Blow a soap bubble, cover it with a clean glass to protect it from the
air, and you may observe, after it has grown thin by standing a little,
several rings of different colours within each other round the top of
it. The colour in the centre of the rings will vary with the thickness;
but, as the bubble grows thinner, the rings will spread, the central
spot will become white, then bluish, and then black; after which the
bubble will burst, from its extreme tenuity at the black spot, where
the thickness has been proved not to exceed the 2,500,000th part of an
inch.