ing the focus to a black spot, or upon
letters, written or printed, the paper will immediately be on fire
under the letters.

Thus, fullers and dyers find black cloths, of equal thickness with
white ones, and hung out equally wet, dry in the sun much sooner than
the white, being more readily heated by the sun's rays. It is the same
before a fire, the heat of which sooner penetrates black stockings
than white ones, and so is apt sooner to burn a man's shins. Also beer
much sooner warms in a black mug set before the fire than a white one,
or in a bright silver tankard. Take a number of little square pieces
of cloth from a tailor's pattern card, of various colours; say black,
deep blue, lighter blue, green, purple, red, yellow, white, and other
colours, or shades of colours; lay them all out upon the snow in a
bright sun-shiny morning; in a few hours, the black being warmed most
by the sun will be sunk so low as to be below the stroke of the sun's
rays; the dark blue almost as low; the lighter blue not quite so much
as the dark; the other colours less, as they are lighter; and the
quite white remain on the surface of the snow, as it will not have
entered it at all.

_Alternate Illusion._

With a convex lens of about an inch focus, look attentively at a
silver seal, on which a cipher is engraved. It will at first appear
cut in, as to the naked eye; but if you continue to observe it some
time, without changing your situation, it will seem to be in relief,
and the lights and shades will appear the same as they did before. If
you regard it with the same attention still longer, it will again
appear to be engraved: and so on alternately.

If you look off the seal for a few moments, when you view it again,
instead of seeing it, as at first, engraved, it will appear in relief.

If, while you are turned towards the light, you suddenly incline the
seal, while you continue to regard it, those parts that seemed to be
engraved will immediately appear in relief: and if, when you are
regarding these seemingly prominent parts, you turn yourself so that
the light may fall on the right hand, you will see the shadows on the
same side from whence the light comes, which will appear not a little
extraordinary. In like manner the shadows will appear on the left, if
the light fall on that side. If instead of a seal you look at a piece
of money, these alterations will not be visible, in whatever situation
you place yourself.

_Alarum._