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EXPLANATION OE THE KRAKEN.
89
By taking advantage of the remarkable power which
carbon in some of its forms possesses, of clinging
tenaciously to a film of air, I have devised a simple
experiment which illustrates this in a striking manner.
Take a piece of sheet metal, as copper, brass, iron, or
any other, and hold it over the flame of a candle or
lamp until its surface is uniformly blackened; then let
it cool, taking care not to touch the blackened surface
with the fingers. Now plunge this in a tumbler, or
other convenient vessel of water, and look at it obliquely
through the water: the dull black carbon surface
disappears, and a bright, glistening, silvery mirror takes its
place. Then take the plate out of the water, and (if the
experiment has been carefully conducted) the blackened
surface will be quite dry: the water has not touched
the carbon, for it carried down a thin adhering film
of air; and it was that which shone like silver, and by
its opacity concealed so completely the black surface
beneath. It is because you looked through a dense
medium, the water, very obliquely upon the surface of a
rare one, the film of air, that this effect was produced.
If you take a tumbler of water, and look up obliquely
through the water to its surface, the surface appears
mirror-like, and reflects objects that are in the water;
but your finger, held just above the surface of the water,
is invisible, on account of the perfect opacity of the
air under these conditions. Many water-beetles and
water-spiders have the power of carrying under water a
film of air adhering to their bodies, which appears like
a coat of polished mail. If the blackened plate be laid
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