rry on a correspondence with another, and who is
fearful of having his letter opened, or intercepted, can adopt the
following plan:

Write any unimportant matter with common ink, and let the lines be
very wide apart: then between these lines write the communication you
wish to make, with any of the above invisible inks you can most
readily procure.

Your correspondent is to be previously apprized of the method of
making the characters visible: and writing in common ink will serve to
lull the suspicions of those who might intercept the letter, and who,
not finding any thing important in it, will either forward or keep it.
In either case there can be no danger, as the writing will not be
visible without the proper application.

_The Mysterious Writing._

Write on a piece of paper with common ink any question; then
underneath it write the answer either in invisible silver ink, or the
invisible green ink, made with zaffre and aqua regia, described in
pages 24 and 25.

You give this paper to your friend, and tell him to place it against
the wall, or on his dressing-table, keeping the door locked, that he
may be sure no person has entered his room: he will next day find the
answer written on it.

_The Restored Flowers._

Make a bouquet of artificial flowers; the leaves should be formed of
parchment. Dip the roses in the red invisible ink, the jonquilles in
the yellow, the pinks in the violet, and the leaves in the green ink.
They will all appear white; and you show them to the company,
observing, that you will restore them to their natural colours, and
desiring any person to fix any private mark on them he pleases, that
he may be sure there is no deception. You then, unperceived by the
company, dip them in the revivifying liquor, used to make the yellow
ink visible, described in page 24, and, drawing them gently out, that
the liquor may drop, and the flowers have time to acquire their
colours, you present them to the company, who will see, with surprise,
that they each appear in their natural colours.

_Winter changed to Spring._

Take a print that represents winter, and colour those parts which
should appear green, with the second green invisible ink, described in
page 25; observing, of course, the usual rules of perspective, by
making the near parts deeper in colour than the others. The other
objects must be painted in their natural colours. Then put the print
into a frame with a glass, and cover the back