e sight hole, it would tend greatly
to increase the effect. The box must be covered in, leaving an
aperture for the smoke of the lights to pass through.

The above exhibition can only be shown at candle-light; but there is
another way, by fixing small pieces of gold on the building, instead
of drilling the holes; which gives something like the appearance of
illumination, but by no means equal to the foregoing experiment.

N.B. It would be an improvement, if paper of various colours, rendered
transparent by oil, were placed between the lights behind and the
aperture in the buildings, as they would then resemble lamps of
different colours.

_The Cameleon Spirit._

Put into a decanter volatile spirit, in which you have dissolved
copper filings, and it will produce a fine blue. If the bottle be
stopped, the colour will disappear; but when unstopped, it will
return. This experiment may be often repeated.

_Invisible Ink._

Put litharge of lead into very strong vinegar, and let it stand
twenty-four hours. Strain it off, and let it remain till quite
settled; then put the liquor in a bottle.

You next dissolve orpiment in quick lime water, by setting the water
in the sun for two or three days, turning it five or six times a-day.
Keep the bottle containing this liquor well corked, as the vapour is
highly pernicious if received into the mouth.

Write what you wish with a pen dipped in the first liquor; and, to
make it visible, expose it to the vapour of the second liquor. If you
wish them to disappear again, draw a sponge or pencil, dipped in aqua
fortis, or spirit of nitre, over the paper; and if you wish them to
re-appear, let the paper be quite dry, and then pass the solution of
orpiment over it.

_Another._

Dissolve bismuth in nitrous acid. When the writing with this fluid is
exposed to the vapour of liver of sulphur, it will become quite black.

_Another._

Dissolve green vitriol and a little nitrous acid in common water.
Write your characters with a new pen.

Next infuse small Aleppo galls, slightly bruised in water. In two or
three days, pour the liquor off.

By drawing a pencil dipped in this second solution over the characters
written with the first, they will appear a beautiful black.

_Invisible Gold Ink._

Put as much gold in as small a quantity of aqua regia as will dissolve
it, and dilute it with two or three times the quantity of distilled
water.

Next dissolve, in a separate vess