Look at a candle through a plate of glass, upon which you have gently
breathed, or over which are scattered particles of dust, or any fine
powder, and you will perceive the flame surrounded with beautiful
rings of colours. By using the seed of the lycopodium, or by placing
a drop of blood diluted with water between two pieces of glass, the
rings of colour will be still more finely exhibited. Round the luminous
body there will be seen a light area, terminating in a reddish dark
margin; this will be succeeded by a ring of bluish-green, and then by
a red ring; these two last colours succeeding each other several times
when the particles are of uniform diameter, as are the seeds of the
lycopodium, each of which is but the 850th part of an inch in diameter.