
C. A. PRIEUR'S RECAPITULATION. 
" Thus our system of colours appears to me reduced to these few 
data : three sorts of luminous rays of a particular unknown nature ; 
red, green, and violet. Combined by two's, the red and green produce 
yellow ; the green and violet produce blue ; the violet and red, 
purple ; and the three together produce white. 
" The first and second propositions seem most contradictory, and 
by no means to agree with the mixing of material colours. We 
