until they are out of sight. If a
lighted taper or candle be applied to the bubbles as they ascend from
the bowl of the pipe, they will explode with a loud noise.

_Another Method._

Put a small quantity of phosphorus and some potash, dissolved in
water, into a retort; apply the flame of a candle or lamp to the
bottom of the retort, until the contents boil. The phosphuretted
hydrogen gas will then rise, and may be collected in receivers. But
it, instead of receiving the gas into a jar, you let it simply ascend
into water, the bubbles of gas will then explode in succession, as
they reach the surface of the water, and a beautiful white smoke will
be formed, which rises slowly and majestically to the ceiling. If bits
of phosphorus are kept some hours in hydrogen gas, phosphorized
hydrogen gas is produced: and if bubbles of this gas are thrown up
into the receiver of an air-pump, previously filled with oxygen gas, a
brilliant bluish flame will immediately fill the jar.

_Singular Impression on the visual Nerves by a Luminous Object._

If, while sitting in a room, you look earnestly at the middle of a
window, a little while, when the day is bright, and then shut your
eyes, the figure of the window will still remain in your eye, and so
distinct that you may count the panes. A remarkable circumstance
attending this experiment is, that the impression of forms is better
retained than that of colours; for, after the eyes are shut, when you
first discern the image of the window, the panes appear dark, and the
cross-bars of the sashes, with the window frames and walls, appear
white and bright; but if you still add to the darkness of the eyes, by
covering them with your hand, the reverse instantly takes place--the
panes appear luminous, and the cross-bars dark; and by removing the
hand, they are again reversed.

_Curious Effects of Oil upon Water, and Water upon Oil._

Fasten a piece of pack-thread round a tumbler, with strings of the
same from each side, meeting above it in a knot at about a foot
distance from the top of the tumbler. Then putting in as much water as
will fill about one-third part of the tumbler, lift it up by the knot,
and swing it to and fro in the air; the water will keep its place as
steadily in the glass as if it were ice. But pour gently in upon the
water about as much oil, and then again swing it in the air as before,
the tranquillity before possessed by the water will be transferred to
the surfa