274 Mr. Brougham's Experiments and Observations cm 
spherical, each will form an ifnage of the luminous body ; and 
by the position of the sides of the neighbouring ones, any six 
of the colours may be stopped, while the seventh emerges ; and 
if this happens in one part, it will happen in all, since that the 
texture and size of the parts is the same throughout, has never 
been called in question. But it will be asked, how are the 
particles to reflect a mixture of different colours ? We answer, 
that a particle having its sides concave, and front convex, will 
produce the effect ; for the colours will be thus mixed in a 
proportion determined by the position of the others. How 
can whiteness and blackness be produced ? If the particles be 
large, then the whole light incident on each will be reflected 
and separated, and all the images being compounded and 
mixed together, a confused sensation, or a sensation of white, 
will be the result. For the parts being transparent, and the 
images formed by the convex surface of the second row of 
particles, these will be larger in proportion to the thickness of 
the particles, or plates through which they have to pass before 
they meet with obstruction, and consequently will not be 
stopped by other particles ; and in like manner the colour will 
be red if the particles are a little less, and so on. If the par- 
ticles be very small, the light will be separated into images also 
small, with which, and with one another, the particles inter- 
fering, the light by many reflections and obstructions will be 
totally lost. How do bodies appear of their proper colours 
though no luminous body be shining, whose image may be 
formed by a reflection? They reflect images of the clouds, 
which reflect the sun's white light ; for if we hold between our 
eye and a hole in the window, illuminated by the light of the 
clouds, a reflecting body, as a pin, &c. coloured images are 
